Oyaji

Roger that - good tip. Can you recommend any sort of jig or sealing method to get maximum flow and pressure when back flushing through the water pump opening? . But was the sediment load in your engine(s) actually causing an overheating problem? Further, you can only get out just so much without stripping down the engine, scouring out all possible sediment mechanically, then finishing in a boiling caustic bath... and then sediment begins to build up again the moment the engine is put back into service. For this reason, over-capacity is designed in. I cannot speak to the specific design considerations of this particular engine, but I'd be surprised if it wouldn't perform up to specs with a great deal of sediment present. Consider: if this was a common problem, provision for regular cleaning would have been designed in from the start!

. Good point. But typically, there is sump space below the water inlet to the block - is that not the case here? Further, scouring action *should* keep at least a channel open for normal/near normal flow... . Unless the engine has sat unused for some time before being put back into service? Even just running straight water can cause problems over the long term, since antifreeze also incorporates an anti-corrosion additive. Electrolysis between dissimilar metals (brass radiators, cast iron block, aluminum water pump are examples) joined by an electrolyte (water contaminated with ions from the metals previously mentioned) definitely adds to corrosion. . Can anyone recommend an "industrial-strength" uber-caustic radiator flush that strips rust/hard water/rat's nest/EVERYTHING deposits from a cooling system? One that you need to wear an apron, face shield, and elbow-length gloves to handle - so strong you dare not leave it in your system for more than a couple hours for fear of eating through the radiator core? Such used to be available, but I haven't been able to get hold of any since the mid-1970s. The stuff was dangerous to handle (which is doubtless why I haven't been able to get it for years), but with hot water in a running engine it would pretty much dissolve everything. . Prestone used to offer a back-flush kit that included a plastic tee-fitting to splice into a heater hose; you simply connected a garden hose for flushing, and screwed on a cap in place when done. I guess it worked okay - are those still available? Back-flushing sure couldn't hurt... but I sure wish the OP would respond to the potential lugging issue in order to definitively rule it out before moving on.

. Absolutely. . Meantime while waiting for the replacement speedo gear, you could also work out the percentage difference between stock tire diameter and multiply your current mileage data by it as a correction factor. (Since diameter has a linear relationship with circumference, you could use either for your correction factor.) Note that tire size varies somewhat between manufacturers for tires of the same size designation, so for best accuracy, see if you cannot "Google" up information for the exact tires you have.

Although a clean cooling system is certainly desirable, in my experience (on all sorts of engines made over the past 70 years) residue at the bottom of the cylinder water jackets is of relative unimportance. Very little cooling of the cooling required to keep an engine at stable and efficient running temperature is provided at the cylinders - nearly all of it is provided by cooling the head. (In fact I can name at least one engine out there with no water jacket for the cylinders at all, having only the head water-cooled.) . To the point of your overheating woes - are you certain you are not lugging the engine? In other words, when you add throttle when running at the condition when the engine typically overheats, does the engine accelerate freely - or only sluggishly or not accelerate at all? Additionally, what is your fuel economy in MPG? . A lugged/overloaded engine will yield poor fuel economy and run hotter than normal, and in more extreme cases (perhaps in combination with other factors too) it will overheat beyond the capacity of the cooling system to keep up with the additional heat rejection load placed upon it. There are a number of possible causes for lugging, all of them related to the load demand that the engine is required to meet at a given operating RPM. As I mentioned before, a simple test for lugging is whether the engine can still accelerate while under load. If lugging is indicated, the next step is to find the cause; otherwise, the fault must lie with the cooling system (and considering all the diligent work you have done, that surely seems unlikely to me).

I was brought up on a farm, so there was always a lot of equipment to keep running. Since he also worked repairing military airplanes, Dad had a very particular approach to maintaining our rag-tag "stable". When I started turning wrenches at age 8, I also learned to keep logbooks on everything we worked on, too - in some ways, similar to the logbooks kept for planes. The early training stuck, and for nearly 50 years now I have kept logbooks for everything. I log not only all repairs/maintenance/parts for my vehicles, but every drop of gasoline and oil added, too. (Really, notes don't take but a minute, and I have found that the minimal time spent in keeping them to be quite worthwhile.) . Any drop in fuel economy is noted at the next fill-up; if 3 fill-ups in a row show a in drop fuel economy that I cannot account for (like a comment "pulling heavy trailer" or "strong headwinds crossing Texas" next to the fuel price - yes, I log that too!), then I go looking for the reason why. . One simple and useful tool in tracking down engine running condition is to "read" the spark plugs. Pull them and lay them out in order, and note the color of the ceramic insulator. What you want to see is a soft dry deposit light in both color and amount of residue, which indicates an engine running well. Here is a chart of examples rated from cold/rich to ideal to lean/hot: . . . Barring an exhaust gas analyzer (as a substitute, I have a simple guage connected to an O2 sensor that reads air/fuel ratio in near real-time - it was damned useful when jetting 4 independent barrels of carbs on my 4-cylinder 914! :D ), this is probably the best place to start looking for evidence of engine running condition. Once you are assured your engine is running fine, you can move on to looking for other causes for your poor fuel economy. . And finally, to answer one of your latest questions - yes there is a telltale odor: an engine running too rich will smell of unburnt gasoline in its exhaust - the richer running, the stronger the smell. (Unfortunately, I don't have direct experience with the Renix system, so I cannot comment on a lot of specifics like your question about RPM behavior on startup - but where general experience can answer, I do what I can.)

Has anyone here found either need to increase or benefit from increasing the volume of the vacuum reservoir, or is the stock capacity perfectly sufficient? . Just wondering...

Barring anyone being able to provide factory figures, you could always take the empircal approach: weigh each end and calculate the ratio yourself. A couple years back my local Farmer's Co-Op charged me $3, which included a printout; there might be similar alternatives nearby for you, like maybe a ready-mix concrete vendor, for instance. (At the time I had thought of weighing each axle but passed on it - now I wish I had, so I could offer you the info. Sorry 'bout that :( )

Uncalled for ignoramus maximus statement that does nothing to answer the OP's question. Actually, with regard to the topic of this thread, I think he might be right on target here. . Will no one else speak to the OP's problem (poor fuel economy)? I already gave my thoughts: improper overall gearing and/or driving habits. . As I read his description, the engine seems to be running fine now with the exception of a small exhaust leak - is that not correct? It would help if the OP could provide some additional background as to just when he first noticed a drop in fuel economy. Was it when the idle went bad? When the oversize tires were first fitted? Any other clues?

Roger - guess I should have read more carefully before I replied... But this thread is not about the vacuum reservoir - it is about making improvements to fuel economy. Any comments about how the vacuum reservoir can adversely influence economy? Would that be only through potential vacuum leaks? (Also, besides providing a reservoir for vacuum to drive the HVAC servos, does it also help the cruise control servo to function during conditions of low vacuum? I can see how that might have an indirect effect on fuel economy as well...) . Furthermore, neither you nor Hornbrod remarked on my mention about the need for proper overall gearing. Since Jeep owners are pretty well known for their modifications to their vehicles - in particular, the fitment of oversize tires - I wonder how much of the deplorable fuel economy results they posted over on the Fuelly website is due to just that. Looks like their 4-liter 6's average only 15mpg there. (Compare that to my results on a 1992 Cherokee with HO 4.0: 22.5 highway, 19.4 city+highway, average economy over 90,000+ miles, every single fuel stop logged.) Since the original poster asked for "every little thing" that could be done to improve his economy, I am interested to hear your takes on the effect of proper gearing. Is it a "little thing", or a big thing? Care to speculate on which has a bigger effect on fuel economy - driving style or tire size? . In my experience BOTH those things have a big effect on economy... on an engine that runs at least decently, more than all other effects combined.

pop the hose off, trim accordingly for new location, rehook Vacuum hoses, start motor. Done. It's a vaccum canister with a check valve in the vaccum line, it simply stores a vaccum that the engine itself creates. Good description of the system, but when you conclude that the evaporative emissions systems "stores a vacuum" you are off the mark. Since the purpose of the canister is to store gasoline vapors that evaporate off the fuel in the gas tank, it is connected to the tank, which is in turn vented to the atmosphere via a check valve (usually in the gas tank cap) that allows air in but doesn't allow vapors out. If there was vacuum in the fuel tank it would likely crush inwards (the canister might crush, too). Thus, the fuel tank and the cannister connected to it remain at atmospheric pressure, whether the engine is running or not. . The purpose of the check valve you mention is not to store vacuum, but rather for safety (by the way, it isn't really a "check valve" that operates only one way - it is an electrically-operated servo valve that opens upon receiving voltage from a running engine). It prevents the charcoal canister (yes, the canister contains fine charcoal - providing about 5 acres of surface area to bind and safely store gasoline vapor) from overflowing and passing explosive vapor to the manifold of a non-running engine, where otherwise on a hot day it might accumulate sufficiently to overflow from the manifold and air cleaner and into the engine compartment... whence upon engine startup, a stray spark might cause an underhood explosion. The other reason for the servo valve is to cut egress of leaking fuel in the event of a rollover accident. . Sorry for the highjack, but I was a homologation engineer. My only intention here is to provide clarity. . Now, to the point of the original post: Knucklehead97, on 01 Aug 2013 - 19:11, said: Okay guys I've recently been noticing that I've really got bad gas mileage. I had 160 miles on the trip when I added 15 gallons to it yesterday. I think I fixed the rough idle, need to get some vacuum line bushings though. I shift at 2300 rpms (to high? To low?) I'm running 30x9.50 mud tires on stock gears, could this result in anything?... Please give me every little thing that could be causing this because I can't afford the gas. Should I readjust the TPS? I don't think proper gearing is a "little thing". Since stock tires are around 27" diameter, running 30" tires adds something like a 10% increase in your overall gearing. That added diameter may be affecting your fuel economy significantly. Engines are designed with a "sweet spot" for best fuel efficiency. If you change your gearing, you are changing the speed at which that "sweet spot" delivers just the right amount of power to meet the power required to maintain that speed. The main factors that determine how much power you need are aerodynamic drag (if you lift your vehicle, this goes up) and tire rolling resistance (a more aggressive tread makes this go up too). It can get pretty complicated when you start changing things from stock... coast-down testing is really the only way to be sure (with the use of some math you can do this at home - but most folks consider it too complicated - Google it up if you are interested). Practically speaking, I think it would be best to just shoot for a little more RPM (~3%-ish) at your chosen cruising speed than stock (to account for things like lift and tire tread) and accept a small (maybe 1 mpg?) drop in economy. What you describe sounds like you have more issues than simply being wrongly geared, but that is for sure one place to start. If you have a spare set of rims with stock tires fitted, that would be a great comparison test to begin with.

Glad to hear dropping down a gear keeps you cool, and that you did not have to resort to last month's drastic "solution" ;) : Lots of guys run over-sized tires without re-gearing. While they may get away with it on the flat (like where I live, for example), once you get into hills and mountains all bets are off! Not only does lugging unnecessarily drive engine temperatures higher than normal, it also wastes fuel by operating the engine slower than the efficient "sweet spot" it was designed to run at. . I hope this thread will help all readers keep in mind the importance of proper gearing.

. . Another week has gone by since your last update - any news for us yet?

ok, i never thought of that, i just thought of one speed but i'll try to get two speed test of 25 and 50 atleast 3 times well i wanna get tested by a cop since they're the ones that issue the tickets, if it's right on their gun i get no ticket :D Redwolf . Sure - they are the ones who issue the tickets - cannot argue that logic, it does have merit. . But - my point is that their radar does not yield consistent results. I expect that this is because they do NOT calibrate their equipment every shift, or that their calibration method is flawed, or that the calibration equipment (usually a tuning fork - the ones I have seen are aluminum - bent, dented, and/or nicked from abuse) is flawed - or some combination of all 3 of the above. And almost never does anyone question the police on their methods... so their word is taken as Gospel, as is the (frequently flawed) reading given by their radar. . That night I recounted above in my previous post I had 2 different police cars check my speed, and not only did their readings not agree with each other, the didn't even agree with their own repeated readings (not even within 5mph). . Furthermore, the police are not there to help you (it is not part of their job), and you could get your friend into trouble for helping you if he got caught doing so. Bad anyway you slice it. . You have gotten tons of good advice so far in this thread - why not take it, do the work yourself, and have confidence in the results?

In my experience, police radar is worthless for a test. The one time I tried, the police who agreed to help me could not generate a result within 5mph consistently (after 5 attempts), and tried to blame it on my driving (even though I was rock solid at 50mph indicated and with rpm steady on the tach, with a quarter mile lead in to their position). Then when I was out later that night doing a distance-over-time test at a steady 35mph indicated in a 45mph zone - the only car on the road at 2am - another cop pulled me over on this deserted stretch of road and detained me on the roadside. After he "snooped" my car through the windows with his flashlight (I told him he did NOT have permission to search it, so he didn't go inside it) and questioned me about my "suspicious behavior" for an hour and a half. Wwearing just shorts and a t-shirt, I was freezing my tail off, standing in a 30mph wind with the temperature at ~50 degrees and falling in the wake of a cold front; I finally got exasperated enough to cuss him and demand that he either take me to jail (for driving 10mph UNDER the speed limit!!!!!) or let me go, because I was freezing my nuts off standing there in that cold wind! . Bah!!! . Sorry, but in my experience, the police are worse than useless for that sort of help.

Hmmm... The radiator hose will only get as hard (from internal pressure) as the pressure relief valve will let it. Dunno what cooling system you have (open or closed), but there has to be a relief valve somewhere. On the open systems, this is in the radiator cap; in a closed system, it is maybe the cap on the pressure tank (I am guessing - I never had one/worked on one). If you think you have too much pressure, better test it to make sure - failure can be either inconvenient or even dangerous (think how scalded you could get while working on a running engine if the weak link broke and sprayed you with superheated steam 265 degrees or hotter!). . . . [edit: Whoops! You clearly mentioned that your cooling system is of the "open" sort - sorry I missed that. Still, all the info there still applies as written, and may help any future reader with similar concerns.]

Interesting that the compression ratio increased a bit. Did you have the head planed while it was off? Or maybe the new head gasket is a bit thinner than the previous one? Either would explain CR up a bit across the board from previous readings. Another possibility could be readings taken before and after passage of a cold front: barometer difference from a high of, say, 30.5 inHg dropping to 29 inHg would account for a 4.5% difference between readings, maybe? (PSIG might cancel this but for the CR of ~8:1? I am not sure, reaching a bit here...) Still keen to hear of your results where "the rubber meets the road" though - please keep us updated....

I like the way you think. To carry this train of thought a bit further, the Eagle IFS D30 had the differential bolted to the engine. I wonder if that saved weight on what would otherwise have had to have been a heavier diff sub-frame? What do you think? In any case, I presume something could indeed be cobbled up, perhaps even by looking for substitutes from other IFS 4WD trucks... If going 2WD only, the Ford Twin I-beam IFS might be worth a peek - it is rugged and does a much better job of maintaining compliance (and thus traction) than would a beam axle...

Still no resolution?

Hehehe - you thought I typed all that? I just copy/pasted - and I used the Windows shortcut keys to make it even easier. :) I thought other readers might benefit from the thermostat info, so I put it up as a supplement. You might be surprised how few people know how they work. Even some of the folks who get the concept of thermal expansion wrongly attribute action of the thermostat to a bimetallic spring instead of the thermowax. Regardless, seeing how the thermowax can over-expand and leak out from overheating gives insight into one failure mode - and encourages testing. Since testing a thermostat is as simple as boiling it in coolant for a couple minutes, seems to me it is a worthwhile test for anyone experiencing a persistent cooling problem. Glad to hear you are on top of your problem.

Have you tested your thermostat in boiling 50/50 antifreeze/water mix to see if it is actually opening? If your engine has gotten hot, I've read that it is wise to replace the thermostat, as an overheating event can cause them to fail. (I have to admit that I seldom replace thermostats after an overheating event - but then I didn't have the persistent problem you've got, either.) This webpage is worth a read (I copied it below, but there are illustrations at the link that are not here so maybe go take a peek): http://installer.aed-inc.com:8191/Stant%20Technical%20Info/TempTalkStats.htm he thermostat has two important jobs to perform; to accelerate engine warm-up and to regulate the engine's operating temperature. A quality thermostat ensures excellent fuel economy, reduces engine wear, diminishes emissions and blowby, improves cold weather drivability, provides adequate heater output, and detours overheating. This is accomplished by blocking the circulation of coolant between the engine and radiator until the engine has reached its predetermined temperature. The thermostat then opens as required in response to changes in coolant temperature to keep the engine's temperature within the desired operating range. Usually located in a housing where the upper radiator hose connects to the engine, most thermostats utilize the "reverse poppet" design, which opens against the flow of the coolant. Thermostats have a wax filled copper housing or cup called a "heat motor" that pushes the thermostat open against spring pressure. As the engine's coolant warms up, it heats the wax causing the wax to melt and expand. The wax pushes against a piston inside a rubber boot. This forces the piston outward to open the thermostat. Within 3 or 4 degrees F. of the thermostat preset temperature (which is marked on the thermostat), the thermostat begins to unseat so coolant can start to circulate between the engine and radiator. It continues to open until engine cooling requirements are satisfied. It is fully open about 20 degrees above its rated temperature. If the temperature of the circulating coolant begins to drop, the wax element contracts, allowing spring tension to close the thermostat, thus decreasing coolant flow through the radiator. On some applications, the thermostat performs an additional function. It closes off a bypass circuit inside the engine when it opens the radiator circuit. The bypass circuit circulates coolant inside the engine so that hot spots can’t form when the radiator circuit is closed. Most thermostats also have a "bleed notch” or a “jiggle pin” that allows trapped air in the cooling system to pass through the thermostat and be removed from the system. When problems arise One problem that can occur is the thermostat will fail “open.” This can happen if the return spring breaks or debris prevents the thermostat valve from fully seating. In this instance the thermostat allows continuous coolant flow to the radiator; therefore, the engine will be overcooled. The tangible effects are poor warm up and heater performance, increased engine emissions and reduced fuel economy. For these reasons, an engine should never be operated without a thermostat in place, even in extreme temperatures. The other problem is the opposite, that is, the thermostat will fail “closed.” This can happen if the wax element has been damaged by overheating (from loss of coolant, a defective electric cooling fan or fan clutch) or corrosion (from not changing the anti-freeze often enough). This failure prevents the flow of coolant to the radiator; therefore, the engine will be overheated. The tangible effects are boilover, the inability to operate the vehicle, and the likelihood of severe engine damage. For these reasons alone, when an engine overheats, it’s a good idea to replace the thermostat whether it caused the problem or not. Replacement thermostats The temperature rating of a replacement thermostat must be the correct one for the application because of the adverse affects the wrong thermostat can have on drivability, engine performance and emissions. Most 1971 and later passenger cars and light trucks require a 192 or 195 degree F. thermostat. The temperature rating specified by the car manufacturer is especially important in many 1981 and later cars because the onboard computer monitors coolant temperature through a coolant sensor to control fuel enrichment, spark timing and operation of the EGR valve. Even on vehicles without computers, thermal vacuum switches that react to a specific coolant temperature are often used to open and close various vacuum circuits that regulate fuel enrichment, timing and EGR. If a colder thermostat is installed, the coolant may never get hot enough to trigger the appropriate control functions or to allow a computer system to go into “closed loop”. Too hot a thermostat can also interfere with the proper operation of engine controls, and increase the engine’s operating temperature to the point where it may experience detonation (spark knock). Thermostat checks One way to determine if the thermostat is doing its job is to feel the upper radiator hose after starting a cold engine. The hose should not feel hot until the engine has warmed up. If the hose starts to feel hot after only a couple of minutes, the thermostat may be stuck open or not closing completely. Once the engine is warm, the hose should feel hot as coolant circulates between the engine and radiator. If the hose does not feel hot, the thermostat may be stuck shut, blocking the flow of coolant. A thermostat can be tested by removing it and suspending it in a bucket of boiling 50/50 coolant and water. The thermostat should be closed when cold, then open after being in the hot coolant for 4 to 5 minutes, and then close again when it is removed and allowed to cool. Replacement tips ¨ Don't overlook the water outlet covering the thermostat. Check for cracks, broken flanges, internal pitting and corrosion, and erosion at the hose neck (a real problem with most aluminum housings). The gasket surface must be flat and free from warping or deep scratches. ¨ Scrape the mating surfaces on the thermostat housing and engine to remove all traces of old gasket material. Use care on aluminum because the soft metal can be easily scratched. ¨ Temporarily stuffing a rag into the thermostat opening on the engine while the housing is removed helps keep debris out of the cooling system. ¨ Install the new thermostat so the copper heat sensing element is toward the engine. If installed upside down, it won’t open.

Better still, don't remove them in the first place when removing the head ;) I don't recall if this works for this engine, but it does work for others. There is the added benefit of less work for both removal and reassembly, besides not needing new gaskets either.

*sigh* Too bad I didn't find this thread sooner - maybe could have saved you a teardown. Incidentally, the coolant you found atop #6 piston almost certainly leaked there at the instant you broke loose the head from the head gasket and block when you took it off. If you had a blown/leaking head gasket/cracked head, your cooling system would not have held pressure, you would have been losing coolant into #6 all the while, and you may even have noticed steam in the exhaust (the cooling system certainly would have been losing coolant). Since the head is off now, it would be a good time to consider a valve job if the head has more than 50,000 miles on it. Valves go bad far sooner than piston rings, and though valves are far more robust than they used to be (like back in the day of leaded gasoline, I am thinking), it still might be worth it simply because you have already done the work of pulling the head already. Lugging the engine raises peak combustion temperature, and higher exhaust temps have a way of eroding the exhaust valve and seat contact surfaces. It wouldn't hurt to check the valve guides for wear, too, while you have the head off. But before investing in those repairs, make sure they check the head for cracks! It got hot enough to blow out coolant (right?), and now you might have damage you didn't have before... Maybe it is a good time to consider a remanufactured head? They are often substantially cheaper than having your local machinist do the work.Honestly though, since you were so dlligent in your compression and pressure testing, this may well be overkill unless money is no object for you. If you haven't done so yet, Google up a technical article (preferably from an engine manufacturer) on "engine lugging" and have a read - it will provide understanding and incentive to avoid it in the future! You were absolutely on target with your earlier observation about performance being "doggy" when under load: being geared ~16% too tall (3.55 / 3.07 = 1.16) and then making your ratio ~15% taller by running 31" tires instead of the stock 27" diameter (31 / 27 = 1.15) gives an overall ratio 31% too tall, which is about like running a gear and a half too high for your road speed. Until you get properly geared, just make sure to manually downshift and not use the kickdown switch in your AW4 (except for brief acceleration, for instance when passing another car). Kicking down to passing gear has your engine running near WOT (Wide Open Throttle), which ain't good for extended run time (like when climbing a hill, or when towing a load) - no, not one bit! I expect that is the very reason that Jeep chose the 3.55 gearing for the AW4 yet went with 3.07 for the 5-speed... You might find you get the results you seek by just dropping down to "drive 2" - but that makes your AW4 an "AW3", practically speaking. :) Sure hope your headache passes soon - good luck, and be sure to let us know what you found out in the end.

Should have said this from the start! AW4 has 3.55 final drive gearing because it is automatic, ie, no driver downshifting required. Driver of a manual knows better than to try to climb a hill/drive under load without downshifting, so the manual transmission driveline got a 3.07 final drive - but the automatic they tried to make idiot-proof and thus it got shorter gearing. If I recall correctly, top gear in both the AX-15 and the AW4 are overdrive, and about the same ratio (~.80 or so), right? Furthermore, by running 31" tires you have compounded the problem. As I recall, last time I did the math for an AW4 to run 32" tires you should be running 4.10 final drive to keep the engine in the "sweet spot" it was designed to run at (peak torque), ie, the same RPM at a given speed that the factory ratio and tire size would yield. Here is a simple test for you: next time you are under load, mash the accelerator pedal and see if you can accelerate appreciably. If not, you are lugging the engine - and it will get hot if you operate it for very long in that condition. (I am sure you can find heaps of references that explain lugging from a technical perspective - worth reading if you are interested.) Another simple test: manually drop down a gear (to the "2" position on the shifter) and see if you can accelerate then. Watch your engine temperature as you drive a few miles - I bet it will be closer to normal. Until you can get 4.10 final drive gearing, you can either go back to the stock 27" tire diameter, or maybe just drive around in D2. Incidentally, your fuel economy should increase pretty dramatically once you get properly geared for your tire size - driving sensibly on the highway should net you around 20 MPG, which is what you would get with a stock truck gearing and tire size.

Any chance you could have installed the thermostat upside down? If so, you would still get flow through the heater hoses but the thermostat would not open properly (since the bulb containing the thermowax would not be in contact with the hot water leaving the head). Heat (and steam) would rapidly accumulate, and back-pressure would blast coolant out the radiator cap. I've actually seen this happen a couple times over the past 40 years or so...