Cooling System Testing?

[ParadiseMJ]

OK fellas...I'm officially desperate.

 

Still struggling with cooling system FUBAR.  When engine heats up and t-stat (new 195 stant) opens it starts blowing coolant out the overflow at idle OR at RPM's.  ALL the cooling components are less than 3K miles or newer.  2 row CSF all metal radiator...1988 4.0L converted to open system...3K miles ago.  I don't have a heater valve, I deleted it when I did the conversion.  I know you've heard this all before, but I can't drive my truck anywhere without it getting HOT and blowing coolant.  WTH??

 

I have tested:

• New catalytic converter, new exhaust manifold, new gasket & flange donut.
• compression - good (great actually) 119-124 within 5 psi across the board. No adjacent discrepancies.
• No water in oil, no oil in water
• NO driveability issues.  Idles smooth at ~700-800
• exhaust gases (block tester) - none - tested it 4 times, with different fluid each time
• heater core - clear - no rust, crud, junk or small animals
• radiator pressure - holds pressure at 20 psi overnight - good, no leaks.
• cap - new 16 lb. - holds pressure @16 lbs for a couple of hours (the longest I've let it go)
• all hoses - no leaks - spring in lower hose
• ZJ HD fan clutch
• coolant QUALTY...it's new, and it's fine.  50/50 Prestone Green (ethelyne glycol) and distilled water.
• air bled from system...4 or 5 times and each time I have had to replace coolant.

How do I test for a.) a bad pump (it's not leaking, wobbling and the belt is good AND yes it's a reverse rotation with the belt routed properly)  or b.) a blocked radiator before I drop the $$ on either. OR is there something else I am STILL overlooking???

 

Help me Obi-Wan Kenobi...you're my only hope.

[dave92cherokee]

It almost sounds like there's still air trapped in the system. When you bled the system where were you bleeding air from the radiator or the sensor on the back of the head? Have you done a complete system flush including the block as there might be some crud clogging up some passages inside the block. You also said that all components are new with less than 3k on them what brand of water pump did you put on as some seem to work better than others.

[HOrnbrod]

Did all your overheating problems start after you swapped in the AW4?

 

Here's some overheating checks I had bookmarked, especially for the water pump. I've seen H20 pumps come off with the pump vanes rusted almost off on a few vehicles. Try the ones in BOLD; you've done all the rest.  :yes:

 

• With the engine off and the fan belt and shroud removed, grasp the fan and attempt to move it in and out and up and down.
• More than 1/16 inch (1.58 mm) of movement indicates worn bearings that require water pump replacement.
• To determine whether the water pump is allowing for good circulation, warm up the engine and run it at idle speed.
• Squeeze the upper hose connection with one hand and accelerate the engine with the other hand.
• If a surge on the hose is felt, the pump is working.
• Any air being sucked into the cooling system is certain to have a detrimental effect.
• It cuts down pumping efficiency and causes both rusting and wear at a rate approximately three times above normal.
• To test for aeration, have the engine fully warmed up, all hose connections tight, and the coolant level up to normal.
• Attach one end of a small hose to the radiator overflow pipe and put the other end into a jar of water.
• Run the engine at a fast idle. If a steady stream of bubbles appears in the jar of water, air is getting into the cooling system.
• Check first for a cylinder gasket leak by running a compression test.
• If two adjacent cylinders test low, the gasket is bad. Otherwise, there is an air leak somewhere else in the cooling system.

[ParadiseMJ]

It almost sounds like there's still air trapped in the system. When you bled the system where were you bleeding air from the radiator or the sensor on the back of the head? Have you done a complete system flush including the block as there might be some crud clogging up some passages inside the block. You also said that all components are new with less than 3k on them what brand of water pump did you put on as some seem to work better than others.

My thought exactly.  I don't know how else I'd get so much air OUT of the radiator when I run it with the cap off.  I've flushed the block/system twice (once with a "quick flush" and once with a full chemical flush) and filled it with coolant twice.  The coolant is sparkling clean.  It's a Bosch pump...and it is working after doing the below test AND pulling the heater hose to see if I was getting a good flow.

 

 

Did all your overheating problems start after you swapped in the AW4?

 

Here's some overheating checks I had bookmarked, especially for the water pump. I've seen H20 pumps come off with the pump vanes rusted almost off on a few vehicles. Try the ones in BOLD; you've done all the rest.  :yes:

 

• With the engine off and the fan belt and shroud removed, grasp the fan and attempt to move it in and out and up and down.
• More than 1/16 inch (1.58 mm) of movement indicates worn bearings that require water pump replacement.
• To determine whether the water pump is allowing for good circulation, warm up the engine and run it at idle speed.
• Squeeze the upper hose connection with one hand and accelerate the engine with the other hand.
• If a surge on the hose is felt, the pump is working.
• Any air being sucked into the cooling system is certain to have a detrimental effect.
• It cuts down pumping efficiency and causes both rusting and wear at a rate approximately three times above normal.
• To test for aeration, have the engine fully warmed up, all hose connections tight, and the coolant level up to normal.
• Attach one end of a small hose to the radiator overflow pipe and put the other end into a jar of water.
• Run the engine at a fast idle. If a steady stream of bubbles appears in the jar of water, air is getting into the cooling system.
• Check first for a cylinder gasket leak by running a compression test.
• If two adjacent cylinders test low, the gasket is bad. Otherwise, there is an air leak somewhere else in the cooling system.

It started well after I swapped the tranny.  Like a year later.  It ran fine all last summer and all winter with the AW4 in there. 

 

The pump seems to be working fine.  In addition to the test you posted I pulled the heater hose, at the core inlet.  Got a good steady flow from the hose via the pump.  Also, with the cap off, the coolant level drops a good bit with any revving.

 

The aeration test...once the engine is up to temp, and above, it bubbles steadily. My quandry is that with the absence of a head gasket leak (or theexhaust gases in the coolant test) how is air getting in there other than being INJECTED in by a head gasket leak??  Seems to me that I have exhausted all my avenues other than pulling the head and taking a look.

 

Sorry to keep hammering on this issue, but I feel I've done everything I could possibly do, with the exception of the head (and I don't wanna do the head).  seems I just have to bite the bullet.  I think a shop would have already done the head after charging me for all the diagnostics first.  I had a very similar issue on my Nissan, it passed all the tests, but replacing the gasket fixed it...so, here I go!!

 

Unless, of course, there are any last ditch tidbits of knowledge out there.

[danbyrambler]

Could be a cracked head - I fought the same symptoms for a little over a year once upon a - - Started out slow & kept getting worse - Finally took it to a decent shop & Everything checked ok - cooling system - compression - leak down - sniffer - exhaust restrictions - - Every test OK except immediate pressure upon starting & so it was decided to replace the head gasket since the miles were around 175K & what else could it be - - time chain, water pump etc all replaced also  - - - valves were good but head was refurbed anyway & the crack was so small they missed it - Alum head & I don't recall how they said it was checked but afterwards I realized I should have asked if they ran the rad pressure test moren once since both valves on the affected cylinder could've been closed & no/very little pres lost - - - - Anyway, it was back to the shop shortly & after some discussion the head gasket was again replaced & then when the third gasket was being installed by the shop owner the crack was found - - Might want to try the radiator pressure test again if the crank wasn't rotated during the previous test.  

:hmm:

[Akula69]

This is gonna sond really stupid (because you already said it was a reverse impeller pump) but, are you sure? I can see how that would push coolant out the tank.

[ParadiseMJ]

Yep, it's got the R stamped on the impeller....and the "scoops"are on the  reverse edge  Just like my XJ...same P/N.  XJ runs cool.  Belt routed on the smooth side.  When I give it throttle with the cap off, the coolant level drops as opposed to spews out. Thanks though. 

[Oyaji]

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...

[ParadiseMJ]

Nope.

 

Only goes in one way.  Spring IN.  The t-stat housing won't let it go in the other way (unless I use a BFH) :brows:

[ParadiseMJ]

Nope.

 

Only goes in one way.  Spring IN.  The t-stat housing won't let it go in the other way (unless I use a BFH) :brows:

 

OK...I take this back.  On a stock 88 t-stat housing it IS possible to put the stat in backwards.   I've been running a 94 housing in my 88...I found that it had quite a bit of pitting in the neck, so I ordered a new housing.  The "knob" on the 88 is larger and allows for the t-stat to go in either way.  BUT, I did have it in the right way. 

[Oyaji]

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.

Edited August 9, 2013 by Oyaji

[ParadiseMJ]

Wow...

 

That's a lot of typing.  I'm pretty familiar with the thermostat.

 

I did not install the thermostat backwards.  I always test my stats.  The present stat is working fine.

[Oyaji]

Wow...

 

That's a lot of typing.  I'm pretty familiar with the thermostat.

 

I did not install the thermostat backwards.  I always test my stats.  The present stat is working fine.

 

 

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.