TajMan Posted November 13, 2007 Share Posted November 13, 2007 You guys are really helping on the mechanical questions threads. First, I rebuilt my head maybe 700 miles ago, yeah new air filter. I just started removing stuff to do my waterpump and found this: Obviously oil coming from the hose that goes between airbox and top of valve cover. Not right though, whats the problem? Is the end of hose right on the airbox some type of filter thats broken? BTW I've been getting horrible gas mileage too. Driving miles uphill I-80 SLC-Park City, like 14mpg! Link to comment Share on other sites More sharing options...
feerocknok Posted November 13, 2007 Share Posted November 13, 2007 Your air filter is clogged, so that will Kill your mileage, but that oil is from the crankcase ventilation, as you said. I'd throw your blow-by tube into a catch-can (gatorade bottle). 4.0s have alot of blow-by; putting it into a can will let you know how much, and save your filter. Link to comment Share on other sites More sharing options...
TajMan Posted November 13, 2007 Author Share Posted November 13, 2007 Interesting. Blow-by pressurizes crankcase, and forces extra oil from valve cover into tube when it splashes up near there? Would that air filter alone really explain my gas mileage? It was new and its 1/2 dry still, I would think it can still get air easy enough.. Link to comment Share on other sites More sharing options...
jtdesigns Posted November 13, 2007 Share Posted November 13, 2007 Interesting. Blow-by pressurizes crankcase, and forces extra oil from valve cover into tube when it splashes up near there? Would that air filter alone really explain my gas mileage? It was new and its 1/2 dry still, I would think it can still get air easy enough.. \ yeah but not as much air as it did before. what do your plugs look like? Link to comment Share on other sites More sharing options...
cozee Posted November 13, 2007 Share Posted November 13, 2007 Most all stock air cleaners are designed to allow just enough air flow. Changing over to an after market unit such as a K&N yields more airflow, hence better performance and mileage. Link to comment Share on other sites More sharing options...
TajMan Posted November 14, 2007 Author Share Posted November 14, 2007 A friend told me he gets 16MPG city in his 4.0 XJ, so that makes it believable for me 14MPG with my clogged air filter and flooring it to go 65MPH uphill a long ways. I've got a new air filter, finishing my water pump, and will put breather hose in a little poweraid bottle I've got. BTW my cylinder compression was 120 - 115 - 120 - 120 - 120 - 120. Link to comment Share on other sites More sharing options...
Eagle Posted November 14, 2007 Share Posted November 14, 2007 Yeah, but the K&N filter listed by K&N for the 4.0L Cherokee & Comanche is about 1/4" too short for the airbox, leaving a gap through which all sorts of nasty stuff can go straight into the engine. The filter element that actually FITS is listed for a Dodge Dakota ... unfortunately, since I don't like K&Ns, I don't remember which years. I also don't think a street or off-road vehicle gains anything using a K&N. The stock air filter has to be designed to allow enough air for operation through the entire range of the engine, which means it'll flow enough to get you up to 4,500 to 5,000 RPM or maybe a bit more. I never EVER see the high side of 3,500 RPM, and for the most part my shift points are around 2,200 to 2,500 RPM. So a stock air filter even half clogged will still flow enough to keep me running. As to why that's happening: All vehicles today have closed crankcase ventilation. (I'm old enough to remember when there was just an open tube out the side of the crankcase to open air.) Modern engines draw air in through the air filter, pull it through the crankcase to pick up fumes from the hot oil, and suck it out of the valve cover through a tube or hose to the throttle body or intake manifold. Most vehicles have a PCV valve to regulate the flow. The 4.0L does NOT use a PCV valve. It regulates the flow by the size of the tubes. The hose from the air cleaner box to the valve cover is the INTAKE. The little, skinny line from the back of the valve cover to the intake manifold is the suction line. What hapens is that this line gets clogged, or the baffle inside the valve cover where this small line attaches gets plugged, and there's no suction. So the excess pressure from any blow-by pressurizes the crankcase and makes the intake hose flow backwards, forcing oil-laden fumes back out that hose to collect in the air filter element. That small line is actually supposed to be serviced by periodic replacement, but nobody ever does it because most people don't know about it. And the replacement is expensive -- although NAPA has the replacements for about half the cost of dealer parts. Or you can make one up using copper or plastic tubing of a larger diameter, so it'll be less likely to get clogged. But you should still remove the valve cover and clean out the baffle, just to ensure that it's open. Routing the inlet hose through a catch can is a last-ditch measure. It's not a repair, it's a work-around. It still leaves the system working in reverse, it just reduces the amount of oil that soaks the air filter element. But ... if all else fails and the engine otherwise runs well ... I'd do it. Link to comment Share on other sites More sharing options...
Pete M Posted November 14, 2007 Share Posted November 14, 2007 I'd do it too. Oh wait, I did. :roll: Link to comment Share on other sites More sharing options...
pingpong Posted November 14, 2007 Share Posted November 14, 2007 I replaced the lil vent line with an 86 pcv valve and grommet from an 86 CJ, and where it goes into the intake I screwed in a brass air chuck, then ran a line between the 2. Poor mans PCV system Link to comment Share on other sites More sharing options...
TajMan Posted November 14, 2007 Author Share Posted November 14, 2007 Blew air though the little line its clear. Installed new air filter. Big tube coming off valve cover is now routed to a nice catch can bottle I have near the ignition coil. I plug-up any unused hose spots now on airbox etc. We'll see how she continues to run (mileage) and how much oil the bottle collects. Link to comment Share on other sites More sharing options...
WNC_MJ Posted April 14, 2009 Share Posted April 14, 2009 Going back to the oil leakage/blowout... Is there any way to rig up a way for the air to pass and the oil stay? I'm losing a lot of oil into the filter and through the air box. I've seen some people put a small conical filter on the valve cover tube... does this work? Link to comment Share on other sites More sharing options...
JeepcoMJ Posted April 14, 2009 Share Posted April 14, 2009 that just means that you have a 4.0 :P Link to comment Share on other sites More sharing options...
dakal Posted April 16, 2009 Share Posted April 16, 2009 thanks eagle, that was a great explanation! :bowdown: Link to comment Share on other sites More sharing options...
Pete M Posted April 16, 2009 Share Posted April 16, 2009 I've seen some people put a small conical filter on the valve cover tube... does this work? I tried that on my truck. All it did was ooze oil all over the valve cover and make a big mess. :( Link to comment Share on other sites More sharing options...
Eagle Posted April 16, 2009 Share Posted April 16, 2009 Going back to the oil leakage/blowout... Is there any way to rig up a way for the air to pass and the oil stay? I'm losing a lot of oil into the filter and through the air box. I've seen some people put a small conical filter on the valve cover tube... does this work? Nope. If the suction tube is plugged, or if you have excessive blow-by, that small filter will still be an outlet rather than an inlet. Instead of oil in the air cleaner, you'll soak that little filter and then spray oil all over the engine. You have to fix the problem. Otherwise, the catch can is the best band-aid. Link to comment Share on other sites More sharing options...
JeepcoMJ Posted April 16, 2009 Share Posted April 16, 2009 Going back to the oil leakage/blowout... Is there any way to rig up a way for the air to pass and the oil stay? I'm losing a lot of oil into the filter and through the air box. I've seen some people put a small conical filter on the valve cover tube... does this work? Nope. If the suction tube is plugged, or if you have excessive blow-by, that small filter will still be an outlet rather than an inlet. Instead of oil in the air cleaner, you'll soak that little filter and then spray oil all over the engine. You have to fix the problem. Otherwise, the catch can is the best band-aid. how about installing a check valve Link to comment Share on other sites More sharing options...
WNC_MJ Posted April 16, 2009 Share Posted April 16, 2009 Okay, don't laugh too much... but I had either an idea :idea: or bad brain-fart :ack: over here... :dunno: What if, in the mean time (of me doing a VC replacement or rebuild), I was to create a catch can / drain tube such as the 'wonderfully illustrated' diagram below? I'm thinking it would work... :smart: The attachment to the dipstick tube would probably be a T-attachment of some sort, that would essentially extend the dipstick by about 1/4", in turn I would re-mark of make a mental note of the new "add, full" lines on the dipstick. Something worth considering... has anyone else done or thought of this? Link to comment Share on other sites More sharing options...
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