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oil blow by/leak
hello,
on my 1987 4.0L auto tranny i was checking all the fluids and i noticed the oil was a little low, which is no surprise because i have a pretty good oil leak. it appears to be in the rear of the motor. i changed the valve cover gasket but that didnt help. any idea on where it could be coming from? im thinking its the rear main seal :cursing: also, it appears to be blowing oil into the air filter from the front plastic tube, any known causes for excessive blow by on these motors? |
Rear Main or maybe the filter....I have replaced all three to get mine to stop leaking. You will have to crawl under and check and see if you can id where the oil is starting at. It is tough because as you drive it blows back on the rest of the motor and transmission. I know that the underside of mine will not rust because of the old oil leaks. It would blow a large film over every thing until I found the leak. I miss it with the first try and replaced the rear main. The major oil leak was in fact the filter.
Hope this help and good luck. |
the oil blow onto your filter is caused by the clogged PCV valve on the valve cover. it is the biggest pain to get off..... and i found that only the dealer carries the part and the gasket but they are cheap. I did mine and changed the valve cover gasket too. make sure you torque everything down and after about 50 miles of driving and then after 200 miles of driving to keep it from leaking. and main leaking areas are:
valve cover rear main oil filter adapter O-rings(at the block) some uncommon ones: head gasket(if it was EVER over heated) front main oil pan |
thanks i guess ill go to the dealership tomorrow and see if i can get a new ccv valve and the tubing, mine pretty brittle and i know from experience ill break it all trying to clean it haha
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dont mean to bring bad news, but its not just a clogged ventilation line, no matter what, there is always an explanation for abnormal findings when it comes to motors..... its called blowby, your piston rings are failing....
The crankcase, that which contains the crankshaft and connecting rods, is the bottom side of the engine - you can see the bottom of the pistons from under there. Compressed fuel and air mixture burns in the cylinder on the top of the pistons. When the rings become tired and worn they allow some of this compressed and burning mixture to leak past and escape into the crankcase. That is called "blow by". In old engines that blowby simply vented into the atmosphere via a tube called a crankcase vent tube. The EPA found bad stuff in that blowby gas and mandated that the engines must suck up that stuff and burn it to render it harmful in some other way. In came the PCV which stands for Positive Crankcase Ventilation, named after the then head of the EPA Pierre Positive. This system makes the engine suck the junk out of the crankcase via the PCV Valve into the intake manifold and back thorough the system. Welll, if that system is sucking the junk out, there must be a source of air to go into the crankcase else you would just implode the engine and the oil pan would collapse. Soooo, they ran a tube from the top of the valve covers to a source of clean air so that dirt would not get sucked into the crankcase. (note: the valve cover covers the valve train but that is also part of the crankcase - air and blow-by move readily between those zones in the engine.) The source of clean air which was chosen is the air cleaner - makes sense, except for the fact that the air doesn't go thorough the air cleaner filter, so they put a little kotex-like pad in there to clean the bugs and stones out of the air. |
Originally Posted by 96_xj
(Post 488507)
the oil blow onto your filter is caused by the clogged PCV valve on the valve cover. it is the biggest pain to get off..... and i found that only the dealer carries the part and the gasket but they are cheap. I did mine and changed the valve cover gasket too. make sure you torque everything down and after about 50 miles of driving and then after 200 miles of driving to keep it from leaking. and main leaking areas are:
valve cover rear main oil filter adapter O-rings(at the block) some uncommon ones: head gasket(if it was EVER over heated) front main oil pan those things are a pain to get off!!! BUT i found them at a store, there generic 90 degree vent valves for chrysler, and you by the seals separate, but they are out there ! just check the akward generic section of autopart stores |
Originally Posted by MASTERS
(Post 489305)
dont mean to bring bad news, but its not just a clogged ventilation line, no matter what, there is always an explanation for abnormal findings when it comes to motors..... its called blowby, your piston rings are failing....
The crankcase, that which contains the crankshaft and connecting rods, is the bottom side of the engine - you can see the bottom of the pistons from under there. Compressed fuel and air mixture burns in the cylinder on the top of the pistons. When the rings become tired and worn they allow some of this compressed and burning mixture to leak past and escape into the crankcase. That is called "blow by". In old engines that blowby simply vented into the atmosphere via a tube called a crankcase vent tube. The EPA found bad stuff in that blowby gas and mandated that the engines must suck up that stuff and burn it to render it harmful in some other way. In came the PCV which stands for Positive Crankcase Ventilation, named after the then head of the EPA Pierre Positive. This system makes the engine suck the junk out of the crankcase via the PCV Valve into the intake manifold and back thorough the system. Welll, if that system is sucking the junk out, there must be a source of air to go into the crankcase else you would just implode the engine and the oil pan would collapse. Soooo, they ran a tube from the top of the valve covers to a source of clean air so that dirt would not get sucked into the crankcase. (note: the valve cover covers the valve train but that is also part of the crankcase - air and blow-by move readily between those zones in the engine.) The source of clean air which was chosen is the air cleaner - makes sense, except for the fact that the air doesn't go thorough the air cleaner filter, so they put a little kotex-like pad in there to clean the bugs and stones out of the air. thats true and very useful HOWEVER, on Higher Milage jeeps the rear CCV valve will get clogged up from miles and miles of little bits of oil, specially if you do not use a funnel to pour your oil in. When you take off the valve cover there is the "shield" that sits about a half inch from the top of the cover and runs the full length on the inside right? well that is to keep oil from getting into those PCV/CCV valves, when you do so many oil changes with out a funnel it allows some oil to get in that layer and when you go to start your jeep the valves get a little bit of the oil in the air system as to which you refer to. Over time this causes a problem and proceeds to show oil blow-by thru the front PCV valve. The reason it is in the front valve is that your engine is sloped backwards so when you pour oil in it runs to the back and that CCV valve gets the little bits of oil that get inbetween that "shield" where the front one gets none. I know this by personal account as i have perfect compression, a nearly spotless engine with minimal wear and tear(previous owner changed oil every 2k and added a quart of tranny fluid at the end of every 3rd oil change and drove mostly highway), and very little carbon build up (when i took off the intake manifold/exhaust manifold i verified this). |
Originally Posted by MASTERS
(Post 489319)
those things are a pain to get off!!!
BUT i found them at a store, there generic 90 degree vent valves for chrysler, and you by the seals separate, but they are out there ! just check the akward generic section of autopart stores |
well went to the local dealership today, it was 29.19 for the whole thing, the gromet/ccv/pcv and the tube with the 90 elbow on it at the end that goes to the intake. of course it was out of stock but itll be in tomorrow at 9 so ill update on it then. gotta buy a new air filter now too...
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Is it possible to get this assembly off without removing the valve cover?
From what I have read they are prone to cracking and i would think the valve cover would need to come off to keep the broken bits from falling in. I want to do this but really do not feel like taking the valve cover off. |
Originally Posted by 87cherokee14
(Post 490404)
well went to the local dealership today, it was 29.19 for the whole thing, the gromet/ccv/pcv and the tube with the 90 elbow on it at the end that goes to the intake. of course it was out of stock but itll be in tomorrow at 9 so ill update on it then. gotta buy a new air filter now too...
Cruiser’s Valve Cover Mod Most early and even later Renix 4.0s could be bothered by excessive oil in the air cleaner box. A fix from my old days as Service Manager at a Jeep dealership follows. Information was provided to me from a buddy at JeepTech during those days. I don’t believe it ever came out in a Technical Service Bulletin. Remove the valve cover and turn it over. Next, remove the fluted tubes that are now facing you by removing three screws on each. Chop 1 inch off each of them. Then, about a half inch up from the area where you just sawed them off, drill a half inch hole in the tubes so the holes will face the rear of the valve cover. Clean and de-burr/sand all rough edges nicely, clean with solvent, and reinstall. Don’t be concerned about the chintzy gaskets that will probably crumble into oblivion when you remove the fluted tubes. They can go back together without gaskets. |
Originally Posted by MASTERS
(Post 489305)
dont mean to bring bad news, but its not just a clogged ventilation line, no matter what, there is always an explanation for abnormal findings when it comes to motors..... its called blowby, your piston rings are failing....
The crankcase, that which contains the crankshaft and connecting rods, is the bottom side of the engine - you can see the bottom of the pistons from under there. Compressed fuel and air mixture burns in the cylinder on the top of the pistons. When the rings become tired and worn they allow some of this compressed and burning mixture to leak past and escape into the crankcase. That is called "blow by". In old engines that blowby simply vented into the atmosphere via a tube called a crankcase vent tube. The EPA found bad stuff in that blowby gas and mandated that the engines must suck up that stuff and burn it to render it harmful in some other way. In came the PCV which stands for Positive Crankcase Ventilation, named after the then head of the EPA Pierre Positive. This system makes the engine suck the junk out of the crankcase via the PCV Valve into the intake manifold and back thorough the system. Welll, if that system is sucking the junk out, there must be a source of air to go into the crankcase else you would just implode the engine and the oil pan would collapse. Soooo, they ran a tube from the top of the valve covers to a source of clean air so that dirt would not get sucked into the crankcase. (note: the valve cover covers the valve train but that is also part of the crankcase - air and blow-by move readily between those zones in the engine.) The source of clean air which was chosen is the air cleaner - makes sense, except for the fact that the air doesn't go thorough the air cleaner filter, so they put a little kotex-like pad in there to clean the bugs and stones out of the air. |
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