4.0L rebuild problems
rkerby
09-19-2005, 05:35 PM
I have a '93 Jeep Grand Cherokee that was recently rebuild by a professional mechanic. The mechanic is knowledgeable and trustworth...and he is stumped. He has been into the engine 3 times...and it is STILL SMOKING. We initially thought it could be the valve guide seals...so he went back in and changed them. It didn't fix the problem. So this last time he pulled the engine and replaced the moly rings that were initially used (thinking they may have not seated) with stainless rings. It didn't fix the problem either. The jeep smokes continuously...not just at start up. The smoke is white. I have heard that there was an issue with the PCV valve on this engine. I have also had some vacuum problems with this engine and vehicle. Please help.
JDPascal
09-19-2005, 07:05 PM
Welcome to AF rkerby
First off, was the smoke a problem before the rebuild??
White smoke is usually an indication of coolant/water in the cylinder so based on your description, I would be looking for a cracked head or a head gasket. Heads usually crack in the web between the valves though sometimes elswhere in the combustion chamber and less often inside the ports.
Not sure on the 4L if there are cooling passages in the intake manifold but there could be a path for coolant there if there is a crack there.
If the cylinders were bored oversize, there could be a shifted core that might cause a thin/porous cylinder wall where coolant might make its way into the cylinder.
If the coolant is getting into the cylinder, then it will likely be in the oil too. If it is not building up quickly enough to see and make the oil milky yet, you can test for small amounts by doing a crackle test by dropping a small amount of the oil from the engine on a hot surface.
If you get a popping/crackling sound like water in a frying pan, you know there is a problem. It should be quiet like new oil out of the bottle on the hot surface.
If I have missed something about your description and gone in the wrong direction here, let me know........
JD
First off, was the smoke a problem before the rebuild??
White smoke is usually an indication of coolant/water in the cylinder so based on your description, I would be looking for a cracked head or a head gasket. Heads usually crack in the web between the valves though sometimes elswhere in the combustion chamber and less often inside the ports.
Not sure on the 4L if there are cooling passages in the intake manifold but there could be a path for coolant there if there is a crack there.
If the cylinders were bored oversize, there could be a shifted core that might cause a thin/porous cylinder wall where coolant might make its way into the cylinder.
If the coolant is getting into the cylinder, then it will likely be in the oil too. If it is not building up quickly enough to see and make the oil milky yet, you can test for small amounts by doing a crackle test by dropping a small amount of the oil from the engine on a hot surface.
If you get a popping/crackling sound like water in a frying pan, you know there is a problem. It should be quiet like new oil out of the bottle on the hot surface.
If I have missed something about your description and gone in the wrong direction here, let me know........
JD
rkerby
09-19-2005, 09:20 PM
I sincerely appreciate you taking the time to reply.
The reason I believe it is engine oil smoke is because it is using oil. It smoked SOME before the rebuild…it smokes much more now! But I will not rule out water burning because the vehicle has been using some water…just not sure if there is a crack/leak in the reservoir or elsewhere.
I have a gut feeling that something wasn’t put back together quite right…ie. vaccum lines, gaskets, PCV valve, etc. I just don’t know what would cause it to smoke. I do know that he has had the head off 3 times and put a new head gasket on each time. It has also been to the machine shop twice to have them do a head job.
The reason I believe it is engine oil smoke is because it is using oil. It smoked SOME before the rebuild…it smokes much more now! But I will not rule out water burning because the vehicle has been using some water…just not sure if there is a crack/leak in the reservoir or elsewhere.
I have a gut feeling that something wasn’t put back together quite right…ie. vaccum lines, gaskets, PCV valve, etc. I just don’t know what would cause it to smoke. I do know that he has had the head off 3 times and put a new head gasket on each time. It has also been to the machine shop twice to have them do a head job.
JDPascal
09-19-2005, 09:48 PM
If the head has been off that many times I sincerely hope that the machine shop has had the presence of mind to crack check the head with dye or magnaflux it.
I hope that has eliminate the head as the source of the problem.....
What kind of oil ring was used for the rebuild?? The compression rings are designed to ride over most of the oil that the oil rings leave on the cylinder wall. If it was a three piece oil ring and the expander ends are overlapped when the rails are installed, the oil ring will do nothing......Seen it happen before. you get smoke forsure then. Also if the ring gaps are not staggered, it can be a problem as the oil passes up the gap. This would be less severe if it smoked at all tho...
Not sayin your man goofed just that it has happened before.
JD
I hope that has eliminate the head as the source of the problem.....
What kind of oil ring was used for the rebuild?? The compression rings are designed to ride over most of the oil that the oil rings leave on the cylinder wall. If it was a three piece oil ring and the expander ends are overlapped when the rails are installed, the oil ring will do nothing......Seen it happen before. you get smoke forsure then. Also if the ring gaps are not staggered, it can be a problem as the oil passes up the gap. This would be less severe if it smoked at all tho...
Not sayin your man goofed just that it has happened before.
JD
roboto1720
09-19-2005, 10:00 PM
If the head has been off that many times I sincerely hope that the machine shop has had the presence of mind to crack check the head with dye or magnaflux it.
I hope that has eliminate the head as the source of the problem.....
What kind of oil ring was used for the rebuild?? The compression rings are designed to ride over most of the oil that the oil rings leave on the cylinder wall. If it was a three piece oil ring and the expander ends are overlapped when the rails are installed, the oil ring will do nothing......Seen it happen before. you get smoke forsure then. Also if the ring gaps are not staggered, it can be a problem as the oil passes up the gap. This would be less severe if it smoked at all tho...
Not sayin your man goofed just that it has happened before.
JD
The white smoke is one of two things. Antifreeze or auto trans. fluid. You have the wrong head gaskets or is sucking trans fluid via a vacum line. good luck
I hope that has eliminate the head as the source of the problem.....
What kind of oil ring was used for the rebuild?? The compression rings are designed to ride over most of the oil that the oil rings leave on the cylinder wall. If it was a three piece oil ring and the expander ends are overlapped when the rails are installed, the oil ring will do nothing......Seen it happen before. you get smoke forsure then. Also if the ring gaps are not staggered, it can be a problem as the oil passes up the gap. This would be less severe if it smoked at all tho...
Not sayin your man goofed just that it has happened before.
JD
The white smoke is one of two things. Antifreeze or auto trans. fluid. You have the wrong head gaskets or is sucking trans fluid via a vacum line. good luck
rkerby
09-19-2005, 11:07 PM
The white smoke is one of two things. Antifreeze or auto trans. fluid. You have the wrong head gaskets or is sucking trans fluid via a vacum line. good luck
In talking with the mechanic and my father we thought that transmission oil via a vacuum line could be the problem... Do you know if the these particular transmissions have vacuum lines that could cause this problem...if so which one would be a good starting place.
In talking with the mechanic and my father we thought that transmission oil via a vacuum line could be the problem... Do you know if the these particular transmissions have vacuum lines that could cause this problem...if so which one would be a good starting place.
JDPascal
09-19-2005, 11:53 PM
Forgot about tranny fluid. Is your transmission going thru oil??? Beautiful top lube tho.........
Only vacuum line on a transmission would be to a modulator servo. Not sure if yours would have one - Look at the back of the transmission near the tailshaft housing. There'll be a line coming off of a little "can". The other end will connect to the intake manifold. Pull the line off and see if there is oil in it. if there is, replace the modulator. You may or maynot have noticed shift problems.
JD
Only vacuum line on a transmission would be to a modulator servo. Not sure if yours would have one - Look at the back of the transmission near the tailshaft housing. There'll be a line coming off of a little "can". The other end will connect to the intake manifold. Pull the line off and see if there is oil in it. if there is, replace the modulator. You may or maynot have noticed shift problems.
JD
Automotive Network, Inc., Copyright ©2026