Engine Oil Leak - Please Advise Me!

[Time_Like_Tears]

Ok, first and foremost, I am one of those girls with a pretty good working knowledge of cars and engines. Most of what you tell me can be easily interpreted and understood. I also prefer to perform as much work on my vehicles as is possible myself.

So, here’s the situation:

1994 Jeep Grand Cherokee Laredo
5.2L V8
269,000 miles

There is definitely an oil leak somewhere. It may also be burning excessive amounts of oil, I am not sure. The leak seems to have started since we bought it and brought it home, but nothing has happened that would cause it out of nowhere. We know the truck was sitting for a long time, as we drove it, stuff might have unclogged/broken loose/whatever.
Upon inspection of the undercarriage, I noticed that most of the pooling was around the back of the engine, and the transmission oil pan was coated. The drip puddle is on the right side, about a foot behind the right front fender. No fresh oil around the oil pan or oil filter, and no oil on the top of the engine anywhere. Valve covers look great, no apparent leaks. I haven’t removed them yet, though.
It’s dripping on the exhaust, causing a hell of a lot of smoke. The smoke comes out heaviest (under the hood) on the right side, a foot from the fender and right up on the firewall. The tailgate gets coated with oil after driving, and it smokes more when you hit the gas. I noticed yesterday that the smoke comes into the passenger compartment through the vents, as well.
I say it’s also burning because of the heavy smoke, but I am not sure.
It’s a 5 qt. oil capacity, and it dries up in about 50 miles.
The oil pressure sensor may be bad or damaged. The gauge in the dash is not accurate at all. It sits at 80 when the oil is full, then as the level gets below the oil pump, the needle goes haywire before it settles on zero.

What I have done:
Replaced PCV valve (completely clogged, it definitely needed to be done)
Replaced oil pan gasket and rear seal (old gasket looked to be original to the engine – yuck. It crumbled.)
Replaced transmission pan gasket and filter (a waste of time, but didn’t hurt anything. The old one was in great shape)
Replaced main seal on crankshaft (another waste of time. Edges were smooth, no burrs or nicks, and existing seal was in great shape)
Fresh oil and filter, and added Seafoam to clean pistons, rings, valves, etc. Should help clear any buildup in the EGR valve as well.

None of this made any difference whatsoever.

I don’t believe that it’s the head gasket, because coolant levels are normal and there’s been no overheating. The leak is obviously someplace we can’t get to without breaking the whole thing down or pulling the engine altogether. Other possible causes we have considered are that there may be a hole in the block, or the oil pressure sensor mechanism is busted. Other than that, we’re stumped.

The engine runs great otherwise. Tranny seems to be in good shape, smooth transmissions.

Can anyone tell me where else to look for leaks? I am really trying to avoid taking it into the shop. I can tear it down and get to most areas right here in my carport.

Thanks in advance for the help!

[Time_Like_Tears]

Bump?

[Gary_T]

Let’s start by clearing up some terminology.

*Replaced oil pan gasket and rear seal
Replaced main seal on crankshaft *

Normally one talks about a rear main seal. On your engine, it’s a two piece (split) lip seal that goes around the rear of the crankshaft by the rear main bearing cap. The terms “rear seal” and “main seal” are ambiguous and confusing to me, and as used imply two different seals. I would like to know exactly what you mean by each of these terms.

So, did you indeed replace the rear main seal? If so, are you sure that it wasn’t damaged in the installation?

Did you replace the front crankshaft seal (timing cover seal)?

Have you gotten a good look at the rear of the valve covers to ascertain whether there’s leakage there, running down the back of the head(s) and block?

The oil sending unit (oil pressure switch, oil pressure sender, not sensor*) is certainly a possibility. Since it contains oil under pressure, a leaking sender can lose a lot of oil. My info shows it to be located at the top of the rear of the block, between the distributor and the right valve cover.

Another possibility is leakage from the rear edge of the intake manifold. This would be close to distributor/oil sender area mentioned above. Although you mentioned the top of the engine being dry, I’m not sure if you a good look at that rearmost part.

If you haven’t already, remove the air cleaner (and anything else in the way) and get a good look at the rear of the engine from up above (climb onto the engine) with a flashlight and a mirror. Make sure you get your eyes on the parts I’ve mentioned above. All of them can be replaced without engine removal.

It sounds like you might be burning a significant amount of oil. Smoke out the tailpipe can only be from that. But make sure it’s actually coming out of the tailpipe. With some leaks, airflow while driving can produce smoke from under the rear bumper and get the tailgate oily. Regardless, you need to get all external leakage fixed before you can assess how much (if any) oil is being burned.

---

*The term “sensor” is used for parts that give input to the onboard computer (ECU). “Sender” is used for parts that give input directly to a gauge.

[Rick]

@Time Like Tears

It’s dripping on the exhaust, causing a hell of a lot of smoke. The smoke comes out heaviest (under the hood) on the right side, a foot from the fender and right up on the firewall. The tailgate gets coated with oil after driving, and it smokes more when you hit the gas. I noticed yesterday that the smoke comes into the passenger compartment through the vents, as well.
I say it’s also burning because of the heavy smoke, but I am not sure.
It’s a 5 qt. oil capacity, and it dries up in about 50 miles.

As usual Gary T is right on with his advice.
I would like to comment on what I quoted above. A leak can cause the tailgate to be covered in oil. I found this out the hard way on an old Chevy Pickup when I lost the rear main seal 300 miles from home. As far as the oil smoke in the passenger compartment goes, there should be a rubber seal at the top / front of the firewall. This seal is designed to keep smoke and more importantly carbon monoxide out of the passenger compartment. It sounds like yours is either missing or damaged. You should consider replacing it.
Five quarts in 50 miles qualifies as a world class oil leak BTW.
I have seen oil pressure senders come apart from the pressure and spray oil everywhere. I would also consider new valve cover gaskets.
If all else fails, a good shop can add a UV dye to the engine oil. They then run the engine for just a couple of minutes, and by using a black light find the leak. I have seen this work when nothing else would localize a leak.

[Time_Like_Tears]

@Gary T

Let’s start by clearing up some terminology.

*Replaced oil pan gasket and rear seal
Replaced main seal on crankshaft *

Normally one talks about a rear main seal. On your engine, it’s a two piece (split) lip seal that goes around the rear of the crankshaft by the rear main bearing cap. The terms “rear seal” and “main seal” are ambiguous and confusing to me, and as used imply two different seals. I would like to know exactly what you mean by each of these terms.

I replaced this and this. I say ‘rear seal’ as connected with the oil pan gasket, and I did indeed replace the ‘rear main seal’ on the crankshaft. I am as sure as I can be that it wasn’t damaged in the installation. I don’t think it needed replacing anyway. The old one was just fine, in fact I saved it because there were no issues that I could see with the condition of the rubber. I checked the crankshaft for burrs and nicks, and all was smooth.

Did you replace the front crankshaft seal (timing cover seal)?

No, haven’t gotten to that yet. Have considered it, and I will be checking into it next time I have my muscle home to help me tear down.

Have you gotten a good look at the rear of the valve covers to ascertain whether there’s leakage there, running down the back of the head(s) and block

The oil sending unit (oil pressure switch, oil pressure sender, not sensor*) is certainly a possibility. Since it contains oil under pressure, a leaking sender can lose a lot of oil. My info shows it to be located at the top of the rear of the block, between the distributor and the right valve cover.

Another possibility is leakage from the rear edge of the intake manifold. This would be close to distributor/oil sender area mentioned above. Although you mentioned the top of the engine being dry, I’m not sure if you a good look at that rearmost part.

Not such a good look, but I did get my hand back there to feel around, and found nothing within my reach of about 1.5 feet. This was with the air cleaner removed. When my muscle comes back, we’ll tear off everything we can from the top and remove the hood so we can really get a good inspection going. I’m thinking it might be one of those two things, as well. Does the fact that the smoking gets heavier when gas is applied indicate either one over the other?

It sounds like you might be burning a significant amount of oil. Smoke out the tailpipe can only be from that. But make sure it’s actually coming out of the tailpipe. With some leaks, airflow while driving can produce smoke from under the rear bumper and get the tailgate oily. Regardless, you need to get all external leakage fixed before you can assess how much (if any) oil is being burned.

Honestly, I think what’s happening is that a ton of oil is dripping on the exhaust, causing all the smoke, then the oil on the tailgate is what’s getting whipped back there by the driving airflow. There could be some heavy burning going on, as well, given the age of the engine and the condition the PCV valve was in, but replacing the valve may have helped that a bit.

Thank you very much for thinking on this with me. Sometimes we get so wrapped up in an issue that we fail to see all sides, ya know?

[Time_Like_Tears]

@Rick

As usual Gary T is right on with his advice.
I would like to comment on what I quoted above. A leak can cause the tailgate to be covered in oil. I found this out the hard way on an old Chevy Pickup when I lost the rear main seal 300 miles from home. As far as the oil smoke in the passenger compartment goes, there should be a rubber seal at the top / front of the firewall. This seal is designed to keep smoke and more importantly carbon monoxide out of the passenger compartment. It sounds like yours is either missing or damaged. You should consider replacing it.
Five quarts in 50 miles qualifies as a world class oil leak BTW.
I have seen oil pressure senders come apart from the pressure and spray oil everywhere. I would also consider new valve cover gaskets.
If all else fails, a good shop can add a UV dye to the engine oil. They then run the engine for just a couple of minutes, and by using a black light find the leak. I have seen this work when nothing else would localize a leak.

I will certainly look for that seal. Sometimes I have no choice but to use the truck (with a couple 5 qt. bottles of oil in the back, frequent stops, and crossed fingers) and I don’t much relish the whole carbon monoxide poisoning idea.

Now, with this information I have been given, I am leaning toward the oil pressure sender. It needs a full scale tune-up, as well, in which I will definitely include the valve cover gasket replacements.

I swear, this is the most frustrating vehicle I have yet owned. Not least because for the money we paid for it and trying to repair it, we could have had my other car (1994 Saturn with spun bearings) in almost perfect shape, new engine and all. Grr.

Thank you for your advice.

[Gary_T]

@Time Like Tears

I replaced this and this.

Unfortunately, those links come up for me as “page cannot be displayed.”

I say ‘rear seal’ as connected with the oil pan gasket, and I did indeed replace the ‘rear main seal’ on the crankshaft.

And here, unfortunately, I’m still confused. If in the above sentence you’re talking about two different seals, what is the “rear seal” connected with the oil pan gasket? My info shows the pan gasket to be a one-piece affair, and so far I haven’t been able to figure out what this “rear seal” may be.

I rather doubt that the front crank seal is causing the symptoms described - I mainly asked in a quest to figure out which seals had been replaced. Nevertheless, it’s pretty easy to see if it’s leaking, though it may require removing a skid plate or gravel shield to get a look at it.

Does the fact that the smoking gets heavier when gas is applied indicate either one over the other?

Yes, I’d say it points to the oil sender, because oil flow and pressure would increase with the revs.

Honestly, I think what’s happening is that a ton of oil is dripping on the exhaust, causing all the smoke, then the oil on the tailgate is what’s getting whipped back there by the driving airflow. There could be some heavy burning going on, as well, given the age of the engine and the condition the PCV valve was in, but replacing the valve may have helped that a bit.

I agree. At first I equated “smokes more when you hit the gas” with the engine burning oil internally, but when the whole message sunk in I realized that your above analysis in conjunction with a leaking oil sender was consistent with external rather than internal leakage.

Sometimes we get so wrapped up in an issue that we fail to see all sides, ya know?

Yep. Happens to us all.

[Time_Like_Tears]

@Gary T

Unfortunately, those links come up for me as “page cannot be displayed.”

And here, unfortunately, I’m still confused. If in the above sentence you’re talking about two different seals, what is the “rear seal” connected with the oil pan gasket? My info shows the pan gasket to be a one-piece affair, and so far I haven’t been able to figure out what this “rear seal” may be.

From my understanding, the oil pan gasket for some vehicles may not include the rear seal, so really my phrasing was intended for someone who may not have specific access to the specs of my truck. So, I replaced the oil pan gasket and the rear main seal.

Lemme try again here -
this and this.

[Gary_T]

Okay, got it. The pictures came up. While some oil pan gaskets come in several pieces, with separate rubber strips for the curvatures at the front and rear of the pan, all the pieces together are still called an oil pan gasket, or more properly an oil pan gasket set.