[SOLVED] Help appreciated finding my oil leak

[TahoeRestore]

2003 Tahoe 170K mi, 5.3L. 4WD. I've been trying to fix an oil leak and am looking for advice on the next step. I have replaced the Oil Pan gasket and the Oil cooler line blanking flange (pic). I cleaned up the surfaces nicely, used RTV at the corners, hopefully aligned the oil pan with the back plate, and replaced the oil pickup tube o-ring. I can't see any oil around the oil pan gasket area, but getting oil drops appearing on the inside mounting bolt for the starter (pic) and a little on the left rear pan long bolt (pic).

I've looked up top with an inspection camera around the Cam Position Sensor and Oil Pressure sensor which I replaced a year ago (pics). I see oily grime up there. It hard to clean and see if it gets wet again. I can't see any sign of a leak around the valve cover gaskets but will probably be replacing those soon anyway since it's not that hard of a job. I would get the new design cover.

I'm concerned it may be the Rear Main Seal or rear engine cover gasket. It looks pretty clean on the fly wheel and inside the bell housing (inspection cam pics).

I've noticed that it continues to leak even when it hasn't been running. It's been sitting for three days and still leaking (floor pic). Isn't the oil level in the pan lower that the gasket at the top of the pan? The front of the truck is on stands so maybe the oil level in the rear of the pan is above the pan's top?

If it's the RMS or rear plate gasket, I'm going to have it fixed by a shop and get a transmission rebuild while it's off. The transmission and engine have no issues so hopefully if it's not leaking there.

Like a lot of you, this truck is my baby and I've been keeping it up and improving it for years. Ideas are greatly appreciated.

Thanks!

 

[B-train]

2003 Tahoe 170K mi, 5.3L. 4WD. I've been trying to fix an oil leak and am looking for advice on the next step. I have replaced the Oil Pan gasket and the Oil cooler line blanking flange (pic). I cleaned up the surfaces nicely, used RTV at the corners, hopefully aligned the oil pan with the back plate, and replaced the oil pickup tube o-ring. I can't see any oil around the oil pan gasket area, but getting oil drops appearing on the inside mounting bolt for the starter (pic) and a little on the left rear pan long bolt (pic).

I've looked up top with an inspection camera around the Cam Position Sensor and Oil Pressure sensor which I replaced a year ago (pics). I see oily grime up there. It hard to clean and see if it gets wet again. I can't see any sign of a leak around the valve cover gaskets but will probably be replacing those soon anyway since it's not that hard of a job. I would get the new design cover.

I'm concerned it may be the Rear Main Seal or rear engine cover gasket. It looks pretty clean on the fly wheel and inside the bell housing (inspection cam pics).

I've noticed that it continues to leak even when it hasn't been running. It's been sitting for three days and still leaking (floor pic). Isn't the oil level in the pan lower that the gasket at the top of the pan? The front of the truck is on stands so maybe the oil level in the rear of the pan is above the pan's top?

If it's the RMS or rear plate gasket, I'm going to have it fixed by a shop and get a transmission rebuild while it's off. The transmission and engine have no issues so hopefully if it's not leaking there.

Like a lot of you, this truck is my baby and I've been keeping it up and improving it for years. Ideas are greatly appreciated.

Thanks!

I'm going to say 100% rear engine cover. The rear main seals rarely go bad, but the stupid cover gasket gets hard with age and then starts to weep. At 23 years old, it's due.

 

[SpareParts]

I'm thinking the oil cooler line bypass. It's actually hard to get a good no leak seal

 

[TahoeRestore]

I'm going to say 100% rear engine cover. The rear main seals rarely go bad, but the stupid cover gasket gets hard with age and then starts to weep. At 23 years old, it's due.

Thanks for the feedback. That's what I'm thinking too. I suppose it doesn't make much difference if the RMS or back cover gasket is leaking since both the seal and gasket should be replaced while it's apart. I just need to decide how long to live with the leak and how much engine/transmission refurb, if any, to have done.

 

[TahoeRestore]

I'm thinking the oil cooler line bypass. It's actually hard to get a good no leak seal

Thanks. I replaced the bypass plate gasket and can't find any leak there. See Pic 6730.

 

[SpareParts]

The only other place i can think of would be the valley cover plate. Can't remember at the moment but i think there is an oil galley plug behind the started that could leak.
If not one of them then you got some real work to seal it up.

 

[afpj]

Time for some UV dye...

 

[Joseph Garcia]

While you have the transmission out, change the plastic oil barbell on the back of the motor with a billet oil barbell.

 

[TahoeRestore]

The only other place i can think of would be the valley cover plate. Can't remember at the moment but i think there is an oil galley plug behind the started that could leak.
If not one of them then you got some real work to seal it up.

Thanks. The leak seems to be from that area, though there is a small leak on the other side of the engine. I'm going to pull the starter and look for that galley plug today.

 

[TahoeRestore]

While you have the transmission out, change the plastic oil barbell on the back of the motor with a billet oil barbell.

Thanks for the tip. We will replace it if we have to take out the transmission.

 

[SpareParts]

Just went and looked at my block. Behind the starter is the crank position sensor.

 

[hagar]

Sounds like its rear seal like others have said, but first make sure your pcv system is flowing properly. It takes very little reduction in flow to cause a pressue build up on ls engines, then they can leak oil out of anything once pressurized.

Also check the dipstick tube where the mount for the tube is attached to the tube. I have seen a couple trucks with leaks that people had been chasing, that was the little tack welds that hold the tube to the metal tab/mount. Once those leak, the oil ends up all over the lower side of the engine block.

 

[Goldwing2000]

The only other place i can think of would be the valley cover plate.

Concur with this. Most likely the valley plate and/or the pressure sending unit. Since you're already planning to do VC gaskets, might as well do intake and valley plate, too. And then you can take a better look at the pressure sender and see if it's leaking, either externally from the threaded portion or internally through the sender itself.

With as clean as it is inside the bellhousing, I would be hesitant to diagnose it as anything to do with the rear cover.

 

[mattt]

One other possibility that is often overlooked is the cam position sensor O-ring. Up top it won't show a leak, but that sensor has an O-ring about half way down it, so the leak is internal inside the block and leaking out at the back in the bellhousing.

 

[TahoeRestore]

Sounds like its rear seal like others have said, but first make sure your pcv system is flowing properly. It takes very little reduction in flow to cause a pressue build up on ls engines, then they can leak oil out of anything once pressurized.

Also check the dipstick tube where the mount for the tube is attached to the tube. I have seen a couple trucks with leaks that people had been chasing, that was the little tack welds that hold the tube to the metal tab/mount. Once those leak, the oil ends up all over the lower side of the engine block.

Thanks for the input. I can't remember checking the PCV valve or those welds on the dipstick tube. I'll be providing updates as this progresses.

 

[TahoeRestore]

One other possibility that is often overlooked is the cam position sensor O-ring. Up top it won't show a leak, but that sensor has an O-ring about half way down it, so the leak is internal inside the block and leaking out at the back in the bellhousing.

Hmm. Didn't know that one. I was looking for a leak on the outside top surface and couldn't see it there very well. More to come. I'm out of town for a bit so won't have any findings for a while.

 

[GregBunney]

Hmm. Didn't know that one. I was looking for a leak on the outside top surface and couldn't see it there very well. More to come. I'm out of town for a bit so won't have any findings for a while.

Would love an update whenever you’re back in town and get around to it, I’m in about the exact same boat haha

 

[TahoeRestore]

Glad to provide an update. I'm doing all I can to avoid an unnecessary transmission removal/rebuild. I decided to repeat the oil pan removal with regasketing/resealing. Since returning home I've done a lot of cleaning and looking. Thanks to all for suggestions on where to look. I'm fairly certain there are no leaks up top. Oil only appears at the back corners of the oil pan at the level of the gasket (pics). None above that line. It still could be coming out of the rear engine plate or around the crank seal, but I don't see it when looking through the bell housing inspection cover. Also now that I have the Oil pan removed, I can't see any oil in that tight area between the flywheel and the back of the engine.

Another clue - My oil leak is worse (pic after 2 weeks in garage) than it was before I replaced the oil pan gasket the first time. I hoping that I didn't do a careful job of sealing the gap where the rear engine plate mates with the block. It's also possible I scraped the sealant when I jostled the pan back in place.

I will provide another update Monday after the sealant cures. Fingers crossed.

 

[strutaeng]

The RMS is quite difficult to pinpoint.

I used dye on my 06 Suburban, and even then, I had to look through the bottom transmission bellhousing cover ( on the 4L80e the cover is removable), through the flexplate holes and right into the RMS crank seal. I was able to barely see a drip.

I think what happens is it tends to leak the most while the engine is running, then the flexplate flings the oil out everywhere via cebtrifugal forces. The flexplate actually stays dry.

My truck had a small leak for a while, then suddenly it started leaking a lot before i had to fix it...SMH

 

[LsHart]

Just went and looked at my block. Behind the starter is the crank position sensor.

Back of intake. Oil pressure sensor good?