LLY: Oil leak

mplecha

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May 13, 2012
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South Carolina
I just got this truck about a month ago. It's an 04.5 LLY 4x4. I noticed a bit of oil on the driveway the other day. Looking underneath, I see a good bit of oil collected at the block/bellhousing area. I'm fairly certain it's oil. There's no oil on the pan, and I haven't been able to find any oil on the engine anywhere. It looks like it's coming straight down as there's not any oil past the front end of the transmission, either. Are there any common leaks in this area I should check first? The truck has the PCV rerouted, already. Thanks, guys!
 

mplecha

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May 13, 2012
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South Carolina
I did some more looking around, and it looks like it's the upper oil pan. I guess the transmission has to come out for that. I don't see any oil coming down block anywhere. It's coming down the area between the oil pan and the transmission at the back end of the engine. Would it be possible for the rear main to leak in that area? I'd think a rear main leak would come out of the little opening at the bottom of the block/transmission junction.
 

LBZ

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Jul 2, 2007
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Moved here.

My turbo drain leaks and it runs down both sides of the trans at the back of the block. A real MF to fix and tough to pinpoint if you don't know where to look. If the oil leak is coming from up high, I would guess that is the source of your oil leak-likely where the flange for the drain bolts to the block.
 

mplecha

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May 13, 2012
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South Carolina
It doesn't look like it's coming from above. Where is the turbo drain?

As best I can tell, there isn't any oil coming down the sides of the block. I can't quite see in there, but all looks and feels dry. I think it's the upper pan unless the lower pan is leaking upwards.. If it was a small drip, I'd leave it, but I've lost at least a quart since I changed the oil 1500 miles ago.
 

LBZ

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The turbo drain is at the top of the engine right at the rear under the exhaust side of the turbo.
It could be the upper oil pan or the rear main seal. If it's the rear main seal leaking, it's a big job (obviously) to change and requires a special seal installing tool to replace. My money would be on the seal as the issue if it's losing that much oil.
There are also a couple oil gallery plugs in the rear of the block that are covered up mostly by the rear cover. These could also be the source of the leak, but I don't believe a leak from them is very common. Some guys pull them out, tap them and put plugs in when they do rebuilds to guarantee they don't have a leak from them.
 

mplecha

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May 13, 2012
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South Carolina
I believe it's the upper oil pan. The leak isn't as bad as I thought. I must have checked the oil on unlevel ground. Been working too many night shifts, I guess.
 

wilsonck

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May 8, 2008
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Calgary, Ab
I bet your problem is the oil cooler. I just had the same problem . Oil filter screws onto oil cooler and both oil and coolant goes through it.