Mysterious oil leak
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5th Wheeling
Joined: Oct 2025
Posts: 49
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Mysterious oil leak
I am having a really difficult time figuring out where this oil leak is coming from..it appears to be from the top part of the engine because it leaks down in between the oil pan and starter. Here's the thing, valve cover gaskets are new and dont leak, that plug thats on the back of the cylinder head isnt leaking, no leaks in the engine valley and rear main isnt leaking.. also verified turbo pedestal isnt leaking (its new with new o rings)
Mountain Pass
Joined: Jan 2009
Posts: 174
Likes: 2
It may be diesel from the fittings on the rear of the heads. These o rings go bad, especially how old these trucks are. https://dieselorings.com/products/7-...l-line-sleeves
Mountain Pass
Joined: Jan 2009
Posts: 174
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I had what I thought was an oil leak. Checked everything related to oil, last thing to check was the rear main seal. Ended up finding multiple diesel leaks from my e-fuel hoses in the valley. That fixed my “oil” leak.
Just sharing my experience, went down the same road as you.
Just sharing my experience, went down the same road as you.
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5th Wheeling
Joined: Oct 2025
Posts: 49
Likes: 5
Thats been removed. New pedastal, new kc turbo, up pipes etc..I will check the diesel leak for the hell of it but its a fairly bad leak and it doesnt smell like diesel. I get almost 13mpg with a 6k trailer so I dont think I have any leaks
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5th Wheeling
Joined: Oct 2025
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This is why im so stumped about it. The top of the engine is completely leak free. Its also getting the transmission bolts wet too so idk..pulling my hair out with this one
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5th Wheeling
Joined: Oct 2025
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Honestly its probably the rear main seal housing..thats literally the only thing It could be..
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Cargo Master
Joined: Apr 2012
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From: Bottom Of Pikes Peak
not true...it could also be the big oil galley plugs on the ends of the heads. could be valve cover gaskets
If you can't find the source, clean everything up and put UV dye in your oil, you will find the source and you don't even necessarily need a black/ UV light...but it's definitely helpful
If you can't find the source, clean everything up and put UV dye in your oil, you will find the source and you don't even necessarily need a black/ UV light...but it's definitely helpful
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5th Wheeling
Joined: Oct 2025
Posts: 49
Likes: 5
not true...it could also be the big oil galley plugs on the ends of the heads. could be valve cover gaskets
If you can't find the source, clean everything up and put UV dye in your oil, you will find the source and you don't even necessarily need a black/ UV light...but it's definitely helpful
If you can't find the source, clean everything up and put UV dye in your oil, you will find the source and you don't even necessarily need a black/ UV light...but it's definitely helpful
Its leaking down the upper engine through that leak hole in between the starter and oil pan. Ive ruled out everything on the top end. Its not the rear main seal because the oil pan is completely clean. Only thing that would make sense is the rear main seal housing and its the only thing i cant check without removing the transmission
Cross-Country
Joined: Mar 2025
Posts: 63
Likes: 28
Is your fuel bowl/stock fuel pump still in place? Has your HPOP ever been pulled/resealed? I understand you say you've ruled out the engine valley, but there are a ton of leak points in the stock fuel/HPO systems. Your rear main seal wouldn't be getting your transmission bolts wet. I originally assumed that my truck was leaking diesel until I pulled my fuel bowl, at which point I learned it was a 70/30 diesel/oil mixture.
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5th Wheeling
Joined: Oct 2025
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Is your fuel bowl/stock fuel pump still in place? Has your HPOP ever been pulled/resealed? I understand you say you've ruled out the engine valley, but there are a ton of leak points in the stock fuel/HPO systems. Your rear main seal wouldn't be getting your transmission bolts wet. I originally assumed that my truck was leaking diesel until I pulled my fuel bowl, at which point I learned it was a 70/30 diesel/oil mixture.
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