Diesel leak

Brennan123$

New member
Jul 1, 2026
1
0
1
Granville ny
Hey so I am completely lost on this problem first time owning a duramax. I have a diesel leak that’s puddling in my engines valley and I believe it runs down and leaks off the bell housing, it only starts to leak when the engine is up to operating temp and it leaks quite a bit I took off the alternator and stuff to look down in the valley more and I replaced the fuel pressure sensor and when I was doing it it looked the cp3 was wet and there was a short hard line that was wet and then obviously the valley was all wet. Can anyone tell me what they think this might be?
 

2004LB7

Super Moderator
Staff member
Dec 15, 2010
8,643
3,120
113
Norcal
Going to be hard for anyone here to see the leak and pinpoint it for you. You can try cleaning everything up and seeing where it starts getting wet first.

My guess would be a leaking rubber line. But that would probably only happen if you have a lift pump. If not then start looking around the metal lines and fittings. Another posablely is the gear pump on the back of the CP3. It is sealed to the CP3 with some O rings. But this is something you're going to need to do the work on.

Photos might help if you can clean out most of the diesel and dry it. Then watch where it comes from. We can help diagnose it for you

Also moved your thread to the fuel section