Can anyone tell me how to check for an exhaust leak on a diesel?? Have been hearing what sounds like an exhaust leak when driving with the window down on the highway. More noticeable when you have the barrier separating the lanes, and also when I use the engine brake. Had someone rev the engine when the RV was parked but couldn't find anything, so I assume it needs to be under a load. Also guess it may be in the Turbo if that's possible. Any comments appreciated !!

Look for black soot marks emanating form the manifold and onto the side of the head. Most likely in the rear third of the manifold. Also look for cracks on the "ears" that the mounting bolts go through.

we had one on ours, same as you, heard it driving with the window open- I felt around the exhaust pipe (cold) and finally found the leak under the heat shield sleeve.

Ours is a Cat 350...had a leak fixed this summer. Elbow from exhaust brake to muffler, 1/2" hole under heat shroud, new pipe + labor $340.

OP here, Also wanted to mention that my exhaust comes out the right side and the noise sounds like it's on the left side and I do have the side radiator on left side

The "look for black soot" IS the correct way to identify an exhaust leak on a diesel.

Exhaust Leak on a 400 Cummins | Good Sam Community

ScottG
Nomad
Sep 11, 2014
Look for black soot marks emanating form the manifold and onto the side of the head. Most likely in the rear third of the manifold. Also look for cracks on the "ears" that the mounting bolts go through.
rav
Explorer
Sep 11, 2014
we had one on ours, same as you, heard it driving with the window open- I felt around the exhaust pipe (cold) and finally found the leak under the heat shield sleeve.
Teacher_s_Pet
Explorer
Sep 11, 2014
Ours is a Cat 350...had a leak fixed this summer. Elbow from exhaust brake to muffler, 1/2" hole under heat shroud, new pipe + labor $340.
SPRING_STREET
Explorer
Sep 11, 2014
OP here, Also wanted to mention that my exhaust comes out the right side and the noise sounds like it's on the left side and I do have the side radiator on left side
wolfe10
Explorer
Sep 11, 2014
The "look for black soot" IS the correct way to identify an exhaust leak on a diesel.
hsteinle
Explorer
Sep 11, 2014
The Cummins 400 ISL has a KNOWN problem of developing a 'leak' in the manifold area around 60,000 miles. It would be best to take it into a Cummins shop and have them check to be sure you do NOT have that developed leak as it CAN cause serious problems including fires.
Scottiemom
Nomad
Sep 11, 2014
Ours was fixed this summer as Teacher's Pet mentioned. I first noticed it when we had fumes in the bedroom whenever we would stop for lunch or for the night. So next day before we left, he pulled up the inspection panel in the rear bedroom and I fired the engine. He immediately saw where the leak was. :E

Dale
Snomas
Explorer
Sep 11, 2014
Mine showed black soot in the engine compartment.
Executive45
Explorer III
Sep 11, 2014
Black soot is the tell. Surprised your engine check light hasn't come on...maybe it's only a matter of time. You don't say what engine you have but Cummins can hook it up to their computers and tell you in a minute where it is. Meanwhile, check the vacuum line running to your exhaust brake for leaks....Dennis
SPRING_STREET
Explorer
Sep 11, 2014
Executive, I have the Cummins 400 ISL engine. Was at Cummins two weeks ago and had the computer put on it for an alternator issue. The only thing that came up was the alternator and low on anti-freeze which took almost 2 qts. They were told about the exhaust leak but nothing showed up and I had the alternator replaced elsewhere because of a 6 hour difference in labor !

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Exhaust Leak on a 400 Cummins

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