Exhaust leaks underhood

[JHZR2]

Anyone have tips for chasing exhaust leaks?

I know on my Cummins 4x4 and my 1991 300D, when stopped at lights with the fan on, I sometimes get stronger than expected diesel exhaust fumes.

I know also that the Land Cruiser that my brother recently bought had some repair putty on the y pipe going into the catalytic converter, at the welded junction.

I don’t have a smoke machine. I do have a shop vac. I’ve seen the ChrisFix video about pushing air up the exhaust pipe by using a shop vac on blow setting.

I can say this - I see no signs of soot, smoke, etc I either the Mercedes or Dodge. I’d think I’d see a black spot. Nothing.

So, what approach do you use?

I may ultimately replace parts, certainly exhaust manifold gaskets, as I know they get leaky, and the Cummins manifold tends to shrink a bit with cycling and heat. But I’d like to get a grasp of the source.

I had some leaks in the post turbo down pipe in my old 1983 300D, but it never smelled in the cabin, I just heard it. This I can definitely smell if underhood with the engine running (but can’t see), and sometimes in the cabin when stopped (never when running). Suggestions?

Thanks!

 

[JTK]

I wonder if you have missing flaps on the body vents if so equipped?

 

[JHZR2]

I wonder if you have missing flaps on the body vents if so equipped?

No I don’t think so. If we take the occasional (and it is occasional) smell in the cabin out of it, it’s most obvious when I’m working underhood with the engine running.

The engine bay is actually sealed all around from the rest of the underhood space and cowl. So the cabin smell is likely after it is idling in place too long when the underhood leak has “come around” underneath and to the cowl. It’s really not much of an issue 99% of the time. But underhood it’s quite obvious that the smell is coming from nearby.

Car burns no oil, has good injectors, good seals around the engine, etc.

You can see how the engine seals around three sides here. The front seals from the hood. So the engine is in a space sealed with rubber seals against the hood.

The Cummins only has a seal at the rear near the cowl. It’s in fine shape.

 

[JTK]

No I don’t think so. If we take the occasional (and it is occasional) smell in the cabin out of it, it’s most obvious when I’m working underhood with the engine running........The Cummins only has a seal at the rear near the cowl. It’s in fine shape.

I didn't word it right above. Cabin vents is what I was referring to.

Your truck should have cabin vents on the back of the cab between the cab and bed.

Cars usually have them at the rear corners, hidden by the rear bumper cover.

 

[eljefino]

Stuff a rag in the tailpipe and idle. If you have a leak it will get louder. If you don't, it will blow the rag out. (This might work worse on diesel engines that pump a greater amount of air at idle.)

 

[2009Caraman]

can't really go wrong with the shopvac method. Tape it in to the tailpipe and let her blow.

Has never failed me.

 

[SC Maintenance]

If you can narrow it down to an area - like using the shop vac method - get a spray bottle and fill it with about 1/3 dish soap - 2/3 water. When cold spray it all around the general area with the leak and start it up. The exact location of the leak will bubble.

Depending on how far upstream you only have like a minute until it gets too hot and evaporates all the liquid off.

 

[JHZR2]

Stuff a rag in the tailpipe and idle. If you have a leak it will get louder. If you don't, it will blow the rag out. (This might work worse on diesel engines that pump a greater amount of air at idle.)

I was thinking a potato, lol. I can try this before the shop vac because I’ll just do it before I drive to work tomorrow (if I have time). More detailed assessment with shop vac maybe on the weekend, and on the Land Cruiser.

 

[wwillson]

If you have an exhaust leak in a diesel, you should see soot where it's leaking.

It's possible you could have caught a wind blowing exhaust back to the air intake for the cabin air. With no soot, this is where I would place my bet.

 

[dishdude]

I was thinking a potato, lol. I can try this before the shop vac because I’ll just do it before I drive to work tomorrow (if I have time). More detailed assessment with shop vac maybe on the weekend, and on the Land Cruiser.

I was thinking bananas, Axel Foley style.

Banana In The Tailpipe Eddie Murphy GIF - Banana In The Tailpipe Eddie Murphy Beverly Hills Cop - Discover & Share GIFs

Click to view the GIF

tenor.com

 

[brianl703]

I was thinking bananas, Axel Foley style.

MacGyver used a potato.

 

[JHZR2]

If you have an exhaust leak in a diesel, you should see soot where it's leaking.

It's possible you could have caught a wind blowing exhaust back to the air intake for the cabin air. With no soot, this is where I would place my bet.

Could be. On the 300d I know I have a leaky return hose so it could be just some vaporizing diesel on the hot injectors. I got new tygon or Viton (whichever is better) hose so I’m not sure why it seeps. That could be it.

On the truck I need to look closer.