Exhaust Smell Under Hood

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NewYorkBeemer

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Just got my car back from 7 months of rust, paint and mechanical work and took it for a drive today! Pic of the car below - so happy to have it back but I am turning my attention to two big areas I need to address 1) electrical and 2) the exhaust smell that gets into the cabin.

On the smell, I've ordered the gasket and seal that bookend the air box for the heater, hopefully that will help and I need to take apart the center console for the electrical anyway, so when I do that I will look to replace the foam pad under that gearshift surround panel. I have a new trunk seal - is there anything else I should look to do to eliminate possible causes of exhaust getting into the cabin? Could the windshield defrost vents be the issue or will the underhood gasket/seal solve that?

I went for a long drive today and stopped to open up the hood with the car idling. I could smell exhaust pretty clearly under the hood and I assume that this is the root of the cabin smell issue. The car drips a couple of drops of oil over the week when I don't drive it (from the transmission/engine gasket(s)), so I would be surprised if the cause of the smell is oil dripping on the headers but please let me know if I am wrong about that and how I can check.

If it's not oil, where else should I look for possible causes? I had the exhaust redone from the first muffler back - but in terms of what's under the hood, are the headers the most likely problem? Any ideas on how I can determine the issue?

One other fact that might be relevant - when I turned on the heater last winter for the first time I quickly noticed a build up of white residue on the inside of the windshield right near the defrost vents, and there was a strong exhaust/burning smell. I don't know if this is from a bad heater core or from the fan pulling in exhaust filled air from the under hood - does anyone have a sense? Also, after I drove the car for a while without the heater, I noticed a similar white buildup in the windshield, though less pronounced. That makes me think it's not the heater since the heater was off but wanted to flag it.

Thanks for any help.

ImageUploadedByTapatalk1416724994.044987.jpg
 
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Love the color of your coupe!
Question, after all the engine work was the engine steam cleaned? Could be old oil burning off or a fresh leak.
There are two points in the "tub" area on either side of the windshield wiper motor where water can drain out. You should have the rubber end on the engine side and the end of that piece is a duck-bill that closes when water is not pouring our. Prevents engine smell alone with the seal along thridge between the engine and where the windshield wiper motor is.
 
while good to get the 2 firewall gaskets and the drain tubes that Stan mentioned, it sounds like you have an underhood exhaust leak. I would take off the heat shields and inspect the junction of your block and manifolds. Or do you have headers? There should be gaskets and copper nuts holding it all on. Check tightness of nuts and if cracks in the manifold(s). If manifolds, each one has a small access nut for the old CO probes, ensure that these are sealed tight. Next check the gasket/tightness of where the manifolds join the 2 pipes of the center resonator. You can also listen with hood open to see if it is louder in a particular area. Then work your way back to the rest of the exhaust. Or have a reputable muffler shop check all points for you. Check for holes in all pipes.

Gas leaks and oil burning smells different than exhaust so those would be different issues. If your heater core was bad you'd have a leak in the cabin so it sounds like nasty air is coming in. Is your coolant normal looking in the reserve tank-no white stuff in it? And yes, great color coupe.
 
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NYB, in a perfect world exhaust smell would come from 2 places, the tail pipe and the crank case vent that feeds into the air filter. My first action would be to get your coupe in a very well lit garage (with the door open), pop the hood and let her run for a while and inspect carefully for any abnormalities. There are ways to prevent the smell from coming in, as noted below, but the source would be the first thing to check. If you have a friend who will inspect with you that helps as well as 2 sets of eyes are better than one. I am always surprised what others pick out- I guess that's my tunnel vision-
 
Stevehose said:
while good to get the 2 firewall gaskets and the drain tubes that Stan mentioned, it sounds like you have an underhood exhaust leak. I would take off the heat shields and inspect the junction of your block and manifolds. Or do you have headers? There should be gaskets and copper nuts holding it all on. Check tightness of nuts and if cracks in the manifold(s). If manifolds, each one has a small access nut for the old CO probes, ensure that these are sealed tight. Next check the gasket/tightness of where the manifolds join the 2 pipes of the center resonator. You can also listen with hood open to see if it is louder in a particular area. Then work your way back to the rest of the exhaust. Or have a reputable muffler shop check all points for you. Check for holes in all pipes.

Gas leaks and oil burning smells different than exhaust so those would be different issues. If your heater core was bad you'd have a leak in the cabin so it sounds like nasty air is coming in. Is your coolant normal looking in the reserve tank-no white stuff in it? And yes, great color coupe.
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Thanks for the suggestions - I will take a close look at the junction of the block and the manifolds - can removing the heat shields be done with the car in the ground or will I need to put it on jackstands to access from below?

The smell is exhaust, not oil burning I have confirmed with a few people now so that helps clarify what I am looking for.
 
Is your coupe euro or US? Evap tank in trunk if US has a line to charcoal canister under battery with a line to air cleaner. All hoses must be connected and in good shape to draw those vapors from the plastic tank in trunk or you may have vapors in cabin. It worked on mine, your mileage may vary.
 
Heat shields are 2 10mm bolts for each shield, accessible from the top. Soak them in penetrant for a couple hours/overnight before trying to get them out, they will likely be corroded.

For tightening the copper nuts on manifolds and down pipes, some will be accessible from above, some will need to be hit from below.


NewYorkBeemer said:
Thanks for the suggestions - I will take a close look at the junction of the block and the manifolds - can removing the heat shields be done with the car in the ground or will I need to put it on jackstands to access from below?

The smell is exhaust, not oil burning I have confirmed with a few people now so that helps clarify what I am looking for.
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Stevehose said:
Heat shields are 2 10mm bolts for each shield, accessible from the top. Soak them in penetrant for a couple hours/overnight before trying to get them out, they will likely be corroded.

For tightening the copper nuts on manifolds and down pipes, some will be accessible from above, some will need to be hit from below.
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We took the car to a muffler shop where were able to see it running up on a lift. The flanges where the pipes from the exhaust manifolds connect with the first muffler, right under the gear shift lever, are leaking - this contributes to cabin exhaust smell. Also saw that the same pipes appears to be leaking some exhaust from the junction with the manifolds, which is the cause of the under-hood smell.

Sounds like it is best to replace the pipes entirely as there are too soft to weld? The guy who owned the shop suggested Bosal and showed me an old parts catalog that had the exact pipes diagramed for a 3.0cs, but I don't see any parts on the Bosal website for classic bmws - please let me know if you have seen those available anywhere or if there are other aftermarket options. At this point I have replaced the entire exhaust from the first muffler back so I am eager to put this aspect of the restoration in the past.

Some goods news came as well, the heater seems to be working fine which is a welcome surprise. I am wondering how much force should I expect from the heater blower with at full blast? I can feel the heat come out of both the windshield and foot vents but it's akin to a 2 out or 4 setting on a typical car - is that normal or should it be coming out harder?

Thanks,
Mike
 
Mike, if you have the header pipes that come down from the manifolds off the car you might be surprised how sturdy they are. I took a sanding disk attached to my grinder and literally polished mine- they were very solid though a little pitted as well. I then sprayed them with hi-temp grey/silver header paint and 1100 miles later they look like the day I painted them. Although many folks have some pretty slick exhaust set-ups I feel some would also agree that an original set up has a very specific sound quality so anything you can save may be worth it.
 
Mike, I would go for the new downpipes if they are available (between manifolds and connection to front muffler). The old pipes corrode and pit at the lower ends (the flange connection near the transmission) so it is difficult to get a good seal with those hard compression ring seals used there. Alternatively, you could cut off a few inches at the lower ends and weld on new (same diameter) pipe to get the better seal (only if you could not find new replacements). You might also consider removing the two manifolds and flat sanding all the mating surfaces as well as getting all new gaskets. Also, if you keep the front muffler then you will need to sand the interior of the two pipes that slip over the new downpipes. It is all fairly obvious once things are apart.

good luck,
 
Correction to my post. Sven is correct. The pipes were really sturdy until you get to the first muffler, then they get rotten. The PO welded new pieces there. I cut them off and welded on flanges so I could take apart easier.
 
Check classicgarage for exhaust parts or Marshal at O2 salvage. Bosal has stopped making stuff even for my e24. As stated, if you are successful, put a coat of VHT paint on it.
 
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