Smoking Crossover



I have a 1994 Buick Park Avenue with 134,000 miles; it has a 3.8 engine. When starting the car after it sits idle overnight, smoke rises slowly from under the heat shield that surrounds the crossover pipe for approximately 5-10 minutes. The smoke smells like plastic burning. There is no sign of any exhaust leaks, or oil getting on the crossover. After the smoke stops, it will not smoke again until the next day at start-up.


Mr. Earl


The smoke could be a very small fluid leak that evaporates on the hot pipe, and never reaches the ground. A closer examination is needed; I would normally go to Midas, and have them hoist up the car for a free inspection. They see so many exhaust problems that you and them will quicky zero in on what is happening.


The crossover pipe on this particular car crosses at the back of the heads, over the top of the transmission/bell housing, and can be seen very well from the top. Rubbing your hand over it reveals no oil whatsoever…it is very clean. Any more ideas?

Mr. Earl


Can you run your hand over the top of the bellhousing? I’m thinking perhaps a bit of seepage from the valvecover gaskets is getting on the housing and the radiant heat from the crossover pipe is smoking it. If the oil return channels aren’t draining freely there could be some pooled oil slowly seping through the gasket overnight.

Just a thought.


Yes, I can run my hand over the bellhousing, but the crossover pipe is bone-dry…nothing is touching it…it’s sort of suspended in midair and has a metal heat shield wrapped all the way around it. The heat shield was made in two halves and spot-welded together; the smoke comes from the cracks where it was formed together. If it was oil seeping onto this, it would have to go uphill, because the crossover pipe is arched up approximately 3 inches, to clear the bellhousing. It really does not smell like oil smoke.

Thanks for your thoughts,
Mr. Earl


If there is a fiber insulating material on the back side of the heat shield, and it’s degrading, maybe fallen particles are burning off?

If it’s just a metal uninsulated shield with an air space between the two components, and something is in there burning that wasn’t there before, I’d suspect rodent activity. You may be cooking their winter stores. Or their accumulated nesting material. Or THEM, if they don’t jump ship quick enough…


I have the exact same problem with my 93 Park Avenue. I have no clue what it is. It does smell like burned plastic inside and outside of the car. And it smokes a lot. I had noticed it before, then I let my car sit for a week. Once I started it, I really noticed it. I thought mabye it was a problem with the intake plenum. I took it all apart and replaced the plenum gasket. Nothing has helped. I guess I will just keep driving it and see what happens.


I assume that you’re running your hand over the pipe and under the heat shield? How hard is it to pull the heat shield? Personally I would look at doing that so that I could get a visual. This would also allow an inspection of the underside of the heat shield.


MIDAS? stop I can not take anymore. paid buy products sold,on a pecentage of the num of parts sold,that smells really bad,go to the dealer.