Pungent "chemical" smell when hot

[glennc]

I've wondered about this for a long time. Many cars, when they get stinking hot from being driven in hot weather, give off this smell from the engine compartment that is hard to describe, but my best attempt would be to say that it is a pungent, "chemical" sort of smell, maybe something that could be caused by hot plastic or rubber or some type of sealant. I've heard other people try to describe what I think is the same smell, but never heard any explanation of what it could be.

I often smell it while walking through parking lots and sometimes from my own cars when they're good and hot in 90-plus-degree weather. Some cars never do it, some do it every time they get hot, others only sometimes.

I don't think it's related to overheating, or being too hot, just from normal engine compartment heat in hot weather.

Anybody know what I'm talking about? Any ideas?

 

[moribundman]

In case of many new (German) cars the cosmoline type engine compartment preservative smells when heated. Also, many kinds of plastic will gas out volatile compounds at an increased rate when heated. The smell definitely decreases with age of the vehicle.

 

[brianl703]

Could it be crankcase gasses backing up through the intake and out into the atmosphere after the engine has been shut off?

 

[glennc]

Well, it doesn't smell like any sort of combustion gas and it's not confined to German cars. My CR-V and our long-gone '84 Subaru were the worst I've had. The 325i does it sometimes but has to be unusually hot (and the cosmoline is gone, thanks to much time and effort).

I thought for a while it might be hot battery gases, but the 325i has the battery in the trunk.