I rarely keep the heat on in my truck when its not warming up, but yesterday I was driving along and noticed the window fogging so turned on the defrosted. As soon as i came on the smell hit me a mix between burnt rubber and crap. Now usually i keep a window down while its warming up so if i bump the lock the keys arnt locked inside and I've only ever noticed a very faint smell that dissipated quickly, i should also mention that i kept an eye on the temp and it stayed at normal or right below. What could this be? It does not smell like death so i highly doubt that it is a dead mouse but maybe mouse crap? It did sit for awhile and i know i have mice in my garage. Thanks for any help
Just in case it matters it is a 1991 f150 with 300 six.

 

Maybe time to replace heater core? I know when mine started to go out it started to stink like anti-freeze and rubber mixed in. I think the leaking fluid softened up the gaskets and made them start to stink. Not a bad job to do yourself, at least in my '95.

 

Accessing the heater core is SUPER-easy on these trucks; easier than changing a headlight. Flip the glove box down, remove about 7 8mm screws, and look inside before buying any parts.


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While driving it today and i kept the heat on the whole time, only a very faint smell. I am going to take the dash out and take a look next chance I get. I smell no coolant so I don't think its the heater core itself but I could be wrong. Thanks for the help so far!

 

You don't have to take the dash out. Just look inside the heater core cover.

 

there is no need to take the dash out just to look at it

 

I didn't mean dash, i ment the glove box like steve said. I didn't have time today but hopefully tomorrow. It was too warm for heat today and its warming up here in PA so I'm in no hurry but i still want to get to the bottom of it.

 

Pull your blower fan off (under the hood). Stuff gets in there and if it's against the resistor pack it'll burn. Had leaves in one truck, the smoke pouring out of the vents was so thick... well there's a story there. Point is that's where I'd look first for a burning smell