Heat smeals like exhaust

[Gunshow]

Hello, First post here on the Diesel Page.

A/C works great in the truck no smell when it is on.
Turn on the heat and it does heat but it starts to smell like exhaust.

I have no experience with heat issues in vehicles so that's why I am asking the forum.

I did use the search function before I posted this topic, but did not find what I was looking for.

Thank you all for your time.

[svcattle]

The search function is worthless at best on any site unless you like reading 5000 pages of material that has nothing to with what you want . As far as the smell maybe an exhaust leak somewhere?

[Gunshow]

I replaced the vacuum pump a short while ago and while I was in the engine bay I checked exhaust manifolds, Turbo and exhaust system all the way to the back and everything looked good.

I just don't understand what the burning smell could be.

[Dvldog8793]

Howdy
Is it possible that the smell is from a small leak in the heater core and what you are smelling is antifreeze evaporating?
With the engine cold:
Try turning on the heater when you are parked and see if the smell is there, if so open the hood and see if the smell goes away.
If no smell for above then get it hot and try the same thing.
Personally I think you will find a small leak in your heater core.
Good luck.

[svcattle]

Have you ran the engine while checking for exhaust system leaks ?

[Gunshow]

Howdy
Is it possible that the smell is from a small leak in the heater core and what you are smelling is antifreeze evaporating?
With the engine cold:
Try turning on the heater when you are parked and see if the smell is there, if so open the hood and see if the smell goes away.
If no smell for above then get it hot and try the same thing.
Personally I think you will find a small leak in your heater core.
Good luck.

I will try this when I have time this week.
If it is antifreeze leaking wouldn't it smell some what sweet like it usually does?

[Gunshow]

Have you ran the engine while checking for exhaust system leaks ?

Yes I have done this.

[Gunshow]

There could be an exhaust leak that just started recently
So I'm going to try and check again.

I'll have to try turning the heat on and using the recirculate button to see if it still smells the same way. There is a possibility the fresh air door is stuck open which then will tell me I have an exhaust leak.

[More Power]

I'd bet your truck has an exhaust leak in the engine bay and that the hood sealing gasket is not doing its job.

There should be a large side-side rubber lip sealing gasket at the rear of the hood that seals against the cowl. At each hood hinge there should be a foam rubber seal. All this works to keep engine smells away from the windshield cowl air intake for the HVAC system.

An exhaust leak should leave fresh soot at the leak site. So, look for soot...

[Gunshow]

Took the time today to look for the culprit of the exhaust smell in the heater.

I pulled the carpet back on the passenger side to expose the firewall. I began to inspect behind the unit and found a cable with a rubber grommet that had been pulled away from the firewall. The hole through the firewall was directly located at the same height as the intake for the heat and A/C so when I didn't have the heat on recirculate, it would pull exhaust smells from the engine bay directly into the cab. I also removed the blower motor from the front of the unit so I could inspect inside and I found old leaves and a thick black film that was clogging up the A coil. I flushed the coil with cleaner then flushed it again with fresh water. I then blew everything dry, reassembled and tested it out.

The results where fresh clean air whether it was on A/C or Heat recirculating or not. So glad to have this fixed.

Thank You all for your help.