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'01 Century gas/exhaust smell from heater [Solved]

I have a 2001 Buick Century, ~120,000 miles that a couple months ago started smelling like gas or exhaust+gas when the heat was turned on. I’ve changed the cabin air filter. I don’t know how much that could have ever helped.
I couldn’t find a gas leak in the engine compartment, but I didn’t give it a really close inspection.
Where should I check for the most likely leak? Or could it be more of a problem with the cabin air intake?
Any help would be great. I’m a grad student so lots of mechanic time is out of my budget. Thanks.

If the smell is really exhaust gas then you need to have the exhaust system inspected and repaired. Carbon monoxide is very dangerous and can easily accumulate in the vehicle cabin. The cabin air filter cannot block carbon monoxide because it is a gas and will enter easily along with regular air. The cabin air intake is necessary and there is no way to seal the cabin from carbon monoxide if it is present. Adjust your budget and get the exhaust system repaired immediately. Roll down your windows if you must drive the vehicle.

You have an exhaust or fuel leak. Both of these can spell death.

So if you don’t have the money, park the car until you do. But just because you ask someone to look at it doesn’t mean it will take lots of time or be expensive.

If you’re determined to figure it out yourself, dig up $20 for a repair manual from an auto parts store. There will be a chapter on fuel & exhaust systems. At the very least you can familiarize yourself with it. “Typing” people through it by internet is unlikely to be possible or fruitful.

One place to check for a gas smell is the fuel injector O-rings. There’s an O-ring where the injectors mount into the intake manifold and an O-ring where the injectors mount into the fuel rails. If any of these O-rings are leaking and the slightest amount of gas lands on the hot intake manifold it turns into a vapor. And this gas vapor can be drawn into intake of the ventilation system and you get a gas odor inside the vehicle.

Tester

+1 to tester, very good point

A small oil leak dripping on an exhaust manifold can smell like a bad exhaust leak, you should get this checked out by a competent mechanic (not a chain anything) and it should cost peanuts to find out what it is.
The price to fix it will of course vary with the diagnosis.

I will take it into a mechanic as soon as I can, but tonight I’ll look for problems near the fuel injector o-rings.

The thing that bugs me about the smell is that it only occurs when the heat is on, not when air is coming in through the vents with just the fan or when the air conditioner is on. This almost makes me think that there’s something wrong with the heating element but I can’t imagine how that would make it smell the way it does.

I would expect that if there was a fuel leak or exhaust leak, the problem would be there whenever air was coming in through the ventilation system.

Thanks for all your help so far.

Is it possible you might have spilled some gas in your car at one time? Such as in hauling a gas can for a mower/snowblower maybe on the floor of the back seat for instance and it soaked into the carpet? Heat will make that smell worse, unfortunately I know from experience.

The heating “element” is a “heater core” - its like a mini radiator with coolant going through it (and the coolant is very hot). The air gets blown over it & comes out hot. If you smelled anything from that directly it would be antifreeze which smells nothing like fuel or exhaust. The AC evaporator is a similar thing, but has super cool refrigerant in it. The difference is in which thing the air blows over.

Chances are that there is some reason so far that your heat is always on fresh air, and thus pulling air from outside while the A/C is on recirculate which is closed to outside air. If you’re on fresh air, all of the air comes in the same way whether it gets heated up or cooled down.

Thanks cigroller for the run-down. I think you were correct about the recirc vs. vent airflow.

I found two problems that I’ve since fixed and the smells seems to have been completely gone.

First, there was an exhaust-like smell that was coming from a cracked old rubber elbow connecting the PCV valve to the vacuum system. This let crankcase gases escape into the engine compartment. Second, my fuel pressure regulator was dying. This was the source of the fuel fumes. The smell was worst when the car had just started because the fuel would leak most when the car is first turned on, then stop. The fuel would quickly evaporate from the engine block, and the only evidence it had happened when I would check after a long drive would be the grime in that area of the engine (which was hard to detect given the general griminess of the engine). I finally discovered the FPR problem when, after a very short drive, I checked under the hood and saw a lot of gas on and around the FPR. I drove the car home immediately and use other transportation to get the replacement parts.

No more gas nor exhaust smells and less than $100 in parts to fix.

Thanks for clearing your thread. Few posters take the time to do this…

No problem! I was just happy to find the source and that it was a relatively easy and inexpensive repair.