Question about rotten egg smell (safety)

If I have a rotten egg smell coming from my car that I think is being caused by a bad battery, transmission oil, catalyst converter or fuel pump I read online as being culprits …but had my battery and transmission oil changed a month ago).

Does that mean I can’t drive it till the offending part gets fixed? I read online that the fumes are toxic and can affect you after prolonged exposure if I recall right. I don’t smell it most of the time except when starting up my car on occasion and then it goes away. It’s random. Does that mean it should be safe to drive otherwise?

Would a diagnostic scan tool help me identify the issue?

More than likely, this is coming from the catalytic converter, and while that is annoying, it is not dangerous. I strongly suggest that you change the brand of gas that you have been buying, and that change just might eliminate the problem.

If you buy various brands of gas, it is possible that one of them is causing your cat converter to emit that smell.

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The smell is hydrogen sulfide. It is toxic, but not bad at the concentrations you might expect coming out of your exhaust pipe. That smell suggests a one or more of: 1) rich mixture, 2) poorly functioning catalyst, or 3) too much sulfur in your fuel. If you smell it only on cold startup, I would not worry too much about it.

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Some folks may recall that the first-generation Taurus sedans suffered badly from the rotten egg smell under certain conditions. In the case of my Taurus, the mixture was okay, but I found that the problem was lessened to a great extent by changing brands of gas. Shell sticks in my memory, but after all these years, I don’t recall if that brand was the problem, or if it was the solution.

Thanks guys, yeah I smell it from inside the car when starting it up (maybe outside too? as it’s ony happened recently) after being left in the garage overnight (and then it goes away as soon as I start driving or only lasts a few minutes), but I have smelled it after parking my car after going driving for like 15 min or so but again goes away.

@VDCdriver do you have any reccomendations for what places would have ideal gas or what I should look out for (chemically?)? I only ever really get mine from Heb here in Texas and at the same location even. I get the regular unleaded 87 octane gas. Probably the only other one I get more rarely is at the Valero down the street. I drive a Nissan Sentra S 2.0 L if that helps. My manual says not to add any fuel additives when filling up gas, and from what I understand most/all places put some kind in their gas? Anyways I know it’s optional at HEB to add fuel aditives (for an extra charge?) but I never get it, so I was getting it considering it may not have had any.

All I can suggest is that you experiment with different brands of gas to–hopefully–find one that has lower levels of sulfur in it.

I have never heard of Heb brand gasoline, so I took a look to see if it is one of the Top Tier gas brands–and it is NOT.
I can’t guarantee that an adequate level of detergents in the gas will help with your odor problem (it probably won’t), but it can’t hurt, and will actually help to keep the injectors clean, thereby helping to prevent a different problem. See which of the listed Top Tier brands is available in your area, and do some experimenting:

Also, you might find this to be helpful:

Check online for a list of brands that are Top Tier rated. This applies to all grades of their gas (87, 89, 91, etc) and involves a certain level of additives that keep an engine clean. Any of those brands would be a decent choice.

Almost certainly some sort of Sulphur compound. Gasoline and car battery first suspects. No experience w/Heb brand, but Valero should have the low-Sulphur gasolines used in most US locales. Good advice above to just try some different brands, that’s what Ray (of Tom and Ray) would tell callers w/this sort of problem. Stations which tend to sell a lot of gasoline. Texas law may allow higher levels of Sulphur in the gasoline than other states, don’t know.

If it was the car battery, you’d likely notice it more when the battery was seriously charging or discharging, not so much when the battery wasn’t being taxed, such as when idling w/fully charged battery.

Gear oil (like is used in some manual transmissions and differentials) can make weird smells if it leaks onto a hot exhaust component. Another idea.

Thanks guys well just so you know I made a new thread about this, but will put this here as being one of any (linked?) issues to this problem, if it is to be considered of course…

From the thread: “My car make a squeaking/squealing noise when I pull out of my garage on a cold start? I only really seem to hear it when I turn on the AC and press the brakes when driving forward or in reverse. I think it happnes too when I only have the AC on but haven’t been able to really test it, but I don’t hear it at all when the AC is off, even if braking.”

Thanks and for number 6 in that rotten egg article, do you know why he says it may make the problem worse?

Edit: Also my manual says this: “Use unleaded regular gasoline with an octane rating of at least 87 AKI (Anti-Knock Index) num-
ber (Research octane number 91)”

I looked it up but am still confused if the numbers 87, 89 and 93 shown at gas station pumps here in San Antonio (regular, mid grade and premium respectively are the AKI number or octane number). I take it octane? Anyways most people said the regular unleaded was fine and the premium is just a waste of money. Do you agree?

My engine type is the MR20DE which is what the manual was referencing

Yes …


The odor might be from a dirty air conditioning evaporator. Is the odor blown from the A/C vents?

All fifty states have low sulfur gasoline to meet federal standards, the sulfur smell from the tailpipe went away 25 years ago.

Is gear oil only used in a manual transmission? I have a CVT automatic. Is this diffrent from transmission fluid?

Well the smell is coming from like under the stering wheel closer to where I place my feet, but it may be from the AC. I know I havent changed my air cabin filter and air filter in some time and know the air filter has particles on it. Could this be a culprit too? I’ve never heard of the AC evaporator, how would you diagnose that to be an issue or not?

There should not be any dirty air entering the car through the foot well.

The A/C evaporator is the cooling radiator inside the A/C unit inside the dash. If the A/C stinks, that is the source of the odor. Replacing the cabin air filter may help but the dust in the filter is dry, not much odor, the evaporator is wet from condensation.

Thanks, also in that article it says to run the car for 2 hours straight to possibly resolvbe the issue. If all else fails would you consider this a last resort? Would hate to waste money on gas just for this and I barely drive as it is…

The only cars that require premium gas are luxury cars or those that are high-performance. I don’t think that a Sentra is in either of those categories.

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Anyone else remember that decades ago - maybe late 70s and the 80s - driving behind a Ford, more than anything else, evoked that rotten egg smell? Must have been something about their engineering, but IDK what.

As I mentioned earlier, I owned a first-generation Taurus, and although it was a good car overall, it was definitely stinky on a regular basis. And, driving behind other Tauruses proved that mine was typical of the group.

I just saw a first-generation Taurus on the road last week

Even though I live in Los Angeles, where cars don’t generally rust out, a first-generation Taurus is a very rare sight

That Taurus wasn’t stinky, though . . . and I was driving behind it for a short while