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Ventilation system odor

About 30 seconds after starting my Honda 2002 CR-V, a somewhat sweet but nauseating odor is emitted from the ventilation system, which disappears after the engine has been running about a minute or so.

Changing the cabin air filters and spraying Fabreze into the system from both ends has not cured the problem.

Any suggestions would be appreciated.

How is your coolant level? If the heater core is leaking slightly you will get a sweet, sickly odor. It’s also not good for your health in a closed environment if the coolant is ethyl glycol based.

Thanks for the suggestion.

The radiator is full to the very top, and I haven’t had to top it off in the past.

On the other hand, the level in the small white plastic reservoir tank to the left of the radiator filler is low, although I have no idea why or if that could make any difference.

That low level in the overflow reservoir is an indication that coolant is either leaking or is being consumed.
I would suggest that you refill the overflow reservoir to the appropriate mark (when the engine is hot), and then carefully monitor the level every few days to see if the level has dropped. Also, check your dipstick for evidence of coolant in the motor oil.

If the level has dropped, then you have a fairly firm indication that coolant is either leaking or being consumed in the engine. You should check all of the hose clamps for the heater as well as the ones on the radiator hoses to see if there is any evidence of leakage or looseness. If everything with the hoses and clamps checks out okay, then you should have a leak-down test and a compression test done on the engine to see if you have a leaking head gasket.

My mechanic looked at the car this morning and concluded that the reservoir coolant level is within the normal range and that there aren’t any indications of leaks in the coolant system. Needless to say, I plan to keep an eye on the reservoir coolant level for the next week or two.

He sprayed an anti-bacterial agent in the ventilation system from both ends–where the cabin filters are and the fresh air intake–on the assumption that the problem may be bacterial growth somewhere in the system.

I’m wondering if the fact that I ALWAYS have the ventilation system on recirculation, never allowing fresh air into it, may be part of the problem. In any event, I’m going to try running the system regularly with the fresh air vent open.

Thanks again for your suggestions.

a late response, but the sweet odor is the classic symptom of coolant leakage, so keep an eye out for leakage under the heater core. it may be just a few drops leaking out for now, accounting for the disappearing smell, but it’s likely to get worse over time. might be worth an over-the-counter stopleak product, starting out with something simple like alumaseal or equivalent added to the radiator before going on a drive, just be sure to turn on the heat so it circulates into the heater core.

Thanks for the reply, but I’ve identified the cause and implemented the solution–both amazingly simple.

By running the ventilation system with the fresh air vent open some of the time, the problem has been cured. Apparently, ALWAYS running the system in the recirculation mode was what was creating the problem.

I’m wondering if the fact that I ALWAYS have the ventilation system on recirculation, never allowing fresh air into it, may be part of the problem.

It could be at least part of the problem.