Civic vti 1999.

I have a small leak in my manifold and mechanic told me if you’re worried about smells just set in on recirculate. I have done and I’m assuming this means no outside air should come through the hvac system regardless of whether your ac is on it the fan is on? Am I correct about this?

My problem is whenever I put the fan on I can smell what I think are exhaust gases coming through the vent. It gets stronger the more I higher revs I drive it on. At low revs I can’t really smell it.

Am I right that recirc should not let anything to be drawn in, and if it’s exhaust gases I’m smelling how might these be getting through/what do I need to look at?

  • 1
    You need to look at getting the manifold fixed.
    – Solar Mike
    Commented Nov 4, 2019 at 20:47
  • 2
    That's a dangerous situation! You know you have an exhaust leak and running the AC on recirc is NOT a guarantee that no fumes, which contain CO (carbon monoxide - a DEADLY poisonous gas) will get into your passenger compartment. Do yourself a favor and get this fixed properly!
    – jwh20
    Commented Nov 4, 2019 at 21:17
  • @jwh20 can you elaborate why/how co or other exhaust fumes maybe getting into the cabin even though it’s been set to recirculate. Commented Nov 4, 2019 at 23:14
  • The recirc damper may not be closing 100% but more likely it's getting in elsewhere. Cars are NOT airtight.
    – jwh20
    Commented Nov 4, 2019 at 23:33
  • Even worse than what @jwh20 says: cars are designed so that the "recirc" button does not wholly close the air intakes: some outside air is intentionally and deliberately allowed to enter the cabin. So: fix the exhaust leak, Commented Nov 5, 2019 at 19:38

1 Answer 1


@jwh20 is absolutely correct - get the manifold repaired as soon as possible. Until then, make sure you're getting plenty of fresh air from opening the windows. This is a life threatening scenario.

A way to commit suicide is to run a car in an enclosed garage. You're doing something similar by letting exhaust gases into the car cabin.

  • So you are saying that my particular car has been designed like this and there is no actual problem with leaks elsewhere?? Commented Nov 7, 2019 at 23:56
  • I’m not questioning you guys seems there is a consensus heret. However I’m also wondering it seems a common situation where people may have an small exhaust leak and they close their window. So why aren’t people dropping like flies. I myself have driven with windows closed though to be fair I do open them asa I get the smell. If it’s really serious then people should be educated on this properly. Commented Nov 8, 2019 at 3:37

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