When the engine gets pretty hot (usually shortly after slowing down after a long freeway stretch, or in prolonged traffic jams), I hear a high pitched gurgling noise coming from what sounds like under the dash. My ears could be deceiving me, but it seems to be between the glove box and the radio, roughly. If I turn the temperature all the way to hot, that usually kills the gurgle for a few minutes, and then it comes back again.

When I check the coolant level after a drive on which there's been a gurgling incident, I'll find that some has gone - it's usually 1-2 inches below the minimum line. So there's obviously a coolant leak from somewhere. I can't find any evidence of leakage from any pipes or seals under the hood in the engine compartment, and therefore suspect that the trouble has to be in the part of the coolant circuit where it goes under the dash to heat the cabin. A seal somewhere is giving way when the coolant expands to create enough pressure to overcome it, I guess.

Before I take the dash apart and go for the trial and error approach in finding the leak, I just thought I'd mention it here in case anyone else has had the same issue and/or it's a well known problem - pointers appreciated.

 

Did you bleed the cooling system?

https://honda-tech.com/forums/showth...1#post39830585

 

Is the passenger floorboard carpet wet? If it isn't, you probably don't have a heater core leak.

Do you still lose coolant even if you don't turn the heat on? If not, you probably don't have a heater core leak.

Are there wet or clean streaks on your firewall, on the passenger side? If there are, you probably have a leak near the heater core.

Have you done a compression test, or a pressure test of the coolant system?

 

Cooling system was last bled when the coolant was flushed and replaced 11 months/21k miles ago.

No sign of any dampness on the passenger side carpet or the firewall behind the glove box and below the dash on both sides. But there again, given the SoCal heat, anything less than a flood would evaporate very quickly anyway. I'll check again immediately after a drive on which I hear a gurgle.

I haven't done a pressure or compression test of the coolant system. I think I just need to heat the engine up by idling it on the driveway, take the glovebox out and see what I can see with a flashlight once the gurgle starts. It needs an oil change next week anyway, so I'll do it as part of that operation.

 

how about if you run your heater in the defrost mode, do you get any residue on the windshield? smell the carpet, antifreeze has a sort of sweet smell to it, especially when it is being burned or has dried into something.

 

Bleed it again. Follow the procedure I posted.

 

Check your thermostat housing, exact thing happend me, leaked thrugh there and also sucked in air there which led to gurgling