When I start my car in the morning after having sat overnight, and I turn the AC-Heater control to Defrost, I get a whiff of stale coolant in the cabin - just for about 20 seconds, then it goes away. This doesn't happen with the AC on, or everything OFF.

There is no gurgling or other noises, and no wet spots on the passenger floorboard. If anything is leaking, I figure it'* in the heater case somewhere, but I can't smell or see anything from the outside to indicate it. I began checking out coolant threads here to see if anyone had these symptoms.

The LeSabre I recently bought has no CarFax service history of any engine work having been done, but it was pointed out to me my plenum may have been replaced without it being recorded - I haven't checked the date on the upper plenum to verify this yet.

My reservoir looks suspicious. The inner surface is coated with very dark stains, along with the usual orange colors mixed in. It'* the dark, almost black, stuff I'm worried about.


I removed the reservoir cap and had a peek - sat overnight, engine cold. The coolant is just a tad below the cold level and is orange in color - that'* a good sign, right?


Then I removed the radiator cap. Coolant was all the way to the top, almost - also orange in color.

I found this YouTuber on replacing hoses and fittings on a 2003.. looks identical to my 2001 - only mine'* a lot cleaner

I was wondering how hard it would be to remove the upper engine cover (I believe GM calls this a "fuel injector sight shield.." ?) - They should get an award for naming that one. Looks easier than opening the front door

It'* possible you have a leak at the heater core. But it only leaks during cool down. Find the water drain on your fire wall and put a pan under it over night. If it collects coolant, you have a bad heater core.