2000 Chev. Sub. low coolant light comes on even soon after coolant topped off; there is an actual slow loss of fluid though none on driveway under car; new hoses, new thermostat, new water pump; mystery to mechanics at 2 shops; ideas?
Bad head gasket?
Bad intake manifold gasket?
If it’s been cold where you are you could have vapor coming out the tailpipe from coolant being drawn into the cylinders and you’d never notice it in the normal cold weather vapor cloud.
I’m not a GM guy, and I’m personally unfamiliar with the intake manifold configurations, but we have regular posts here on defective intake manifold gaskets allowing coolant to be ingested. Perhaps one of the more knowledgable guys here can elaborate.
A second possibility is a headgasket breech. That can be detected with a pressure leakdown test of the cylinders.
Leaking intake manifold gasket. The symptom is classic, and GM vehicles have had chronic problems with this. Do not let it go or keep driving it until you pinpoint the problem as the leaking intake is likely allowing coolant into your oil. This is really bad and will kill the engine.
So get someone to check for that asap.
I have a 2000 Blazer that developed an intake manifold leak at 44k miles in early 2004. Same symptoms as yours, it started losing coolant slowly about 1 pint/month. When I had the oil changed the mechanic noticed a few drops of coolant as the last of the oil drained out. He referred me to the dealer who comfirmed the diagnosis. The dealer did a 50/50 goodwill repair. As other posters noted, coolant in the oil will ruin an engine. The coolant displaces the oil from the main bearings.
I’m surprised the mechanics didn’t think of this as it is very common in GMs of this vintage.