1988 buick century custom 2.8L mpfi v6: low idle + coolant issue

The car only has 95k miles on it but I have been driving a lot lately (have a job 5 day/w that barely pays for gas and not worth the 30 min drive) between work, school (15 minute drive from home which I need to shower at after work) and social life on the weekends (once a month 1.5 hour trip, to another state). I’ve turned the idle up, but this problem persists. I have refilled the coolant to the cap (didn’t know I wasn’t suppose to I’ve had this car since 5/09 and already had to fix a shorted fuel injector) and the coolant light continues to stay lit (not to mention that the coolant disappears from the reservoir within a day, if not hours), and filling it to the full line has yet to help. It has been suggested that the head gasket may be leaking and that if the coolant may explode the engine soon. I was wondering if there is a definitive way of knowing whether or not it is the head gasket (I can’t afford a $55 expenditure that I didn’t need)?

The GM 2.8 liter engines are well known for head gasket failure.

First thing to check is the oil to see if it’s contaminated with coolant. If it is, it’s likely a head gasket leak. If it has a radiator cap remove it while the engine is cold. Start the engine and while it’s idling see if bubbles form in the coolant. If it doesn’t have a radiator cap see if bubbles form in the coolant reservior while the engine is idling. If you see bubbles in the coolant it’s most likely a head gasket leak. And if there’s steam coming out of the tail pipe that’s most certainly a head gasket leak.


so if its not a leaking head gasket, then what would cause the low idle? (I most likely have a pin hole coolant leak so that it will only leak while it is under pressure, right?)

Your reservoir emptying in a day is more than a pinhole leak. Look around the water pump weep hole. Get the coolant system pressure tested. If there’s no obvious signs of a leak than it’s probably a head gasket.

If you’re convinced it’s not a head gasket leak then get a compression test.

So the low coolant light never goes out, but the coolant you put in the reservoir disappears within a day? I’ll bet that it’s not only using it within a day, but within a few minutes. Because what’s happening is that you are way low on coolant and you haven’t put enough in to fill the whole system back up. So you fill up the reservoir and as soon that the coolant system is up to pressure it sucks all of it in.

So what you need to do is watch it while it warms up and keep the reservoir topped off until it finally fills up and the light goes out. You could also speed the process by adding coolant directly into the radiator (with the engine cold!). I will also add my usual change the radiator cap while 'yer at it because they’re cheap and can cause all sort of weird cooling system problems.

So if I’m right about this, though this means you still have some sort of coolant loss problem, it means that the rate is a lot slower than you think and so it could be something minor like a leaking water pump weep hole. Also, the idle issue is probably due to the coolant temp sensor being high-and-dry due to the low coolant.

I used to have an identical car for many years and there is one odd little leak they can have. There’s a pipe that runs coolant from the water pump area over to the throttle body which runs almost entirely over the front exhaust manifold. I had a coolant consumption problem on mine where I couldn’t find a leak but I could vaguely smell antifreeze. It turned out that pipe was leaking onto the exhaust manifold, where it would immediately boil so there was no sign of a leak. I also at one point had a small leak out of where, ironically, the coolant level sensor screwed into the radiator.

BTW, my Century was actually just about the most reliable car I ever owned. I put about 250k miles on it with nothing but standard maintenance, an alternator and a few front clips from hitting deer. Everything was working perfectly on it when I junked it just because the body was so beat up.