12-26-11, 08:26 PM
I have a 1999 Deville and have recently received three "Low Coolant" warnings in the span of approximately 18 months; when checked it appears there is approximately 1/2 to 3/4 of a gallon of coolant missing from the reservoir. I haven't had any issues with overheating, it's constantly runs in the 190 - 205 range regardless of highway or city driving. The car is located in Las Vegas where the temperatures fluctuate between 120 and 30 degrees depending on the time of year. The loss doesn't appear to be linked to any regular mileage intervals. I can't see any oil in the coolant, the oil is clean when it's replaced and I've never noticed any coolant puddles on the ground after it's parked. Any assistance you could provide would be appreciated.
12-26-11, 08:43 PM
Do you smell coolant when you open the hood? When your windows are down?
Are you filling the coolant to the proper level? It's the half line of the tank - approximately 2.5 inches down the neck - there's where the coolant has to be.
Pressure test the cooling system to find external leaks, it may be dripping onto hot parts (i.e. exhaust) and evaporating before making the way to the ground.
12-26-11, 08:48 PM
Before you do too much reading in here and in Deville - concerning head gaskets and other failures - do some snooping: With the engine cold, look for damp spots at or near all - all - coolant hose connections. Typical culprits are the radiator upper and "lower" hoses, heater hose connections, the actual plastic nipples at the radiator end tanks, and the coolant reservoir itself. (Know that a Northstar with failing head gasket(s) does not normally put oil in the coolant or vice versa.) A quart or two of coolant every 6 months is NOT a lot (ANY coolant loss is cause for checking) and if you're using the orange/yellow DEX-COOL the residue from evaporation is a chalky dull white. 1999 ??? Your pressure cap may also be suspect. Devilles vent excess or weeping coolant onto the ground as opposed to the later Sevilles where any coolant blowoff simply runs down the rear of the reservoir.
The proper coolant level - cold only (never check it hot) - is about halfway up in the reservoir.
If you can absolutely guarantee the physical integrity of the visible cooling system, then it's time to do a cylinder block/head leak test for the presence of exhaust gases in the airspace over the coolant in the reservoir. Either "rent" the tester and fluid from a large local parts house or use www.sjdiscounttools.com/lis75500.html (http://www.sjdiscounttools.com/lis75500.html)
Even if you do not find any leaks I would hold off on the block test until (and IF) you start overheating. Unless you are overheating I think it is almost a guaranteed negative result.