Heater not very hot

I drive a 2000 GMC Safari van. This has been one great vehicle, but I am having problems with staying warm in the winter. My temperature needle only gets up to one-fourth of the way, and my heater does not get very hot. Someone suggested a new thermostat or either engine coolant. I filled my coolant reservoir to capacity, but it was almost all gone the next. But there was no coolant on the ground. Does anyone have any kind of answers for me? Thanks for any answer I can get!


If you replenished coolant one day, it was almost all gone on the next day, and there is no evidence of an external leak, then there is only one conclusion and it is not a good one. The engine must have an internal leak, either from a head gasket or perhaps from an intake manifold gasket. (Offhand, I don’t know if the engine in this van is one of the GM engines subject to intake manifold gasket failure, but I thought that I should mention it, just in case.)

The next step is to see if there is evidence of motor oil in the coolant (you would likely see a dark, greasy line in the coolant overflow reservoir) or coolant in the motor oil (it would look like a chocolate milkshake). Oil in the coolant means that you should have the problem repaired as soon as is convenient. Coolant in the motor oil means that you need to get it to a mechanic today, before you burn out any bearings.

Even if you don’t find clues such as the ones above, your mechanic can do a Leak Down test in order to assess whether you have a head gasket problem.

That vehicle used a coolant called DEX-COOL that was supposed to last forever, but ended up being corrosive and basically dissolving the engine from the inside out.

But don’t take my word for it… Google “DEX COOL”

Anyway, another option is that it has corroded the automatic transmission cooling lines inside the radiator and when the pressure rises, it pushes the coolant into the transmission.

Go to an auto store and get a bottle of water soluble UV dye specifically designed for adding to the engine coolant. Should cost about 8 bucks.

Drive a good bit then examine your engine oil and automatic transmission fluid the next day under a blacklight. Whichever one glows is where your coolant is ending up.

Bad news is that if it got into your transmission, failure is inevitable as the coolant dissolves the binder from the friction material.