Engine Coolant and Heater on a 1990 Cadillac DeVille?

[butturinij@uwplatt]

Okay, starting about a month ago, I noticed that my engine coolant was leaking just about as fast as I would put it in. I would add coolant one day, and then the level would be down again when I would check the next day. There are no visible leaks. Also, my heater is blowing out cold air. Could these two problems be related? Any advice would be appreciated.

[MagicRat]

Welcome to AF.

These problems are not related. The cold air problem is related to your ventilation blender door mechanism or the heater core shut-off valve(if it has one).

The coolant leak could be a number of things. The coolant is going somewhere. Have you checked carefully underneath the car and inside the engine for any trace of leak, especially when the engine is warm?

These engines have external cylinder head bolts and sometimes will leak coolant at the bottom of the cylinder heads, where the bolts are located.

If there are no visible leaks, look at the transmisison and engine oil dipsticks. Does the oils look normal? If they look like a big, frothy milkshake, then coolant is getting into the oil, which is big trouble.

Have you ever serviced the cooling system (that is, drain the old coolant, flush the system and install new coolant?)
These cars have all-aluminum engines and need this service done every 2-3 years to prevent corrosion. If you have not done this in recent years, then do it.
But, before filling the system, go to a GM dealership and buy a package of six AC-Delco cooling system tablets. These are 6 reddish-brown tablets. Put all six tablets inside the lower radiator hose (NOT in the overflow tank), then fill the system with new coolant.

If the gods are smiling, your leak may just go away in the following few days.

BTW, all aluminum Cadillac engines from 1982 through 2003(?) are intended to use these tablets, whether they are leaking or not, according to GM. So many of these aluminum engines leak a little that the tablets are intended to be in the coolant all the time. GM says just to install 2 tablets but everyone I know says use all six tablets.

[butturinij@uwplatt]

I have not noticed any frothy stuff when I have changed the oil, but I have not looked at the transmission fluid lately. I have not noticed any leaks on the car, I looked thoroughly for those. I will try draining the system, though. Thanks for your help