Expert: Rob Painter - 10/25/2010

Question
QUESTION: I have a 1999 Cadillac and the a/c works and the blower works but no heat will come out, and it's getting cold outside. I have plenty of anti-freeze. What else could it be. Thanks

ANSWER: Hello,

You are desribing the symptom of no heat, but there is no one fix and one or more problems could be presenting itself.

No heat could be a vacuum issue at the vent doors in the heating unit. If the heat door is not closing, you won't have heat. This is not a common problem, but is to be considered. The same holds true if the water heater control valve (if equipped) is not holding vacuum. This valve controls the difference between a'c and heat. This too is not a common problem, but must be considered.

The a'c and heat are two different entities and engine coolant/ anti freeze have nothing to do with a/c operation.

You state the anti freeze is full. That's a good start and at least it appears that we are not dealing with the notorious head gasket issue caused by overheating this style engine.

You could be dealing with a bad thermostat. When is the last time the engine was flushed? Should be done every three years. Flushing will commonly take out solidified sediment both from the heater core and the radiator.

How warm is the engine getting? 200 plus and still not blowing heat, heater core could be plugged. To check feel the hose going into heater. If hot on one side and cold on the other hose, heater core is plugged and needs replacement.

If engine is below 200 degrees, you need a new thermostat.

If upper radiator hose is hot and lower is cold, the radiator is plugged and either needs boiled out or replaced.

One other condiition could be a bad radiator cap which does not hold sufficient pressure.

As stated though, the cheapest and most needed thing is an engine cooling system flush if not done in the last 11 years.

Good luck!

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---------- FOLLOW-UP ----------

QUESTION: I'm bad I have a 1991 Cadillac, is that going to make a difference in the answer? My husband thinks it maybe the themostat is stuck, the car has been sitting for 2 years in a garage, started 1 or 2 times a month. Thanks for your help. Michelle

Answer
Hello,

I love it when people leave out details lol.

However, my answer is still accurate as it applies to your car. If it still has the original anti freeze from 1999, it is no good and after about 3 years (many variables) the anti freeze breaks down and becomes acidic. This will plug a radiator and heater core especially if the car sits parked for years. Yes, the problem can be the thermostat, but no matter what, system has to be flushed. I would flush the system first because it has to be done.

The benefit may be you have heat without changing the thermostat.

You better put some stable in the gas tank too and change the fuel filter if you don't want future problems with the fuel system.
Before they started putting additives in for emissions (many years ago) gasoline did not break down. Now if the vehicle is parked over a couple months the gasoline turns to varnish affecting everything in the fuel system. You can even damage the fiuel injectors!

Look, I don't spend a lot on my cars, but simple cheap maintainance. I also am not pulled to the side of the road because or breakdown.

As for Cadillacs cooling system, there are enough issues from the factory. You run this engine the least bit hot, it can easily cost over $4k to fix. There are no good junk yard engines! They are all junk!!

You need to take care of the engine cooling system!!!

If you look at the archives, you will see where countless people destroyed their aluminum engines from over heating due to lack of simple cheap maintainance.

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