Auto Air Conditioning & Heater Repair: Heater, coolant system, temperature gage

Question
I have a 1991 Dodge Caravan, with a 2.5L 4 Cyl. The engine heats up, radiator, and hoses get hot. However, heater hoses never heat up. I have changed all hoses, new radiator, new cap, and new thermostat. I can't find any restrictions in the heater core. When the van is sitting at an idle the heater will warm up some. When I start to move the van the heater gets cold, but the engine is still hot. Also, the temperature gage gets to normal almost immediately then goes to hot for a few seconds and then returns to normal. Sometimes it does this several times, other times it may go to hot and stay a while. The hoses do not bulge nor does the radiator overflow. Can you help me with this problem? Do you have any idea? -Thank You, Steve Vaughn  

Answer
The first things I would do:

1. Get a complete past repair history of the vehicle.

2. Look in the radiator and the overflow container and be POSITIVE that they are at the recommended full levels.

3. Look for signs of WHITE smoke from the exhaust when first started in the morning.

4. Pull all the spark plugs to make sure that they all look the same at the electrode ends.

5. Perform a coolant system pressure test of the cooling system to see if any AIR BUBBLES appear in the radiator with the radiator cap removed.



Anyone or all of the above procedures would give me my cause.



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