07-22-2018, 05:40 AM
I have a 89 Deville 142000 miles on a 4.5L . I don't know the history of this car. After driving 2-3 miles the Engine Collant/ Fan light comes on. At that point the upper radiator hose is real hot & rock hard, the filler cap is cool to the touch, if I open the filler cap about 1/8th of a turn hot coolant blast into the overflow tank. Do I start with the radiator first or flush the entire system first ? What about the thermostat ?
PS. The coolant fan is working. Any pointers? Thanks Dave

Blue Bowtie
07-22-2018, 06:59 AM
If the upper radiator hose is hot it is probably due to coolant flowing. That would indicate the thermostat is open, as it should be.

If the system holds pressure, that would indicate that there are no external leaks.

Since the system builds pressure so quickly, it may indicate the radiator is not rejecting heat as it should, which could be from a partially plugged, dirty, or restricted radiator.

If it has not been done in the past several years, it would be good to drain, flush, and refill the cooling system. Follow the instructions provided with the cooling system flush/cleaning solution. Once refilled with fresh coolant mixture the system can be diagnosed further, if necessary.

It is also important to clean the exterior of the radiator, specifically the fins through which air must flow. It is not uncommon to accumulate debris between the radiator and AC condenser in a vehicle of this age, so this cleaning is even more important.

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