1990 Chevy Truck Engine will not maintain temp

CHEVYMAN38

MEMBER
1990 CHEVROLET TRUCK
V8
4WD
MANUAL
175,000 MILES

The engine will warm up to 210 like its suppose to and hold for a few minutes, then it will drop to under 150 degrees and slowly rise back up to temp. This keeps up in a pattern and we have already replaced the thermostat once and got a new radiator cap. It will also only make heat when u hold the motor over 1500rpm, anything less and its cold. We tested the old thermostat in a pot on the stove and it was working right in the hot water. What else should I try?

Thursday, January 3rd, 2008 AT 7:35 PM

2 Replies

ROWTIEAR

MEMBER
91 POSTS

It sounds like your thermostat is doing what it's supposed to.
It sounds like you're having some sort of circulation problem.
Try removing the hoses from your heater core and backflushing it for a few minutes with a garden hose.

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Thursday, January 3rd, 2008 AT 8:36 PM

CHEVYMAN38

MEMBER
2 POSTS

[quote="rowtiear"]It sounds like your thermostat is doing what it's supposed to.
It sounds like you're having some sort of circulation problem.
Try removing the hoses from your heater core and backflushing it for a few minutes with a garden hose.[/Quote

Thanks, we tried that and we got some brown stuff out of it. We also replaced the hose and fitting that comes off of the intake manifold and goes to the heater core. I think that was were the major problem was. After all that and a new thermostat, it is working fine.

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Sunday, January 6th, 2008 AT 7:01 AM