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I just returned from Chicago to Georgia in my '93 F150 w/165K miles. It ran just fine, but I noticed that the temp gauge would move slightly, back and forth, while on cruise control on level ground. I've taken this trip several times before, and it was always steady. Coolant level was normal. Anything to worry about?
A/C going off and on (or other loads)?
Alternator not able to keep up with changing loads.
Originally Posted by TexasGuy001
The fluctuation on the temp gauge could also be from the thermostat opening and closing.
Both good suggestions.
When was the last time you flushed the cooling system? I had a similar issue w/ my 91 F150 but never really worried about it. After flushing out the cooling system it steadied out and I haven't had the problem since.
He said that he has taken the trip before with the same thermostat and it did not do this so I discounted the thermostat.
Part of the Temp gauges job is to average out the reading so it does not do it with the thermostat as the engine temp operates in its normal range from 180 to 220 with a 195 thermostat.
Coolant boils at 262. 212 water+5 for coolant +15x3 for cap pressure =262.