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1989 ford E150 van

Many years ago, we replaced the thermostat. Because it started running hot, we replaced with a hotter thermostat based on a mechanics suggestion. Every now and again going up hill and especially in warm temps the gauge suggests that the engine is about to overheat. Also, the temp gauge reads really cold in the cold, and there isn’t enough heat inside.
Some mechanics have offered to replace the fan clutch but then they don’t seem to think its a big deal. Any ideas?

The fan clutch is a big deal. This is a viscous clutch. This means as the clutch gets hot from the heat from the radiator it causes the fan to spin faster. Then as the clutch cools back down it allows the fan to slip which slows down the fan speed.

Tester

@Jewelair how is the fan clutch not a big deal?! I’ve seen plenty of vehicles overheat due to a faulty fan.
How old is your coolant? Perhaps the system, including the heater core, should be flushed.

This probably should be addressed. It could be the fan, but it could also be a plugged radiator, or a failing water pump. Have you tried a local radiator shop? They might be able to offer some helpful ideas, if you’re not confident about the fan diagnosis.

Try a thermostat that isn’t rated hotter. The right one should keep things cooler. Why in the world would anybody install a hotter one for an overheating problem?

If there hasn’t been a new radiator installed in the last 120,000 miles, it’s needed now.

Try flushing the heater core. No, just replace it. Ford heater cores will fail if flushed. You will probably need a new one if you change the radiator on a Ford.

Because the thermostat can open at 192 degrees. But once it opens, the engine coolant can operate at 230 degrees or higher. After that, the thermostat isn’t involved. It’s up to cooling system to keep coolant temperatures under control.

Tester

The fan clutch was a suggestion, not a firm diagnosis. More to the puzzle, the fishy/weird/scary piece, is that it reads hot randomly on the highway (hundreds of miles from help, of course). One minute it’s hot then it cools down spontaneously with no change in speed, terrain, conditions, etc.

The coolant has been flushed several times by yours truly and the thermostat has been replaced, too. I think we’ve had the water pump replaced once or twice over the years. I don’t think we’ve changed the heater core or radiator. But I’ll need to call one of our mechanics to verify. Still the gauge reads really hot when going uphill or in a head wind, especially when driving in warm calm weather.
All these conversations are great! Thanks so much.