'87 Brat with SPFI swap, brand new Subaru thermostat didn't fix the problem. The temp gauge is always above half, and climbing the mountains will make it go just below the red. It doesn't get that hot when sitting idle, only under load. If I stop the car, I can hear the fan turned on, so both the computer and dash gauge believe the car is hot.

 

Water pump? Radiator? Really bad contacts on my sensors?

pluged rad pluged rad and pluged rad head gasket no pluged rad

If Headgaskets are good; I Kindly Suggest you to do a Radiator Flush using a Chemical additive that removes the Dirt that the Radiator could have, then Rinse with enough Water and Finally pour Fresh Coolant.

 

When a radiator remains with coolant and unused for Long times, the Coolant buildup sludge that can close the passages and Limit the flow.

 

If that doesn't Help, the Radiator could be very Clogged and / or the Waterpump could be starting to Fail...

 

Kind Regards.

Could also be that your timing is on the retarded side, when I had mine all jacked up it would get a little warm under heavy load.

classic radiator symptoms...time of year...and age - the car is a quarter century old.

Yeah. While climbing tonight, I realized there is a built in test for the radiator... the heater core! Turn it on full blast, and if the car gets cooler, most likely it's the radiator.