Engine slightly over heats?

[BeatupRolla]

I've checked the radiator fluid, radiator fan wires, thermostat sensor wire and fuses, they all seem to be good. Thermostat was replaced 2 months ago.

Car slightly over heats, usually when it does it hits the 3/4th mark on the temp gauge, it never heats up passed the red line and only does this once in a while. Any guesses on what could be the problem? Could bad compression cause this? i think i might have that since some times it feels like i have a loss of power and the idle is either 1000rpms or 500rpms, always different when i come to a complete stop its one or the other..

[BeatupRolla]

Alright so after some thinking and a bit of driving i'm starting to think its the coolant sensor. Why i think it is the problem is because it does take FOREVER for the car to warm up to the right temperature, it takes about 10-15 minutes(driving) for the car to warm up from completely cold to warm(just under the middle on temp gauge) or about 10kms of driving.

I am not sure if the car is supposed to be like this or not, i do have the 88 with the old crappy cluster.. maybe it just takes forever to load? i can easily swap out the coolant sensor from the newer parts car i have but i would like to know first that if i took out the coolant sensor would all the coolant spill out? if it does i might not screw with it but if it doesnt leak coolant i just might do it since its pretty much unscrew old one and then screw in the new one.

[blb]

Low compression will not cause overheating.

You can try swapping the coolant temp sensor if you want to.....most likely not the probelm....... just hold your finger over the threaded hole as you remove the one sensor and replace with the other one and you won't lose much coolant. They are easy to check of you have an ohm meter to check the resistance at a given temperature. See the chart in the service manual for specifications and tolerances.

Is the electric radiator fan on when the temp gage reaches the 3/4 mark? If not, you have a cooling fan control circuit issue.

It's worth a try to replace the thermostat again, except this time use a genuine OEM Toyota thermostat from a local or online dealer. Some of the aftermarket thermostats don't work very well in some Toyota applications.