My SE has had cooling problems for quite some time and this may have contributed to the demise of the original motor (If not the 210,000 miles on it). I am stubborn and stuck with the original radiator far too long. Had it flushed and dipped twice, to no avail. Finally got a replacement radiator when I put my most recent motor in. Now I have the opposite problem. The needle doesn't come off of "C" very much and the heat in the car is only slightly warm. Is this strictly a thermostat issue or could this also be caused by the Rich/Lean setting on the Variable Resistor? I have the proper thermostat in the car. I'm afraid to use one that opens at a higher temperature.

 

it isn't a common problem to have the engine run too cold. here is a list of things to check. the variable resistor won't have any impact on coolant temps

1. water thermostat. if this is not, OEM or NTC brand, you should just replace it. it is crucial that the thermostat block the bypass port and the aftermarket ones are suspect.

2. fan clutch. the fan clutch should come on when you start the car, and then freewheel until the coolant temp hits about 91c. if yours doesn't it may run cold. at idle you should be able to stop it easily with your fingers, be careful though.

3. radiator too big. i ran a HUGE radiator in my last T2, and you needed to drive pretty hard to get the coolant all the way warmed up. a little unlikely but possible.

4. bad temp sender/gauge. maybe its warmed up, and doesn't show it?

5. bad oil cooler thermostat. if the oil is too cold it may keep coolant temps down.

 

A bubble in the system could do the same thing, but normally a bubble makes the engine over heat. I agree on the thermostat, also, how old is your radiator cap?

 

Mine was #4. The sender was bad and I was actually mildly overheating. May have been the cause to the engines demise.

 

My SE runs 1/4 to 1/3 most of the time. Sometimes when I first take off it will go up to 1/2 then quickly drop back down. So obviously the Thermostat is opening up or the fan is coming on.

 

Checking coolant temperature sensor, dash gauge and replacing sensor:

https://www.rx7club.com/1st-generati...gauge-1074146/

 

The fact that his heater output inside the car is low tells me that the gauge may be reading correctly and the engine is just running cooler than before - much cooler. Thermostat is the simplest/easiest to change and would have the most effect on bypassing hot coolant from engine to the radiator and thus to the heater core. Followed closely by the engine cooling fan frozen solid and running at full engine speed - but the car would sound like a P51 mustang on takeoff when you get on it.

Also, recognize that the new radiator has gone from worst possible case (clogged, overheating) to best possible case (running cold) because now it's about to work at 100% efficiency compared to before. Also, with cooler outside air temps, you can expect it to take longer to heat up - moreso with a fully functional radiator. HTH,

 

Put your hands on your heater core hoses once its warmed up and see if both the imput and output hoses are hot. if not you might have a block heater core. they should both be pretty hot once the car is warmed up.
It also might tell you if your coolant is indeed being circulated. you might have a bad water pump.

 

Feel the upper and lower radiator hoses when the car reaches full temp after idling with the hood open. If the upper hose is cool to the touch and the lower hose is hot, then you have a stuck open thermostat. Easiest thing is to just take the upper hose off and peek inside. Test the thermostat off the car with a blow dryer or heat gun to watch it open and close.

 

There are two different aftermarket thermostats, one at 180 degrees and one at 195 degrees. I will try a 195 degree thermostat until I can find an OEM one. My son works at Mazda and he is saying none are in stock.

 

I advise against the 195.Too hot for my taste unless you live in alaska or something.

 

stock is 180, or 82 c

 

An alternate temperature thermostat (195 F) did help a lot. At least now it gets off of "C". The thermostat I had in there was an NTC brand with a by pass.

 

NTC is the OEM brand.

 

I have seen many brand new thermostats being bad and sticking open. Especially if you replaced it before the rad and it caused it to overheat they have a built in safety that they stay open when coolant is above a certain temperature.