Engine transplant needs exact thermostat

Cooling system fails to warm up

DEAR CAR TALK: I have a 1992 Ford Ranger with a four-cylinder, 2.3-liter engine. I bought it off my father as a spare vehicle. At some point, my father had a used motor installed. When I needed to replace the thermostat, the one that’s listed for a ’92 Ranger didn’t match. After some searching with the auto-parts clerk, we found a 195-degree thermostat from a 1975 Pinto that matches. It fits, but the motor doesn’t warm up properly: The needle on the temperature gauge climbs to the ”C” mark, then goes back down. Also, the heater will not warm up. How can I find out the exact type of motor I have so I know I’m getting the right part? And do you have insight on why it’s not warming up? — Mike

Yes, that probably is the same engine Ford used in the ’75 Pinto, showing how much technological progress Ford made during that era.

I’m not sure how you can tell exactly what year it is, other than by having an experienced Ford mechanic take a look at it. Vehicles come with decals on the undersides of their hoods that identify the engine. But when you swap out the engine, the decal stays behind.

Still, a Ford 2.3-liter engine is the only engine that will fit in there without major modifications, so I’m sure that’s what you have.

Maybe that thermostat you bought is faulty. Maybe it’s been sitting in the box for 40 years and it could be stuck open, allowing the coolant to flow to the radiator when the engine is cold. That could explain both the needle in the gauge and the lack of heat in the car.

But if that doesn’t change no matter how long you run the car, it could be that your cooling system has air trapped in it. The temperature sensor is supposed to be immersed in coolant; instead, yours is surrounded by a pocket of air. Air would explain the lack of heat, because air is blocking the coolant from getting to the heater core in the passenger compartment.

So start by trying another thermostat — it’ll cost you 20 bucks. And when that doesn’t fix it, you should have the air bled out of the system.