Engine's Normal Operating Temperature

Question

I read in the Motor Oil University article on Bob the Oil Guy's websites that:

The automotive designers usually call for their engines to run at 212°F ( 100°C ) oil and water temperature with an oil thickness of 10. ... The engine is designed to run at 212°F at all external temperatures from Alaska to Florida.

I installed a 82.5°C thermostat on my 97 Mazda 323 BA 1.8L BP DOHC. The radiator was replaced by the previous owner and is not OEM. I'm using a premixed glycol-ethylene coolant rated between -10°C to 118°C which specifically says on the bottle not to add water. The service manual calls for 65% water to 35% coolant in environments over -15°C.

After all those details, here's my question:

When I hook up to the ECU, I find that most of the time the engine temperature stays between 85°C to 92°C. Rarely, when standing in traffic for a long time, the temp will get up to 97°C, at which point the ECU turns on the fan and the temp rapidly returns to the previously mentioned range.

Is this normal? If not, any idea's?

So far I haven't found anything regarding normal operating temps in the service manual, although that doesn't mean it's not there of course.

Answer 1

Yes, it's normal. Maybe just a tiny bit on the cool side. But if you're in traffic a lot that cooler thermostat is a good thing. All the cars I've owned would run between 85 and 95 degrees Celsius. 85 at highway speeds, then creeping up to 95 or 96 when in slow traffic, at which point the fans kick in.

Pro tip: the hotter an engine runs, the more efficiently it burns evil hydrocarbons.

If your car is running too cold for your liking (or according to the opinion of a good mechanic), there are basically three things you could do:

1. install a hotter thermostat
2. drain your oil and fill up with a more appropriate option (ask your mechanic)
3. take the car to a tuner to have them lean out the air/fuel ratio slightly and play with the timing.

The third option will increase the temperatures inside the combustion chamber and exhaust and also provide slightly better fuel economy/performance. Of the three though, #1 and #2 are your best options.