Water temperature: Aftermarket gauge vs. Power FC?
 

I did some repairs to my gauges after some wires broke, and I've noticed that the gauge's water temperature was 20 degrees Celsius lower than the Power FC's gauge (55 C versus 75 C).

How different can temperature be depending on where it's measured?

My water temperature sensor for the gauge is in the right side of the radiator (left if you're in front of the car).

My oil temperature gauge, which I may have switched up with my water temperature (not likely, but possible), quickly went up to about 75 degrees.

I take that back... it was more like a 30 degree difference.

The reason it is different is your gauge is in the wrong spot. The power fc reads the factory sensor in the back off the thermostat housing. That is usually the place where you'd put a temp gauge. Placing it in the radiator will be measuring coolant that has already exchanged it's heat with the air passing thru the radiator.

Unless your car is an automatic, there should be a spot that can be drilled and taped for your after market gauge sender. This would also be a great time to replace the thermostat and seal if you have not already done so.

Vince

Before I repaired my Defi gauge harnesses, it seems to work fine.

The sensor is on the hot side of the radiator. It should work as long as the thermostat is open.

The oil temperature is actually bang-on with the water temperatures, so I maaaay have switched them.

How fast should the oil cooler thermostats open, and how fast should they temperature increase while idling?

Exactly. Coolant temperature will be lower at the radiator than at the engine. The gauge sender really needs to be behind the thermostat to get an accurate engine coolant temperature reading.

Having your temp sensor in the radiator will give you false confidence in the temp. It will be lower, and take longer to start climbing. Having it at the thermostat gives you a real indication of actual temperature and temperature changes.

The oil typically takes longer to warm up than the water, but should stay consistent unless you are beating on the car. It should also climb when sitting still for long periods since there is no airflow.

Vince

replace the factory engine coolant sensor for the ECU. I have seen them read inaccurately with age.

The sensor is actually in the hot side radiator inlet, not the radiator tank. It's not any colder than the water pump, so long as the thermostat is partially open.

If the oil temp increases slower than the water temp, then I definitely switched the wires up (the original terminals are color-coded, the replacements are all the same color.).