Ok, I finally got around to wiring up my autometer water temp gauge for the center panel I had made months ago. I'm a bit curious though about the difference in temperature between the autometer temps and what the haltech is telling me. The haltech reads about 8-10 degress hotter than the autometer gauge. Does anyone know which is more accurate or what the deal is?



Cruising around ambiant temps about 70-75 degrees, i'm seeing 185-189 on the haltech and 175ish to 180 on the autometer. Plus I have a fmic, my next project is doing the "shark mod".

 

It depends where you place the probe. The water coming out of the engine should be 10-20 degrees hotter than the water coming into the engine.

 

The sending unit that came with the gauge is placed near the oil dipstick, i'm not sure where the haltech is reading from. Thats probably the difference. Where do most people get their readings from? Which side is more important to know?

 

Most temp guages read from the sender under the oil filter, while most ECU's (factory included) have a more sophisticated sender in the thermostat housing.

When the engine is cold & the thermostat is closed the bypass is open which effectively pumps the water round & round the front of the motor. The ECU sensor will see immediate temp rises and adjust the mixture to suit. The guage sensor will see a slower rise so will take longer to come off the pin. Mazda tell you acceptable warm up is when the needle moves off the pin, but in fact the motor is already warmer than this. Clever really.

The thermostat housing is is the hottest point in the motor, so the ECU temp readout will be the highest, so is the important one.