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Pete_89T2 · 07-07-2012, 10:17 AM

I think the choice depends on what you are using the temp sensor for. Are you using it just to drive a gauge to monitor temps, or is it being used as a coolant temp input to a stand alone ECU?

FWIW, Mazda engineers chose the real iron location for the dash temp gauge, and the water pump housing for ECU control purposes. For the latter ECU case, you'll want to sense coolant temps as it exits the engine in a place that sees steady & uniform coolant flow and isn't as heat soaked by the thermal mass of the structure it bolts into, so the sensor can quickly respond to small changes in coolant temp due to engine load. The WP housing fits the bill nicely here.

For a guage, where you just need it to warn you of trends toward impending doom, the rear iron location works nicely because it's physically closer to the spark plugs where combustion happens (localized hot spot), so it will respond to a boilover trend before the WP housing location would. Also, the physical location in the rear housing would probably heat soak a bit more than the WP housing site, so your gauge would have less pronounced fluctuations vs. load. Ideally, once the engine is warmed up to operating temp, you won't want to see too much of rate of change in the temp gauge reading, but you would want it to rapidly respond to a boilover condition.

07-07-2012, 10:17 AM	#4
Pete_89T2 Lifetime Rotorhead Join Date: Apr 2010 Location: Elkton, MD Posts: 874 Rep Power: 16	I think the choice depends on what you are using the temp sensor for. Are you using it just to drive a gauge to monitor temps, or is it being used as a coolant temp input to a stand alone ECU? FWIW, Mazda engineers chose the real iron location for the dash temp gauge, and the water pump housing for ECU control purposes. For the latter ECU case, you'll want to sense coolant temps as it exits the engine in a place that sees steady & uniform coolant flow and isn't as heat soaked by the thermal mass of the structure it bolts into, so the sensor can quickly respond to small changes in coolant temp due to engine load. The WP housing fits the bill nicely here. For a guage, where you just need it to warn you of trends toward impending doom, the rear iron location works nicely because it's physically closer to the spark plugs where combustion happens (localized hot spot), so it will respond to a boilover trend before the WP housing location would. Also, the physical location in the rear housing would probably heat soak a bit more than the WP housing site, so your gauge would have less pronounced fluctuations vs. load. Ideally, once the engine is warmed up to operating temp, you won't want to see too much of rate of change in the temp gauge reading, but you would want it to rapidly respond to a boilover condition.