I did a search, but didnt find anything definitive about the variation in water temp readings based on location of the gauge sensor.

I have an aftermarket (Prosport) water temp gauge and have the sensor installed in the middle of the upper radiator hose. I also have a Bullydog engine monitor plugged into the OBD. So, between the Prosport gauge, Bullydog, and stock gauge I have three different readings.

The Prosport gauge reads about 10 degrees hotter than the Bullydog (OBD). This concerns me as I track the car and want to make sure I am reading the "right" temp. So for now I use whichever is showing the highest temp so as not to blow things up. I am hitting 240 degrees on the Prosport when I shut it down (no more than 5 laps....max). Side note, I will be installing the RX8Performance Dual Core radiator this weekend, which I hope will help.

My questions
1) Should I install the Prosport water gauge sensor somewhere other than the middle of the upper radiator hose?

2) Is it better to reference the temp reading from the Prosport gauge (upper radiator hose) or the Bullydog (OBD) when driving the car hard at the track?

 

Does the bullydog show the same temp as an obd moniter? if it doens't then it's a calabration issue with teh bullydog.

Otherwise you have the prosport in the right place. And it's directly past the stock sensor. So it is seeing the same temp fluid. The only way to decide for sure would be calibrate them togther. If the bullydog or prosport has the option.

 

What year is your car? The stock ECT sensor is cheap, I suggest replacing it as it is a very important sensor. That said, Prosport gauges (I have them) are known to fail fairly often compared to higher end stuff (stack, spa, etc) and have issues (but prosport is great at CS and stands behind their products).

I never saw the point of an aftermarket coolant gauge when you can have OBD data.

 

The BullyDog plugs into the OBD port - otherwise said, it is my OBD monitor. I dont have any other gauges connected to the OBD port but I will get one to double check that. Good suggestion.

It’s a 2004. Thanks for the advice on the ECT sensor, I will get one.

Yeah, probably a good point. I was being a bit overkill with the two gauges. The thing with the BullyDog is that you choose the number of cylinders (they must be rotary haters). I’m pretty sure you go with 4 cylinders for the RX8, but given that bit of questionability I chose to add backup gauges as well. I’m not doing a ton of power adders – I’m a road-race / HPDE guy so I am more focused on suspension and making sure I don’t destroy the engine.