My car is finally running well following its tune up by Bailey Performance (recommended by the way!) but im having a strange inconsistency on coolant temp's

My brand new TIM gauge (with matching sender) is reading approx. 15deg C below the figure given by the megasquirt.

Megasquirt is configured correctly, with the standard GM style sender.

Is there usually such differences in senders? They are both plumbed into the raceline rail about 5 inches from each other?

Also can I ask the question to where the fan switch be best located? Should it be in the Stat housing or Rad?

I really would not worry, its like having a car with GPS on the sat nav, the shown speed will rarely match the speedo.

Where exactly is the sensor that is reading the lowest located ---- by any chance is it downstream along water rail from the the other sensor?

If you want to double check the readings spend £15 or so on a 2 channel K-type Digital thermocouple Thermometer
DUAL TWO CHANNEL 2 K-TYPE DIGITAL THERMOMETER THERMOCOUPLE SENSOR 1300°C

The fan switch should really go in the radiator (or at least very close to it) the fan's job is to control the radiator temperature not the engine temperature.

[Edited on 1/3/16 by britishtrident]

Mine is similar, I view temp guage as an indicator I'm not bothered about the numbers just know where normal is, and when fan cuts in.

Is the sender in a position where its flooded all the time, i had a similar issue and it was down to the sender being it the top of the pipe. Moved it into the bottom of pipe and it read totally different

Did you calibrate the sensors and input the resistances into megasquirt? errors in the calibration could cause what you describe.

When the engine is cold i.e. been left in the garage for a day or so, do your air and coolant temps read the same or very close to the same values?

But,

As the engine has been tuned using those sensor calibrations I would not change them now.

If you have a poor earth, or even an extended supply or earth wire it can have a significant effect on temp readings - remember the "gauge" is actually just measuring overall resistance on a path to & from & including the sender.

As others have said, as long as what you see is consistent, fan kicks in & out as it should & you get used to what is "normal" for your car then the actual no.'s become quite irrelevant

This is usually caused when you think you have the sensor configured correctly but don't (check out the variation in the tolerances of the sensor and you'll see that there's a fairly large range of acceptable values). The stock GM values are fine and if it's tuned with that sensor and curve then stick with it, but I've found even between identical sensors the squirt will read slightly different values due to manufacturing tols in the sensors (as per r1_pete). 15 degrees is nuts, and to me suggests one of them is WAY off, but that really doesn't have to be a problem. The other problem comes from non-standard sensors and getting accurate sensor curves for the squirt, but you don't have that here.

It is perfect demostration of the lack of circulation when you fit a Raceline Hotter Rail and a drilled thermostat.

Thermistors and thermostats must be in circulating coolant flow to accurately sense water temperature.

Without proper by-pass flow


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With proper by-pass flow adjacent to thermostat.


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Yeah, my assumption was that correct coolant layout had been observed, I totally forgot to think about the OPs hardware setup!

I would very much doubt the accuracy of the Tim gauge. They were always cheap and cheerful. If you have a gm sensor for the mega squirt that should be pretty close. Otherwise your into a k type thermocouple and matching reader.