calibrating Temp Gauge

[andrewh]

Am in imagining it or did I read somewhere it possible to calibrate the temperature gauge ?

I have a gauge that reads high I think. Is there anyway to test it and the sender are accurate?

[mark10337]

Hi

Yes of course it is. The temperature sender should be a TT4201-00 unit.

The temperature vs resistance curve for TT4201-00 is as follows:
30 deg C = 180 ohms
40 deg C = 156 ohms
60 deg C = 84 ohms
80 deg C = 49.4 ohms
100 deg C = 31 ohms
110 deg C = 10 ohms

so this can be tested with a multimeter and a thermometer. Probably easiest off the car, and in a pan of water or similar. The Smiths gague can be accurately calibrated using some resistors with the above values, which should make the gauge read correctly. It can be adjusted by removing the two cork dust covers on the rear and moving the mechanism inside until the readings are correct.

[andrewh]

thank Mark. I am sorry, somehow I missed replying to your kind post. I am still trying to work out whether the gauge is reading too high or not. Its certainly indicating very high readings but the engine doesn't seem that hot. Its giving pretty acceptable readings from an infrared thermometer ,but right up to the top on the gauge. Does the voltage regulator have an influence on the actual reading or i that a red herring?

[Heuer]

Yes, the regulator supplies 10v to the fuel and temp gauges - if it is supplying 12v it will cause the gauges to read high. There are some recent posts on how to test it: viewtopic.php?p=84678#p84678

[andrewh]

thank you David. It may be that I have the green wires on the wrong terminal on the stabiliser. I will check my 3.8 and see how thats wired and read the topic. What makes me think it may be that is that the temperature goes up very quickly from cold start, more so than normal in my view.

[mark10337]

just check the voltage on the terminal. Does the Fuel gauge read high also?

On the voltage regulator B terminal = 12v and I terminal is the 10v output.

you can also measure the resistance on the sensor (against 10v not 12v)

[ralphr1780]

Andrew, if you still have the bimetallic strip voltage regulator, you need an analog multimeter to read the output voltage as a digital one will not reflect correct reading.
If not yet done, I recommend moving on to an electronic voltage regulator that you can assemble easily yourself or procure from few suppliers.

[andrewh]

thanks chaps. It appears I had the Voltage regulator wired incorrectly so I was putting 12v plus through the gauge. Anyway, now all seems good. I was a bit suprised though that even running the car at idle and uptown 1500 rpm in todays heat it still didnt get hot enough to kick in the fan. Quite a difference to the 3.8 which would have been starting to steam like a Traction Engine. Both engines have been totally rebuilt, chemically and physically cleaned out and both have alloy Fosseway radiators!

Is a 4.2 that much more efficient on the cooling , bear in mind the fan didnt kick in or need to!

[cactusman]

Touch wood my 3.8 with a coolkat fan is well behaved in traffic...comes on regularly if stationary but the temp gauge remains steadfast at just past 70 on the gauge..

[andrewh]

thanks chaps. It appears I had the Voltage regulator wired incorrectly so I was putting 12v plus through the gauge. Anyway, now all seems good. I was a bit suprised though that even running the car at idle and upto 1500 rpm in todays heat it still didnt get hot enough to kick in the fan. Quite a difference to the 3.8 which would have been starting to steam like a Traction Engine. Both engines have been totally rebuilt, chemically and physically cleaned out and both have alloy Fosseway radiators!

Is a 4.2 that much more efficient on the cooling , bear in mind the fan didnt kick in or need to!

[chrisfell]

As it happens, today I noticed my temp gauge was reading a little low. It stayed reading low after a short rest, but after a longer rest the gauge returned to reading much as it has done for the last 14 years and 50,000+ miles. Curiouser and curiouser.

[mark10337]

If it was reading a little low whilst driving it may suggest the thermostat is starting to stick open or a fault on the sensor.

[chrisfell]

If it was reading a little low whilst driving it may suggest the thermostat is starting to stick open or a fault on the sensor.

Nope, not the thermostat. Even though the gauge was reading low the otter switch still came on when I'd normally expected it in urban traffic. Usually the otter switch comes on when the gauge is half way between 70 and 90, as you would expect. Last night the gauge was reading nearer 60 when the fan came on. And then later after a rest it started behaving itself. Either the sender or the gauge must be at fault.

I will keep a look out for this in the coming days.

[Series1 Stu]

Check all your connections right through. Especially the earth points. Don't forget the engine earth strap too.

Cheers