electric temp gauge

Post by **mike.perry** » Mon Mar 09, 2009 12:09 am

I fitted a new temp. gauge with an electric sensor to my Series MM and it read 3/4 across the dial (120deg).
I was informed by the suppliers that it needed a voltage stabaliser so I wired in one that I removed from a black speedo but it still reads 3/4 across the dial.
Any solutions?

Post by **PSL184** » Mon Mar 09, 2009 5:36 am

When you say "electric" I assume you mean the type that earths out through the sender unit in the thermostat housing? If so, check you have wired voltage reg the right way round. The 2 terminals furthest away from the long tab are in 12v in and the 2 nearest the tab are the 10v out. Also, the body of the reg has to be made to a good earth so use the screw hole in the mounting tab to earth the reg somewhere solid. Other possibilities are a faulty sender - test by substitution - or the wrong sender for the gauge - some have a coloured colar around the sender which represents different values. Last consideration is that the gauge is correct and your engine runs warmer than you were expecting so you would need to test with the wifes temp probe out of the kitchen drawer

Post by **mike.perry** » Mon Mar 09, 2009 11:05 am

As the engine is a s/v the sensor is tapped into the rad. header tank.
I will check the correct wiring on the stabaliser. Also I had not appreciated the earthing of the v/s. I have it secured to the gauge clamp bracket which may not be earthing.
Thanks for the info but it will be a month before I get a chance to fix it.
I will let you know the outcome

Post by **PSL184** » Mon Mar 09, 2009 3:08 pm

Mike, just out of interest, what connections are there to the gauge itself?

Post by **mike.perry** » Tue Mar 10, 2009 3:12 pm

Two spade connectors on the back. I tried swapping the wires over but it didn't make any difference. I'll check your earlier solution next month.

Post by **PSL184** » Tue Mar 10, 2009 6:01 pm

The gauge will need earthing too then I would imagine.....

Post by **bmcecosse** » Tue Mar 10, 2009 7:35 pm

Not really - it earths out through the sender. The stabiliser needs earthing to give a path for the 'heating' current through the bi-metallic strip - the 'approx 10 volt' output going to the gauge. Note - you won't measure that as 10 volts - it's an interrupted supply which overall will 'average' 10 volts into a resistive load like the gauge !

Post by **PSL184** » Tue Mar 10, 2009 9:15 pm

It should earth out through the sender, agreed, and in all honesty sounds like it is, I was just mentioning it in case it was still erratic after earthing of the V/R. There can be a lot of paint between the rad, its mountings and the chassis of the car preventing a good earth.....

Post by **bmcecosse** » Tue Mar 10, 2009 10:14 pm

Which may well be why it's not working properly!

Post by **mike.perry** » Fri Mar 27, 2009 3:09 pm

As I am away at the moment your suggestions will have to wait until I return home but here's hoping that you have the solution. Cheers

Post by **PSL184** » Fri Mar 27, 2009 3:12 pm

If its not then we'll think of another for you

Post by **mike.perry** » Thu Apr 16, 2009 8:37 pm

I tried wiring up the gauge and volt. stab. as per your instructions and nothing, zilch, zippo. I wired the gauge direct and got over 90deg.
I guess the v/s is knackered. Any way of testing it or shall I just find a new one. I have only got the black speedo in the traveller and I don't particularly want to take that apart.

Post by **PSL184** » Thu Apr 16, 2009 8:47 pm

Mike, see if you have output from the V/S - It will read about 12v to start with then drop off as the unit warms up (as the bimetallic strip makes and breaks a few times) Did you have the correct wires on the in and out terminals?

Post by **mike.perry** » Sat May 09, 2009 10:50 am

Progress so far. I checked the voltage stabaliser for continuity, put a test light across the terminals and it lit. I have had the radiator rebuilt and as it had the sensor fitted to it I couldn't go any further. The radiator is now back in the car but I put the voltage stabaliser somewhere safe and I can't remember where!!!!!!!!!!!

Post by **mike.perry** » Sat May 09, 2009 12:28 pm

I have found the voltage stabaliser.
With engine at running temp I have tried the following combinations.
1. Wire temp gauge directly to 12v supply. Result reads 120 deg.
2. Wire in v/s 12v input Term B, output Term I. v/s not earthed.
Result reads 120 deg. (workshop manual wiring diagram P. N44)
3. Earth v/s. Result reads 0.
4 . Swap wires on gauge terminals. Makes no difference.

Any other sugestions please?

Post by **bmcecosse** » Sat May 09, 2009 1:29 pm

Zero would be correct if it's cold - what happens you heat it up ?
But really -mechanical temp gauge is very much better !

Post by **mike.perry** » Sat May 09, 2009 11:06 pm

As I said at the beginning of the last entry, I warmed the engine up to operating temp which should be about 80 deg.
I found a diagram in the Mini workshop manual page N16 showing the correct wiring for the v/s and temp. gauge which agrees with my wiring.
The only mechanical temp gauge I have is the dual oil pressure / water temp gauge I have on my traveller. I have not been able to find a gauge with a backlight or the correct size sensor which is why I bought the electric gauge, besides it matches the ammeter.

Post by **bmcecosse** » Sat May 09, 2009 11:23 pm

Hmmm - I thought you were trying it out 'off the car' - hence query about temps. Well - I guess it's just not compatible with the type of sensor you have ! Shorted directly it should slowly go to high temp reading, and on open circuit should read lowest. This (shorting) happened to me on my TR7 - gave me terrible fright, until I realised the HOT reading was there next morning before i even started the engine. Easily sorted with new sensor - much easier than head gasket change on TR7 engine !!!!!!!

Post by **mike.perry** » Sat May 09, 2009 11:55 pm

I bought both the gauge and sensor from the same reputable supplier at the same time so I would have thought that they would be compatible.
Maybe I ought to try a different v/s.

Post by **alanworland** » Sun May 10, 2009 12:01 am

My 'Jaeger' temp gauge was taken from a Jaguar I believe with its sender. The sender is fitted into a 'T' piece fitting at the rear of the head (the other part of the 'T' supplies the heater valve)
This assembly is wired with 12v (no stabiliser)
The sender is a Smiths TT4400/00 and measures :-

19 DegC 575 Ohms
27- 360
42- 138
53- 101
56- 84
60- 72
65- 58
70- 45
75- 38
80- 32
85- 25
90- 21
95- 17
100- 14.5