coolant gauge help

[peterMG]

Hi

I am racing a stripped down MG maestro

I have an after market coolant temp gauge fitted that does not work.

the supplier says it is using the standard VDO parameters for voltage = temp.

does anyone know

what voltage comes from the Maestros coolant temp stat for what temp
i.e. at 20C you get voltage x
and at 90C you get voltage y

and what should the input voltage be to the stat

or alternativley, anyone know of a seperate coolant temp gauge that works I could buy

[e692wtt]

I seem to recall that the temp gauge is earthed via the fuel ECU and then the temp gauge 'sender' on the cars as they left the factory, so you're looking at it the wrong way in terms of 'volts out of the sender unit' if I understand what you are saying? It's been a long morning though...

You need to look at the changing resistance of the sender unit as the coolant temperature varies, to determine how this compares with the spec of the temp gauge. If the 'aftermarket' gauge meets standard criteria then the temp gauge should work correctly. But...

I fitted a Mini temp sender to my Monty (1.6 S-series engine) when I bypassed the fuel ECU, and the temp gauge works fine (earthed directly to the temp sender). Mebbe this is the way to go as opposed to keeping the original sender unit which allows the fuel ECU to determine the coolant temperature and then 'suggest' what the temp gauge might like to show??? This only applies to non-fuel injected engines and engines with the 2 seperate ECUs unless you make a seperate drilling for a second, non-standard temp sender...

Hope this helps.:)

[G Force]

Hi There, The MG maestro 2000 0 series and 1600S series engines both use negative temperature co-efficient type coolant sensors. ie. high resistance when cold and low resistance when hot. Which is probably why you can't get your gauge to work. The sensor has a range of around +30K ohm to 100 ohm. The trouble is that this type of sensor is needed to supply coolant temp info to the engine management so you would need to keep the original sensor. If you can fabricate the thermostat housing to take another sensor as well you could run your gauge off say a mini or metro sensor.

Cheers Gary :)

[peterMG]

thanks for your input

I now realise how little I know about electrics

understand how it works now.

is the rating of the maestro sender compliant to the VDO european standard? This is what the gauge supplier i've got says it complies with.

anyone know what the VDO european standard is?

as the standard sensor is twin bladed, i would make the assumption one blade is for the engine management and the other is for the temp gauge

is this correct?

if it is, and the sender has the rating as in one of the replies, does anyone make an aftermarket standalone dial gauge to match it?

or is it poss to get the temp gauge out of a maestro dashboard and run it on its own somehow. it might not look pretty, but as the car is stripped for racing, this is not a problem

thanks again for your input

regards

peter

[G Force]

Hello Peter. I think the maestro gauge its self does not work much different to your race gauge. The difference is the temp sensor does not directly control the gauge on the maestro it is the fuel management ecu that earths the gauge in response to information it takes from the temp sensor.

You could as already sugested try fit a second sensor on the engine. Or try and drive your gauge with the fuel ecu, if you have the original ecu and harness the temp gauge earth is on the blue green wire (efi) only worry is if the internal resistance of your gauge is different to the maestro you risk damaging the ecu. :)

[e692wtt]

Originally posted by peterMG
as the standard sensor is twin bladed, i would make the assumption one blade is for the engine management and the other is for the temp gauge

If memory serves, one of the two blades has a pink/green wire connecting to it and is connected to the fuel ECU, and the other blade has a pink/black wire connecting to it which is connected to earth (ie the battery negative terminal, eventually).

If you fit a manual choke (ie carb engines with 2 seperate ECUs) you can bypass the fuel ECU and use a Mini or Metro temp sender to get the temp gauge to show 'representative' temp readings. Or you can fit a Moni temp sender elsewhere around the hot end of the cooling system and drive a gauge directly this way. Let me know if you want details of the former method, send me a private message mebbe?:)