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Temperature Gauge / Sensor

vincematthews

vincematthews

Member
The Temperature gauge on my '87 2.5l oval dash has stopped reading - not a flicker when turning the ignition on. Fans cut in so I know the water is getting up to temperature. I've pulled the two wires off the sensor in the engine block when cold and measured the resistance between the two terminals - apparently open circuit.

My question is should there be a resistance across the terminals or should I check each terminal to earth in turn?
Just trying to establish whether its the sensor, wiring or gauge before I start buying bits.

Thanks
 
I think it will be across terminals. Such sensors usually are, and often fail.

When it comes to buying a new one, do some careful cross-referencing of part numbers with Bosch. You may well find that identical parts are sold for other cars at a much lower price. The temperature sensor for an S2 is the same as a BMW part that cost about a third as much as the Porsche part.


Oli.
 
Is that from a BMW dealer to a Porker dealer or what a motor factor will try and sell you?

Have you checked the resistance at the two wires or at the sensor terminals?
 

ORIGINAL: ChasR

Is that from a BMW dealer to a Porker dealer or what a motor factor will try and sell you?

Have you checked the resistance at the two wires or at the sensor terminals?
Click to expand...
'Twas listed prices from the various specialists for the item under a Porsche part number and then the price when search for under Bosch and BMW part number. I seem to recall the price was £40 for the Porsche-numbered part and £15 for the BMW-numbered part. When the BMW part arrived it had the same Bosch number stamped on the side as the (failed) part that came out of the engine.

Good point about checking resistance at the ends of the wires as well as at the sensor terminals.


Oli.
 
That's fair enough. There are a fair few people producing cheapo switches and thermostats on the market now with variable results (I once bought a wheel bearing which didn't register the ABS sensor via a well known German and Swedish supplier!)). Bosch seems to be a safe bet :).
 

ORIGINAL: zcacogp

I think it will be across terminals. Such sensors usually are, and often fail.

When it comes to buying a new one, do some careful cross-referencing of part numbers with Bosch. You may well find that identical parts are sold for other cars at a much lower price. The temperature sensor for an S2 is the same as a BMW part that cost about a third as much as the Porsche part.

Oli.
Click to expand...

Thanks guys
I'm getting open circuit when checking across the terminals of the sensor.
I had it in mind that I read somewhere that one terminal on the sensor supplied the gauge and one terminal supplied the warning light.
If this was the case, checking ohms across the terminals wouldn't be the right thing to do?

Which fault condition would checking the resistance across the spade connectors on the 2 wires tell me?

I can't believe its such a pig to get to - they must have been able to find a more accessible place to put it. Porsche Design . . .
 
The one-terminal-gauge-one-terminal-warning-light is true for the oil pressure sensor, but I don't think it is the case for the temperature sensor. Having said that, I am starting to wonder whether I am right, as the temperature sensors I am thinking of only have one terminal and they register the resistance from terminal to earth - I may be confusing it with the fan switch sensor, which has two terminals.

Sorry, I'm not being much help here. Someone who knows what they are talking about will be along soon, I'm sure.


Oli.
 
This is the set up I've got . . . apologies in advance as I can't remember where I borrowed the photo from.

Clarke's gives a test proceedure for the gauge (if you have a handy potentiometer) but does -not- explain how the sensor works.

FBCAABA6C1B8435F825CB93389F9ADE7.jpg
 
As a shot in the dark, if the sensor is a dual sensor, you would check the term inlays by earthing them to the body of the sensor itself.
 
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