1990 coupe NG temp sensors

[R5T]

Afternoon all, after having my baby on the road for a few weeks, the cold start is getting worse and worse and I'm still having a few teething problems. My temp gauge has always worked fine, but has suddenly stopped functioning, although if I've been on a run for 15 mins or so and pull up in traffic the needle will begin to rise but will not go above the second Mark.

I replaced the coolant temp sender on the top of the outlet elbow (foolishly not genuine) and the mfts on the underside of hose is slowly leaking. I'm pretty sure the sensor has gone but it's so corroded and scabby I can't get a p/n from it. It is a brown capped sensor, with 4 wires going in. I've been told that the sensor could be 3 or 4 pin depending on superseed parta etc.

Has anyone got a part number for this sensor and is it definitely my mfts ? Also if anyone knows which part number the other sensor(on top) should be then it would be greatly appreciated. I've decided to bite the bullet and replace both with genuine to save future problems.

Many thanks

Sam

[R5T]

no worries lol answered my own question ... im looking at £170 plus VAT for both sensors from audi ... not looking good

Sam

[Cuppatea]

Mine was 4 pin originally, replaced with a used 3 pin and thats all thats available as new from what i understand but works on my 3B. The plugs break up and plug covers deteriorate too.

Anyone bought from these before?

http://sites.internet.lu/folders/cus...S2.htm#COOLING

They have mfts senders listed.

[John.]

Originally Posted by Cuppatea

Mine was 4 pin originally, replaced with a used 3 pin and thats all thats available as new from what i understand but works on my 3B. The plugs break up and plug covers deteriorate too.

Anyone bought from these before?

http://sites.internet.lu/folders/cus...S2.htm#COOLING

They have mfts senders listed.

A good friend just got one from CAC, apparently you need to open an account with them.
The 4th pin(so I've been told) is an earth, as long as the switch gets earthed through the housing it's screwed into then all is good.
John.

[R5T]

Cheers people, if this sensor was kapput would it have any affect on the running of the car ? Ie. Idle/cold start ? Or is it just for the gauge etc ?

Sam

[missfire]

No. I knew it sent a signal to the ecu, used to think it would effect running but I don't think so.

It sends to the temp gauge, and sends an overheat signal to the autocheck system, the AC compressor, and the ECU to limit boost in turbo engines. It does effect running in my 100t, if it overheats, but not in an NG.

I think it's a fuel pressure problem, pump, accumulator etc. think it needs a fuel pressure test. Also seem to remember coming to this conclusion last time you were trying to work it out.

The old one had a +12 supply John.

[John.]

Originally Posted by missfire

It does effect running in my 100t, if it overheats, but not in an NG.
...........................
The old one had a +12 supply John.

Thanks for the info. Any idea if it would effect running on a 7A, in particular idle speed.
Cheers.

[msh]

Originally Posted by John.

The 4th pin(so I've been told) is an earth, as long as the switch gets earthed through the housing it's screwed into then all is good.
John.

Wrong. Forth pin is power, as the original hella MFTS contained some electronic circuitry which required power to work. Since aftermarket senders use ordinary temp resistor and two bimetalic switches, they don't need power.

[John.]

Originally Posted by msh

Wrong. Forth pin is power,

Yer 6 hours late!

[missfire]

Originally Posted by John.

Thanks for the info. Any idea if it would effect running on a 7A, in particular idle speed.
Cheers.

Now your asking.. sorry don't know about these fancy 20v thingies! Or even where to look for sensors on one of them, never had one! yet..

On the 100t it's nice and simple. The MFTS sends to the temp gauge and sends those overheat signals. The ISV is controlled from the wee single pin sensor on top of the coolant flange, after-run circuit from the one on the 'back' of the flange and the ECU signal comes from a wee single pin sensor under the steering pump bracket.

On the NF (same as the NG) there is what appears to be a thermotime switch (two pin) on top of the flange. That one send to the ECU. The ECU controls the cold start valve and I presume the ISV too. On the older engines this two pin sensor actually is a thermotime switch and controls the cold start valve directly.

I think.

Always good to put a disclaimer in.