Coolant Temp Sensor & Temp Gauge

**amz** · 10-02-2009,08:25 PM

I own a VW Golf Mk 4 115bhp PD engine. The gauge on the dashboard has been fluctuating since Aug 08, and after googling, I had the temp sensor replaced with a new 4pin green one. The problem seemed to have been resolved and the temp gauge showed 90degree's, although the mpg consumption was still fairly high.

Now, the temp gauge has started to fluctuate randomly again, and sometimes, it doesn't seem to move at all.

The car does blow out VERY warm air after driving around for hours, but the gauge can show only 50-70degrees (never 90degrees). I was told that it could be the Thermostat, so I've had that replaced today (part £9 and labour £30). The mechanic said that the old thermostat was stuck open.

However, the temp gauge doesn't move much now either. I've just had it connected to the VAG-COM, and it does show the engine coolant temp as 70-90degree's although the gauge needle doesn't get much off the mark.

I'm thinking that it could be the sensor again, but the mechanic doubts this as it has only been 4months since the last one was put in. Its a fairly cheap job (£10 part, £15 labour), so I'm thinking why not?!

Question is - on the VAG-COM, what sensor is used to display the engine temp showing 70-90degrees? Is it the coolant tank sensor, 4pin engine temp sensor, or what? (I'm just a bit sceptical that if the VAG-COM is using the engine temp sensor to show the temp, shouldn't the gauge show this too?)

What else could cause this problem, as i'm running out of idea's, and it's becoming costly. The temp sensor and thermostat have both been changed, but i'm planning on having the temp sensor changed again.

Any advice...?

P.S. Re the 4-pin sensor, i assume the 4 pins feed into different parts? i.e. 1 pin could be faulty which leads into the gauge?

**VAGMAN54** · 10-02-2009,08:48 PM

one side feeds ecu 2wires,the other 2 does the gauge,seems funny that the gauge and vcds read the same so surely that would rule out the sender unit,if you have only got warm air coming out of the heater it could be the water pump,but if the thermostat was stuck open then surely it would have made a difference now its been changed if it hasn't then it carnt have been open or is the new one stuck open too ?

**amz** · 10-02-2009,09:50 PM

Hey, thanks for the quick response.

Sorry, I might have not explained myself properly, the VCDs show the temp increasing from 0 through to 70 and then continuing upwards (I guess to the 90's), but at that stage, I switched the engine off, as the neighbours starting looking at me weirdly! In that time period, the dashboard gauge didn't move at all..... so VCD showing 70+ degrees, whereas gauge showing 0.

There is cold-warm coming out fine from the vents... that's working perfectly fine. The car runs fine too, although I have noticed fuel consumption to have increased too. It's just annoying to see the temp gauge to be 0. I was unsure whether the VCDs show the temp based on the engine temp sensor, or the coolant sensor (inside the coolant tank).

Could this be a case of a faulty temp sensor?

**herby0001** · 11-02-2009,02:56 PM

I'd say it was the temperature sender. When I bought a genuine one from VW, it cost around £20, not £9. Are you buying genuine parts?

**amz** · 11-02-2009,04:21 PM

It's a genuine VW part, but not directly from VW. It's via one of their employee's.

Is it easy to change? Do I need specialist tools? Being quoted £10-£15 labour to change.

**VAGMAN54** · 11-02-2009,09:57 PM

sounds like temp unit to me to,easy to change,release pressure from header tank ,replace lid,remove plastic clip,remove sender,fit new sender with new "o " ring,refit clip,top up water/antifreeze mix away you go

**amz** · 17-02-2009,04:15 PM

Hey, just to follow-up on my temp problem.... I bought a replacement temp sensor for £8 and had it replaced yesterday. It took the mechanic less than a minute to replace! The gauge works perfect now.

Thanks VAGMAN54 and herby0001

**herby0001** · 21-02-2009,11:12 AM

Good result then! Thanks for letting us know.
Cheers!

denibabe · 13-03-2009,10:06 AM

hi,would temp sensor cause the engine idle to be a bit lumpy untill the engine is warm ,cus thats what mines doing and if i leave it for an hour i get back in the car and the same again till its warm .

denibabe · 13-03-2009,10:07 AM

Originally Posted by denibabe

hi,would temp sensor cause the engine idle to be a bit lumpy untill the engine is warm ,cus thats what mines doing and if i leave it for an hour i get back in the car and the same again till its warm .

sorry my car golf gttdi 130