Coolant Temp Sensor, Thermoatst, or both?!

I've got a 130TDI QS

My temperature gauge won't get to 90, it will manage about 85, then drops slowly to about 70, then goes up and down slowly in that range.

I initially thought it was just the coolant temp sensor, so have ordered one - waiting to fit - need the engine to be stone cold (incidentally, my car uses the 2pin petrol coolant sensor, not the diesel 4pin one?!)

I still have heating in the car, but describing the temp needle behaviour to a fellow car geek, he reckons it could be the thermostat.

Anyone with any thoughts?

As the CTS is easier to change its a good place to start.
with a cold engine, remove the coolant tank cap to release the pressure, replace the coolant tank cap to seal the system, this will minimise the coolant loss when you change the sensor.
Its a good idea to get a new "O" ring also..

I would say deffo the cts,had the same problem on mine,was up and down,like a whores knickers,get a funnel and a lenght of tube,place under the sensor and ease it out slowly until you get a nice trickle out and wait till it stops(with cap on as previously stated) when it stops take out ,and replace,would advise genuine part plus new o ring about 29 quid... easy job just a little awkward to get at.

Thanks guys, I'm fine for changing it (done a fair few in my time with VAG cars!) and I think it's easier to get at than the MkIV Golf, despite ths stupid idea to mount the engine longditudionally!

I'm going to do it tomorrow - back from work by 4, change it at 9pm, so hopefully cool enough. Can't think of a time in the next few weeks when I'm not out doing something!


So general opinion is that the thermostat is probably fine? Or do the coolant sensor first and see? How will I know if the thermostat is buggered when I've done the cts?

You say you have the 2 pin version, does that mean that you have 2 sensors 1 for the ecu and one for the dash guage. If so you will find the other attached to the bottom radiator hose next to the radiator. I dont know which does the dash though

Ok, what Kind of bloody pollock puts a coolant temp sender facing down at the back of a frigging engine? What a stupid place to put it, I can't get to it! Well, I can, but I have sausage fingers and I just can't get to it enough to do anything useful with it!

Aaaaaaarrrrgggh!

I see you,ve found it!!!! be prepared to leave some knuckles behind,oh I forgot to mention thr horseshoe shaped clip that locks it in situ, try not to break it.

Yes, well aware of that clip.

I don't see how I'm going to do it without loosing a ton of coolant, and my car takes about 7 litres. How much is coolant, £5/litre? It's oily and greasy round there, so I doubt I can just catch it. Actually, could I just unplug a coolant hose at the front behind the bumper - near the radiator - and drain the lot. Then I can change the frigging sensor in peace and refill when done?

No dont drain it there,if you air lock the heater matrix its a **** to get out, just rig up something to catch as much as you can with a tube underneath the car its quite expensive stuff g12 antifreeze, do it like I said and it will drain just enough to get the job done.

OK, I'll have a go, I have a funnel - I think I'll take that part of the undertray off to let it drain down into a container. How much will come out do you think?