Help! Temp sensor replaced now reads lower!! Genuine VAG

[Itguy]

Hi everyone

I seem to be having real problems with this.

I replaced my thermostat at the weekend with no effect on our slow warm up problem and today have replaced the ECT engine coolant temperature sensor with a genuine VAG 06A919501A.

The one I took out was the same part number but without the A on the end.

I've just been out and done 25 mins of driving (7c outside) and it didn't get to 90 on the gauge. It got to about 80 then went to 78 and back to 80 so I can only assume that's where it would settle. The old sensor did get to 90 and sit there (tested after I fitted the new thermostat so I am comparing apples with apples).

Does the new sensor need calibrating or something in VCDS? Something need resetting??

This is starting to drive me crazy. Surely it shouldn't take 20+ mins to warm up?

Did the plumbing change on the later engines after ours (ours is an 05).

Thanks

[xjay1337]

Was the thermostat a genuine one..?

[Itguy]

Yep and tested in a pan of water with a thermometer before fitting

[doylebros]

Is the aircon switched off?

Is the aux coolant pump running?

Have we got an air lock - Is the system pressurising -  extract from a post else where - no pressure means we can be stuck with an air lock!

The radiator cap actually increases the boiling point of your coolant by about 45 F (25 C). How does this simple cap do this? The same way a pressure cooker increases the boiling temperature of water. The cap is actually a pressure release valve, and on cars it is usually set to 15 psi. The boiling point of water increases when the water is placed under pressure.
When the fluid in the cooling system heats up, it expands, causing the pressure to build up. The cap is the only place where this pressure can escape, so the setting of the spring on the cap determines the maximum pressure in the cooling system. When the pressure reaches 15 psi, the pressure pushes the valve open, allowing coolant to escape from the cooling system. This coolant flows through the overflow tube into the bottom of the overflow tank. This arrangement keeps air out of the system. When the radiator cools back down, a vacuum is created in the cooling system that pulls open another spring loaded valve, sucking water back in from the bottom of the overflow tank to replace the water that was expelled.

All just thoughts

[xjay1337]

VWs run a sealed system.
They're slightly different from the Hondas and what not which have rad caps and overflow tanks.. The Golf is a self-bleeding system. When I changed my coolant after you topped it back up it was fine.
aircon on/off wouldn't have anything to do with the temp unfortunately :(

[doylebros]

Them two fans running on the front with the aircon on is going to be cooling the system.

[Itguy]

I'm going to take it to work tomorrow for a longer run, but I suspect it will still be under reading.

How could this be with a new sensor compared to the old one??!

I presume then that there is nothing in VCDS which would help?

The aircon was off when we went for the drive (Econ mode on). Cabin temp was set to 22c and auto fan speed.

[xjay1337]

No you can use VCDS and even the climatronic displays to display engine temperature but it will be the same as the dashboard display (within reason).
Either the thermostat is faulty or the CTS is faulty.

[doylebros]

You can check the temperatures in the system with VCDS and do logs but that's it as far as I'm aware.

I'm not sure if there's also a gauge sensor - would have to check it out.

What I would be checking is if those fans are running regardless of the switch position and look to see if that's aux pump is running with VCDS.

It may also be self venting but air lock would be high on my list!

Finally, checking on Google the year 2005 seems to be a cold car - plenty posts with this problem!

[Itguy]

Can't be the thermostat as I've tested it prior to fitting.

I know I can test the coolant sensor by using my multimeter and checking the resistance while warming up but is there a list anywhere that says what ohms should = what temp?

Must be a bit odd though having a faulty genuine one? Somehow I'd need to prove it to them for them to swap it at the TPS I  bought it from though too?

I'll see what tomorrow brings but as the old one did eventually get to 90 it might be that I just refit that and be done with it, although I'm annoyed that this new one doesn't work correctly.

From reading other threads someone suggested that the type of coolant used may have an impact? It does have pink coolant in at the moment but I don't know if it's genuine VW or not. Someone said that VW put additives in to aid fast warmup?

[doylebros]

You do get new items faulty but it's rare.

You may need to check the sensor wiring physically?

Ignoring what the gauge says "does the cab get hot" that's what you need to know!

If it's hot then it's electrical display issue  - put your own thermometer in the cab and check how hot it gets on full heat.

[bacillus]

Just my 2 cents but on our cars there are two coolant temp sensors!
One is below the intake manifold and I'm assuming this is the one you changed. The other is below the vacuum pump (battery side of head). Unclip it, clip looks like this


 
Pull it out, and put the new one in. There is an O ring (N90316802) on the sensor which ideally should also be replaced as well before putting the clip back.

[Itguy]

It's the one on the side of the engine that I swapped not the one underneath in the rad hose off the thermostat.

The cabin does get hot and heat starts to come out of the vents quite quickly. I'm sure the car is physically fine but I obviously want the temp sensor to be right so the fuelling is correct.

[bacillus]

I was suggesting you try changing the other sensor as well if you're convinced the thermostat is ok.

[xjay1337]

Can't be the thermostat as I've tested it prior to fitting.

I know I can test the coolant sensor by using my multimeter and checking the resistance while warming up but is there a list anywhere that says what ohms should = what temp?

Must be a bit odd though having a faulty genuine one? Somehow I'd need to prove it to them for them to swap it at the TPS I  bought it from though too?

I'll see what tomorrow brings but as the old one did eventually get to 90 it might be that I just refit that and be done with it, although I'm annoyed that this new one doesn't work correctly.

From reading other threads someone suggested that the type of coolant used may have an impact? It does have pink coolant in at the moment but I don't know if it's genuine VW or not. Someone said that VW put additives in to aid fast warmup?

Someone wrote it on the internet somewhere so must be true!