Hi

 

I have an issue which I think I have worked out the answer for, but thought I would post my thoughts on here to see if there is any other possibilities.

 

I have noticed that the temperature guage has been reading low, for a while, it rarely makes it to the vertical and sometimes does not even get out of bed. Another issue is that the red radiator warning comes on the first time I start the car in the morning, but if I let it warm up for 5 minutes, stop the engine and then start it again, the light does not come on.

 

I think that the fault is that the coolant temperature sender is going on the blink, I found a thread on here in the Fabia section dealing with that, and it mentions the location of it on the 1.9TDI. Mine is the 2.0 TDI but on looking at the engine there is what looks like the same sender in the same place as in the photo on that other thread.

 

Added to this is that I have noticed a reduction in MPG, according to the trip computer, from the mid 50's, down to the mid 40's and yesterday on a long motorway journey it went right down to 40.

 

I am guessing that the increased fuel consumption is due to the car's brain being confused by the low temperature and it is pumping more fuel in as it thinks it is not burning properly. Does that sound a reasonable guess to anyone? Has anyone else encountered this when their temp sender has died?

 

Thank in advance for any replies.

 

Phil

Its either the temp sensor or it could actually be running cold, or a mixture of the two. Thermostats don't last forever and start opening early as they age, usually you don't notice unless the problem is really bad as the temp gauge will read 90 even if the coolant temp is at 70.

 

On a 2008 model, personally, I would change the thermostat anyway (helps with emissions, mpg and of course the heater gets warm faster) but by the sounds of your warning light it could be the temp sensor, either that or the level sensor in the expansion tank.

 

Make sure you buy genuine parts, aftermarket sensors and thermostats can be hit and miss.

 

Edited 8 February, 20197 yr by SuperbTWM

Yep, the temp reading is CTS or thermostat, and on a car this age I'd tend to CTS first because if the actual coolant temp is over 70C but not overheating you should get a reading about 90C.

 

As for the spurious overheat warning, with a cold engine, open the expansion bottle. If you can see a pair of metallic prongs descending into the coolant, scrape a flat screwdriver down each of them a few times. If you can't replace the said bottle (under £20 for a genuine part) and you should be sorted on that one.

Agreed on cleaning the metallic sprongs (or replace the bottle). 

 

Besides cleaning the sprongs, topping up the coolant level so its about 2mm above max also works.

 

Basicly those metal pins are measuring the resistance of the coolant. Lower level, higher resistance => warning. But since they tend to become dirty and oxidized (don't know if thats proper English) they can give false readings, even with sufficient coolant. Cleaning is easy. Besides the flat screwdriver you can also use a (hard) toothbrush.

 

As for the temperature: If its the thermostat, the gauge usually DOES go up after a long drive (unless its really freezing). If it sometimes doesn't come at all, the sensor is more likely.

 

When my thermostat failed, I could reproduce it: After a long drive leaving the car stationary -> Temp goes up to 90 degrees. (No airflow since I wasn't driving). Enabling the AC (thus starting the fans) and the temperature dropped..

 

In both cases: If the engine is cold (or at least, the ECU thinks it is) it increases fuel to the engine to reach its temperature. This would explain your poor MPG.

(Doesnt have anything to do with thinking its not burning properly, but it does it to reach its optimum working temperature by adding more fuel)

 

Edited 9 February, 20197 yr by DJSmiley

On 09/02/2019 at 19:33, DJSmiley said:

they tend to become dirty and oxidized (don't know if thats proper English)

Yes, that is normal (American) English usage. Proper English would say "oxidised".

Thanks for all the replies folks, lots of really helpful stuff.

 

I have scraped the prongs, and taken the electric connector off and sprayed it with WD40 and clipped it in and out a few times, so that should sort the red light out. I wont know until I try and start it tomorrow morning.

 

I have also bought a new CTS and thermostat, both proper VAG ones, not cheap alternatives. The CTS is here, but I am waiting on the thermostat, might as well do them both with one drain of the system.

 

I have also gone and invested in a Ross Tech Hex V2, it seems like the right tool for dealing with error codes etc. That should also arrive tomorrow too :)

 

Thanks again, and hopefully a good 'all sorted' post will follow soon.

 

Cheers

 

Phil

Cleaning the metal sprongs did the trick on stopping the red coolant warning on startup, cheers for that.

CTS and thermostat still to do

Cheers

Phil

So before I drined the coolant and did the CTS and the Thermostat, I thought I would just pop the electrical connecter for the CTS off, spray some WD40 in there and pop it on and off a few times to make sure the connection was OK. This seems to have fixed the problem. Temp has gone back to vertical for the first time in about 2 weeks on the last two days.

So I have a VAG CTS and Thermostat in my 'car bits' box which I will hang onto until I do the next service/oil change and will probable fit them at the same time.

Cheers for the advice folks

Phil