Flashing Coolant Warning Light and cold running.

[Teg]

Hi All,

Done a bit of searching on the forum but still unsure of the answer. Im getting the below symbol appear o the instrument cluster shortly after starting the car at any temperature. Is anyone able to advise whether this is an issue with the coolant level sensor or this MFTS sensor?


Also, my car only runs at just above 50 degrees normally. When in traffic or just idling it goes up to and above 90 and then fan cuts in. But once driving along again it drops back to 50. Would this suggest it has the wrong Thermostatin? or possibly no thermostat

Any help very much appreciated. MOT next month and assume it would be a fail if this light is still coming on.

Thanks

[Error404]

Coolant warning won't cause an MOT failure AFAIK. You could check the MFTS plug is in good order as they tend to get brittle and break up causing problems.
Could be dodgy MFTS or coolant tank level sensor can get gunked up also.
Do you have the plastic cowling between the block and the radiator fitted?

[Bowie69]

Sounds to me like your thermostat is knackered too. it shouldn't run at 50C, whilst still giving a good hot reading when in traffic, from this I would say your MFTS is fine, but your thermostat is not.

The warning lamp s coolant level sensor, have you checked the level? It only needs to be a little down to trigger it in my experience. The sensor is under the radiator header tank.

[Teg]

Thanks for the comments,

Coolant level is fine so guess the sensor must either be broken or gunked up.

Think I will drain it down and replace the thermostat aswell.

@ Error44, do you have a picture of the plastic cowling between the radiator and the block? I dont think I have this but will double check wen I get home.

The header tank is not very old as was replaced by the previous owner. Think I might just have to swap afew bits over for new and see whats causing the problem.

Thanks

[Error404]

If you have that cowling missing the MFTS gets a nice supply of fresh air over it can read lower at road speed, giving you a false temp reading. Mine does this.
If you check the ECU temp sensor in VAGcom it will tell you what the actual coolant temp is. If your ECU sensor is reading low at road speed then you stat is lazy/damaged.
You can often clear a load of crap out of the coolant tank if you remove it and give it a good shake with some strong detergent in there

[andy10v]

The same warning symbol is used for low coolant in the header tank and overheating as indicated by the MFTS.

Unplug the level sensor in the header tank, if the coolant warning does not come on that is the fault.

Unplug the MFTS, if the coolant warning does not come on then the fualt is with the MFTS/plug/wiring.

It is entirely possible to have a MFTS/plug/wiring that operates the temp guage correctly and sends an overheat signal.

Only coming up to temperature when stationary, and temp dropping at speed sounds like thermostat stuck open or missing. They are not expensive, good maintenance and good to know the car has the correct coolant.

[Cottis]

I had this a couple of times on the car not long before I sold it. The thermostat and MFTS was going to be the next thing on the list for me but it was not reading as low as 50deg when I noticed it playing up a little. Sounds like it has got worse.

Like you say, it had an OEM header tank on it only a handful of miles prior to you buying it, so I doubt there are issues with that.

[Teg]

Yeah thanks Cottis. I think the thermostat is completely dead now. Think I'm going to replace the thermostat, coolant level sensor and MFTS. Will replace all the Hose clamps whilst at it.

[Bowie69]

I would be wary replacing the MFTS, as all the aftermarket ones seem junk, so you may just end up introducing a new problem!

Mine is still the original Audi one from 1991, and works faultlessly.

Do it one at a time and you have a fighting chance of finding out what the issue is.

[Fat Audi 80]

If you go in and do the MFTS and thermostat, make sure you do the small water hose under the water rail at the same time, it is tricky to get to at the best of times...

[Fat Audi 80]

Oh, and oil pressure switch just above the thermostat....