Autocheck water temperature warning?

dgacampbell · 13-08-12, 01:12 PM

I pulled the 90 out of the garage this morning to give it a short run up to temperature as I do every so often to keep things from seizing as it spends so much time locked up in the garage.
So very shortly after starting the car, the Auto check comes on coolant warning..........
Of course I turned the car off straight away. out and checked, coolant bottle full to max line.
Water pipes as warm as one would expect for only running a few minutes.
My first thought one of those damn sensors I replaced earlier in the year has quit.
So I restart the car run it up to temp, all the while the Autocheck beeping, but temp gauge reacting as normal, fan comes on as normal.
I open the bonnet again, water pipes are hot and rock hard, yet expansion tank was still cool.
Waited a while for everything to cool down, opened expansion tank and to let the pressure out (squeezed the water pipes, all hot) and bubbled some of the coolant out of said tank.
Thinking I maybe had an airlock, although don't know how that could have happened as it has been fine up until now?
Got under the car and the water pipe that goes to the bottom of the radiator is still cool.
Anyone got any Ideas?
For those that don't know my car It IS a 1990 90 2.3NG.
TIA
Dan.

dgacampbell · 13-08-12, 01:20 PM

Just to add to that getting hot air through blowers.

Cyberplod · 13-08-12, 04:21 PM

Sounds awfully like a thermostat stuck closed, or not fully opening, unless I'm missing something (which is very possible...) and the water pump is OK

msh · 13-08-12, 05:17 PM

Sounds like crappy sender, apart from cool expansion tank point. I dunno what's the temperature when overheating warning should kick in, but long time ago I got my 3A once to 105c and nothing.

alex · 13-08-12, 05:35 PM

Mine is layed up a lot and i have had this happen a couple of times ! the first time it did it i didnt know what it was i didnt know the car bleeped ! , when i drained the water once hot i back flushed and sure enough the thermostat wasnt open !

Brian83 · 13-08-12, 05:36 PM

Had this same problem recently - it was the dreaded MFTS. It seems that when the original 4-pin sensors break the temperature guage stops working, but when the 3-pin sensors break, they tend to send a signal to autocheck so that it thinks the coolant temp is above 120degC!!! Autocheck gives the same symbol on the dash whether the coolant is low or the temp over 120degC.

I think the MFTS acts as a normally open switch (although is much more complicated), so that a ground signal is passed when the coolant temp is high - I think it's as simple as if you unplug the MFTS and the Autocheck doesn't appear you've found the problem. I think this is what I did, have looked for my notes but can't find them

The other possibilty is that you have a dud coolant level sensor? (unlikely). This I know you can check by just unplugging (but doesn't help if the MFTS is malfunctioning as well)

Brian83 · 13-08-12, 05:38 PM

Here's my thread from my problem - makes good bed time reading. Best bit is a helpful link posted by another member on here, loads of good info there

http://www.classic-audi.co.uk/forum/...ad.php?t=23055

dgacampbell · 13-08-12, 09:54 PM

Thanks guys!
hope it isn't MTFS, just replaced It and other temp sensor along with thermostat a few months back.
Will have a look see on thursday afternoon. Have ordered a thermostat from Audi this time, last one from ECP (no harm having a spare if it is not at fault)
Need new coolant from stealers anyway, gonna remove rad and flush properly, have a gut feeling the bottom of the rad is full of gunk. as when i opened the bleed bolt on rad, water pumped out, but expansion bottle did not drain?
(I had the fear that the new waterpump had packed in)

Thanks for link, will have a good read through.
appreciated chaps!

Dan.

dgacampbell · 27-08-12, 09:01 PM

Ok, I never updated this lol.
I replaced the thermostat with a genuine vag one (£26) the one I had fitted previously from ecp opened at the same time as the new one in a pot of water heated on the cooker.
There was a build up of gunk in the bottom of the radiator, which is quite unsettling considering the cooling system had been flushed and refilled with the correct vag coolant twice in a year, once not long after i got the car due to the previous keeper having mixed coolants, and a few months back when timing belt and water pump where changed. Now a third time.
This cured the coolant flow problem but not the autocheck warning.
I can only conclude that having washed the engine bay out before going on a weeks holiday, water had managed to get down into the contacts on the mfts

, some wd40 followed by a heavy dose of contact cleaner cured that, and now all is well.

13-08-12, 01:20 PM	#2
dgacampbell Senior Member Classic Audi Club Member Join Date: May 2011 Location: Co.Armagh, N.Ireland Posts: 1,442	Just to add to that getting hot air through blowers.

13-08-12, 04:21 PM	#3
Cyberplod Grown up member Join Date: Feb 2012 Location: County Durham Posts: 43	Sounds awfully like a thermostat stuck closed, or not fully opening, unless I'm missing something (which is very possible...) and the water pump is OK

13-08-12, 05:17 PM	#4
msh 4 ring whore! Join Date: Jun 2008 Location: Rucava, Latvija Posts: 3,816	Sounds like crappy sender, apart from cool expansion tank point. I dunno what's the temperature when overheating warning should kick in, but long time ago I got my 3A once to 105c and nothing.

13-08-12, 05:35 PM	#5
alex Grown up member Join Date: Mar 2010 Location: kent Posts: 188	Mine is layed up a lot and i have had this happen a couple of times ! the first time it did it i didnt know what it was i didnt know the car bleeped ! , when i drained the water once hot i back flushed and sure enough the thermostat wasnt open !

13-08-12, 05:36 PM	#6
Brian83 Grown up member Classic Audi Club Member Join Date: Jul 2011 Location: Loughborough & Lincoln Posts: 662	Had this same problem recently - it was the dreaded MFTS. It seems that when the original 4-pin sensors break the temperature guage stops working, but when the 3-pin sensors break, they tend to send a signal to autocheck so that it thinks the coolant temp is above 120degC!!! Autocheck gives the same symbol on the dash whether the coolant is low or the temp over 120degC. I think the MFTS acts as a normally open switch (although is much more complicated), so that a ground signal is passed when the coolant temp is high - I think it's as simple as if you unplug the MFTS and the Autocheck doesn't appear you've found the problem. I think this is what I did, have looked for my notes but can't find them The other possibilty is that you have a dud coolant level sensor? (unlikely). This I know you can check by just unplugging (but doesn't help if the MFTS is malfunctioning as well)

13-08-12, 05:38 PM	#7
Brian83 Grown up member Classic Audi Club Member Join Date: Jul 2011 Location: Loughborough & Lincoln Posts: 662	Here's my thread from my problem - makes good bed time reading. Best bit is a helpful link posted by another member on here, loads of good info there http://www.classic-audi.co.uk/forum/...ad.php?t=23055

13-08-12, 09:54 PM	#8
dgacampbell Senior Member Classic Audi Club Member Join Date: May 2011 Location: Co.Armagh, N.Ireland Posts: 1,442	Thanks guys! hope it isn't MTFS, just replaced It and other temp sensor along with thermostat a few months back. Will have a look see on thursday afternoon. Have ordered a thermostat from Audi this time, last one from ECP (no harm having a spare if it is not at fault) Need new coolant from stealers anyway, gonna remove rad and flush properly, have a gut feeling the bottom of the rad is full of gunk. as when i opened the bleed bolt on rad, water pumped out, but expansion bottle did not drain? (I had the fear that the new waterpump had packed in) Thanks for link, will have a good read through. appreciated chaps! Dan.

27-08-12, 09:01 PM	#9
dgacampbell Senior Member Classic Audi Club Member Join Date: May 2011 Location: Co.Armagh, N.Ireland Posts: 1,442	Ok, I never updated this lol. I replaced the thermostat with a genuine vag one (£26) the one I had fitted previously from ecp opened at the same time as the new one in a pot of water heated on the cooker. There was a build up of gunk in the bottom of the radiator, which is quite unsettling considering the cooling system had been flushed and refilled with the correct vag coolant twice in a year, once not long after i got the car due to the previous keeper having mixed coolants, and a few months back when timing belt and water pump where changed. Now a third time. This cured the coolant flow problem but not the autocheck warning. I can only conclude that having washed the engine bay out before going on a weeks holiday, water had managed to get down into the contacts on the mfts , some wd40 followed by a heavy dose of contact cleaner cured that, and now all is well.