CTS or thermostat

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AttackOfTheEddieMunster

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Hi

I have a '99 S3: driving along the temperature gauge sits on about 60, park up for a few minutes, or stop the car and start it a few minutes later, the gauge will go to about 80-90. Is this a CTS issue or thermostat?

Regards
 
also CTS is 10 second job. thermostat is much harder so i would do CTS first and see if it fixes it. I replaces thermostat and it was a pita. turned out to be CTS. bum
 
audi upgrades
The thermostat isnt as difficult as its made out. There was an excellent guide posted here last week or the week before.

I did mine last weekend after changing the cts which had no effect. Temperature sits at 90 perfectly now.

The only issues I had was the two screws holding the plastic trim in front of the intake manifold were seized solid and I broke the dip stick tube.
 
Sorry to highjack, thought it be better than starting a new post as it’s related. My temp gauge takes an age to move, half hour journey will barely get to 10C, never gets to 60C! Changed temp sender but no luck, will thermostat sort problem?

Thanks
 
Last edited:
VeVeX said:
The thermostat isnt as difficult as its made out. There was an excellent guide posted here last week or the week before.

I did mine last weekend after changing the cts which had no effect. Temperature sits at 90 perfectly now.

The only issues I had was the two screws holding the plastic trim in front of the intake manifold were seized solid and I broke the dip stick tube.
Click to expand...
its not hard to fit just very tight where it what makes it hard!when you have shovel hands like me they dont go well with tight spaces!
 
Sorry VeVeX didn’t realise it starts at 60C, I meant it would rise a tad above 60C but never gets to 90C. Then again my journeys recently have been short 15 min to work and gym etc. Did attempt the thermostat the other day but couldn’t get to the bottom bolt, lost a load of coolant, luckily had some g12 spare. Not sure i want to attempt it again!
 
whats the best place to get the CTS from?
i got a thermostat from euro car parts today for £10

but the CTS they had was £17.. is that about right?
 
Anyone know the part number?
A few places have said there are 2 different types so i dont want to get the wrong one
 
blue or green. stick your head under the bonnet and look :) gsf will do it off your number plate
 
yeh, mine looks black, i gave euro car parts my number plate, and they got 2 different ones
 
wd i be best removing mine, and taking it in n having them match it?
 
pin layout is different. match your pin layout to either a blue or green one and buy that...
 
Same prob with my S3 but pardon my ignorance but whereabouts is the CTS thanks..
 
ebay or gsf are about £17 delivered. same part as used in mk4 golfs at a guess so vw would be likely to sell it.

look at engine. right hand side of head there is a big coolant pipe with the sensor on top. thats were mine is.
 
Thought I would chuck my temperature woes in here to listen to ideas/suggestions.

Changed the Thermostat in October as my newly aquired 1999 S3 APY would rarely break 75 degrees, this worked fine.

This week the temps have fluctuated with no particular pattern so I changed the CTS today, reconnected everything and topped up the coolant as it had dropped slightly and took it for a drive. Temp reached 90 sat there for 2 minutes and then started dropping down to 64 and rising back up again. It does seem to rise more steadily when idling and crept up to 109 degrees with no fan kicking in.

The cluster gauge doesnt seem to tally with the readings on channel 49 of the climate control either but I have put this down to a delay between digital/analog outputs?

Also worth noting that I have travelled around 90 miles on 3/4 of a tank, which is shocking especially as I have been taking it very easy as I know the car is not working as it should.

Could the thermostat be shot again so soon or is it likely that I have a picked up an airlock fitting the CTS?

Thanks in advance

Alex
 
audi upgrades
The Cluster lies.

It has an internal buffer, which makes it display 90c at any temp between 80 and 100 or so. Use channel 49 instead of the cluster for accurate info. (that said, if the cluster is showing 100c and 49c is showing 60, then its probably a dodgy sensor)

Was the thermostat a good quality part? Does the temperature vary with speed, IE the faster you drive the lower it gets?

Was the CTS genuine? Cheap pattern ones can be completely useless.
 
aragorn said:
The Cluster lies.

It has an internal buffer, which makes it display 90c at any temp between 80 and 100 or so. Use channel 49 instead of the cluster for accurate info. (that said, if the cluster is showing 100c and 49c is showing 60, then its probably a dodgy sensor)

Was the thermostat a good quality part? Does the temperature vary with speed, IE the faster you drive the lower it gets?

Was the CTS genuine? Cheap pattern ones can be completely useless.
Click to expand...

Thanks for the info, the 2 readings do seem to tally but the cluster reading is delyaed to the 49c reading.

The termostat and the CTS were both supplied by my local Trade Parts Specialists so both are OE items.

From driving it again this morning, when left to idle from cold it saw a linear climb to 97 so i turned the car off and had a shower, etc. Car had cooled down, got in it and drove it for 40 minutes, it never once broke 75 and fluctuated between 58 and 75 degrees with no real pattern to its fluctuation.

Iam going to drain the system and flush it through, then replace coolant and allow it to settle to eliminate the possibilities of airlocks in the system.
 
aragorn said:
Was the thermostat a good quality part? Does the temperature vary with speed, IE the faster you drive the lower it gets?
Click to expand...

That's what happens on mine: I changed the thermostat, same problem. If I let the car idle in traffic, it'll rise to 90 quite happily, but the instant I drive it, it'll drop down to 60 and stay there no matter how long I drive it for.

Humour me, but how do I get the 49 information to come up?
 
Theres nothing wrong with his CTS, its working perfectly.

The fault lies in the thermostat.

Why replace parts that arent broken?

On the A4, you hold recirc and press "UP" on the climate control unit, then the display will change to "1c". You can then use temp +/- to make it read 49c and press recirc again to display the actual coolant temperature.
 
AttackOfTheEddieMunster said:
That's what happens on mine: I changed the thermostat, same problem. If I let the car idle in traffic, it'll rise to 90 quite happily, but the instant I drive it, it'll drop down to 60 and stay there no matter how long I drive it for.

Humour me, but how do I get the 49 information to come up?
Click to expand...

Its absolutely a thermostat fault.

The CTS simply reads the temperature. The thermostat controls the flow of water thru the radiator. When the thermostat fails, it lets too much water flow thru the rad, and as a result the water cools down to much. When you stop, the airflow thru the rad ceases, and the temp starts to climb. Set off again and the airflow returns, dropping the temp back down.
 
aragorn said:
Theres nothing wrong with his CTS, its working perfectly.

The fault lies in the thermostat.

Why replace parts that arent broken?
Click to expand...

That's the argument though: the thermostat has been changed, for a genuine Audi pattern part, and the issue is still there. If I start the car, but remain idle, the temperature will rise to 90 as normal. The instant you drive the car the temperature will drop. Park again, the temperature will rise to 90 as normal.

Might the CTS be reporting the wrong temperature to the engine, and therefore the dash gauge?
 
Ok, lets assume for a minute the temperature happened to be perfect, and was actually rock solid at 90c. Why then would the CTS decide to randomly show a low temperature only when your moving... then again randomly (but perfectly timed) decide to read correctly shortly after you stop.

Get 49c up on the display, and you can see the temperature climb and fall with speed.
 
aragorn said:
Get 49c up on the display, and you can see the temperature climb and fall with speed.
Click to expand...

Right - if I use the 49c method that can discount there being an issue with the CTS, i.e. the CTS is sending the temperature to the ECU, which in turn we'll see on the display? If the display rises and falls in temperature we therefore know that the CTS itself is working correctly?
 
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