Engine (coolant) temperature dipping below 90 with AC on?

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Hi guys,

another thing I noticed today on the S3 8P. I was cruising home this eve at 80 kph with AC set at 21 deg with outside being 26 and noticed that the temp gauge was reading slightly below 90. It went back to 90 as soon as I stopped at a traffic light then did the same after I took off. I tried it with AC off and it did not budge from 90. Is this normal or I have an issue with thermostat/sensor/fans? I don't recall seeing this slight dip. I reckon it's dropping down to 87 maybe. Anyone experienced the same?

Cheers
 
Dont worry to much, 87 is nothing to be concerned about, if it drops below say 60 then its usually a coolant sensor, check the readings with vcds to confirm whats on cluster is same as the direct reading.
 
Mine is usually around 87C as well,so I wouldn't be concerned.
 
Sweet. Thanks guys. Will check this weekend with VCDS.
 
Mine was (A4 1,9 TDI though) also sitting at 80-87 degrees.. Only 90 when acceleration a lot..
Replaced the coolant stat.. Now it sits at 90 and stays there

Edit: no faults showed on VCDS
 
Wahlstrom said:
Mine was (A4 1,9 TDI though) also sitting at 80-87 degrees.. Only 90 when acceleration a lot..
Replaced the coolant stat.. Now it sits at 90 and stays there

Edit: no faults showed on VCDS
Click to expand...

I noticed today that's its doing it even with AC off. Basically if I cruise for a while then it dips below 90 and comes back to 90 when in traffic or short distances between lights. When ac on the fans kick in and they turn off when in ECO mode of off. So if anything it might be the thermostat. Will keep an eye on it.
 
I've had my thermostat replaced recently because of the same issue and it now sits at 90 all the time after warm up. Reckon you might be in the same boat it's really common on the 8p's. thermostat is only 32 quid just a pita to get to it.
 
JamesO said:
I've had my thermostat replaced recently because of the same issue and it now sits at 90 all the time after warm up. Reckon you might be in the same boat it's really common on the 8p's. thermostat is only 32 quid just a pita to get to it.
Click to expand...


Any DIY available?
 
JamesO said:
Sorry mate I had mine done by a mate, but I know he had to remove the alternator
Click to expand...

Thats cool mate. Thanks. I'm thinking about doing the timing belt too at the same time plus clean the valves and might as well change the coil packs and fuel filter. Would u know of a place in the UK where I can purchase the parts from? I live in Aus and here they charge us like wounded bull for everything.
 
Today it happened for the first time on MY09 S3, the water temperature dipped slightly to 87, and then it went back to 90. And it happened 2-3 times today. How do I know is it a thermostat problem, or a temperture sensor problem? Is there a way of knowing what could be the problem. So that I don't have to buy for etc. the sensor, when the problem could be in the thermostat instead? What is more common to fail the thermostat or the sensor, in a 4 years old car, with 75k kilometers.
 
Mine sits at 91deg not sure if it's just dodgy alignment on the dial.
 
Personally I wouldnt worry unless it drops by 10-20 imho.
 
autolatry said:
Mine sits at 91deg not sure if it's just dodgy alignment on the dial.
Click to expand...
There is no dodgy alignments in Audi, the needle on the dial has to be on 90 C straight in micromilimeter on the line, it is a very precise and accurate dial..
 
Last edited:
NHN said:
Personally I wouldnt worry unless it drops by 10-20 imho.
Click to expand...
But the working/operating temperature is 90 C, I would like it to be as when it was new, and if it is a sensor fail, it is possible that it could overheat(for. etc if a thermostat fails) and I would not know this because of the fail sensor..And I don't like to go in high rpm's when I haven't achieved operating temperature. Aldo if it's a sensor fail, and not a thermostat fail, the operating temperature should be 90, I'm just not getting the correct reading, correct me if I'm wrong?
 
Oh no. Don't say there is something else up with it.
I bet changing the thermostat on a 3.2 requires taking the car to NASA or having to burn open the housing with a special thermic lance or something equally rediculous.
 
autolatry said:
Oh no. Don't say there is something else up with it.
I bet changing the thermostat on a 3.2 requires taking the car to NASA or having to burn open the housing with a special thermic lance or something equally rediculous.
Click to expand...
It doesn't have to be a thermostat problem, it could be a temperature sensor problem also. I spoke to my mechanic friend today about the problem, we spoke shortly because he was at work, he works at the Audi dealers in my hometown, he said to me that the themostat problem on my S3 is uncommon, but possible, but he would rather take a shot at changing the sensor first. I didn't have time to ask him is there a way of knowing what is the source of the problem, before buying maybe unneeded parts, 'cause I don't want to buy a sensor if it's a thermostat problem etc... And I want to know exactly the current temperature, I want it to be accurate, and I want it to be on 90 after warming up of course. I don' think it is too much of a hassle to change the sensor or the thermostat. I will call him again tomorrow to ask him thoroughly and will post here what I will found out.
 
Hi , my S3 occasionally drops to about 87 degs . Will this affect economy and/or running ?I havent noticed a change and was going to leave fixing it until the next service or if it gets worse , Cheers for any advice ...
 
No.

As has been advised, start worrying that if on a motorway cruise it drops to 75 or below.
 
Change the sensor on the right hand side of engine. I've measured temps via OBD port, if it indicates 90 on the dial, temps can vary from 83 to 97 deg and still show 90.
Get your temps up to normal and put car in neutral, rev the engine to 2000 rpm and listen if the fan comes on. Monitor temps. If the fan comes on and the gauge is still showing low, change the temp sensor. It's giving u dud info.
Replaced mine last month. I also change the thermostat after 5 yrs of service. Looked like new unit. Sensor was my problem.
 
Lincoln S3 said:
Hi , my S3 occasionally drops to about 87 degs . Will this affect economy and/or running ?I havent noticed a change and was going to leave fixing it until the next service or if it gets worse , Cheers for any advice ...
Click to expand...

c_w said:
No.

As has been advised, start worrying that if on a motorway cruise it drops to 75 or below.
Click to expand...

I8AGTI said:
Change the sensor on the right hand side of engine. I've measured temps via OBD port, if it indicates 90 on the dial, temps can vary from 83 to 97 deg and still show 90.
Get your temps up to normal and put car in neutral, rev the engine to 2000 rpm and listen if the fan comes on. Monitor temps. If the fan comes on and the gauge is still showing low, change the temp sensor. It's giving u dud info.
Replaced mine last month. I also change the thermostat after 5 yrs of service. Looked like new unit. Sensor was my problem.
Click to expand...

I have a 4 year old S3, and I had a temperature problem this year in february. I went to the seaside on a week time vacation, I was 350 kilometers from home when I first noticed that the temperature dropped below 90 when the car already heated up, and acchieved this temperature, and this never happened before. The car was well serviced, and 6 months before I completely changed the antifreeze G12 with the new G13, there was nothing else that could be done to prolong the life of the thermostat. Aldo at first we did not know was it a thermostat or a sensor problem, it turned out to be a thermostat at the end. When the mechanic took it out it was like new but still, it was malfunctioned. After the new one was set, (and another 3 new litres of the G13 concentrated antifreeze were bought and poured :yahoo:) everything went back to normal. The temperature sits now at precisely 90.

My advice to LincolnS3 is, it's not a big problem if a temperature dips to 87 degrees, but if it's a thermostat problem, and the thermostat opens before then it should wich causes the temperature to drop, but if a thermostat closes before then it should and the temperature starts to grow over 90? What then? Does it pays off not to change the thermostat and overheat the engine somewhere on the road? I'm talking in a case if You don't pay attention to the temperature gauge and don't stop.. It's up to you..
 
Seriously it is not a problem for your gauge to sit at 87 deg & how do you actually know its 87 deg anyway?!!

The thermostat is a mechanical reaction to temperature & it doesn't open and close at precisely 90 deg
 
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