Confused

[stoxy01]

Hi Folks. I'm at my wits end. My 2010 A3 Convertible 1.6 is overheating. I've had the thermostat changed and had it in the garage but they can't find the problem. The water pump is working fine etc. After about 20 miles or so the temperature guage goes up, it fluctuates up and down and sometimes to the point where I get the red warning light on stating to switch engine off and check coolant level. The coolant level is fine and I'm not loosing any water etc.I'm wondering if there is some kind of sensor problem. When the temperature goes right up, I lose power and have no idea what to do. Any advice would be greatly appreciated. 

 

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[Steve Q]

I'd have to agree and say it's a sensor if the cars not loosing coolant or actually over heating. It might be worth getting a diagnostic check carried out to see if any fault codes flag up. 

Cheers

Steve

[Magnet]

Hello James,

Personally, I would not suspect anything until you have actually measured the temperature at the point where the gauge reads high - in other words, confirmed it is high. There a cheap contactless thermometers which should give you an 'external' measurement, but others more familiar with modern technology! might confirm my belief that actual running temperature can be monitored by plugging in to the diagnostics- your trusted  local garage might help there. 

If indeed the temperature is proved to fluctuate then I would first suspect the thermostat - yes, I know it's just been changed, but new cannot be taken serviceable, particularly if an aftermarket part was used. Do you know if a main dealer part was used, or an aftermarket? 

Hope some of the above helps. 

Kind regards,

Gareth. 

[cliffcoggin]

James. You imply, but did not actually confirm, that the engine temperature is correct while the gauge reading is wrong. Does steam vent from the header tank eventually? Can you smell any overheating in the engine bay? (Overheated engines have a distinctive odour.) If those signs aren't present, then the chances are that the sensor is faulty, but given the complexity of modern electronics on cars I would not be certain of it. Maybe an ECU fault can generate the fault. 

[stoxy01]

9 hours ago, Magnet said:

Hello James,

Personally, I would not suspect anything until you have actually measured the temperature at the point where the gauge reads high - in other words, confirmed it is high. There a cheap contactless thermometers which should give you an 'external' measurement, but others more familiar with modern technology! might confirm my belief that actual running temperature can be monitored by plugging in to the diagnostics- your trusted  local garage might help there. 

If indeed the temperature is proved to fluctuate then I would first suspect the thermostat - yes, I know it's just been changed, but new cannot be taken serviceable, particularly if an aftermarket part was used. Do you know if a main dealer part was used, or an aftermarket? 

Hope some of the above helps. 

Kind regards,

Gareth. 

Hi Gareth, I think it was an Audi part that was put in. It was purchased through my local car parts shop. The car has been in the garage and the mechanic did loads of tests including a diagnostic and couldn't find an issue. He had it running for ages, ticking over and it would not overheat. It just seems to do it under load.  

[stoxy01]

5 hours ago, cliffcoggin said:

James. You imply, but did not actually confirm, that the engine temperature is correct while the gauge reading is wrong. Does steam vent from the header tank eventually? Can you smell any overheating in the engine bay? (Overheated engines have a distinctive odour.) If those signs aren't present, then the chances are that the sensor is faulty, but given the complexity of modern electronics on cars I would not be certain of it. Maybe an ECU fault can generate the fault. 

Hi bud, I'm familiar with the overheating smell but there is none when the car is apparently overheating. There's no steam neither. It's also been on a diagnostic and nothing has shown. My mechanic couldn't find a fault.

[Magnet]

OK James, 

So what do you intend to do next to resolve this? 

Kind regards,

Gareth.

[stoxy01]

I have absolutely no idea Gareth. I was hoping there would be a solution that I could identify on here. I could buy a new heat sensor and try the process of elimination bud

[Magnet]

Looks like you now have an aftermarket thermostat fitted to your car - ...' purchased through my local parts shop'. If it were mine, I would not be replacing the sensor ....'process of elimination', but I would be first doing what I suggested - no need to repeat what that is. 

I would be preparing myself to invest in a genuine Audi thermostat. 

Kind regards,

Gareth.

[cliffcoggin]

Gareth. Surely if the thermostat was defective it would lead to real overheating which James says does not happen. I favour your approach to solving the problem by actually measuring the temperature with an independent device. I am not too impressed with the cheap infra red instruments, but the meters that have a contact probe are generally very good. Come to that, James could also remove the thermostat and test it hot water.

[Magnet]

Hello Cliff,

I'm very much with your logic if the defective thermostat fails to open when it should, but failure to open at all is only one mode of failure. The opening of a thermostat is controlled against a spring, and it's the ability to retain a constant force against that spring which might be in question here. It's all very well for the hot coolant to initially open the thermostat, but as we know, it has to remain fully open (against the constant pressure of the spring) at all times once the required temperature has been reached. It's its ability to do that that I am questioning here. 

Of course, I could be barking up wrong trees here, since James does not share with us the pre-new-thermostat history of any problems - if there were any- or indeed whether there was a thermostat fitted at all! In other words, did this car have some inherent other issues which were masked by the old thermostat? 

It is not uncommon for posts not to include all the useful detail which is necessary to offer some progressive advice - but we can only hope we do our best with what we are given.

Kind regards,

Gareth.

[stoxy01]

Hi Guys, 

The temperature issue has inherently got worse over the last couple of months. Initial diagnostics suggested it was the thermostat but replacing that did not fix the issue. I've had it in the garage and the overheating did not occur whilst the mechanic left the engine idling for a number of hours. It only seems to happen when at load, i.e on a run out. Garage changed the thermostat and has tried the water pump etc but could not identify the problem. I am not technically savvy with this kind of thing, hence why I thought I would try this thread. It's looking likely that I will have to secure funds to get Audi themselves to look at the problem which I'm sure you will agree will be quite expensive. It's just a bit frustrating as I've ran Audis for years without any issues and I'm at a loss.

Thanks for your input though.

James

[cliffcoggin]

Do let us know the outcome James. Not just to satisfy our curiosity, but to possibly help others who may come this way.

Cliff.

[Magnet]

Hello James,

I'm sorry to hear you are still at a loss, although suggestions have been made to try to establish the extent and possible origin of the issue. Now that you tell the thermostat was changed due to the same problem, rather than the normal thermostat mode of failure ( not opening, or opening too early), it really does put a different light on it, and demonstrates the importance of stating the historical detail. 

If you are genuinely at a loss then I run the high risk of boring by repeating:- get the actual running temperature checked at the point where the needle reads high. Find another garage and get that on-the-road check done. The investigation starting point really does rest there, unless you want to replace more parts in an attempt to try to eliminate the problem. 

Once we know the outcome, I'm sure others will follow with more advice. 

Meanwhile:- does the car loose any coolant? 

Is there any smoke from the exhaust when you carry out the following test?:- Take the car for a 10 mile run and get an assistant to rev. the engine to 2000rpm and hold it steady at this rev. for 2 minutes while you observe any smoke from the exhaust. 

It woukd be great if you could report back on this. 

Of course, there could be many causes of the problem, but the above should give a better indication of how to move forward. 

Good luck with it.

Kind regards,

Gareth,