Jump to content

Strange temp guage readings


csh1234
 Share

Recommended Posts

Hi all, just bought a 4.2Q Sport, 1998, full Audi SH, 113k miles. Driving around today I noticed that the temp guage reading varies between approx 70 degrees when traveling at 60 plus and increases to 90 (but no higher) when stationary or moving slowly. I am guessing this is not normal and probably sounds like a dodgy thermostat? Does this sound likely? Is there only one thermostat? How difficult is it to change? Any advice on getting a workshop manual?

Cheers

Chris

Link to comment
Share on other sites

Many thanks! I certainly love the car (at the moment!) - amazingly different to our previous car - a 540i, which (on paper) should be reasonably similar. The A8 is more relaxing to drive, but also feels more sporty!

Thanks for the replies - I did see the bit in the manual, but thought that it ment that the temp 'could' rise into the right hand side of the guage (above 90) under significant load, I expected the temp to get to 90 then stay there under normal driving conditions.....the A8 also takes much longer to warm up than the 540...

Cheers

Chris

Link to comment
Share on other sites

Mine sits very low at motorway speeds too... to the point where I was going to replace the thermostat this weekend (but not sure if there is any point now!). I've also noticed that while the rngine has no heat (ie on the the motorway) the car suffers badly from misting up. Stop and let the car warm up and misting goes away...?

Seems to me the A8 is overcooled - I may try blanking part of teh radiator off to see if it has a benefit...

Link to comment
Share on other sites

Seems to be a split in how different cars are behaving. I expected the car to get to 90 quie quickly and stay there regardless of ouside temp (within reason!) and driving conditions. I would have thought the thermostat 'should' prevent overcooling. Assuming the thermostat closes when the temp falls much below 90, which would seem reasonable, the remaing cooling would be due to oil cooling, using the interior heating, and airflow over the engine. I would not expect the effect of these to be suficient to significantly affect the temp of the engine....

Link to comment
Share on other sites

I absolutely don't want to alarm you here - just that mine did this for a bit, then after a while started rising above 90 when I was at speed (ie the opposite to you are seeing now)

I replaced the viscous fan, which kinda helped, but did not resolve the problem.

In the end I got the whole front end done (cambelt, pump, thermo) for a 'scary cost' to find it was indeed a dodgy thermostat.

I'm no mechanic, but changing the thermostat itself I believe is no easy job, and needs lots of stuff removed, hence I had to go the 'replace the lot' route.

Since it was fixed, it now rises to 90 and sits dead on regardless of speed, motorway or otherwise.

Sound though, that other folk are seeing various things, so maybe it is indeed normal, and I mine was 'normal' then went 'bad'

Link to comment
Share on other sites

Thanks for all the comments, I am thinking that the evidence suggests that the thermostat is not working correctly albeit has not (yet) failed completly. May I ask TheYeti roughly how much a 'scary cost' would be? The annoying thing is that the service history shows a cambelt change at Audi at 90k (now 113k) at a huge cost (cambelt bit approx £700, total bill approx £1700, with new brake bits and goodness knows what else..!) but no mention of a waterpump or thermostat, which I am beginnng to understand would have been sensible to replace at the same time...

Link to comment
Share on other sites

To replace the water pump, cambelt, tensioners etc, thermo and viscous fan (all original parts) cost me just shy of £800 all in. The viscous fan was £150 tho from Audi. This was of course a good independant I now have in Glasgow, whom I've now spent some £3000 with over past 4/5 months - so he was kind to me!

Be choosy tho, I took it to another guy and he wanted £1400 for same job. Lord knows what Audi themselves would want.

This is for a 3.7 QS facelift (2000) - not sure if its all exact same but think its very much so.

One thing - I asked him to replace water pump as he was doing all this, even though he suggested it had metal impellers on these - but I thought otherwise - turned out he was right and it was metal, so water pump was actually fine. If yours is a slightly older 4.2, I think I read on here that those were plastic blades, so if thats true, I would replace the pump for sure, just in case.

As I said before, don't jump to this conclusion, but it deffo sounds like the way mine was behaving.

One thought, if temp drops at speed, does that not signal that the viscous fan might be duff, as its spinning too much when it dont need to? Search on here for viscous, loads of posts - thats much easier to replace on its own.

Use the "carrot" test, worked for me!

I really hope you dont need to go this route. Good luck.

Link to comment
Share on other sites

Good luck with the replacement - hope its not too cold - I really hate that sort of job when you can't feel your fingers! I would be very interested to know how much has to be dismantled to get to the thermostat, and any tips - I am pretty sure I will be doing the same job in the near future..

Link to comment
Share on other sites

Right... looked at this and it would seem very straight forward.

Remove all the plastic covers from the top of the engine.

Remove the hoses at the front of the engine (one doesn't need to be removed but do it just to gain a bit more access, the other goes onto the thermostat housing).

There are 2 T27 head bolts at around the 2 and 8 position on a clock face. Remove these and it loosk like the whole lot comes out.

I've had to abandon mine for the moment as my t27 torrx snapped so its off to Hellfrauds for a new one. But since its also started to chuck it down not sure if I'll get back under the bonnet today....

One thing though. With the thermostat hose off (and a whole lot of water everywhere) you can put your finger onto the thermostat top. Feels like mine was closed (as expected since the engine was stone cold)....

More later!

Link to comment
Share on other sites

Please sign in to comment

You will be able to leave a comment after signing in



Sign In Now
 Share

×
×
  • Create New...