Water Temp Problem

[m_o_w_g_l_i]

Hiya,

I've got a 1.8T Sport '98 A4 and the water temp is all over the place!

The interior of the car can be warm yet the gauge is showing 60 - 70, sometimes it does rise to 90 but then settles down low again.

I have changed the temperature sender and the fault is still there, it used to work perfectly until about 1 week ago.

Any ideas?? My first thoughts are the gauge itself. Thanks in advance.

 

[imported_GezzerS4]

My S4 water Temp Gauge is the same, never reads over 90, but will sometimes fall to 60, and sometimes to 0, I presume that it is an earth fault or the gauge itself, been like it for ages, I have used Vag-Com to measure water temp independently of the gauge and it reads fine, still giving 90 when gauge is 60, so in my case the temp sender is reading correctly and sending right info to modules that need temp info, so I have not bothered to track it down further.

 

[madkebab]

Had the same problem. Replaced the thermostat and all is now sorted.

 

[m_o_w_g_l_i]

How easy a job is replacing the thermostat then? As I have tested, the interior warms up as expected but the gauge is all over the place. Might go for that anyway, its only a few quid for a thermostat isn't it??

 

[hop2407]

IIRC - The Stat is pretty cheap however the labour charge will be quite dear. The reason I say this is because I had my Water Pump changed and asked on here if there is anything else worth changing whilst the front of the car is stripped down - The chaps on here recommended changing the stat, even though there was nothing wrong with my old one (would save on future labour costs - sods law an' all that)

I may be wrong and a good mechanic might be able to get to it without hours of labour

 

[madvw]

nope, its a PITA on a b5 A4. it's located on the bottom of the radiator, and hence involves draining the coolant first.

to make it an easier job most people will remove the bumper to get to it, hence the labour.

The actual thermostat replacement is easy, just, as per usual, its buried.

 

[m_o_w_g_l_i]

Cheers, I think that it is definately the thermostat. I'll get it done.

 

[m_o_w_g_l_i]

OK, an update. Its fixed!! It was the thermostat as stated above. Symptoms were:

Driving round town from cold, 30 mph, car warms up slowly but eventually indicates 90 on water temp gauge. Set off from cold on a 50+ mph run and gauge only reaches 70. If I then drove in v slow traffic or town at 30 mph gauge would rise to 90. If then got back above 50+ mph gauge would stay at 90 no problem.

I think that the thermostat was stuck wide open, so, when setting off on a high speed run the radiator was being cooled at a similar rate to the water heating in the block. As I slowed down the heating process was greater than the cooling air and the car warmed up to its normal operating temperature.

Hope this helps someone in the future. Local inde' charged me £50 to replace the 'stat which I thought was a bargain. Especially when you take into account that the temp sensor on the engine also sends a signal to the ECU to tell it the current running temp of the engine - increased fuel consumption.

 

[madkebab]

Glad to have been of assistance

 

[Road Razor]

I've had this problem when I first bought my A4. The coolant needle never stops bouncing. Normally the needle reaches 90deg C as expected, but it drops to 50deg. Sometimes drops back down to 0 and stays there. After they replaced the sensor they've fixed the problem and I've not had any problems since.

 

[gillbe]

It's all about bleeding...A short history of my thermostat woes- may help another:-
Partner usually drives the A4, but I decided to get it valeted so used it for the day. Noticed water temp gauge never rose above 70C and interior climate heating was just luke warm at best.
Took to my local inde - changed the thermostat £68, job done?
Not so! Now no heat inside whatsoever. Gauge got to 90C, then 6 miles later plunged to 70C and stayed there. Next journey, same sequence and no heat.
Back to inde - this time they flushed the system (thought that was a given on changing 'stat?) No real improvement.
Third day back at Inde - rechanged the thermostat. Claimed some interior heat as a result, but felt my heater matrix was blocked and needed replacing.
Saturday:- what to do? - it's freezing, the temp gauge now happily reaches and stays at 90C but still no interior heat. Try yourself - having searched this and other Audi forums I concluded that I needed to flush the matrix myself - it couldn't hurt. Bought a funnel and two washing machine outlet flexi hoses. Removed both pipes where they feed into the heater matrix. Flexi pipes fit on a treat. With a bucket ready to catch the contents, I poured enough water into the outlet until all the antifreeze mix was out of the matrix - save until later. Then fed a hosepipe into the outlet and reverse flushed. Followed by 2-part radiator flush kit and lots of fresh water. No obvious signs of any blockage or debris. Concluded matrix was OK. Reconnected pipes. topped up with saved antifreeze mix, left expansion bottle lid off and ran car until thermostat opened (top radiator hose gets hot|). Slightly pulled off the matrix outlet hose - this exposes the bleed hole. Now just keep squeezing the top hose until no more air comes out of the bleed hole. Lo and behold, hot air inside. Ran the car a couple of days, rechecked coolant levels, all OK. Bled two more occasions and everything is OK. (except fuel consumption is still 10mpg worse than I remember - that's in another thread)
Conclusion - if matrix stays cold, bleed it and bleed it some more.
Total saving £540 ! (Matrix replacement is £150 + 7.5 hours labour!) Inde shrugged it off as a lesson learned.

 

[imported_VaulterTim]

Awesome piece of information... I'll definately file that at the back of the old grey matter for a rainy day /ubbthreads/images/graemlins/wink.gif

Cheers

T

 

[Broken Byzan]

Thanks for the tip