'02 A6 4.2 - Slight Overheating Diagnosis Advice

[CAL4.2]

It's been getting pretty hot here in Los Angeles, and just last Friday, my coolant temp has crossed the half mark for the first time. It's gone as far as the 5th tick as shown in the pic below with oil temp at 225 degrees.

Besides the obvious possible culprits of failing thermostat or water pump which would force me into an early timing belt and tensioner change as well, has anyone experienced this and had it turn out being something else? The car only has 61k miles, but I realize age is another factor (12 years old)

Is it safe at the 5th tick at 225 degree oil temp?



Thanks.

[kavillage007]

does that happen while the car is running, or does this happen when you have been driving for a while and then turned it off for few minutes, and then turned it back on???

[CAL4.2]

It only happens when the car has time to reach/exceed normal operating temp. Were you thinking coolant temp sensor?

[kavillage007]

I need more information from start to end, how this happens. The reason being is that it is normal for the temperature gauge to go to the hot side if you have been driving it for a while and then you park and turn off the car for lets say 5-10 mins, then turn it back on. But in that case the gauge would come back to center soon after you start driving again.

If this is not the case, and if the temp gauge goes to high side while you are driving for let say an hour, and then come to red light, then you want to check the radiator fan. In fact check all three fans...The one driven by the clutch should be running all the time. One on the outside close to the front bumper should be running with AC on. and the one next the clutch driven fan on he passenger side should be running when the car reaches optimal temp. That is the fan that should turn on especially during the stop lights and traffic. If this is not working it would cause overheating during stop and go traffic and red lights.

[stef2.7t]

I need more information from start to end, how this happens. The reason being is that it is normal for the temperature gauge to go to the hot side if you have been driving it for a while and then you park and turn off the car for lets say 5-10 mins, then turn it back on. But in that case the gauge would come back to center soon after you start driving again.

If this is not the case, and if the temp gauge goes to high side while you are driving for let say an hour, and then come to red light, then you want to check the radiator fan. In fact check all three fans...The one driven by the clutch should be running all the time. One on the outside close to the front bumper should be running with AC on. and the one next the clutch driven fan on he passenger side should be running when the car reaches optimal temp. That is the fan that should turn on especially during the stop lights and traffic. If this is not working it would cause overheating during stop and go traffic and red lights.

Ok, but what if your car doesn't have that "front" fan? Car begins to drift into hot territory during stop 'n go traffic. Sorry to thread Jack.

[kavillage007]

So you only have 2 fan?? check you passenger side radiator fan.. That is controlled by two things. 1) thermoswitch which detects the coolant temperature. 2) fan control module...drive the car..once it starts to over heat, pull over and keep the car running (put it in park)...now open the hood and check if the passenger side fan is running.

[stef2.7t]

So you only have 2 fan?? check you passenger side radiator fan.. That is controlled by two things. 1) thermoswitch which detects the coolant temperature. 2) fan control module...drive the car..once it starts to over heat, pull over and keep the car running (put it in park)...now open the hood and check if the passenger side fan is running.

Yup, 2 fans, and no it wouldn't come on.

[02 A6 2.7T]

It's been getting pretty hot here in Los Angeles, and just last Friday, my coolant temp has crossed the half mark for the first time. It's gone as far as the 5th tick as shown in the pic below with oil temp at 225 degrees.

Besides the obvious possible culprits of failing thermostat or water pump which would force me into an early timing belt and tensioner change as well, has anyone experienced this and had it turn out being something else? The car only has 61k miles, but I realize age is another factor (12 years old)

Is it safe at the 5th tick at 225 degree oil temp?



Thanks.

Happened to me last summer about 2 weeks after I bought my S6, exact same symptoms with 58k original miles. Turned out to be the thermostat so I did the full TB, water pump and thermostat service. Keeping in mind the age of the car, and that the 4.2 TB service interval is only 75k miles, it's probably about time ...

[CAL4.2]

Thanks. That's what I needed to hear before going to my Indy shop and letting them undergo the TB service.

[kavillage007]

Thanks. That's what I needed to hear before going to my Indy shop and letting them undergo the TB service.

This can still be a fan control module failiur....you can test it by jumping the pins at thermoswitch conmector...i just diagnosed my fan issue...in my can I have 3 fans..one clutch driven, and 2 electric fans..(1 ac condensor and 1 aux radiator fan)...so on my can the aux radiator fan wasnt working...i took out the fan it turned out to be a jammed coil...i took it apart and banged it on the ground to loosen up all the dirt and charcoal powder like stuff...then sprayed some MAF cleaner...reassembled it...works great now...you can also test the fans directly by provided power supply from the battery to the fan connectors...fan connectors on my car are right by the power steering res...lift the cover that is on top of the res...

[kavillage007]

Are both fans on ur car electric???

[CAL4.2]

This can still be a fan control module failiur....you can test it by jumping the pins at thermoswitch conmector...i just diagnosed my fan issue...in my can I have 3 fans..one clutch driven, and 2 electric fans..(1 ac condensor and 1 aux radiator fan)...so on my can the aux radiator fan wasnt working...i took out the fan it turned out to be a jammed coil...i took it apart and banged it on the ground to loosen up all the dirt and charcoal powder like stuff...then sprayed some MAF cleaner...reassembled it...works great now...you can also test the fans directly by provided power supply from the battery to the fan connectors...fan connectors on my car are right by the power steering res...lift the cover that is on top of the res...

I'm taking it in to the shop on Wednesday and will let everyone know what they find. I told the shop to have a TB/Therm/Water Pump kit ready to go in the event that it's not the fans that are misbehaving.

On a side note, it seems that most of the time, the culprit is a failing thermostat. Why do Audi/VW thermostats fail so fast? My 2001 Mustang GT has 131k miles on the original thermostat with zero issues.

And secondly (More of a rant than a question), why would VAG place the thermostat, a $15 part, in such a difficult location to access?
My Mustang requires popping the hood and removing 2 bolts shown below to change the thermostat while the VAG product requires removing the front end of the car... Seems extremely impractical.

[kavillage007]

I have a feeling that this might the control module issue.,...let me know what u find,...thanks

[kavillage007]

Any updates? Please leave suggestion/solution for the next person who might encounter similar issue. Thanks...

[mithril]

Ok, but what if your car doesn't have that "front" fan? Car begins to drift into hot territory during stop 'n go traffic. Sorry to thread Jack.

CDN market 4.2L C5's (A6 and S6) did not have second "push" electric fan like the cars destined for the US market. Possibly something to do with the fact the US is typically warmer so extra cooling is needed there. In our climate the only time that electric fan makes a real difference is in summertime stop and go. When it died on my old 4.2L A6 I'd see an increase of about 10C in coolant temps when sitting at idle in traffic and then they'd drop right back down to normal as soon as the light turned and there was airflow over the rad again.

Either way, it's most likely your secondary fan. That fan should automatically turn on with the car if you're HVAC is on and not in Econo mode. Easiest test is to jumper 12V to the fan, if it doesn't turn on then you know the fan's dead and that's a really easy fix. If not then you need to trace it back and test at the thermostat and the fan control module.

[CAL4.2]

Update - My independent shop said it sounded like failing thermostat to them. I had them do the Thermostat, TB, WP, Accessory Belt, Belt Tensioner, Belt Roller, and coolant sensor and it fixed the issue.

So, I shouldn't have to worry about this for another 75k.

[CAL4.2]

I have a feeling that this might the control module issue.,...let me know what u find,...thanks

So only when sitting idle in 97 degree heat today, my coolant temp went right inbetween the 4th and 5th tick today. The temp goes back to the middle/4th tick after I get moving.

Does this sound like control module or a clutch fan issue? Any way to troubleshoot?

[kavillage007]

sounds like you aux fan not turning on....

[kavillage007]

when ur car is at optimal temperature, park your car and see if all of the fans run... check the passenger side radiator fan...

[CAL4.2]

Ok, I'll check to make sure all fans are on next time I go for a drive and will report back.

I've only had the coolant temp go slightly above the 4th tick once since the Thermostat/TB job was done, and that was while sitting at idle for about 10 minutes in 97 degree heat. So, the issue has dramatically improved.