Overheats QUICKLY in 4th Revving ~5k

[psilo]

I just got my car back from the auto-body shop after a fenderbender repair. The entire front end was basically rebuilt including a new (used, reconditioned who knows) radiator and I changed the Green top temp sensor myself just a week before.

This issue happens when I get on the highway for the first time every day, but only happens once. I will rev high in first and second to merge with traffic on the main road by my house, and off the stop lights (I mean I'm not obnoxious but it's a manual so...) The car will have warmed up by time I reach the highway onramps. So far I haven't watched it happen but I'll get to 4th and be pulling up to ~75 to merge with traffic and hit 5th to cruise once i'm up there but on the way, still in 4th, I"ll hear the 'chime', I look down and I see 'Coolant' flashing and I'll look at my temp gauge and it's nearly all the way ~260!!!! I'll throw it in neutral for a couple seconds and knock a quarter off the temp gauge then I'll maintain speed in 4th or 5th to keep airflow and the gauge will keep going back to nominal ~190.

This happened yesterday and then I was hesitant to keep driving but the car was fine. I drove 2 hours on the highway 75-95 about and didn't have any issues. Did the same drive back home a couple hours later too and didn't have the issue again.

Any ideas? It's such a weird issue. My first guess might be the thermostat is opening late, maybe the wrong one was installed but then it would maintain a higher temp during normal operation wouldn't it?

I'll scan codes when I get home, maybe some clues there

[gregg3gs]

Sounds like the coolant was not property filled in.

I would do the following:
-check the fluid level, add as necessary.
-turn the heater to on position and temp as high as possible, this should air the system out.

Another way is to follow the manual.

[NFX123JMP]

The coolant system on this car is a massive pain in the arse to bleed. Follow the Bentley manual and it tells you to use VW/Audi special tool xyz or whatever. I'm not sure what exactly that tool does, or where you would buy it.

The most difficult and frustrating job I have attempted to perform on any Audi or VW vehicle was to bleed the coolant to restore the heat in my B6 (pulling the engine and replacing the torque converter in my B5 S4 was less frustrating...although more time consuming.)

The problem is that the heater core is above or level to the coolant reservoir. An easy way to confirm you have air in the system, is with the car at operating temp look to see if the coolant appears low. Then, carefully and very slowly unscrew the reservoir cap. If coolant starts rushing back into the tank and/or bubbling, you have air in the system.

I made a device from PVC pipe and a tire valve that I could use along with a bicycle pump to pressurize the system to 15 to 20 lbs. Then I proceeded to bleed the system as specified in the Bentley. That finally worked. No longer did I have to rely solely on the seat heaters to keep warm.

If you need the Bentley pages or photos of my bleeder device send me a PM.

[gregg3gs]

The coolant system on this car is a massive pain in the arse to bleed. Follow the Bentley manual and it tells you to use VW/Audi special tool xyz or whatever. I'm not sure what exactly that tool does, or where you would buy it.

The most difficult and frustrating job I have attempted to perform on any Audi or VW vehicle was to bleed the coolant to restore the heat in my B6 (pulling the engine and replacing the torque converter in my B5 S4 was less frustrating...although more time consuming.)

The problem is that the heater core is above or level to the coolant reservoir. An easy way to confirm you have air in the system, is with the car at operating temp look to see if the coolant appears low. Then, carefully and very slowly unscrew the reservoir cap. If coolant starts rushing back into the tank and/or bubbling, you have air in the system.

I made a device from PVC pipe and a tire valve that I could use along with a bicycle pump to pressurize the system to 15 to 20 lbs. Then I proceeded to bleed the system as specified in the Bentley. That finally worked. No longer did I have to rely solely on the seat heaters to keep warm.

If you need the Bentley pages or photos of my bleeder device send me a PM.

That sounds like a good idea. What size PVC pipe did you use? Did you have to re-thread?

[NFX123JMP]

I used 1 and 1/4 PVC pipe. At Home Despot you can purchase the pipe, a 1 1/4 to 1 1/4 rubber coupler and then an end cap.

I used an automotive valve stem, but you could also use an air fitting.

Using PVC cement, glue the cap on one end of the pipe. Next drill a hole in the cap that is just barely large enough for the valve stem to pass through. You should have to force the valve stem through the hole so it forms a snug air tight fit. Finally, put the 1 1/4 inch coupler on the opposite end and tighten it down to the pipe. The other end of the coupler fits over the threads on the expansion tank. Secure that end as well.

Now using a bicycle pump or air compressor put about 10 psi into the device. (DO NOT over pressurize or you will launch the device like a rocket into your hood).

Once you have the system pressurized, bleed as normal, periodically checking to maintain pressure in the cap.

NOTE: my days of struggling with coolant system bleeding are over. I just discovered the AirLift cooling system refill and flush tool. Google it. The only downside is that you need shop air to use it. Wish I would have known about AirLift 3 years ago.