Overheating after doing a coolant flush

[Seifer780]

I took the vehicle to Audi to perform a coolant flush. I also noticed that it was leaking because the coolant level in the reservoir was receding, which indicates a leak. So I took it to get it flushed since there was some bad coolant as well as inspect the leaks. They found that the thermostat housing SEAL was compromised as well as the coolant temperature sensor SEAL as well. Ok, that's fine. It can be repaired soon from another specialist shop at a rate lower than $110 an hour. My friend noticed that when he drove it home, it started overheating. The needle was about halfway in between the 1/2 and 3/4 mark on the temperature gauge. I figured that air was just bleeding out and to drive it home and let it rest, in a sense.

This morning, he started it up and when he backed it up, the temperature needle started moving. It was idling for about 5 minutes before driving away. At the end of his driveway, perhaps 125 feet, it had already reached operating temperature. About 5 minutes later, it was at full hot. Needle was completely maxed out. No more than 10 minutes from start up, and in city driving going no faster than 30-40 MPH. Took it back to Audi immediately and was charged $112 diagnostic fee to find out that the above mentioned seals were bad. They say that air bubbles are getting into the system from the leaks, therefore causing the car to overheat.

Here are a couple things to consider that have already been discovered and confirmed. The thermostat is working. The water pump is working. The old coolant was tested for chemical composition and was at proper operating spec. The system was even flushed again at their expense and not ours, thankfully. Yet it is still overheating. Can anyone help identify why it is overheating?

2003 A4 B6 1.8T 102,000 miles on it.

[Turbavanttro]

almost sounds like the system is not properly bled, meaning the coolant might not be circulating properly. based on your posted info anyway.

get it to your shop dude why dick around with that issue. dont try to save 10 bucks, do your car a favor and take it in.

[old guy]

Air in the cooling system can definitely cause you engine to overheat. An air pocket at the back of the motor where the coolant temperature sensor is located can also give you a false overheating signal. If the sensor is in the air pocket it reads the steam temperature which can get substantially hotter than the coolant temperature.

[Seifer780]

Old guy, that's the closest thing to what is wrong that has been heard all day, including what was said from Audi. Giving you credit too, Turbavannto, Old guy just said it better. That's another thing that we suspected and that is likely the non-linear element. Because there was no steam coming from the motor, there was no pinging or rough idle or any other classic symptoms of engine overheating other than the reading from the temperature gauge.

[Turbavanttro]

the good new is bleeding the cooling system is easy. drain the coolant, replace the seals, and then refill/bleed, you should be good to go. its not too hard to do yourself if you are so inclined.

good luck seifer.

[audinaut]

If you're going with Old Guy's thinking......

• Clicky thingy
• Another clicky thingie
• Lastly, a clicky link

[Seifer780]

Everybody thank you for your information contributions! I am taking it to the specialty shop right now to have it diagnosed and repaired. I'll be back when this is all done to let you guys know what happened. You have all been a great help!

[Seifer780]

I picked up the car from Audi, took it to Alpine, which is the name of the specialty shop and they confirmed that it was leaking from the housing. Here is what I was typing as I was speaking to the mechanic.

“Temperature sensor seal is $80
On the front, leaking where thermostat housing bolts onto the engine block. Attempt to replace just the gasket. Don’t know for sure if the housing is bad. Over time, the housing will warp and won’t seal correctly. Recommend to replace entire housing. If the seal alone is replaced and it doesn’t stop the leak, the risk would be to pull the housing off all over again. They warp over time and falls out of tolerance to properly seal because it’s cheap ABS plastic. If they repair the housing, price is at $250. If it’s just the seal, it will cost $150 for that particular job.
Coolant Temperature Sensor Seal: $80
Thermostat Housing: $260

Total: $340”

The store that stocks Alpines part is the same that Audi uses, only cheaper. The caveat was that we would have to wait a day, so I asked him if Audi might have it in stock. Turns out it was $10 more. So I was like "Ok, let's do it!" They are currently working on repairing it, and it should be done sometime this afternoon.

[Seifer780]

Everything is good as good as new! Thanks for everybody's help!