1997 A6 Quatro Cooling Problems

[glhglh]

(vin wauga84a7vn059907, does this mean it is a C4?) The cooling system on my daughter’s car is overheating. Fairly new water pump, new thermostat, system recently flushed. When the motor is running (idle or while driving), having the “defrost” button (turned on or off), seems to make a big difference in the engine cooling system. When defrost is on, idle is smooth, radiator fans running at idle, water pressure in system seems to be normal, temp gage normal, water hose from overflow reservoir and the hose leading from the engine to the radiator, seem to be the same temperature, pressure in the reservoir seems normal. At this point, simply turning the defrost button off, causes the water in the reservoir to fill up and increase pressure, water temperature rises, the temperature on the outside of the reservoir goes from 125 degrees to 160 degrees, the pressure release valve in cap blows, and the radiator fans quit running. By simply turning the defrost button on, the motor immediately starts to idle smoother, radiator fans start running, pressure in overflow reservoir is reduced, and engine temperature is reduced. Before discovering the effect of the defrost button being on or off, while trying to define the problem, we noticed (after a short drive), the hose from the reservoir to the engine, was quite hot, while the hose from the engine to the radiator, was much cooler. We loosened the clamp on the water hose from the engine to the radiator, and kept idling. The reservoir got hot, and started leaking (hose from engine to radiator, still cool). While idling, we turned the defroster On, and immediately, the hose blew off, a lot of coolant blew out. We reattached, the hose, and from then on, both hoses seem to remain about the same temperature. We started this problem solving process, because we were told by my daughter’s mechanic, that the heater coil needed to be replaced, and before starting that gigantic task, thought narrowing the problem down might help. Not sure if the “power” of the defrost button to regulate the coolant flow, confirms that the heater coil needs to be replaced, the radiator is plugged, or what. Any ideas?

[cerverappz]

Yes, you have a C4. Radiator fans run when the AC is running, and the defrost button turns on the AC. The snowflake indicates the AC is running. Try a new radiator fan switch because the fans are probably not coming on when the defrost (AC) is off.

[upallnight]

Doesn't anyone read the other peoples' threads on this forum before posting a question?

Look at sugaryling's thread, you could have sediment blocking the Hot water from reaching the sensor at the bottom of the radiator.

[audiqv8]

Here the link to make it easy.

http://forums.audiworld.com/showthre...2825152&page=3

[upallnight]

Originally Posted by glhglh

(vin wauga84a7vn059907, does this mean it is a C4?)
The cooling system on my daughter’s car is overheating. Fairly new water pump, new thermostat, system recently flushed. When the motor is running (idle or while driving), having the “defrost” button (turned on or off), seems to make a big difference in the engine cooling system. When defrost is on, idle is smooth, radiator fans running at idle, water pressure in system seems to be normal, temp gage normal, water hose from overflow reservoir and the hose leading from the engine to the radiator, seem to be the same temperature, pressure in the reservoir seems normal. At this point, simply turning the defrost button off, causes the water in the reservoir to fill up and increase pressure, water temperature rises, the temperature on the outside of the reservoir goes from 125 degrees to 160 degrees, the pressure release valve in cap blows, and the radiator fans quit running. By simply turning the defrost button on, the motor immediately starts to idle smoother, radiator fans start running, pressure in overflow reservoir is reduced, and engine temperature is reduced.

Before discovering the effect of the defrost button being on or off, while trying to define the problem, we noticed (after a short drive), the hose from the reservoir to the engine, was quite hot, while the hose from the engine to the radiator, was much cooler. We loosened the clamp on the water hose from the engine to the radiator, and kept idling. The reservoir got hot, and started leaking (hose from engine to radiator, still cool). While idling, we turned the defroster On, and immediately, the hose blew off, a lot of coolant blew out. We reattached, the hose, and from then on, both hoses seem to remain about the same temperature.

We started this problem solving process, because we were told by my daughter’s mechanic, that the heater coil needed to be replaced, and before starting that gigantic task, thought narrowing the problem down might help. Not sure if the “power” of the defrost button to regulate the coolant flow, confirms that the heater coil needs to be replaced, the radiator is plugged, or what.

Any ideas?

The only reason to replace a heater core is if it is leaking or if it is clogged. If it is leaking you can smell the ant-freeze inside the car. If it is clogged, you will have no heat, but the engine will not over heat.

Since you engine is over heating because the fans are not coming on I would check to see why the fans are not coming on. The fans only comes on when the temperature of the water around the radiator fan sensor is Hot enough to trigger the sensor to tell the relay to turn the fan on.

If you have an infared reading thermometer you can check the temperature of the radiator from top to bottom.

If the bottom is really cool compare with the top you have a clogged radiator.

If the temperature is hot at the top and bottom you have a bad radiator fan sensor.

[glhglh]

Actually we do, and did. did find gunk where the sensor screws in. reflushed the radiator, tried again with the sensor, still the fans only work when the defrost is turned on.

Then replaced the sensor. And still the problem.

Because we had other things to do, but will continue with the trouble shooting of the sensor switch and wire (per the 2002 post of audiqv8) tomorrow.

We planned on reposting after completing those tasks.

[glhglh]

The auto shop my daughter took the car to insisted it was the heater core, but we could not find any of the symptoms: smell, leak in car, leak around heater, both hoses in/out of heater core hot.

that is why we were trying and asking about other things.

[upallnight]

You can test the old fan sensor by heating water until it boil and using a ohm meter to see if there is continuity when the sensor is placed in the boiling water. Be careful not to scald yourself.

The other component to test is the relay for the fan. There are two relays that control the radiator fans. One relay is the one for when the radiator get HOT and the other relay is for when the AC compressor is engaged. You will want to test the relay that controls the fans when the radiator get HOT.

See audiqv8 electrical diagram on the other posting about fan not coming on. You can remove the relay and jumper the connections if you know what you are doing. This will verify if you have a break in the circuit. The fans should come on if you jumper the circuit at the relay location. If you don't know how to jumper a connection there may be a video on youtube explaining how to jumper a relay.

Good Luck.

[glhglh]

By following the great instructions here, we tested the sensor switchy, and were able to get the low speed and the high speed fan to turn on. Therefore, we think the low speed relay is the problem.

on the 1997 a6, is that under the driver side dash? anyone know the part number?

[upallnight]

If your low speed come on the relay is fine. You said that you changed the radiator fan sensor that is located at the bottom of the radiator. Assuming that you didn't get a bad sensor, the only item to check will be if HOT water is getting to the sensor.

You mentioned that there was some gunk in the area where the sensor is screwed into the radiator. Instead of trying to force the debris out where the sensor is screwed into the radiator I would look for a fitting that would fit in place of the sensor and try to back flush the radiator. Either that or take the radiator or car to a radiator shop and have them back flush the radiator.