Overheating A4

My 02 A4 (1.8T)overheats only when I drive uphill. The engine temp goes back down when I get to a flat surface or turn the heater on to let out the hot air. My mechanic thinks it might be a restricted radiator but is not entire sure this is the problem. I’ve also heard that it could be my water pump, which was done during my 60K service (I’m at 105K now). Please help!

If the water pump installed in your car has a plastic impeller that could be the problem .

Thanks for the response. How do I know if my water pump has a plastic or metal impeller? I had it replaced awhile back, and I’m guessing my old (unreliable) mechanic installed one with a plastic impeller.

You have no way of knowing if you have a plastic impellar, but if you do it would be unfair to blame the mechanic. He’d have installed whatever pump is epcified as a replacement. Many OEM pumps come with plastic impellars, and cast impellars can erode too.

The pump’s capacity to pump can be flow checked.

So can the radiator’s flow. However, the ability of the radiator to flow coolant is only part of the problem. A radiator can be coated with residue on the inside and have a reduced capacity to disspate heat even though it’ll pass coolant. There is a device called a pyrometer that can show internal problems by showing “hot spots” in the radiator, which are a sure sign of internal problems.

It’s also possible that the thermostat is not opening fully. This too can be tested with a simple hotplate, an oven thermometer, and a pyrex vessel.

Are there any other unusual symptoms, like contaminated coolant?

Sometimes a warning appears saying ‘low coolant’ or ‘check coolant’ when the temp rises a lot higher than usual. However, the coolant level was always fine and the warning light would go off as the temp decreased (and I started going downhill). This doesn’t happen too often, and when it has happened, the warning light usually disappears quickly.

Do you know if your have G-12 VW coolant in there? It is orange. Is your car due for a timing belt change? The diesel A4 engine is due at 80,000 miles and I seem to recall so is the gasoline engine. If so you really really want to have it changed now as if it fails it is very expensive. You should get new water pump at that time since it is cheap to replace then.