guyg
24-04-2007, 12:09 AM
I have recently seen a lot of threads regarding overheating problems that seem to stem from faulty water pumps, so I thought this might be worth making into a 'sticky'
The water pumps an many of the VAG engines are fitted with a plastic impeller to avoid corrosion. Unfortunately, the plastic part has a habit of becoming loose on the shaft. When this happens, it spins lazily or not at all and there is little or no circulation. Sometimes, the impeller breaks up altogether.
The symptoms will be as follows:-
From cold, the temperature will rise and usually stabilise at normal running temperature for a very short time. The temperature will then start to climb again until the engine is stopped. [If there is absolutely no pause around 90C, then try changing the thermostat, but these rarely fail closed].
There will be no observable coolant flow in the header tank [although this is not conclusive on it's own].
There will be no coolant loss unless the engine was allowed to become hot enough to boil the coolant, in which case some will be lost via the pressure relief.
There will be little [if any] output from the heater and the rad fan will come on with little effect.
These are a pain to change, so if you're having a cam belt change, as a bit of PM, it's probably worth changing the water pump at the same time [they're around £30] especially on the A4/Passat/Superb where the front of the car has to be dismantled to gain access.
Hope this helps...
Cheers
Guy
The water pumps an many of the VAG engines are fitted with a plastic impeller to avoid corrosion. Unfortunately, the plastic part has a habit of becoming loose on the shaft. When this happens, it spins lazily or not at all and there is little or no circulation. Sometimes, the impeller breaks up altogether.
The symptoms will be as follows:-
From cold, the temperature will rise and usually stabilise at normal running temperature for a very short time. The temperature will then start to climb again until the engine is stopped. [If there is absolutely no pause around 90C, then try changing the thermostat, but these rarely fail closed].
There will be no observable coolant flow in the header tank [although this is not conclusive on it's own].
There will be no coolant loss unless the engine was allowed to become hot enough to boil the coolant, in which case some will be lost via the pressure relief.
There will be little [if any] output from the heater and the rad fan will come on with little effect.
These are a pain to change, so if you're having a cam belt change, as a bit of PM, it's probably worth changing the water pump at the same time [they're around £30] especially on the A4/Passat/Superb where the front of the car has to be dismantled to gain access.
Hope this helps...
Cheers
Guy