Will a new impeller solve my overheating problem??


Still trying to get to the bottom of the overheating problem on my 1.4TDI. I have described the symptoms on here before and the general consensus was that I am suffering with a head gasket failure.

Had the car in at a VW specialist for an MOT the other day and asked them to give the car a Holts Wondarweld treatment while there. The head mechanic said no to that. When I told him the symptoms he said it was an impeller failure and that I need a new water pump.

The main symptom is that I can drive the car all day long at 50mph without any problem but if I take it up to 60mph it very quickly starts to overheat. The mechanic's logic is that it is not necessary to have a fully functioning impeller until I hit the higher speed.

My concern is that his logic fails to address the secondary symptom which is that the header tank stays pressurised even when the engine is stone cold. Even after sitting for three days the tank will still spurt when I remove the cap.

My mechanical knowledge is very limited. Can someone explain to me what is causing this pressure in the header tank. Note: there is no emulsion in my oil and no steam coming from my exhaust.

My best guess is that exhaust gases are somehow getting into the coolant - despite the fact it seems no coolant is getting into any of the cylinders. Is that possible?

Note: the header tank gets over-pressurised even if I keep my speed low enough that the engine never goes above 90 degrees.

The garage wants £450 to do the water pump and cambelt. I am worried that I could lay out that money for no good reason if there is a head gasket failure. I have already had a new radiator and a new thermostat and neither of those jobs made any difference.

If it is a head gasket failure I will not be able to afford to have that rectified on top of everything else. Cosmetically the car is rough as old boots and just not worth the expense.

What's the verdict on here? Does it seem odd that the mechanic seems to think a new waterpump will cure the over-pressurised coolant problem?

Oh, one other symptom - I am losing coolant at a rate of roughly half a litre for every hundred miles driven despite there being no visible leaks.


A2OC Donor
If the cooling system remains pressurised then something other than heat is pressurising it. Worse than that it can stay pressurised despite a loss of coolant. That must be disappearing down your exhaust if it is not on your drive or in your sump. I suspect a cracked head or head gasket failure.
If everything otherwise was good I’d imvestigate the head and gasket. As this car is not otherwise good it is probably a donor car.


Admin Team
Sounds like a pinhole in the head gasket to me. I had one once years ago, no emulsion, no steam, just constantly hot pressurized coolant.


i have a similar issue. coolant system stays pressurised for a few days. head gasket test kit shows light bubbling only when revs around 3000rpm. fluid in text kit went from blue to greeny-yellow but only after about 5 minutes. trying to decide what to do. I reckon its a small leak in gasket from cylinder to cooling.


You could always set a test drive challenge.
Have route that the car always overheats...
then agree with the mechanic on the scope of work done and the bill...if it works...
then do the challenge...if it passes then pay the bill.
if it does not then you don't,,,,

Just a thought...
also maybe take it to another garage...for second opinion...


Not impressed with this "mechanic"

Simply run the engine at 1500 rpm and check coolant flow back to header tank in small pipe, that tells you if the water pump is doing its job end of story!

If it passes then it's time to test the cooling system for the presence of hydro carbons with either a liquid test kit or even the probe from the petrol exhaust emissions tester (do not put in the actual coolant thou).

If this fails then due to the AMF not having an egr cooler the head needs removing

Best of luck


Big thank you to everyone who has commented. I now feel more confident in my own assessment.

It certainly appears the issue I'm dealing with is a pinhole in the headgasket or a tiny crack in the head.

As such I will be telling the garage NOT to proceed with fitting a new water pump. It is disturbing that they said replacing the waterpump was my best option despite my telling them the cooling system was over-pressurising.

With regard to what I should do next - since the car is not worth the heavy cost of a head gasket repair I suppose my only option is to try and keep the engine going as long as possible with the help of some K-Seal or some such product.

I will start a new thread for some feedback on which product people think would be best for that purpose.

Thanks again for all the help.