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Robert, UK Qualified Car Technician
Category: Volkswagen
Satisfied Customers: 4716
Experience:  Fully qualified / self employed garage technician in the UK
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I have sludge in the coolant system of my 2005 passat, can

Customer Question

I have sludge in the coolant system of my 2005 passat, can it be flushed? would the sludge have caused damage to water pumps and thermometers etc.

Submitted: 4 years ago.
Category: Volkswagen
Expert:  Robert replied 4 years ago.



Hopefully I can help..


What colour is the sludge your seeing in the system?


Has this been on going problem or one you've just noticed recently?


Has there been any engine running issues before hand or overheating that you've noticed?

Customer: replied 4 years ago.

Hi Robert the sludge was a creamy caramel/toffee colour with a consistency of mayonaise, we have had no running issues with the engine, and we have just noticed the sludge, there have been no overheating problems in the past and it does not overheat at the moment. however the fans are continuously on and there is no heating in the car.

Expert:  Robert replied 4 years ago.

Hi.there thanks for your reply..


Ok - usually that sort of colour would suggest that you are getting cross contamination issues with the oil and coolant..and the usual culprit for that is either head gasket failure or the cylinder head itself,if fitted with an oil cooler then sometimes these can do that too - you don't say how long you've had the car so im not so sure whether this could be an old fault maybe headgasket done on it before and the system never cleared out properly...however its not going to be easy to get rid of that and will be messy and does required lots of flushing/draining and water "hose pipe" sent into the engine to clear all that out aswell as back flushing radiator and heater your going to have the drain the system off a few times - then with the engine coolant system refilled "thermostat removed ideally an housing back on" - a good Bio Degreaser For Engine Cooling Systems added and or anything like small amount of dishwasher powder in the coolant tank and run that through for about a half hour then again drain off and flush out the engine again with a good hose pipe so you forcing the water through and getting rid of the sludge as you go each time until the water starts to run allot of hoses after running that through the engine above - the degreasers will be required - but let the engine cool off first each time before opening any parts of the system to flush out...The colour of the sludge as mentioned above could be headgasket related so it could be worth maybe getting garage to check this out testing wise for that..if you dont have access to a good strong hose pipe etc then im sure the garage would be able to as above the flush the system out for you too at the sametime..The sludge can sometimes cause issues with the coolant system - as it doesnt flow as effectively as the water/coolant mix to keep the engine at the correct temperature - this could have an impact on the water pump if hasnt gone already being able to force that around and causes the headgasket to go due to overheating - but does put more strain on it to force that coolant sludge about aswell as blocking up the thermostat and matrix internally "no heating in the car" aswell as the radiator internally - it can also cause certain coolant system monitoring sensors which test the coolant temp to bring on the fans or show erratic reading on the dash if that sludges building up around as above it can be flushed out but will take a bit of time to get it all out..I do hope this helps