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Matt, Mechanical Engineer
Category: Car
Satisfied Customers: 22748
Experience:  BEng hons Mech engineering, in auto industry 22 years
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Why do i need to remove the thermostat when flushing the engine

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why do i need to remove the thermostat when flushing the engine on my wv golf 1.6 year2000? with thanks.Paul
Hello Paul

its best practice to remove the thermostat when doing a reverse flush to provide the best flow and so the best chance of removing the dirt and debris

however as most thermostats and heater circuits have a small bypass circuit then its usally possible to flush with it fitted but thats a work around

Also check that the small diameter bleed hoses that run from the top of the radiator and the top of the engine aren't blocked as this allow the air to vent back to the header tank automatically.

Also its possible the belt is slipping so its worth replacing its especially if the rubber ribs are cracked or it looks shiny on flat side of the belt - while its off check that the tensioner and other pulleys all spin freely the exception to this is the AC pump ( if fitted) I'd also suggest ensuring that you've got all the air out of the system as this sort of episode can leave pockets of air trapped and prevent the coolant from circulating properly. So check that the small hoses that run from the top of the engine and radiator that run back to the header / expansion tank are free flowing and not blocked If these are OK then remove the tank pressure cap and run the engine from cold with the heater set to full hot

As the engine starts to warm, squeeze the large hoses running to the radiator to help displace any air - all the time keeping an eye on the level in the header tank, making sure it doesn't drop below the minimum and open any bleed screws built into the top cooling hoses - closing them off as soon as they start to gush water

Once the engine is up to temperature the tank should be quite full. Switch the engine off and leave it to cool Then top up to the mark once its all cold and replace the cap

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Customer: replied 2 years ago.

hi Matt,thank you for your information.The garage that worked on my car didnot know that the the thermostat needed to be removed and just flushed the engine,without removing any hoses.Could this have caursed the engine to overheat.

Customer: replied 2 years ago.

Awaiting answer to my further question

Customer: replied 2 years ago.

I am still waiting for my further question?

Hello Paul

sorry about the wait

like most experts on here I'm not online all the time
in answer to your quesiton then yes this may have caused an issue as the usual way is to remove the top hose and the thermostat then flush through into the engine through the thermostat hole to push water through in the opposite direction to normal

if the stat wasn't removed then its possible any dislodged dirt / debris could have been caught behind it
Hi Paul

do you still need help?