Engine Coolant Flushing

[Steveenduro]

Hi. I'm planning to replace the Coolant temp sensor and thermostat on my 1.9TDi the weekend.

Any ideas on the best way to flush out the old coolant (been in there for 6 years now). With the engine off, do the heater matrix controls stay open by default (electronic climate control).

Thanks.

[Masked Marauder]

The coolant always goes through the matrix anyway, all the controls do is direct the airflow over the matrix.

 

To change the coolant remove the bottom hose from the radiator and the pipe to the rear heater from the front to rear pipe and allow the coolant to drain.

 

COOLANT IS HIGHLY TOXIC AND PETS AND KIDS LOVE THE SWEET TASTE. Please take extreme care as as little as a tablespoon full can kill a cat or small dog. Hose away any spills with lots of water and dispose of the drained coolant correctly.

 

Next put the hoses back on and fill the system with water, leave the expansion bottle cap off and run the engine until it is warm, but not hot. Drain as before.

 

Replace the hoses.

 

Finally pre-mix your coolant one part water to one part antifreeze. Make sure the antifreeze is the same colour as the system was previously filled with. Don't mix violet and green anti-freeze as they are different types. You will need 4.6 litres of antifreeze and 4.6 litres of water.

 

Fill the system, leave the cap off the expansion bottle, start the engine and run it hot, until the radiator fans cut in (make sure the air-con is off) topping the expansion bottle up as required.

[Steveenduro]

Thanks MM.

 

Changed sensor (and removed skin from arms in process). Drained coolant from front hose and rear heater pipe. Flushed with clean water.

I can only get 4.5litres of coolant back into it. I ran it until hot, squeezed pipes, took it for a blast so temp settled on 90deg.

I'm not sure whether some old coolant remained and system is full, or if there is not enough coolant in system.

 

Any help appreciated.

 

Thanks

[Masked Marauder]

Well if there are no airlocks then a lot of the coolant must have stayed in the block. Is the header tank still on the MAX line? If so and all is well then what would concern me most would be the anti-freeze strenghth, you may want to drop a couple of liters back out and top up with neat anti-freeze.

 

How much water did you put in when you flushed it?

[Steveenduro]

Flushed with hose, so not sure of exact amount. Like you say, I think that I must have had some remaining fluid - probably water. I'll drain some out and fill with neat coolant. I guess it's better to have too much neat coolant than too little.

 

Steve