How to properly drain/flush the radiator

86SA_GTI · 12-01-2007, 06:57 AM

As the title, can anyone please help me?
The water is a bit gross.

**golf3** · 12-01-2007, 07:02 AM

As far as I know...

Take off the hose connecting to the bottom of the radiator, let it all drain out...
Flush it out...
Put back together, fill it up again with original vw coolant, and every now and again grab the top coolant hose and pump some of the air through...

That's pretty much it...

**h100vw** · 12-01-2007, 07:07 AM

The usual trick is to revrse flush it with a hose pipe.

There are products in the shop for cleaning out cooling system. I have never used any so can't vouch for their effectiveness.

If you are doing a proper job then I'd drop the lid off the thermostat housing and drain the block as well. I would also disconnect a heater hose and quirt the hosepipe up ther as well.

I usually put eveything back together and run the car to temp with plain water in it. Then drop that out before filling with coolant.

Gavin

**tommymac** · 12-01-2007, 12:11 PM

as above

**Bora Sport** · 12-01-2007, 12:38 PM

Key points to remember.

Don't poor cold (cool) water into a warm/hot engine unless the engine is running.

Also when you do fill it up after emptying all the water out you leave the top off the expansion tank and run the engine (idling) until the thermostat opens and a good guide is to let it idle until the cooling fan comes on. This gets all the air pockets out. Once the fan is running and the coolant level is ok then screww on the lid.

**peedman** · 12-01-2007, 05:02 PM

Good trick it to park it on a hill minus the cap and let it idle so the air bubbles flow up and out.

**moto** · 13-01-2007, 12:46 AM

I've never found this straightforward. If you want to drain completely you have to let the water go from both sides of the thermostat. But take care. When filling, the bloody thermostat can create problems. It only opens to allow circulation when its hot and since hot water only gets to it when it can circulate, it can stay closed when it ought to be open. You can easily be running the engine to pretty hot and dry inside the block. And since the temperature is measured on the radiator, and since the radiator is quarantined from the block when the thermostat is closed, you wouldn't know.

If you drain from both sides of the thermostat then refill with boiling water and start the engine as soon as the reservoir bottle is full. If the level doesn't drop quickly then pay lots of attention.

Once you've got the thermostat opening a good tip is to take a drive for 15 kilometers with a bottle in the boot. Then stop and let it cool down. When its cold the level should have dropped quite a bit because it will have pumped the airlocks out. Add the coolant then.

Also, no one's mentioned it but its good practice to use demineralised water with the coolant.