Hello,

I regularly check the coolant level in my 300tdi header tank and I have never really noticed any activity in the header tank whilst the engine is running apart from the level dropping slightly as the engine is revved. Yesterday I decided to clean my intercooler which required the removal of the top radiator hose to get the cowl out of the way and I ultimately lost a bit of coolant. Everything back in place and I started topping up the coolant at the header tank. Started the engine took it for a run so it was hot, no signs of over heating etc. Got back home, removed the header tank cap with the engine running - only a little pressure but seems to be a lot of activity in the header tank now. Constant flow of coolant into the header tank along with bubbles but no signs of coolant loss or burning coolant (i.e. no white exhaust smoke etc.) and the coolant doesn't smell like anything more than antifreeze. The header tank is not really pressurising excessively, just a little hiss as the cap is removed. Is there a flow of coolant into the header tank which would create this activity or should the coolant in the header tank remain calm?

Thanks,
-Tom

Bleed the system sounds like you have got a bit of air trapped

As for movement in header tank that is normal its just the return pipe

Sounds like an air trap pos.

That's what I was hoping to hear! I removed the plastic bung on the radiator yesterday and the level was right up, so no problems there. Some tool had clearly had problems finding the right size socket to fit the bung on the thermostat housing so rounded it off but I managed at get it out with a pair of mole grips. In fairness, I did need to top it up a tad there, the thermostat was perhaps only half submerged in coolant but it took half a pint or so to top it up. I have ordered a new thermostat bung which should arrive this week so I will have a good go at getting all the air out of the system later in the week. Any tips on the best way to tackle it? My 200tdi just seemed to bleed its self!

Thanks,
-Tom

I just top mine up with the expansion tank cap off and filling it up via the radiator bung. Seems to prevent any air locks

lose the plastic bung and use brass ones. And if you decide to stick to plastic ones, change them every time you disturb them. They have a habit of shearing off. I lost mine during an overland trip. Luckily i was parked in the hotel car park at the time.

pos said:

That's what I was hoping to hear! I removed the plastic bung on the radiator yesterday and the level was right up, so no problems there. Some tool had clearly had problems finding the right size socket to fit the bung on the thermostat housing so rounded it off but I managed at get it out with a pair of mole grips. In fairness, I did need to top it up a tad there, the thermostat was perhaps only half submerged in coolant but it took half a pint or so to top it up. I have ordered a new thermostat bung which should arrive this week so I will have a good go at getting all the air out of the system later in the week. Any tips on the best way to tackle it? My 200tdi just seemed to bleed its self!

Thanks,
-Tom

Click to expand...

300 tdi should be filled til it overflows from thermostat housing plug ,any excess in expansion tank wont hurt and it will find its own correct level (about half way )check the same way regulary ,expansion tank level doesnt necessarily indicate engine level

Tip: unbolt the header tank and raise it up - then fill through the header tank until bubble free coolant comes out of radiator filler and thermostat housing then replace both bungs.

What you are trying to do is make the level in the header tank the highest point in the coolant circuit - sorted

why bother undoing expansion tank when you can fill it enough to get it to overflow thermostat housing

That's all sound advice, thanks for the tips. My new thermostat housing bung should arrive tomorrow or the day after all being well, so I will go down the route that James suggested with regards to the header tank, checking the level at the radiator primarily and then at the thermostat housing thereafter as suggested by Daz.

-Tom