I'm replacing the engine in my 2.0tdi so all the coolant has been drained (cam belt and pump replacement at the same time), it's completely empty. This is the first time I've come across the intercooler being water cooled in the inlet manifold.

On earlier models I've just filled it up the old fashioned way, been fine every time, but is there a special procedure for this model with the revised intercooler? I'd rather avoid buying one of those new vacuum systems unless absolutely necessary.

I am not aware of any difference in the fill-up procedure, I would go slow and steady until cold fill, then start it up to have the engine water pump displace the liquid from the reservoir, so stop and fill up again, and do this one more time. Then run it to operating temp, an eye on the gauge, and eye on the level, and the ear to hear the fan(s), and watch all is fine.

Leave it overnight and check cold level the morning after.

You might want to check the level every time for the next few days, is good practice.

Remember to leave the heater on max heat/full so the matrix also fills up.

Some engines like my beloved Rover V8 are a pain to fill to level properly, sometimes it takes me a few days and more than one top-up ....

1 hour ago, leolito said:

Remember to leave the heater on max heat/full so the matrix also fills up.

This is bad advice for 2 reasons: The heater matrix has a flow regardless of temperature setting and also if you have the heat set to max it will draw all the heat out of the coolant and the thermostat will take forever to open making the bleeding and filling procedure take forever especially on a diesel.

The easiest and best way and as per the manual is the vacuum fill system which is a piece of cake as long as you have an air compressor at hand.

Alternatively you just have to fill it up and be patient and keep topping it up. A TDI warms up very slowly so you can't harm much, its more a case of making sure the charge cooling loop gets filled up nicely.

Having VCDS is probably usefull as you can cycle the two electric water pumps. Also, make sure you disconnect the connector on the main water pump, otherwise you won't get full circulation until the micro circuit reaches around 70 odd degrees

Edited 24 March, 20251 yr by SuperbTWM

I stand corrected, I sense I am too old-fashioned in these matters ... good corrections,thanks! ☺️

1 hour ago, leolito said:

I stand corrected, I sense I am too old-fashioned in these matters ... good corrections,thanks! ☺️

Very humble buddy. I would have said the same thing about heater on full (think it was to get rid of any air bubbles in the system?) so shows my old-skool process too.

Well, now I think when more awake, it is correct most modern vehicles utilize the heater matrix as integral part of the cooling, so it makes sense that "turning up the heat" probably only opens up the flaps and gives power to the fan, not changing the heat contained already in the box because of the coolant flow.

However from experience, some heaters are a bit "reluctant" to self-purge, and thus the (erroneous) suggestion to increase flow, which probably is independent of heat demand.

Then the electric water pumps are a new world on its own ... at least for me adds a new level of worriness, usually engine on/aux belt on = pump runs, still can fail, but it runs.

Now with "electric power", you could have engine on but pump off or failed ... oops 🫣

11 hours ago, SuperbTWM said:

This is bad advice for 2 reasons: The heater matrix has a flow regardless of temperature setting and also if you have the heat set to max it will draw all the heat out of the coolant and the thermostat will take forever to open making the bleeding and filling procedure take forever especially on a diesel.

Maybe the matrix does have flow all the time, but I think having the temp set to hot but the fan OFF would be fine.

Every cooling system Ive filled I have left the heat up high and just have the fan off.

You won't get much cooling with fan off.

No idea why people turn it up full blast when trying to bleed system.

Just out of interest how do you bleed the system?

My old Passat B5.5 you had to pull one of the pipes out a little bit going through the firewall until water come out of the hole on the pipe

20 hours ago, leolito said:

I stand corrected, I sense I am too old-fashioned in these matters ... good corrections,thanks! ☺️

I think in cars of old (60's, 70's maybe into the 80's) the temperature was adjusted by altering the flow to the heater matrix via a valve in the coolant circuit, so in this case you are absolutely right, having the heater set to cold would be isolating the heater matrix. Now all the control is done on the airflow side with flaps and such.

So you are not wrong, just a little out of date

Well, not so much! 😁

After all, I've done work on C4 Audis and W124 Mercs which had the valve ou mention until the mid-90s .... so I am in the "youngtimer" category 😄

Interesting the though to use VCDS to run the pumps independently ... is this like you do to bleed the ABS?

Sorry if this is of no relevance to the OP, but I do think it is somehow ...

OK, I've done a little bit of research of my own and agree that this is not entirely straightforward due to the auxiliary water pumps, the exhaust cooler and the liquid intercooler.

There are 2 options.

1. Bleed the system using VCDS (I have VCDS but need a bit of instruction.

2. Vacuum bleed, although I've heard conflicting things about this.

If you have a compressed air supply, to me it is a no-brainer, for £25 on ebay you can get a vacuum filler.

That said, I don't think the system will be particularly difficult to bleed by just running the engine and topping it up as you go although I have never had to fill up the charge cooler circuit from empty so who knows how well that will go.

You can manually cycle the main water pump, the auxiliary water pump and the charge cooler pump with VCDS. There may even be a setting specifically for helping with bleeding the cooling system.

I think the VCDS route is probably the preferred method, I just need a bit of help finding the right menu. I have VCDS but am by no means proficient, I only use it for reading and clearing codes.