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Just wondering if I can get some advice on the CFWA 1.2 TDI (Match and petrol not an option!) 2012/61 6R.

After 10min of driving the temperature light flashes on and power dies, also heaters give up. Check under bonnet and coolant level is up, top rad hose is rock hard and stone cold, but the little one attached to the rad is hot. Symptoms haven't changed despite a few parts swapped:

New radiator, new thermostat (replaced 2x to be sure), full coolant drain and replace.

I have a new secondary water pump (the electronic one) on the way to try that. The only reason I haven't had the main water pump changed is my more experienced mechanic mate thinks it's pushing plenty of power (and was only changed with the belt 2yr ago). Trying to find ways to test.

Is there something obvious I'm missing, like a thermostatic valve in the water lines/tee pieces?

When initially drained, there was a fair bit of sandy sediment in the coolant, and both the radiator & original thermostat.

When the engine is shut down you can feel air coming up through the top hose from the engine, with an audible "click" as it moves. Sounds suspiciously like a butterfly valve chattering.

Fingers crossed someone will have had the same head scratcher!

Thanks in advance, Steve.

did you read for error codes and check the measured values of all temperature sensors?

iichel wrote: Mon Aug 12, 2024 10:10 am did you read for error codes and check the measured values of all temperature sensors?

Yes, no errors showing up, and had it out for a drive with live diagnostics. Main temperature took a short while to get up to critical where it would cut throttle, about 120+ degrees. Radiator outlet was showing between 45-65.

It seems to be overpressuring then releasing when shut off.

water pump still working? sounds like something is not flowing (no drive, clogged)?

iichel wrote: Mon Aug 12, 2024 11:21 am water pump still working? sounds like something is not flowing (no drive, clogged)?

Water pump is my fear - not the best job on them, the previous mechanic is absolutely adamant it's pumping, but, I fear it may be on its way. I'm going to replace the secondary pump since it's a very cheap part first... Failing that I think the only remaining thing it could be would be the main pump.

the secondary pump is only for the egr cooler and not the main circuit

iichel wrote: Mon Aug 12, 2024 1:08 pm the secondary pump is only for the egr cooler and not the main circuit

I did have that hunch, but I thought at 20 quid and a quick fit, wouldn't be a bad shout since I've changed about everything else
Another possibility would be a pesky airlock, but, from experience I've never had one so stubborn.

I'm putting my money on a failed water pump, but I'm just a guy behind a keyboard.

iichel wrote: Mon Aug 12, 2024 5:22 pm I'm putting my money on a failed water pump, but I'm just a guy behind a keyboard.

I have a very strong hunch that guy behind a keyboard could be right
Thanks for your interactions, very much appreciated - it kinda validates some of the logic we have been using.

So... Allowed the car to sit while I gathered my thoughts... Consulted the below diagram, had the idea to fill the header tank, pop off the pipe below, have a friend start the car for a short period of time, so I could both monitor the pipe and fill the header as needed. Flow from the pipe, which should have come from the pump from the block and it was literally a trickle, nothing more forceful than the flow when The pipe was taken off.

We think from this (other opinions are very welcome) the pump has indeed died.

Looking to test my logic to see what others think.

it's a shame the pump housing is integral part of the engine so you can't really check it. the return of the radiator seems to have the thermostat.
i guess you could check the top hose of the radiator for any flow with running engine @ idle, but make sure you don't get a pink shower...

iichel wrote: Mon Aug 12, 2024 11:17 pm it's a shame the pump housing is integral part of the engine so you can't really check it. the return of the radiator seems to have the thermostat.
i guess you could check the top hose of the radiator for any flow with running engine @ idle, but make sure you don't get a pink shower...

We did this, but at the tee peice circled above which is same pipe. Not much flow...

When car is up to temp after being driven the top hose goes rock hard with what feels like compressed air/steam. Knock it off and twist the cap to pressure release, the top hose clicks and pops then slowly fills with hot water. If a pump doenst fix it, I am literally at an impasse!

Does the system have one of those "teabags" of silica in the expansion tank?, they occasionally burst and cause all sorts of cooling issues.