Breezy_Pete

No, it never got anywhere near the top of my to-do list.

Maybe previous owner took thermostat out?

Ping me your VIN by private message and I'll try to find.

There's only two buttons on the scan tool. 😁 Total milage since car was built; only done about 15-20k since transplant, at a guess.

😊 Thanks for asking. 'New' engine is serving us very well. Done a couple of little jobs on it very recently, Coolant temperature sensor (2004 vintage) started throwing fault codes and a warning light last week - proud of the missus for scanning it while out and about with handheld tool that lives in the glovebox. That got swapped out for another I had sitting around. Faults gone. While doing that I noticed that the little heatshield on the exhaust manifold was hanging on by one screw, so I bunged a replacement on yesterday. MOT a month back mentioned (nothing but) deterioration of the fuel hose that I'd replaced (with new, generic) at the time of the swap. Tester said he himself was struggling to find aftermarket stuff that didn't crack, and to let him know if I found anything decent! I decided to grab a genuine replacement from Skoda, hopefully that won't go the same way. About another 5k til the car passes 200k miles, I think. Oh, and a nice man in a big van came and took away all my scrap metal for me on Saturday, including the old engine, after I'd stripped it of all the possibly useful bits. 😁

I find it always takes a journey or two, as opposed to just letting it sit idling, before the coolant level settles down after any such change. Make sure it's got enough antifreeze in, fair chance a freeze-up was what killed the old waterpump I should think. Probably why the previous owner got rid?

Well done, glad you found the problem. I thought that lack of return flow in the little hose at top of expansion tank was pointing in that direction.

Measure mV across ends of each of the strip and blade fuse in engine bay with everything off and closed except bonnet. That should start to narrow it down.

I'd expect a trickle from that hose, increasing a little when engine revved.

Please let me know where you find output tests for the rad fan(s), I just failed to do so.

Sounding much more like a simple coolant temperature sensor/connection/wiring fault now. When I read the bit about the cabin heating going cold at the same time as the very high indicated temps, I couldn't imagine what could be going on with the coolant (which flows through the matrix all the time, regardless of settings). Then it occurred to me that there might be a safety interlock which prevents cabin air being directed through the heater matrix if the coolant temperature is being measured at e.g. >120C. No idea if that really is 'a thing', but it could be.

If the A/C isn't working well enough to trigger any such activity, this image should help you to test instead by linking contacts of the radiator thermoswitch connector (daylight job, and not that easy to access, approx 100mm above radiator bottom hose connection):

If it has A/C that does work it gives a quick way of checking the radiator fan(s). Within a minute or so of switching on A/C the fan should start up at low speed (relatively quiet). If instead it does nothing for a longer time then comes on at full speed (loud!), you probably have a failed low speed function on the fan. It's triggered via the refrigerant pressure when A/C is on, so no need to have hot engine to try this.

I would investigate the radiator fan function first. Does the car have A/C, and if so does it work?

Probably thermostat failing. Are both radiator hoses hot near the radiator? Radiator fan may also have problems.

Where did you earth the module?

@UrbanPanzer has given the only info the OP wanted. It's a really good place to earth the recipient car for best chance of good cranking speed 🙂

The clamp on that positive post looks really loose? Trick of the pic? Looks like massive gap on the left. Whose car?

Yes, reversible pump at front. Yes, parallel connected. The two wires are labelled WW and INT where they go into the rear wiper connector. Wash/wipe and Intermittent? I guess maybe if WW is 12V and INT is 0V it will do a wash of rear window and a programmed number of wipes. If both are taken to 12V maybe that triggers intermittent wiping until both go back to 0V? And the washer pump won't run cos there'll be no potential difference across it?

If it's a CAYC engine the oil pressure switch (F1) wire goes via pin 1 of a 14 way black connector pair 'front left in engine compartment', ending up at instrument cluster (K) 32-way connector pin 27. When they say left, that's as viewed from drivers seat facing forwards, so right side of bay as you look in from the front bumper. it's a black wire going into the 14-way, a green/black coming out heading to the cluster.

Yes that's what I meant. 12V should be quite safe to apply anywhere since I feel confident that's what is supplied to the washer motor in either polarity. No idea what signals make the rear wiper do its thing, but presumably brief enough or low enough voltage to not activate the washer motor (except when requested).

CAN pairs are explicitly labelled on wiring diagrams as CANH and CANL in my experience. Single wire LIN also similarly marked.

Not any sort of bus JR, since they also drive the washer pump which is just a dc motor as far as I'm aware.

For the sake of completeness, part number found as N 015 082 10 "Hexagon collar nut" £1.60 + VAT each at time of writing.

If you ping me your VIN I may be able to look it up.