Having replaced the heater core, I put everything back together again, like Humpty Dumpty, and now the thing “appears” to have an air lock.
Symptoms are the NANOCOm is giving me a warning when its plugged in the the temp is going above 100C. I shut vehicle down and drained radiator and entire system from nut at bottom of rad. Refilled system again following steps in RAVE. Started up…. Same issue NANOCOM not happy with 100C.
After numerous various methods of bleeding system and usually getting the steady stream from top of radiator nipple I was still getting NANOCOM 100C warning.
I then replaced Thermostat and water pump but the problem is still there.
Bottom of thermostat is ambient temp, top is hot. Bottom of radiator is ambient and hose to top is hot. Running the heater gives heat so long as there is high RPM.
Is there a way to bleed this bleed in vehicle that’s tried and true? I’m at my wits end with it.

Can you put a U bend in to bypass the heater core? & if so what then? wd be interesting to see if the problem is with the heater core or the rest of the circuit... Do you definitely have the right direction of flow at all points?

The flows are correct. I put everything back how I removed.
I’m going to remove the rubber hoses attached to pipes into the heater core and manually fill one hose until fluid comes from the other one. I’m suspecting that the air lock is associated with the core.
What’s also throwing me is that the temperature sensor has been replaced recently and, as per a previous write up, is calibrate differently from the original one. My NANOCOM is telling me the temperature is exceeding 100C yet my instrument gauge is showing 1/4…. Not even half!!!!
I’ll report back tomorrow….

I've found that a Thor is more difficult to get all the air out and have put it down to the 'humps' in the hoses to the heater matrix. I found that by pushing them downwards so they are no longer the highest point in the system helps. If you can squeeze the top hose and hear the coolant moving around, there's still air in there.

I use a vacuum pump on the bleed hose from radiator to the header tank whilst filling, and them keep the vacuum going as the engine warms up. Seems to always get all the air out with no problems.

Some peeps suggest parking it uphill, or jacking the front up, so the air tends to move towards the rad.

Well here are this mornings results
I disconnected both hoses to the heater matrix and using gravity (had a 3 gallon jug raised about 3’ attached to a hose then connected to the input line to matrix) I forced water through the matrix. There was some air in system but nothing dramatic. I then topped off the steel hoses feeding/receiving fluid from/to the matrix at engine side.
Results, I now have heat through the vents but only when I rev the engine RPMs. Not so much a result but a step.

Question, am I being led down a rabbit hole by the NANOCOM giving me the 100C warning?
After starting the engine with NANOCOM plugged in the temp reading from this unit gradually goes up evenly to 100C and then gives me the “100C eng temp” warning. (Side note I have installed a new thermostat, new water pump and viscous coupling). When I go below car and touch the thermostat (which reminds me of a heart with all the tubes feeding into it) all the upper pipes are hot but the lower pipe leading from the thermostat to the bottom of radiator is ambient.
There is return coolant flowing from the upper nipple on radiator and system is pressurizing.

I’m assuming that the thermostat “opens” at a set temperature but mine is not. I can’t tell if the temperature of the hoses feeding into the thermostat is high enough to trigger it to open, but there is always the coolant at other side of thermostat counteracting the temp of coolant. My understanding of thermostats is that they wont open if they don’t need to and can stay close on a drive if conditions are not met to open it.

If someone could go plug in their NANOCOM during engine start and let me know if their temp goes above 100C during start (mine takes about 3 minutes to get to 100C) I’d appreciate it. I’d also be interested in knowing at what stage their respective thermostat opens. I’m half thinking that taking it on a drive could run those air pockets out but am reluctant to do so with this NANOCOM warning. The temp gauge in cabin is staying put at 1/4 mark.

I’m at a loss with this as it only happened after replacing the matrix…..

As it only started after you had partially drained the system and refilled it, that would suggest you still have air in there. I think you are being misled by the 100C warning which may be down to the change of sensor. Do you have an infra red thermometer to measure the actual temperature? However, the lower pipe from radiator to thermostat being cold doesn't sound right at all. If the top hose is hot, then it should be at a lower temperature after the coolant has passed through the radiator but not that low. Do you have the old one to put back in and see if anything changes?

SUCCESS!!!!

I couldn’t for the life of me understand why the temperature was so high so quickly on the NANOCOM yet temp gauge in vehicle wasn’t matching. I bled it correctly and had changed the water pump, viscous fan, heater matrix and the thermostat (all part of my refurbishment of cooling system).

The only thing that it could be was a bad temperature sensor. So I plugged the NANOCOM into the other P38 I had and watched it read correctly up to 90C and stay steady, matching the gauge in the Holland & Holland.

I removed the “new” temperature sensor off the H&H and swapped it with the one that was now obviously reading correctly. BOOM…. Worked. Gauge in H&H reads correctly and the NANOCOM reads correctly.

Who would have thought that the temperature sensor could be faulty? Although, I should have guessed this because when I initially installed it the gauge in car never went above the 1/4 mark (as mentioned in another post here).

I’ve ordered another sensor (MEK10060) for the other RR and I will be interested to see how it works when I install it.

Thanks for all the replies and suggestions……

Lesson learned, not all new parts work….