Mark M

Sooooo ... first thanks for all your input. I changed the thermostat and that, together with the new radiator, improved things slightly but not completely. ie the coolant didn't gush until the car was pushed hard. So I went back to the first answer from Steve Q and worried over the secondary (electric) fan and - in checking all the wiring to diagnose it - seem to have nudged it back into being a reliable ally. This now seems to have sorted the temperature issue. Hoorah! Along the way I learned that a good seal on the thermostat housing is not guaranteed and had to position the new Circoli thermostat twice (after losing coolant overnight to a medium flow weep after attempt 1) and change back to the old O ring and use silicon to make sure I didn't have to go back in for a third try. I also learned the value of having a 1/4" drive socket set for those pesky bolts. And I learned the value of taking off the negative battery terminal since the alternator's live supply is right there waiting to say howdy to any bleeding knuckles. And I learned to value your inputs - thanks again all. I have been using OBDII to watch the coolant temperature as I drive along. At what temperature is the secondary electrical fan set to kick in?

Thanks for your concern. I'll talk with my spanner man and let him know of your suggestion. And I'll let you know what happens. Could the thermostat be responsible for no return to the coolant tank and could it be the source of the rust in the system? Thanks Magnet

I know a man who does, but we were a fumbling in the dark a little as to our diagnosis so thanks to you for your input. We now have a plan!

I thought I'd do both and get that car moving again. Gordian knot severed ...

Re reasons for considering the water pump: after a YouTube wormhole session I (no way a mechanic) checked the return to the coolant reservoir and no flow! I blew down the return pipe and got bubbles so no blockage. Deduction: knackered pump. Reinforced by the fact that even after changing the radiator and flushing with clean water there seems to be rusty orange discolouration of the coolant water and I couldn't immediately think of any other metallic part in the circuit.

The water pump is because I'd run out of ideas. I haven't changed the thermostat. Is that logical? The reading on the temperature gauge seems to reflect reality. Does the car's 'intelligence' work off the same reading as the gauge?

Pretty sure they do, but not certain they do in a timely fashion. If I park up after or during a journey they are making the noises so I assume they do.

Driving goes fine until there's a long uphill stretch or I'm pulling a trailer and the temperature gauge begins to climb over 90. If I park up it cools. If not the coolant erupts. I've pressure tested, put in a new radiator, and am about to put in a new water pump but am not sure I've got the bottom of this. It feels like some of the capacity to disperse heat is faulty, as if something is supposed to kick in when extra heat is generated - but doesn't. No fault codes as far as I can see via OBD11.