I am unconvinced that the problem is solved.
I haven't tried the old temp sender yet and tested the temp gauge so one step at a time.
If it was me, I would be trying fitting a header tank. Previously we disagreed on where to locate one,
but I will stubbornly stand by my opinion on this because I tested the positioning using coolant as the level indicator.
Trouble is Ian, not trying to be belligerent but I don't see how a header tank would help with cooling issues. The temp doesn't rise past 3/4, Tony runs Evans and he has the same temp reading, a header tank would only help in a situation of coolant loss, which I have none. Yes it's a good mod but in this case it should run fine as standard.
Not intending to be clever, but I did suggest starting with the sender some time back.
Re. header tanks, these have been used since the 70s including by BL. To begin with these were largely plumbed into
the top of the radiator but this method was soon revised to the now standard plumbing into the bottom hose/bottom of radiator.
The purpose of the header tank is to prevent cavitation by ensuring that the water pump has a constant uninterrupted supply.
Avoiding cavitation ensures that the coolant is in contact with all the surface of the engine, thereby making heat transfer efficient.
Slant four engines are prone to cavitation at the back (hence their inclination to blow head gaskets between cylinders three and four).
Triumph twice revised water pump impeller design and Saab offer a fourth variation and both went for a header tank (TR7).
(Saab completely redesigned the water pump twice, the second of these being a long lasting effective external design 900).
In order for a header tank to be it's most effective it should be located as high as possible.
Re. Tony's experience with Evans coolant, he is using Classic Cool 180.
This is not suitable for Dolomites. It should be Power Cool 180.
Tony contacted Evans and they confirmed this.
I used PC180 in my old Dolomite 1850. It ran at halfway on the gauge all year round using an 88 degree thermostat,
which is the same reading as when I was using water/antifreeze.
Evans Coolant has a lower heat transfer coefficient than water but this is offset by EC staying in contact with all surfaces.
The so called expansion tank that Triumph employed is the weakest link within the cooling system.
Jod Clark wrote an article for Dolly Mixture describing how he cured an overheating 1500SE by replacing it's tank.
Using Evans Coolant will mask this weakness because it doesn't pressurise the cooling system.
If I could only make one change it would be to fit a header tank.
Evans coolant would be my second change.
Hope this clarifies things.