Probably air in the system. I agree with Wrightpayne, 3mm hole in the stat at the top, then to refill ...
Expansion tank cap and top plug on radiator removed, then fill slowly (very slowly) via the bleed T in the bypass/heater circuit, holding the T as high as you can and definitely higher than the expansion tank. When coolant comes out of the top of the radiator fit the plug. When the expansion tank is up to level fit the cap. Keep filling via the bleed T until you can't get any more in then fit its' cap. Job done, works every time.
Don't mess about raising the front and trying to fill via the expansion tank, it doesn't work and you'll still have air in the system.
Lotus Seven Club AR Working Group
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Thank you, general consensus seams to be that I still have air in the system. I will empty it and try again via the Tee this time.
The more I think about this the more I think I may have a problem with the thermostat. I think I will buy a new one anyway before I drain it down so that I can test the old one and replace before refilling. I am wondering if it is not operating but when revving it is forced to open.
Please can somebody confirm the part no. to me. Is it PEL10016 and 88 degree rating? Any particular make recommended or online place to buy one?
Thanks in anticipation
Drained coolant today, checked thermostat and it did not fully open. I guess when revved it opened further. so it was probably that possibly plus an air lock.
Fitted new thermostat with 3mm hole drilled in it and filled with coolant slowly through the tee. No air and keeps a very steady 85 deg, when left idling the temperature climbs slightly, fan kicks it and temp drops back to 85 deg again.
Thanks to Stu and every one else for the helpful advice.
Just need to be allowed to go for a drive now.........
Thanks for the update.