Hi Martin,
Rad rans running constant.....is this from cold start or just once warmed up?
Also what does the idle run at when warmed up? Should be around 850rpm......if it is around 1200rpm and constant rad fans then this is usually the ECU seeing a problem from the coolant sensor and switching fans on full time and raised idle to circulate the coolant quicker.
I had similar problems when I reengined - turned out to be an airlock that caused water temp at the ecu sender to go to overheat and cut the fans in.....but because the water wasn't circulating due to the air lock the temp gauge was low. Another pointer towards coolant problem would be if the temp gauge drops / rises when revving the engine.
Check the vent valve on the rad top pipe too....often air accumulates there if stuck in the front part of the system.
I solved by plumbing in extra vent valve on the heater circuit and a vent line back to the header tank.
Limpabit's advice about thermostat is also good - while you're checking it is there put it in a pan and boil it up to test operating temps.
...while I remember - the K series has 2 temp sensors for coolant - both on the same outlet elbow above the gearbox at the back of the head. One is for the gauge only, the other is the signal for the ECU. I can't remember which is which but it's an easy google search!
New temp sender isn't dear and you can change them without draining the coolant down if you are quick!
Cheers
Rich
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