When I ran the car the plan was to get it up to temperature then change the oil. However I noticed the temperature gauge crept over half, which lead me to look at the coolant situation. Should have been the first thing I checked!
What I found was that the radiator had clearly developed a hole – old coolant clearly visible around the bottom of the radiator – and would need replacing.
New radiators are easily available and the workshop manual suggested it was easy enough, so another job I could do.
Following weekend, I flushed out the system through the old radiator (top hose just disconnected, garden hose in the top of the radiator) and removed the old radiator. Lots of corrosion around the bottom of the brackets, so some Kurust on that to stabilise things. This also required removing the undertray, and I have one or two sheared bolts to resolve now.
Then I fitted the new radiator, more flushing, then new coolant.
However, when I started the engine, I found this:
Quickly traced to the power steering system- it doesn’t look too bad to sort- I suspect I disturbed the rust that was keeping it fluid-tight. Better it lets go now than during use! Another post on this shortly.
I also noticed the radiator fan never kicked in. It’s possible to diagnose the radiator fan and relay on the MX-5 by shorting a pin in the diagnostic connector to ground and checking the fan runs. The workshop manual suggests the next thing to check is the thermoswitch on the front of the engine. Method: pull the sensor, check it for continuity in boiling water.
Reality- pull the sensor:
New sensor about £12 on eBay- ordered- trivial to fit.