I have a 1.8 k-series SuperSport. Recently got the car out of storage and the engine temps are misbehaving.
For the first 30 mins of driving everything is as it should be; the coolant temp hovers around 80 Celsius in all conditions. However, thereafter the temp will do two things. Yesterday, the temp rose to around 95-98 Celsius whilst waiting at a light. Today, the temp remained at 85 but rose to around 95 just after I pulled away from a light. Conflicting behaviour. The only difference is that I bled the system in between.
I jacked the nose up, got the engine running, released the clamp on the return from the heater matrix until coolant trickeld out, then I released the bleed screw on the top of the radiator in 3 second bursts to let any residual gas escape.
I have also tightened all clamps on the coolant system. There is enough coolant and it's in good condition. I can't find any air leaks. The fan kicks in and is also in good condition.
I have been running around with an OBDII reader plugged in so can confirm that the ECU coolant temp sensor and the gauge are moving in the same direction. Not necessarily at the same rates but the trend is consistent across both so I don't think there's any major measurement error.
What could be going on here?
1. I still have air in the system somewhere and my bleed technique needs work!
2. Thermostat is on the way out
3. Head gasket failure
At a bit of a loss now so would appreciate some advice.