We had Fotty boil over a couple of weeks ago. Kept an eye out and couldn’t find a leak/problem. Had it in the garage for MOT last week so had the system flushed and refilled - they found no issues. Tonight my wife pulled over in the supermarket because of a sound “like something plastic was bouncing around under the bonnet” and there was a strong smell of burning/overheating - just like when it boiled over.
So I drove out with the other car and I drove the 5 home, and in the 3-4 miles home I had to pull over twice and switch off as the temp needle headed east. The fan was going fine, but while the engine was real hot (hence the gauge) I could very comfortably touch the radiator cap. Reasoning here = the hot water is not getting to the radiator to cool down.
I had a similarish problem which Geoff Walton diagnosed as the radiator. Whilst my radiator wasn’t cold, it wasn’t as hot as it should have been, he thought it might be furring up. I have ordered a new radiator. Apologies to Geoff for stealing his advice!
Had a chat with Andrew Stott from Autolink and came to the conclusion thermostat is lucky, but probably the pump (they recommend replacing them with your third timing belt change as they don’t last much long than 150K).
So another look in the cold light of day. Took the rad cap off, and the new coolant from the flush and refill two weeks ago was nowhere to be seen. Filled it up, to be followed by a drip drip drip from the crank onto the undertray - so water pump it is then!
Also checked the oil (recently flushed and refilled) - that was down to min as well. Looks like the drip from the back of the engine is getting worse - cam shaft sensor o ring…
The darn things cost me about a grand this year - the fun of a classic car you drive every day [:S]
It could also be you need a new radiator. My car is 1992 model and that was the cause of my problem. If you can try to get under the car and find where the leak is before spending any money.