Dear Dave Stevens,

Hope you're well and stay so. I've long thought that the coolant overflow tank's cap gives pressure relief to the cooling system.

No radiator plug is needed in a car with an in-radiator temperature sensor that controls the electric fan. An example a '93 940 with Rex-Regina fuel/ignition management.

About 15 years ago, the in-radiator plug in a '94 940 - not needed for a temperature sensor given Bosch fuel/ignition management - worked loose. Happily the day was cool (about 50°F / 10°C) and the trip was short.

On my return, I topped-up the coolant. I replaced the plug and used brass wire to secure the new plug. I drilled a small hole in the radiator's side-tank fin, through which I put the brass wire that I ran through the slot in the plug's top. I then wrapped the wire around the base of the side-tank's nipple for the in-radiator authomatic transmission fluid cooler. This secures the plug.

I'd recommend securing the press-fit in-radiator temperature sensor or the plastic plug (where no sensor is needed).

Hope this helps.

Yours faithfully,

Spook