Dear All,

I've been battling with my engine coolant system for the last few weeks - the coolant level in the radiator keeps dropping. It has been necessary to top up before driving.

Today the problem seems to have gotten bad enough to make it really obvious:-

The radiator on my W123 1981 300D does not have an expansion tank.
Instead an overflow rubber tube is connected at one end to the radiator neck (where you refill the radiator with coolant) and it is ty-wrapped to the side and bottom of the radiator just above the return hose (coming from the engine back into the radiator).

The overflow tube seems to be where the coolant escapes. I get lots of dripping when I stop - but I think it is a continual drain as the top coolant tube (from radiator to engine) can become alarmingly empty...

Obviously I need to fix it NOW!

I guess I need a new radiator cap.

But before I rush out and get one I thought I would check with some experts as I could be missing something.

Has anyone had experience of an engine coolant system without an expansion tank?