New Member - 1st problem coolant overflow

[MB-TEXada]

Hello, first I would like to thank all the contributors to this site - I have made extensive use of it in our search for and recent purchase of a 1966 230SL with a 130.980 motor. We run a farm and have kept a 74 MBGB running for a few years now so have basic mechanical skills.
Anyways, the first issue cropped up today after our first 2000km wth the car. Coolant started pouring out of the expansion tank overflow after some "spirited" driving. The temperature gauge was a little high - about 180'. I've never seen it over 185' and usually its abut 165'. Once it cooled off I added 32oz of coolant to bring the level back up to 4cm below the expansion tank neck and idled the engine back up to 180' on the gauge then drove normally for 20 minutes or so checking regularly for overflow. Then I floored it back up the hill to home and after climbing 700' at 3000-4000 rpm I stopped and coolant was again overflowing - much less this time. After cooldown the level in the tank was back to about 4cm below the filler neck.
I hope its just some air in the system burping its way out but I haven't messed with anything that could have introduced the air. I have done nothing to the cooling system other than checking the coolant level occcasionally and looking for any sign of oil in it when I bought the car. The only thing that changed was driving more aggressively than I have so far. I planned to flush the system anyway - Would that help stop the overflow?
Engine oil has always appeared clean of any water and the level goes down not up. There is a little steam in the exhaust at cold start but none that I notice once it's warm so I am hoping air isn't getting in though a head gasket issue. The heater bypass valve is stuck open and I've seen no evidence of leaks in the core area or any hoses.
So, should I worry a great deal? Is this in any way normal?

[jacovdw]

I would be a little concerned if my engine started to push out coolant like the way you describe and running a little warmer than usual.
It is not normal and should be investigated further.

Have a look at this thread also from a short while ago: http://www.sl113.org/forums/index.php?topic=15189.0

It is possible that there might be/have been an air pocket remaining somewhere in the cooling system that was "burped" with the spirited driving, but I doubt that.
With head gasket failure, you don't always have to have coolant in the oil. It depends on where the gasket is failing and how severe.

A small leak from the combustion chambers might pressurize the cooling system to the point where you have overflow and the residual pressure in the cooling system when the engine is switched off might cause coolant to leak back into the cylinders.

Usually the head gaskets fail between the cylinders and as you have a M130.980 motor the spaces between the cylinders are not that much. You also have an additional slot cut into the engine block between the cylinders to help with cooling, thus not leaving much surface area for the head gasket.

Unfortunately these engines do not tolerate overheating very well and I would advise that you do a compression and leak down test to start off with.

[Garry]

I run my fluid level in the expansion tank around half full and it will move between one quarter to three quarters full depending on e temp outside, the speed and how hard I have been going etc. If I filled my tank to 4 cm below the neck I am sure mine would overflow on hot days too.

Where has the 4 cm below the neck in the expansion tank come from, is it in the manual?  That seems very high and I  am away from my car so cannot check the owners manual.

[jacovdw]

Garry,

The 4cm level is mentioned in the Service Manual.
There is also a yellow decal with the 4 cm reference (applied to the overflow tank) that is sadly missing from a lot of pagodas.

[bogeyman]

I'd buy a new cap - just to be sure.

[Ulf]

Mine used to overflow regularly (only a small amount though but even a few drops of coolant looks huge on a garage floor), I just stopped constantly topping it up and the level has settled to fill appr. half the expansion tank and has remained constant for about a year now. My temp stays rock steady and I know for sure that there is nothing wrong with my engine. But then again, the cause of your overflow could be something different.

[MB-TEXada]

Thanks for the timely reponses. Looks like half head gasket doom and half don't fill your tqnk so full, either way I am doing a leak down test as soon as possible.