I've owned a W124 wagon with an Om603 for years now. The cooling system has always bothered me. The #14 heads are known for cracking and I don't believe it's just a weak casting. Some have issues with them and some don't. I live in California were its usually hot and it's very hilly with long grades.

My car has never over heated but never stayed at the same temp when climbing hills. The temp swings range from 80c to just under 100c which in my opinion is a lot! My cars head has been cracked for quite some time. I finally found and bought a #22 and did a few revisions before I got it up and running.

First I drilled and tapped the thermostat housing to run a line to the drain plug on the block using ANS fittings. This routes water to the last cylinders and helps to get rid of hot spots. Second I gutted a thermostat and used the outer ring to re install the thermostat water neck with the rubber O ring. Then took the water neck on the head and cut and welded on a universal Thermostat housing that uses a chevy thermostat. Chevy T-stats are $8 at any auto parts store with many temps available. Versus the $30 Mercedes T-Stat.

The first week I drove without a clutch fan on the rad and even at stop lights it would take minutes for the temp needle to start to move off 82C. The highest it would see standing still at a light was about 87C. I have since installed my clutch fan but figured I'd post pics of how small my temp swings are now. My temp used to reach over 90C in no time climbing this same grade. With the new thermostat position at the top of the head my temp needle barely moves under throttle going almost 70 mph!

Also my cooling system was all new less than one year ago and I had 2 different engines with #14 heads that both showed the same temp fluctuation with the stock thermostat location. Only difference now is the #22 head and the thermostat relocation and coolant re-routing to the the rear cylinders from the water pump housing.