I thought about the cap isssue too and its on there pretty good (and its new). I just went out for lunch and saw where the antifreeze ran out and down the ground in the parking garage. I topped her up with water and took a 10 min drive in stop and go traffic with the cap off to see if perhaps she'd "burp" any air out of the system and so far the temp is back to about just below 80 cruising to about 82 standing still in 80 degree weather. I'm suspecting the air pocket issue and only the hot rush hour ride home will tell me something else (as this is going to be at least an hour and a half of stop and go in the sun).
I hope there's someone here to shed some light on their normal operating temps. I'm thinking I'll have to replace the coolant (again) with just the 50/50 premixed antifreeze and running her for about a half an hour without the cap to make sure the air is out. Also, I remember that before I changed the coolant, a tech from the MB dealer said to just fill it at the expansion tank and it would go into the radiator with no problem which I did. The last time I changed it to the water, I actually took the top radiator hose off and filled it that way (and didn't have these issues afterward). Could this also be the culprit? Any other ideas? It seems that its pretty much cured so far with the cap off but still weary at this point.
1970 250C SOLD
1971 250C SOLD