engine overheat

[old guy 44]

Working on my granddaughters 94 SL 500 and wondering if anyone has encountered my problem.

The D... plastic radiator broke and took out the head gaskets. Replaced the gaskets and the radiator with an ALL ALUMINUM radiator. First thing I encountered was that the left side of the engine did not fill with coolant. fortunately I figured that out before it did any damage but the only way I could get it to fill was to disconnect the heater hose at the rear and pressurize the coolant tank to force the coolant over.

That seemed to fix the issue but when I drove it it was fine on the surface streets (40-45 mph) running about 80-90 degrees. As soon as I got on the freeway (65 +-) the temp instantly started rising hitting well over 100 in less than a minute. got off the freeway, took surface streets home and the temp settled right back down.

My first thought was that possibly the thermostat was not making the changeover from internal circulation to circulating through the radiator so I attempted to pull the t stat housing and two of the three bolts seized in the aluminum. My immediate response was severe violence so I just parked it in the side yard until I get over it. Sometime this week I will pull the water pump but in the mean time has anyone run into anything like this?

To anticipate the obvious first question I did check the new gaskets hole for hole against the old ones before installation. And the second question when I got home the coolant tank was still full but you could hear it gurgling so there was obviously a hot spot somewhere.

I really don't want to go back into the engine but I need to weigh that against my feelings for my granddaughter. Any ideas would be greatly appreciated

[Sugar Bear]

Kinda doubt it's inside the engine. Do you have anyway to check for exhaust gases in the coolant? Might be worth getting that out-of-the-way. Guessing it ran cool, no problems until the rad neck broke, yes...no???

Check the radiator for cool spots with an infrared thermometer indicating blockage. Is the aux fan pulling air in i.e., turning the correct direction?

Good luck!!!

[speednjay]

Check for a blocked catylitic converter

[nulu]

If I remember you can get the intake manifold gaskets on the wrong side causing a similar issue

[old guy 44]

I thought of that yesterday so I pulled the manifold. The left gasket has an extra hole in the rear. I have been doing this long enough that I did not think I would do something that dumb but checked anyway.

With the water pump and intake manifold off I duct taped the intake ports and ran water through the engine backwards. Getting good flow both sides.

I did check the water pump where the thermostat is supposed to block the recirculating port and there is no print on the pump or thermostat of any recent contact so maybe????

I have been thinking for the last 6 months maybe this is the last thing and so far it has not been. The only up side, if you can call it that, is in the current climate she does not need the car for school. Just needs a wifi connection.