The impossible to solve overheating problem

mvh said
Incomplete combustion may affect O2 in the exhaust, but that is not measuring rich or lean. Rich or lean refers to the mixture in the cylinder at the time of combustion, which is entirely controlled by the fuel system. The composition of the exhaust gases is only an indicator of this.

Based on what you say you have tried, I am wondering if you caused a blockage in a water passage when you were replacing the freeze plugs; for example, driving part of a rusty plug inward. What did the interior of the water passages look like?

But I still think your electric fan is inadequate. It looks like the Autozone special I tried installing in front of my 273 Commando in younger days. The 273 was getting a little hot idling in traffic, but with the low-CFM electric fan, it ran hot all the time until I ditched it and put the metal fan back on.

Anyway, you should be able to tell if there is a cracked head or combustion leak into the coolant. With the motor running and the radiator cap off, are there bubbles in the coolant? Drain some coolant into a cup and sniff it -- does it smell like exhaust? Put your hand in the exhaust stream for a moment -- when you pull it out, is it wet? Does it smell like coolant?

The interior passages of the lowest freeze plugs looked pretty bad like it the photo. I cleaned them out as well as I could. You just made me think of something .. Long story short one of the lower freeze plugs was replaced by a rubber one like shown ... could it have gone in too far and is blocking flow?

I have not checked for bubbles in the coolant or done the smell test. Exhaust looks clean but never sniffed it. I will check for bubbles in the coolant and check the exhaust tomorrow!