1978 BF 75 Overheat Running Hot

Got some other issues knocked out now this. I do not think water is circulating into the cylinder jackets. Plenty of water from the pump but all seems to be going through the bypass hose to the thermostat(which I removed thinking it was the issue). Temperature of the block will reach over 200 degrees at which point I shut it down. So plenty of water from the pump but still hot block and head. What should be my first course of action? Might there be an obstruction behind the oil dipstick assembly?Should I remove the head? When I remove the bypass hose there is quite a bit of water pressure so why do the head and block heat up so. Oil is full.Thermostat removed.

It sure does sound as if there is a blockage where the bypass passage "T"'s off from the block passage. This would be the only reason I could think of that you have great flow in the bypass but the block and head are overheating.

Since this would be internal to the bottom of the block, the only remedy might be to take off the extension case and water tube and then try and force air and water or both backwards through the block from the thermostat housing passage. You would probably need to do this with the bypass tube plugged to get the most flow through the block.

If you can get a big GUSH of water to come out the bottom of the oil case where the water tube hooks up then you will have effectively cleared the block.

That's all I have to offer but hopefully someone else may have an easier solution.

Good luck.

I ran the engine in a salt away solution and let it sit overnight. I then followed your advice on the back flush. Made some crazy connections to the garden hose and each water inlet and outlet. The engine is now running at about 155 degrees. That was fun. Thank you for your help.

Actually about 160 at the head and 185 on the cylinder barrels. Is that acceptable?

Weeeeeell......hmmmmm. To be perfectly honest I don't know for sure. But my instinct tells me no, it's not right. I hesitate because I don't know where and how you're obtaining the readings.
In a purely technical sense I would say that the thermostat is not opening all the way and is "reheating" the block. The only thing wrong with that theory is that the head temp sounds spot on.

Since it sounds as if your flushing efforts did a great deal to improve things, im thinking you may want to do some more flushing and then see if the block will run a bit cooler. Compressed air in conjunction with with water can be very effective at clearing the cooling passages and I would try that if you have a compressor and a rubber tipped air gun.