Hello
New her and having a problem .I have a 1978 245 that seems to be over heating. The temp gauge will go to red in about 3 to 4 min. of running and it's over flowing the overflow tank. I flushed the radiator and changed thermostats but it's still doing it. I pulled the water pump and it looks good as does the system as a whole. I ran water thru the thermostat hole and it seems to be flowing thru every thing and there was no water in the oil or oil in the water. Any Ideas thanks.

 

I'd say Head Gasket.
Even though you have no water/oil mixing, there are other ways bad HG can act. Remember, the HG separates coolant, oil, and compression, and sometimes these can combine for some crazy symptoms. In this case looks like compression is blowing OUTWARD, causing the overflowing. Also, what else is there? You have done everything else that can cause overheating... No big deal, though, as long as the car hasn't been overheated, has it? Doing the HG is not hard on a Red Block.

 

Itdid get up to the red but it was and still runs fine just over heats and blows water. I haven't drivin it since I noticed it was hot but I'm not sure how long it was run before I noticed it. but i'll have the head checked when I replace the gasket. I was hopeing that wasn't it but that thought was in the back of my mind.

 

You may get away with just changing the gasket, still, have a machine shop check the head for warpage... When you take the head off, you should be able to see the break in the gasket...

 

The cover of the watertank (valve inside) could be defect. Happens that overheating is caused by this.Try changing it with another and see if it works. You also could be having air in your system. Run the engine and put the heater blower on full to get rid of the air inside. Maybe your problem.

 

you also could have an engine block thats heavily corroded inside such that the water passageways are largely plugged. this happens if someone ran plain water for a long time, rather than a proper antifreeze mix. or if they didn't change the coolant frequently enough. or if the water used was very 'hard'.