1973 450 SEL running hot at high speed

Hello~

This is an amazing message board. This is my problem, the steps I have taken.

I have this 1973 450 SEL. Its an electronic fuel injection gas V8. Recently, it started over heating. After a few minutes of driving it would shoot to the red line.

I immediately replaced the water pump, the thermostat (67 degree C type) and the main hoses.

This seemed to fix the over heating problem. Now when I drive for long distance at above 55 MPH the car will go above 175 on the dial and continue up if I don't slow down. I drive at 65 and after 45 minutes the temperature will go to red line at 250.

After careful research, I replaced the 212-switch which turns the electric fan on at 185 degrees F (I think). The belts seem okay and the radiator was replaced 2 years ago and I recently flushed it out. I also replaced the radiator cap because the old one didn't work.

Now the constant high temperature and high pressure is causing the expansion tank to leak at the seems and the hoses are going one by one. I guess they are very old so I am okay with replacing what needs replacing.

I use a 75/25 anti-freeze/water mixture. I use 10W-30 motor oil Chevron brand. I drive fairly easily, no racing or towing. Poor gas mileage.

MY QUESTION: Why is it running hot at high speeds?


Of all the things I have done, I haven't changed the fuel filter. I haven't checked the timing. I haven't checked any vacuum hoses. I haven't checked the injectors. I have recently changed the spark plus and one of the wires may be "leaking" but I doubt it.

Any help would be greatly appreciated! I am trying to restore this classic and I want to ensure long life. Please help. I am desperate. Any input would be great.

Thanks