I have a 1973 F880 grain truck with a 534 in it. Coolant isn't circulating. I don't think it is a water pump issue. Thermostat is good. Before I look into radiator issues I wanted to verify, does this motor have two thermostats? After doing some research online it sounded like some had said there were two thermostats on the old 534's. If it does where is it? The truck is a couple hours away from me and when I looked at the thermostat was before I had read there may be two of them so didn't have the chance to look.
There are indeed two thermostats. One low temp and one high temp. Both are in the intake manifold.
The rear thermostat (low temp) is on the rear side under a plate that is secured by three bolts. The front or high temp thermo is located between the manifold and water outlet. Again secured by three bolts