1990 740 Regina 5 speed dies when hot

The car dies out gradually and if I press the accelerator when it gets warm it completely falls flat on its face. Happens more when it is warm outside. When it?s cold outside it would behave better. But it also had an issue where the lower hose was not getting any fluid whatsoever. So I took the thermostat out hoping that would help as well as help with the bogging.

Try checking a few things. This kind of thing may be a couple of problems. Fuel pressure should be checked. To accelerate you need spark advance, and some enrichment. The fuel pressure regulator vacuum hose provides some fuel and the spark computer provides advance. Engine speed sensor ok? system voltage ok? Look around the engine air handling and vacuum hoses carefully for air leaks.

Not sure I understand what you mean about the cooling system hose. Definitely don't run your engine long without a thermostat or a restriction replacing the thermostat. You can overheat the engine without it.

I had a Regina 940 for years, you may have more than 1 issue, but I would definitely check the fuel pressure. There is a Schraeder valve on the fuel manifold where you can hook up a pressure tester. If I recall correctly, you need 35 psi at idle, but when blipping the throttle (accelerating) you go up to 45 psi. Many times with old fuel pumps the pressure stays the same or decreases. If so, time to buy a pump.