My 92 ford f150 has been running hot?

For example the temp gauge reads to the letter "L" in the word normal on the gauge. I noticed this first happened when I had some mud looking sludge in my radiator. The truck would run hot while driving on the highway for no more that 15 minutes. Since then I've flushed the radiator, changed the water pump, I've even bypassed the heater core to make sure it wasn't clogged and causing the overheating. I have no visual leaks that I know of and I also have no thermostat as well. Fan seems to be working properly. Could I have a bad radiator or possibly need to put a thermostat back in the vehicle?

Put a new thermostat back in. Your radiator could still be clogged. Flushing it out at home sometimes isn't enough.

You might need a new radiator, one time that happened to me too and I was sure the radiator was fine but I changed it and that was the problem.

The only other thing it would be is a blown head gasket, all it takes is a pinhole leak to over heat the car.

If you're looking at the "L" that's the oil pressure gauge. The temperature gauge is "C" and "H." Without a thermostat the coolant pass through the radiator too quickly and doesn't allow proper heat transfer. Start the engine with the radiator cap off and check if the water is flowing in the radiator. If it's not, you still have a blockage.

What's a good thermostat to use? I've previously used a 195 twice and both times my truck started to overheat. Any other suggestions or just a coincidence that maybe they were faulty?