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2000 Ford Ranger 4cyl coolant system trouble

Noticed on after driving 200 miles that the temp gauge in my truck showed cooler than normal operating temp, and made sure to pay attention after that and it continued to read cool. So we figured it has over 100,000 miles easy fix we will replace the thermostat. After replacing the thermostat and flushing the system the temp gauge stopped working and no more heat. So we replaced the heat sensor, gauge and heat still don’t work. Heated the sensor to test it to make sure it wasn’t faulty and it registered on the gauge. After running the truck for 10 minutes we checked the coolant temp and it was at 130F at the sensor. Pulled the thermostat to see if it was stuck open and operating nothing was wrong with it. Replaced the heater control valve after flushing the heater core. Truck didn’t and still doesn’t leak coolant. Drove the truck 10 mins (gauge didn’t move), stopped and had a friend look at it left it running for ~25 mins while we were looking at it (gauge moved to less than a quarter over cold), as soon as we started the 10 min drive back home the gauge dropped back down to cold and stayed that way till we got back home and no heat the entire time. Return hose, radiator, and hoses running to the heater core get warm. Fan clutch isn’t locked up, can turn easily by hand I’m out of ideas and so is Google, any suggestions? Why would the sensor read when warmed up outside of the housing but when screwed in it doesn’t read the coolant temp?

Ford states that if heated air doesn’t come out of the vent system and the temp gauge doesn’t move or moves very little there’s air trapped in the cooling system.

When the engine is cold fill the coolant reservior with coolant. Start the engine and let it idle for fifteen minutes. With the engine idling loosen the upper radiator hose clamp and insert a small flat bladed screwdriver between the upper radiator hose and the hose neck on the radiator. Allow the engine to continue to idle until the temp gauge starts to rise and heated air is felt out of the vent system. Remove the screwdriver from the upper radiator hose and reinstall the hose clamp.

Tester

The fan cannot lower coolant temperature below the thermostats lower limit if the thermostat is working as designed. How was the thermostat installed? On these thermostats

Some have a rubber seal attached to the base while others don’t. If a thermostat without that rubber seal is installed using either RTV or a gasket the thermostat becomes a useless bauble rattling in the housing. Coolant will by-pass the thermostat if improperly installed.

ok so now we got those problems fixed (the thermostat had gotten knocked off center in its housing). drove it around everything ran great then went out around an hour later and it wont start. can hear the engine turn over but it never catches. I think we pissed off the gremlin in my truck. any thoughts? also I have it where when we get a pretty good rain it leaks into the drivers side floorboard (enough to soak a big bath towel). we found a leak and plugged it and that reduced the amount coming in but cant figure out where else it is leaking from. took the door panel off, gaskets around the door look fine, checked and it isnt coming from the back window and following the floor down, and checked and its not coming from behind the pedals. any ideas?
Thank you for your help.

How much anti-freeze has been dumped on the timing belt? You may have stripped some teeth on the belt due to anti-freeze deteriorating the rubber and lubricating it to skip easily over the cogs on the pulleys.

about a teaspoon, we tried to make sure to wipe any that fell onto it off. how difficult is it to replace the timing belt? it is starting to show some wear and I’m trying to figure out if it is something that i can do myself or would need to take to a mechanic