1991 doge dakota wont start in cool weather

natural for engine temp to rise in Traffic - Until Themostat opens ) cooling fan sensor kicks on fan . But Antifreeze is not just a Cold weather item . Coolant is Absolutely Necessary for Hot Days . You must be full to recovery bottle setting of cold when checked prior to start up . Coolant for your make / model is Reddish - Pink colour and should have a reading of -25 thats negative 25 degrees the Lower the Better even - 50 .. Why ?? - 50 is 50 %% antifreeze / Coolant Concentrate MIX Gives Hot weather cooling Ability or very cold weather starting / winter HEAT .

What sensor for the cooling system? You will have a sender for the gauges and a sensor for the ECM, neithe rof which will cause overheating.
Is the cooling fan working? Engine driven? Make sure the clutch is good. With the engine off spin the blade. It should stop once you let go. If it spins for more than a second the clutch may be bad. If it continues to spin after the motor is turned off its bad.
Electric fan? Is it coming on? Turn on the a/c. That should at least let you know if the fan motor itslef works.
And if its running 220 degrees (mid gauge) that is not overheating. My car in this 98 degree weather can go to 220 in traffic.

Check cam/crank position sensors

It sounds like your air conditioning is actually not the issue here. If your a/c is working in the morning, there is no reason it shouldn't work at a different time of day. What most people don't realize is how hard an a/c system must work to cool off a car that has been sitting in the sun all day during a hot summer. Even if you leave your windows down to avoid the greenhouse effect (which can make a HUGE difference if you don't) the interior of your vehicle is still probably a dozen or more degrees hotter than the temperature outside. This is because only so much air can circulate through cracked windows, and because of the direct sunlight shining onto your vehicle's interior and upholstery. Even once the a/c system is up and cooling the air inside your car, it is still struggling against the heat stored in your car's interior, which is giving up its heat to the surrounding air as it cools off. This can take quite awhile, and if your drive home is a short one, the a/c system may never have time to fully compensate once the car's interior has cooled to match the interior's temperature. To make matters worse, if your drive home is one through the city, you can expect your a/c to suffer. The air conditioning system needs good, steady airflow over it's condenser (a radiator-type part located just behind the front grill) and lots of starts and stops in a city or heavy traffic area can obviously prevent this. Above all though, the most important thing to remember is that with even a perfectly functioning a/c system, you can usually only expect about a 30 degree drop on average from the outside air temperature. So, if it is 100 degrees out, depending on the ambient pressure and humidity (also things which can affect an a/c system's efficency) you may only get air that's 70 degrees out of your vents. I would recommend always rolling your windows down half an inch or so, and park in the shade whenever possible. Also, putting a sunshade in your front (and sometimes even rear) windows, and having your side windows tinted (when legal) can go a LONG way toward keeping your interior as cool as possible when sitting parked in the sun for long periods of time

Also replace the camshaft sensor and fuel filter.

Too tight.....the the torque for the 4 banger is 72 in lbs

the 6 cylinder is only 80 in lbs.

Any tighter and you start to squeeze the gaskets to where they will leak.

The problem is over tightening.

If you over tighten your fastners you will sqeeze your gaskets too much and they WILL leak.

You can use black silicon sealant LIGHTLY but you don't really need it. If you have the V6...the torque on them nuts are only 80 in lbs each

I had a problem with a 1991 Honda Accord and the fix was a weird one. My car would run fine and start fine if it was cold outside. If I left my car in the sun and the interior got hot, my car wouldn't start.

(Since you drove to San Diego this may be the problem)

I found out that if I left my windows open and let the inside of the car cool down, it would start. Strange.....

Apparently, there is a main relay box under the steering wheel that triggers the starter motor and fuel injection. In the Honda's made around 1991, the contacts in that box would expand and would not let the electricity flow.

I guess you can repair the relay box, but replacing it might be a better bet ($50). I took my car to three different mechanics before any of them had heard of this problem.

The fix was simple, but the problem was hard to diagnose.