Well if by hot you mean the engine overheats the answer is simple. While driving in town ( city driving ) you engine is not pushed as hard as on the highway. On the highway the engine is getting a constant flow of gas with no break where as in the city you drive to a certain speed letting of the gas when the speed is reached, slow down, or stop. The engine is also going at around 5000 rpms depending on your vehicle then the rpms go down when it shifts but if you slow up it goes back up to the high rpm's.
While there's probably nothing technically wrong with the above answer, it also doesn't help with your overheating problem.
If the engine gets hot at highway speeds and cools off when you slow down, there is likely a restriction in the cooling system. Could be a bad thermostat, plugged radiator, or perhaps plugged water passages in the block or heads. Start with the thermostat since it's the cheapest and easiest thing to try. Sometimes a radiator can be flushed, but usually you end up buying a new one. If the block is plugged up, it is probably a very old, poorly maintained engine and will need to be disassembled and cleaned.
If this is a new combination and has never cooled properly, perhaps you just need a bigger radiator.
Thermal relay is defective causing the fans not to run when they should. Replace the relay.
Because your car is getting hot!
Because you are using them more often than you would if you were highway driving.
Big Town - 1950 Hot Car Murder 5-8 was released on: USA: 29 November 1954
I suggest replacing the thermostat, that might work.
The fan or water pump,
Your electric fans have stopped working. Turn on you A/C with the hood open. If no fan is running either the fan is bad (most likely) or the relay is bad (not as likely). Y-THINK-Y
Safty featcher so as not to destroy engine
more airflow over the radiator keeps it cool on the highway, in town more sitting in traffic and lower speeds let it run hotter. If it is nearly over heating start with the easy things check the radiator fluid. if it is full then it is probably the thermostat sticking either open or closed. since it runs cooler on the highway I would think it is stuck open allowing the water to circulate through the radiator.
it would depend on how hot the car is and how thick the burger is, but I would never do it
If by this you mean only "hot heat" when drive at highway speeds likely thermostat bad and/or almost stuck and takes long time warm up from high engine RPM during highway driving.
If a 1988 Lincoln Town Car is blowing both hot and cold air when the air conditioning is on, there could be a problem with the thermostat. There might also be a problem with the level of refrigerant in the air conditioning pump.