Sounds like you still have air in the system. Make sure it's topped off and bleed all the air out.
Possibilities: Cooling fan not working. Low on coolant. Clogged radiator, radiator hose or block.
thermostat needs replaced
The most likely causes for the S10 Blazer to overheat at highway speeds but not in the city are a failing radiator fan clutch, a clogged radiator, or a failing water pump. At highway speeds, the engine is working harder and generating more heat, which could overwhelm a system that is not functioning properly. It's recommended to have the cooling system checked by a mechanic to diagnose and fix the issue.
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.
change the thermostat. sounds like it is stuck open, allowing high flow through the radiator at highway speeds where the air flow rate accross the radiator is enough to keep it cool. In the city the fan thermostat turns the fan off to maintain temperature. Nice easy and inexpensive fix. Should also improve milage slightly.
Something can be wrong with your starter.. have you tried push starting the car? Check your coolant systems.. radiator, water pump, thermostat..
could be a bad radiator, or not enough flow to radiatorAddendumI had the exact same problem and it turned out to be a plugged up radiator. I also had this problem, so hose flushed the radiator, and the problem still persisted. Turned out that the thermostat was sticking; not opening fully. I put another one in, and it's running cool now. Change your thermostat. They need to be changed anyway, so do it, and I'll bet your overheating problem will be cured. Cheapest cure there is.I recently went thru this on a 99 dodge ram 1500, replaced the thermostat, still had probs with over heating on the highway, after that noticed that my water level in my radiator kept going down, changed the water pump and that was the issue. after about a week of overheating and running low on water. if replacing the thermostat doesnt work, you need to check to see if you have any water leaks at all on your water pump, then with as old as my van is, i just make sure once a week to check my water level and keep water in my resivoir as well, never had a prob since.
Replace thermostat with a 195 degree one. Check engine coolant leval in radiator sounds like it is low on coolant.
My 2000 would overheat at idle; in park & slow traffic. Ran normal on the highway. I 1st replaced the fan relay everyone has been blogging about, engine still overheated. Next attempt for victory, I replaced the temp sensor switch; defeated again. I then replaced the thermostat & haven't had a overheating incident since.
no flow in radiator
Check the operation of the cooling fans. However, if you are driving at highway speeds the cooling fan would not be needed, therefore it could be a defective thermostat or a clogged radiator, in which case a radiator shop could clean and refurbish it. If not driving at highway speeds, the check not only the fan, but the thermostatic switch controlling the fan and the fuse/circuit breaker for the fan system
Check your fuel filter. When was the last time you also checked your air filter.