What makes my car overheat at high speed?

Question

Got a dodge 1996 Cargo Van - fix the overheat once before, new pump, new hoses...etc. Still the mechanic does not know why the car runs hotter in frwy than the streets, esp going uphill with or without cargo. So confusing!!!

Answer 1

sounds like not enough airflow to the radiator

Answer 2

Here are some obvious things to look at:

1. Is the radiator fan coming on? (Assume it's electric.)
2. IS the cooling system full of a 50/50 mix of antifreeze and water? IF you run pure water or pure antifreeze it will over heat. It must be a 50/50 mix.
3. Is the cap on the coolant tank or radiator holding 15 pounds of pressure? A system theat isn't pressurized will over heat.
4. Is the coolant tank losing water or coolant? Most are a two piece plastic welded seam tank and the seam will frequently leak and allow pressure to escape and this will cause over heating. You can watch this happen when you start the car from cold and as the engine warms up you will see the fluid rise to the top of the tank and stop at the pressure cap. This is either the tank or the cap letting pressure escape.
5. Do you have to keep adding coolant but you can't see where it is going or leaking? This can be a sign of a small leak into one of the cylinders. Without jumping into a head gasket repair, you can use what Cadillac has been using in their motors for many years. It's a small round brown "horse pill" that you drop into the radiator or add to the coolant. I think it's one tablet per gallon of coolant. They sell these "Bars Leaks" tablets at Kmart and other stores. This is a must for engines that have two different metals in the engines like aluminum block and cast iron heads or vice-versa.It is actually ginger root and it seals the micron sized head gasket leaks when the motor is warming up and prevents coolant from getting into the combustion cycle or cylinders. It works.

Good Luck!

Answer 3

What engine? 318? or V-6? Is the fan shroud on the radiator intact? It's possible you've got an air-flow problem in your radiator (full of leaves, bugs, etc.). It's relatively cheap to have it boiled out and re-sealed. You could also buy a new or rebuilt higher capacity radiator. How about the thermostat? Could be faling to open completely. Cheap fix there too.

Answer 4

Because the engine is probably being pushed to hard. Don't go to fast. You could also try replacing the radiator. It might be old and full of rust.

Answer 5

sounds crazy but the catalytic converter could be cloged causeing exhaust heat to return to eng

Answer 6

could be a number of things....Could be the thermostat is not working corectly......Could be you do not have enough coolant / anti freeze mix in your radiator.....You micht need to have your radiator flushed......It could be anything.......best of luck