Thread: overheating

im not sure what it could be but i have a problem with when im driving on the highway for 30 mins or more at a constant 80 90 mph and the car starts to get real hot when i begin to slow down, it wont get any hot when i am driving in the street, and when i get to check under the hood water is just poring out of the overflow bottle. any ideas what might be happening? my coolant seems to look alright but the cap develops some sticky black gunk on it as well.

If you have not serviced your cooling system lately, a good flush with a commercial cleaning product and a new Nissan thermostat might solve the problem. Make sure that you properly bleed the system as you fill it to prevent overheating from air bubbles in the system.

The cap itself might be faulty and not holding pressure. As billc mentioned you might have to see if you dont have a blockage.
If you dont have a radiator pressure tester, open the cap and while the engine is running, check for small bubbles as the water circulate. If indeed it continue with little air bubbles at operating temprature, you might have a blown cyl head gasket.

I think either the cap is no good or the neck of the rad is no good so it is not holding presure.

did u do anything to ur fans....check the rotation on them..... change the cap of the radiator and also check the thermostat..... boil some water and cook it.....then look to see if it opens and if it opens all the way

big a$$ crack in the overflow bottle, probly didnt help anything either, did a new thermostat and flush, cap really is not too old. need to i guess find one in a salvage yard.