Overheating on freeway only??

[RustBucketRacing]

Just bought a K20 with a 383 and electric fans sealed to the the radiator, restricting all airflow except from the fans. It runs at 170 around town all day but on the freeway heats up?? Could the fans be restricting the air coming through at highway speeds??

 

[nvrenuf]

Most likely this is a coolant flow issue. Check the radiator and see if it looks crusty inside.

 

[Hogback Fabrication]

What fans and what radiator? If you don't know, pictures are always a start.

 

[K85 Octane]

collapsing lower hose or maybe no T-stat, but if the stat is missing it might run cooler around town

 

[EIB8400]

I had the same issue only I was running the stock set up. It ended up being my radiator. Put a new one in and the problem went away.

 

[mrk5]

I would bet your radiator is plugged up.

Although it also could be the fans not allowing enough free airflow at highway speed. I've seen factory electric fan shrouds that have little doors that will flap open with airflow thru the radiator at high speeds but at low speeds the fans suck the little flaps closed so they pull air thru the radiator better.

 

[Hoss7979]

What kind of water pump are you running and what kinda fans....push or pull?

 

[dyeager535]

Just bought a K20 with a 383 and electric fans sealed to the the radiator, restricting all airflow except from the fans. It runs at 170 around town all day but on the freeway heats up?? Could the fans be restricting the air coming through at highway speeds??

It's most likely the radiator. Freeway speeds move far more air than the fans do, if it cools with no load on the engine (idle) then the problem is most likely to be radiator inefficiency.

If you want to test the fan shroud theory, take them off and run it on the freeway and see if the problem goes away. From what a couple of folks have found, on flat ground, 25MPH+ you generally don't need fans. You just don't want to have to stop for any length of time.

Not sure why, but people seem to ignore the cooling system on most vehicles, whether it be routine maintenance, or making sure it is up to the task that is being asked of it.

Put a 195* thermostat in there while you are at it. If it warms up to 170* and stays there (other than on the freeway) someone put the wrong thermostat in, and didn't understand how cooling systems work. That is a clue that the radiator is junk and that someone knew there was an issue already. Common to install a cooler t-stat when there are overheating issues, when in fact the thermostat only sets the engines minimum temp, and has no bearing on it's maximum temp.

 

[skunked]

The most common problem would be the radiator as mentioned already, too small or restricted.....

check the lower rad hose for a spring, it could be collapsing.

What's your timing look like?

Are you running a cat?

EFI or carbed? Could be a sign of lean condition.

 

[Fordum]

I pretty much agree with everyone else, but let me throw in one other idea. Check your fan belt. At highway RPMs, the water pump, and fan if you still have one, can put a lot of load on the belt. Low tension or glaze could cause it to slip. The best radiator and fans in the world will do no good if the water is not circulating right.

 

[diesel4me]

In rare cases sometimes the water pump impeller is made of stamped metal instead of cast iron,and will rot away,leaving only "nubs" instead of blades to pump the coolant...usually the result of long neglect and rust build up...this might only show up under higher rpms and speeds..

 

[rayfin]

If you fans were turning the wrong direction the airflow would slow the fans on freeway. Just saying. Are you pulling or pushing? If you were pushing air forward and the wind was blowing backwards...