runs hot at highway speeds
 

I have or rather my son has a 78 camaro with a stock crate 350 in it with 350 turbo trans. He was headed up 75 and the temp gauge climbed to about 240 to 250 degrees. He got off at the nearest exit and checked the water level and had to add some. When he took off again the temp dropped down but climbed up again when getting up to speed on the highway. He say the temp is ok driving around town but runs hot out on the highway.

I was looking for some tips on troubleshooting this.

first could it be a bad water pump and or the clutch fan is weak?

sounds like a bad clutch fan. exactly the reason i made the switch to an electric set up

There may be adequate airflow at highway speeds even if the fan is crapping out.

Maybe the motor is leaning out? Plugged fuel line and/or filter(s)?

A few things that can cause overheating problems at freeway speeds are: colapsing radiator hose, restricted radiator (corrision in the tubes most often), partial stuck t-stat, air in the cooling system, blown head gasket (lets air into the cooling system), also debris in the radiator fins (leaves, dirt etc) can limit airflow, a bad radiator cap that cant hold pressure.

Basicly you need to look real close at the cooling system and start checking things out.

now that i think about it i had the same problem when my radiator was crapping out. aside from being a small 2 core, it was old. replaced it with a nice aluminum 3 core and ive never overheated again. id say maybe try and flush the radiator first.

I think I will try a flush first. I never pulled the radiator in that car. It had a good motor no coolant leaks so never touched it.

try a flush and clean the rad fins of any debris check pump for proper operation at high rpm's. Check your mixture maybe to lean and check timing and make sure its not to far advanced. I seen exhaust glow form mixture and or timing issues. Things may run hotter with the steady rpm highway cruising.
Good luck!.

Ps. make sure a hose is not collapsing like the bottom hose... Its supposed to have a steel spring/sleeve... Not sure what its called but its to keep the hose from collapsing.

Never mind dont touch your timing but id still check to see if you may be running lean.

Have the radiator cap and cooling system pressure checked. THEE most overlooked overheating problem is the radiator cap!

+1

+1, if the pressure isn't an issue, look to the radiator. Mine was doing this last year, it would very gradually heat up, and heat up even faster on the highway, and would never go down until i shut the car off. Ended up putting in a new radiator and it fixed the issue. My old stock one was getting gummed up with deposits, not allowing the water pump to flow the water through to cool.

back flush systems are pretty cheap and very easy to install!!

I do not have the spring that goes in the lower hose. Do you still them in?

Yes you do need the spring in the lower hose.

Michael

My brother in law has a Weiand water pump on his Chevelle. When he raced his temp would shoot up to the sky on the big end. He told me he didn't know what was causing it. We let the car cool down, then started checking. I had him start the car and he whapped the throttle. The lower hose was completely collapsing because of the high volume water pump. He has since installed a spring and now no issues.