im so lost i almost wanna cry :(

[WOLFMANmike]

SBC 350 stock accept for intake headers and carb ... the truck started to have over heating problems so i spent money i dident have to spend and bought a new cooling system brand new 3 row aluminum radiator and electric fan and shroud ... brand new high vol water pump new thermostat . new hoses and still gets hot ... now heres the kicker even on the hottest day we have had if you drive around town it cools perfect at 160 to 180 .. but start to cruise at speed on the freeway at 2900 rpms and climb a slight incline 230 deg .. set timing nothing no change new fuel lines no change .. then rebuilt a different carb and still no change under a load it gets hot .. im ripping out my hair

[LT1 Burb]

Is your fan going the right direction, and is it a puller and not pusher fan. The way I see it is the air at speeds is not going properly through the radiator, or if it's an auto the tranny is adding heat to the rad.

[66Gilbert]

Is the engine block the original bore or have the cylinders been bored?

[scuderia]

Head gasket leak? I'd do a pressure test...

[WOLFMANmike]

Originally Posted by scuderia

Head gasket leak? I'd do a pressure test...

i thought about the head gasket but ive got no water useage no steam in the pipes and no milky water ... it has never boiled over either ... as for the fan going the right way yes infact when i pull ove on the side of the freeway the front of the rad is very cool ... i sware its like a lean condition or timing . but its all been checked and its dead on ... as for the engine bore i think its stock . but here is the thing if it was over bore then it would have been a over heating problem right from the start .. not something that came into play later on meaning i was driving the truck for almost a year with no probs .. im assuming that if it were say air pockets in the system it would not only be at cruise speeds

[Slow Build]

It could be your lower radiator hose collapsing. I was just reading the C/10 Builders Guide (Summer 2015) and in the tips section (page 126) tip number 13 is to put an anti-collapse spring in the lower rad hose. The last line of the tip reads "If your experiencing overheating on the open highway but not in traffic, install this spring". If that's your problem it's an easy fix.

[geezer#99]

You need to get the air going thru the rad at highway speed.
You need to create a low pressure area behind and below the rad.
Easiest way to do that is install an airdam directly beneath the rad.
That will create a low pressure area so the air has somewhere to flow to.
You make one from a piece of plexiglass or find one from another truck you can modify to fit. You might need to use one that bolts under the front bumper like on the 73-87 trucks.

[AcampoDave]

I'm wondering if you have all the factory air control sheet metal in place. I.e baffles etc. Can you post some pics of your set-up?

[PGSigns]

I sounds like it may be lean at the 2900. What carb are you running? How big and air cleaner do you have on it?
Jimmy

[vince1]

I think Slow Build might have the answer. Just squeeze on the lower hose. If you can squeeze it together it doesn't have a spring inside.

[vince1]

Another thing you could try is take out the thermostat and run a garden hose into the lower rad hose to see how fast it comes out the top. Maybe there is an internal blockage.

[Brad54]

Try replacing your fuel pump.
A weak or failed pump will cause this problem. Had it on my '61 coming home one time. The spring broke and the arm pivot came out the side of the pump, so there was no fuel pump.
An engine will create enough vacuum to draw fuel through the lines and through the carb. It would start and idle just fine, but at speed at lower RPM, it started to stutter out like it was running out of fuel.
However, if I kept the RPM up (driving in 3rd gear, 1:1, rather than 4th OD .72:1), it ran just fine--but hot. Because it was running lean.
It was getting enough fuel to run, but it was running real lean.
At idle, the glass fuel filter I installed was full, which really made the final diagnosis difficult.
The pump arm's pivot was actually hanging out the side of the pump, which let me figure it out.

(I ended up using a zip tie to close off the secondaries on the 4bbl, so it was creating more vacuum through the primaries, and drove 180 miles home with a zip tie for a fuel pump)

Also, double check and make sure that fan is right. The blades need to be oriented so they the leading edge is digging into the air behind the radiator and pushing the air to the engine--leading edge closer to radiator, trailing edge close to engine.

But my guess is, fuel pump.

-Brad

[T and S]

X 10 on the spring in the lower hose. Sounds like with the mods u made u may be sucking it shut. If it does have a spring, I would remove the hose and make sure the spring is in good shape, not broken or anything. This is one of those things u can check / do for free or very little money.

[scuderia]

not sure if this is available to you but if you can get the truck on a dyno you can simulate the freeway and see if there's anything obvious going on...

[61K10]

is your e-fan on all the time? turn it off going down the hwy and see what happens. friend had the same problem-metal shroud-e-fan and the combo was restricting the air through the rad at hi speeds. just a thought.

[jtrichard]

Do you have the right combination of water pump and belt system? A friend bought a camper and cooled fine around town took it out on the freeway and the temp just started to climb .......Come to find out PO had the water pump replaced and they had put a "V" belt pump on a Serpentine belt drive truck

[Monte's62]

I think slow build has your answer. I had the same problem on an old nova one time. When the engine was revved to a certain rpm you could see the hose collapse. She only ran hot at highway speeds. Installed a new hose with spring and she ran perfect.

[padresag]

Originally Posted by WOLFMANmike

SBC 350 stock accept for intake headers and carb ... the truck started to have over heating problems so i spent money i dident have to spend and bought a new cooling system brand new 3 row aluminum radiator and electric fan and shroud ... brand new high vol water pump new thermostat . new hoses and still gets hot ... now heres the kicker even on the hottest day we have had if you drive around town it cools perfect at 160 to 180 .. but start to cruise at speed on the freeway at 2900 rpms and climb a slight incline 230 deg .. set timing nothing no change new fuel lines no change .. then rebuilt a different carb and still no change under a load it gets hot .. im ripping out my hair

how many lb pressure cap are you running and are you using anti-freeze?
ron

[MARTYZ]

Hot engine and cool radiator is circulation issue, SlowBuild is on right track

[BigDan3131]

Try turning off the fan on the freeway, at speeds over 40 you shouldn't need it on. What gauges are you using? It could be a bad gauge or sending unit too.

[Hollow65]

My electric fan comes on when the engine is over 160*. no over heat here, single 16" with no shroud. Check that hose Mike.

[WOLFMANmike]

hey guys just wanted to say thank you so much for helping me with all your ideas and such .. this is what makes this board so great . is that people take the time out of their busy days to help another person out .. and the info one here aka all of your ideas are always spot on ...i love this board and all of the people like your self that make it the best damn chevy truck board on the internet ... that being said the problem was the lower radiator hose . it was closing off at higher speeds or RPMS until this was was mentioned i never would have thought this would be a issue and even with a new hose but it was ... now she ran on a hill climb now hotter than 195 today ... but fix one issue and another will pop up lol i rebuilt my Edelbrock 1406 carb new everything inside it but if i floor it and open the secondaries runs hard and pulls strong . but after letting off the throttle she gets a nasty ruff shaking idle and almost wants to die idle drops way to low and runs ruff . park it shut it off . come back out and start it up and its fine as long as you dont floor it again so back to the drawing board again lol

[geezer#99]

Great you figured it out, but now it's your turn to take some time.
Where'd you get the coil for the hose?
Did you buy or make one?

[WOLFMANmike]

Oh sorry lol no I went to Auto zone and bought the hose .. they called it a universal lower hose .it's one of those ugly lumpy hoses you have seen before I'm sure but it's lumpy because it's built with a spring in it . Most people use them on the top mostly for easy bending