1976 K-10 runs hot down the highway

[warlok1469]

I have a 1976 K-10 pickup. Just installed a 350, .030 over, appx 9 to 1 compression, around 300hp that a friend (and I) built and put in his truck, put on about 500 miles, then put in my truck. All is fine when running around town. Runs at 185 deg and stays there well. Yesterday I went down the freeway for about 20 miles and it slowly and gradually got hotter and hotter (up to 220 deg) and started to run ****ty till I got off the freeway. Then it went back down within a few miles to 185 deg. and was OK. Same thing on the way back home. I know these are good: thermostat, gauge (mech), cap, radiator is clear, new 50/50 mix coolant. I have a stock 2 row radiator and with the other engine I had (about 200hp, 8 to 1 comp 350) it ran hotter as well (up to about 195-200) on the freeway. All the guys I know with 4 rows have no problem. Should I try one with 4 rows or could this be something else?  

[73customC10]

i had that problem in my camaro so i throw 2 big eletric fans this should help. or if you dont need the heat take out the thermistate.

[VileZambonie]

Yes on the 4 row but check that Tstat again and make sure it's opening.

[1976Scottsdale]

160 thermostat instead.  Also, use a good 3 row or 4 row.

[warlok1469]

OK, I was wrong about one thing. The rad in it is a 3 row, not a 2 row and it looks perfectly clean and flows good. I boiled the thermostat and it started opening at 175 and was fully open at just over 180. I forgot to mention I also have a new fan clutch as well.
Is 1 more row on the radiator really going to make that much of a difference? I can't believe that it would make that much of a difference that it runs perfect at 185 everywhere then gradually goes that high on the freeway. I don't have the money to keep throwing at this and need it fixed.
Thanks

If you kill a man, you're a murderer.....kill many, and you're a conquerer..... kill them all,..... YOU'RE A God!!

[joesgarage71]

You have the right shroud on it right? Is the fan at least 3 inches from the radiator? The lower radiator hose might be collasping at higher speeds. Is there a spring in the hose? The three core should be good for your small block.Heck I have a three core in one of my big block trucks no problems.
Steve

[GMCTed]

I had the same problem as you, my suburban temp was fine around town but as soon as i got on the highway the temp would rise to 220+. i replaced the radiator thinking that it was clogged and replaced the thermostat and that didn`t help. a friend suggested that i change the water pump. without any other good explanation why it was running hot i changed the water pump and that was the problem.  

[warlok1469]

The lower hose doesn't have a spring in it. I guess I'll try a water pump, lower hose, and new thermostat. Thanks

If you kill a man, you're a murderer.....kill many, and you're a conquerer..... kill them all,..... YOU'RE A God!!

[warlok1469]

Well, now I have a new t-stat, t-stat housing, upper and lower hoses, heater core and hoses, water pump, and I tried my neighbors 4 row radiator. Still doing the same thing. I tried a 160, 180, and a 195 t-stat - nothing. No matter what I do, no fix. WHAT NOW????????????

If you kill a man, you're a murderer.....kill many, and you're a conquerer..... kill them all,..... YOU'RE A God!!

[Blazin]

You mention that this is a new motor. Are they the correct head gaskets, intake gaskets? Just a thought.  

[BILTUP]

How is the tune-up on the carb?  Running lean on the highway will heat it up.  How is the fuel pump, filter, lines?  You might have a fuel delivery issue which is leaning out the carb during long driving periods on the highway causing it to heat up as well.

[warlok1469]

All gaskets good. Carb is rebuilt (Carter AFB). I put a clear fuel filter that I can see between the gap of the hood to make sure I was getting proper fuel - stays full (Carter universal electric 5-7psi, 72gph pump).

Here's what I found today. I noticed that it had a slight (barely even noticable) miss/stumble at idle so I reved to 2k rpm and got worse and at 3k (where it is at 75mph) it was a really bad miss/stumble. I disconnected my vac. adv. and it went away at higher rpm so I checked my timing and it was up around 24 for some reason. I think my balancer ring may have spun. Anyway, I retarded it to 8 and it stumbled all over the place. After playing around a bit, with it set at about 15 deg. and the vac adv disconnected, it runs good through the RPM range (idle to 3500) So I tried it out on the highway and it still got hot but not as bad. About 8 miles got to 210deg. Also it sat at 195 for about 4 miles and then heated up more.
But when I pulled off the highway, I got out fast to see if there was anything was weird. Well, the cap must have vented and ran out the overflow. It's a new cap (330deg, 16psi) so I tried another one and the same thing. Why would it be venting?? And could this be the problem??

If you kill a man, you're a murderer.....kill many, and you're a conquerer..... kill them all,..... YOU'RE A God!!

Edited by: warlok1469  at: 3/7/07 7:53 pm

[Lt.Del]

Ok you tried everything.  I have a suggestion though,

If your catalytic converter, if you have one, gets clogged with carbon rust whatever, the back pressure of the exhaust will create serious heating issues.

Check out your exhaust???    

SgtDel
aka "Andy"

www.delbridge.net

1979 Big 10 383 stroker
1991 Blu 'Burb 3/4 ton 4x4

[warlok1469]

nope no cat. exhaust is free.

If you kill a man, you're a murderer.....kill many, and you're a conquerer..... kill them all,..... YOU'RE A God!!

[BILTUP]

You might have to go diggin back into that motor if you've tried and checked everything thrice!!  Be absolutly sure everything is the way it is supposed to be.