Thread: help input!!! sbc just getting hot when driven over 30 mins.!!!!

Tweet

hey guys I have a '69 sbc 327 w/ 2.02 heads 74cc . the piston are .40 over flat tops ; so the compression is about 8.8 :1. ; trans is a turbo 400, rearend is 3.73 gears, radiator is a brass/copper 4 row hd from walker. have a mech fan, with shroud
also a elec. pusher in front. the timing is 13 btdc total timing is 34 @ 2900 rpms
the problem:...
when I am just cruise around the engine will stay around 180, I can leave it in park & the truck can idle all day & not get hot.
but when i am driveing it down the road @ 60mph or faster the temp slowly starts going up & would go to the point of over heating, but when I slow down to 30mph the temp will drop all the way back down to 180 in less than 5 min? I have replaced the termostats, water pump no change. am I possibly running to much intial timing? (I do not know the cam specs, but the engine has a lope idle)should I retard it to 10 btdc?
does this sound like a timing problem? any help would be appreciated

I don’t know about the timing, and cam but it doesn’t seem like it should run hotter while moving and bringing in fresh air. I had a 40 Chevy coupe 350 dual quads, mild cam just the opposite, idle in traffic it would over heat. I would have to pull off the to the side of the road let it cool down, run it 70 or 80 it was fine but when traffic would slow it would over heat. I had a new 4 row radiator installed and a heat shield, I think it was my engine was sitting too low and the air was going across to much of the top part of the engine the reason I say this is I also had a 41 Chevy 350 the engine set higher and it ran according to the thermostat. Just a thought maybe your gage is off!!!

Someone should be able to help. Where is Denny, he could tell you?

Richard

Sounds to me like the pusher fan is blocking air flow at highway speeds. You should have plenty capacity without it. Consider taking it out and give her a whirl.

Kitz

Ditto to Jon's comment.

Sounds dumb, but check your fan. Be sure it isn't turning the wrong way! A newer fan off a reverse rotation pump will act like yours is, turning faster and fighting the natural air flow at speed. Or even could be the pump turning backwards!

Pope may be on to something to check....I changed one of my trucks to serpentine...went to Chevy and bought a reverse water pump and put it on....the thing would idle for hours here in Tucson with no problem. It would run at low speeds with no problem. But, at about 50mph, it got hotter than a dickens. I tried everything...one day I was leaning over the grille looking at what to do next and realized that the air was blowing out the grille, not being pulled in. I had reused the old fan....wrong direction. Sitting still, the air thru the radiator was going the wrong way but it still worked....going down the road, the fan was trying to push the air forward and the ram effect was pushing against the fan. Simple stuff, big pain.

hay there hr57 have you gone back to bacics how old and what condirion is the radiator sounds like it may be partialy pluged also does it have the ca pacity to do the job a combination of old radiator and marginal capacity has plaged us hot roders for years have a good radiator shop check it it like chicken soup it cant hurt good luck ted I KNOW ALL THE RULES AN I KNOW HOW TO BREAK EM

I agree on the pusher fan, particularly if it has a shroud. The shroud blocks part of the airflow to the radiator. It does not sound like a timing problem.

have you checked to make sure the bottom radiator hose can not collapse at higher rpm the water pump can create enough suction to collapse a hose.many bottom rad hoses have a spring in them to prevent this.you may be able to see this if you rev up the engine and watch the bottom hose for any sign of collapsing.good luck and keep us posted

Originally Posted by wrenchinrick

have you checked to make sure the bottom radiator hose can not collapse at higher rpm the water pump can create enough suction to collapse a hose.many bottom rad hoses have a spring in them to prevent this.you may be able to see this if you rev up the engine and watch the bottom hose for any sign of collapsing.good luck and keep us posted

you were on the money, had someone rev the engine & hold it a 3,500 rpm , & bottom hose collapses nhalf way, going to swap it out this weekend

I hope this solves your problem good luck

just a note if this doesnt solve your problem.I would start by having the radiator checked on a flowmeter at a radiator shop for being partialy plugged as was suggested in the earlier thread . a quick and cheap way to know for sure.alot cheaper than a cooked motor

There's also a differance between a (non a\c) water pump and a (a\c) pump, one flows more then the other. can't remember which flows more, sorry.
Dave