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#1457573 Tue Jul 05 2022 06:12 PM
Joined: Feb 2007
Posts: 470
Tramp Offline OP
So here's what I'm dealing with.
I've got a 64 long bed step side with an 87' suspension, 91' T5, and a 98' 350.
When I installed the SBC, I had the radiator rebuilt, using the original tanks with a new 3 row core. I've tried everything I know to get the temps to stay down, and recently found that the 350 needs at least 4.5 - 5 gallons to stay cool, and my radiator now has a capacity of barely 2.5.
When I do my searching for a replacement, nothing with the capacity I need, has the correct dimensions for a direct fit, even when it says for a V8.
Any thoughts on this? Appreciate the advice.

dj durant

1964 Chevrolet C-10 Pickup Truck
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Tramp #1457578 Tue Jul 05 2022 06:40 PM
Joined: Apr 2005
Posts: 11,560
“Grease Monkey” “Former herder of cats”
What modifications have been made to the engine that it requires more coolant than a normal 350?

'62 Chevy C-10 Stepside Shortbed (Restomod in progress)
'47 Chevy 3100 5 Window (long term project)
‘65 Chevy Biscayne 4dr 230 I-6 one owner (I’m #2) “Emily”
‘39 Dodge Businessmans Coupe “Clarence”

"I fought the law and the law won" now I are a retired one!
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Tramp #1457582 Tue Jul 05 2022 07:07 PM
Joined: Feb 2004
Posts: 26,328
Kettle Custodian (pot stirrer)
What temperature are you trying to maintain? Unless boiling coolant is overpowering the pressure cap and spewing out of the overflow, the engine IS NOT overheating. A 15 pound radiator cap will keep the coolant liquid up to 257 degrees F., and I seriously doubt you're running that hot unless there's something very wrong with the engine like a cracked head or a blown head gasket. Is the fan and the water pump turning the right direction? Most engines that came from the factory with a serpentine belt system use a reverse rotation fan and water pump. Normal temp can be a minimum of what the thermostat opening point is, to 20-30 degrees or more above thermostat temp when idling in slow traffic, or running air conditioning, etc. It looks like you might be chasing a nonexistent problem. A 350 engine block and cylinder heads alone has a coolant capacity of well over 2 gallons, almost 3, not counting the volume in the radiator.

I have solved real overheating problems, not imaginary ones, during trailer towing with my 59 Suburban, by installing a cross flow radiator specified for a 454 motorhome engine, and making it fit the radiator support.

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Tramp #1457770 Thu Jul 07 2022 02:04 AM
Joined: Feb 2000
Posts: 4,652
First off, how long has been over heating?
How long have you been chasing this problem?
What type of fan are you using?
Is the water pump correct for the direction of rotation?
Are the pulleys sized right where the water pump spins faster then the crankshaft?
Whats in front of the radiator?
What type of temp gauge are you using and have you verified it's accuracy?
What does the temp do at idle, low MPH, and HIGHWAY speeds?

More coolant doesn't effect the way it heats up or cools off, as long both radiator and engine are full with no air pockets, more coolant will not help or hurt. More coolant takes long to heat up and cool off, but it won't effect anything once the system is at operating temperature.

Tramp #1457775 Thu Jul 07 2022 02:29 AM
Joined: Mar 2010
Posts: 10,575
How far is the fan away from the radiator?
If you have a serpentine belt system, you need a reverse flow water pump and a left-handed fan. You probably already know that. I did too, but 'knowing' doesn't always help. smile

Tramp #1457782 Thu Jul 07 2022 03:18 AM
Joined: Oct 2005
Posts: 3,907
"Hey! I sound like Darth Vader!!
Originally Posted by Tramp
.....and recently found that the 350 needs at least 4.5 - 5 gallons to stay cool, and my radiator now has a capacity of barely 2.5.

Would like to know where that number came from. My bone stock '98 C3500 7.4L only takes 2 gallons and some change.

I'd start with, what do you consider over heating? A '98 5.7L was designed to run at somewhere around 220 degrees all day long.

Last time I accidently put in a wrong rotation water pump, I ran cool at idle and saw the temp rise like crazy at highway speed.

Tramp #1457796 Thu Jul 07 2022 04:30 AM
Joined: May 2005
Posts: 289
I will add a couple more to the list. Some head/block combinations require an external bypass for the coolant. Temps will fluctuate wildly if you don't have that bypass. Also, be sure your fan has a good fitting shroud with about half of each fan blade inside the shroud. That makes a huge difference.


Tramp #1458462 Tue Jul 12 2022 02:28 AM
Joined: Dec 2018
Posts: 2,491
Tramp Is your water pump turning the right way ?? Clear back in 1967 I made my own cross flow from junkyard radiator. It handled a 2x4 283 summer and winter. I can't think other sbc's are any harder to cool.

Tramp #1458598 Wed Jul 13 2022 03:33 AM
Joined: Jul 2014
Posts: 489
I picked up a mis-boxed flexi fan for my rig one time. It was fine up to about 30 MPH then the temp started to rise. I was standing in front with the hood open scratching my head when the thermostat opened and it began blowing hot air at me. I took the fan and box back to the Auto Parts store and they determined that it was mis-boxed and was reverse rotation. It was a perplexing day.

51 3800 PU, 62 261 (w/cam, Fenton headers, 2 carbs, MSD ign.), SM420 & Brown-Lipe 6231A 3spd aux. trans, stock axles & brakes. Owned since 1971.
Tramp #1458950 Sat Jul 16 2022 03:18 PM
Joined: Feb 2007
Posts: 470
Tramp Offline OP
Hey all! Thanks for the help and I apologize for not getting online sooner.
I've talked with my cousin about the heating issue, and he's a pretty good wrench. He has a 40' Ford P/U with the flathead, built up from a 53' Merc, and had some issues with high temps also. It took several different fans before he got a handle on it. I did the Google thing, and that is where I got the coolant info. There's nothing in front of the radiator, as it's mounted just as it was when I had the 230 in it. No A/C.(yet) and all new gauges(new dash). Until just recently, it would warm up to 180' and creep up to 200' and then back down. I flushed the radiator recently and put in new antifreeze. Now, if I run to town, about 5 miles, it'll get to 220' or better real easily, and then come back to180', and then climb back up rather quickly. I'm running a serpentine belt setup and the belts and pulleys are turning clockwise. Not sure about the water pump being reversed. I ran this truck all the way from central Kansas, pulling a U haul car trailer with a 38' Chevrolet on it without any problems, and now this. I don't have a shroud on it yet, and understand that it needs one as the fan is nearly 4.5 " from the face of the radiator. Being built as you're reading this. A/C is planned for later this year, and I'd like to have this figured out before adding the additional demand on the radiator.
It's just an engine, built by men, and sooner or later it'll get figured out. Until then, I'm going to need to up the dosage on my meds to keep from boiling over like the truck.
Thanks for the help.
Keep on keeping on.

dj durant

1964 Chevrolet C-10 Pickup Truck
In the Stovebolt Gallery
More pix on Flickr
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