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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.
Tramp

What modifications have been made to the engine that it requires more coolant than a normal 350?

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.
Jerry

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.

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.

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.

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.

Mark

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.

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.

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.
Tramp

Look at the blade angle on your fan. It's supposed to PULL air through the radiator as it turns, not push it. A reverse rotation water pump will try to flow coolant the wrong direction if the serpentine belt is mis-routed, also, even if the fan blades happen to be angled correctly. I have an idea the direction of rotation of your fan and/or water pump is the problem.
Jerry

“4 1/2” from the radiator “ is not good for optimal cooling. You also may have a air bubble in the system. Coolant should be only about 1/2 inch above the fins in the radiator. As HRL said, find out if your water pump is rotating the right way. Fill the system properly and add a properly spaced fan shroud. Start the engine and hold a piece of tissue paper to the front of the radiator. If it sucks tight to the radiator when the engine is reved up the fan (not necessarily the water pump) is rotating correctly. Good luck.

Howdy Rowdy,
The fan is pulling air through the core and back towards the firewall.
I'll have to do some homework to find out what's going on with the water pump. I appreciate all the help, and will let you know what happens.
Tramp

Your comment about the serpentine belt system gives me pause.

V-belt drives have the crank and water pump (all of the pulleys, actually) turning the same direction. As a general rule, serpentine belt systems will have the crank and water pump turn opposite directions to get more wrap on the crank due to the added force on the belt.

If you didn't change the water pump for the serpentine drive, that could be your problem right there.

Tramp, that symptom of repeated spiking temperature then dropping seems exactly like mine before I added the external bypass to the water pump. The stat opens then allows a batch of cold water to enter the motor then it closes and repeats. When it closes without the bypass, hot spots develop before the stat opens again causing the temp gage to show the spike of temperature. You have to have an external bypass if the passenger side cylinder head does not have it built in. If your water pump was rotating the wrong direction I don't think the temperature would drop back to 180 when it over heats.

Mark

A water pump rotating backwards will severely restrict circulation, but won't make it flow backwards. A centrifugal pump like water pumps will still pump in the right direction, but flowrate will be WAY reduced. And if the vanes are straight and radial to the shaft, they can run either direction and won't restrict the flow as much as angled vanes.

Tramp Seems like with that much space ahead of your fan that the aluminum radiator people could produce a core thick enough to solve your problem. Once on a 421 Pontiac we just barely caught the fact that mice had put a nest in the block water jacket mostly over a weekend !! Any chance that could be your trouble ??

I've done some homework, and found that the water pump is turning in the right direction.
If I were to have a new radiator built, there is definitely enough room to make it plenty thicker, thereby increasing the coolant capacity.
59 talks about adding an external bypass to the water pump, and I'll have to do some more homework to better understand that possibility. What he said is how it's acting.
Also, all of the sites that talk about coolant capacity say the 350 needs 17 quarts, which would include the block and heater core to fill. The 348 and 409 call for 23 quarts. I'm thinking of draining the coolant that is in the truck now and measuring to make sure just how much coolant it does have. I know when I flushed and refilled it this last time, it took one gallon of antifreeze and just over another gallon of distilled water to bring it up about an inch above the core. I also installed a new pressure cap 13#.
Having a new radiator built can be done here locally, but it would cost me $800 or more.
Again, I appreciate all the help. You can be certain I'll be doing the happy dance in my skivvies in front of the post office, and take an hour to draw a crowd when this gets straightened out.

Instead of having a custom one built, try one of these? Champion Radiators [championradiators.com]

Also, the bypass is that 90* hose that goes from the top of your water pump to a port below the thermostat.

If you think that bypass might be the problem, try driving with the heater on max heat. You don't need the fan on, just coolant flowing through the heater. The heater circuit will act as a bypass and if your temp is more stable, then you have found the problem.

Mark

Mark I'm going to take the truck out today and hopefully that will be the issue. Now that I think of it, the high temps came on when I pushed the Thrift Air off on the way to town.
Here's hoping.
Tramp

Tramp Wish you could use a big bolt radiator,my 51 6400 runs cool at 185 degrees even in this 95 degree heat. just use 50/50 in it. Even in a slow moving parade,in the cold my round heater core wants to seep but I hate to gunk it up with stop leak. So may have to bight the bullet and buy a core from Carter's

An old timer once suggested to me to drill an 1/8 inch hole in the thermostat to keep air lock from happening in the block.
In no way am I suggesting this will fix your issue.......

Have you tried a different therm. It seems like half the therm. I used to get were defective.
Like Wrangler says itsa good idea to drill a small hole in it. I can't imagine why you need a bypass. I have worked on cars & trucks with SBC engines for many years & never had an external bypass.
The aluminum radiator from Champion is a good idea.

George

I've never seen a small block with an extra bypass hose, just circulates through the heater. The big blocks had the bypass hose, so did my 6.5 Detroit Diesel.

Here's one.

I had the same problem on my small block with the vortec heads until I added the bypass. I couldn't use the little 90 degree hose and fittings because I already had plumbed the heater into the top of the water pump. The problem has to do with the iron vortec heads that were used on late 90's trucks that requires the bypass. Some used the heater coolant circulation for the bypass because the heater control valve bypassed back to the water pump when the heater coolant flow was closed off.

I think Tramp did his happy dance when he fixed the problem.

Mark

I had only one Vortec small block, that was a '98 4.3 in a half ton, all stock, so I'm not qualified on them. Prior to that were all '70's and '80's 350's and 454's. I tend to keep things as stock as possible and have not had overheating issues so the bypass mod was not in my sights. With my '57 283, I added an overflow bottle so I can keep the cooling system free of air, it does what I want.