Overheating small block chevy

[Uncle Mike]

I have a 1966 Chevy pick up that I have rebuilt. I’m having an issue with towing a vintage travel trailer (24ft)up a steep grade. It has a completely rebuilt small block Chevy 350: HEI distributor set at 38 advanced without vacuum, 180 degree thermostat, sniper efi, auxiliary fan, transmission cooler and mechanical fan with shroud. It tows great but will get into the 230’s within a two mile steep incline. I’m wondering what I’m missing. It will tow fine on straight stretches. Any ideas would be appreciated! Pictures attached.
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[Steeveedee]

Nice truck! Do you have any pics of what it looks like under the hood?

[cwcarpenter98]

I love the truck and the camper! Great setup.

What size is your radiator? Is it a 2 core, 3 core, or 4 core?

On your shroud, is it sealed up well around the radiator?

Also, are you running the short water pump with the factory shroud or long water pump with factory shroud? The long water pump puts the fan too far into the factory shroud which could cause an issue.

[The Rocknrod]

Not so sure 220 when towing a trailer up hill is out of the norm. If your engine normally operates at 180° F - 190° F on a hot day, the coolant can get up to 200° F - 210° F. If you ran just water, you are pushing the boiling point. Any additional strain on the system (like getting stuck in traffic, passing a truck, going up a hill or towing) and the fluid will boil. Hence the need for a 50/50 coolant and raising the boiling point via a pressurized radiator cap (temps shown here - https://www.dewitts.com/blogs/news/1...g-should-i-use)
Like cwcarpenter98 said a fan clutch and stock shroud goes far. The Hayden #2947 fan clutch is the short version of the heavy duty fan clutch FYI. On a short water pump with the engine in the stock position (last two holes) it should put a nice 6 or 7 blade 18 inch fan in the right position in the fan shroud. Assuming you have a quality radiator of course (read more on the types of cores available here - https://usradiator.com/cores )

[Uncle Mike]

I will get some pictures tonight of the motor. At the auto swap meet in Portland as of this moment. I have a shroud on it with a 18 inch fixed fan. I checked factory specs and have it’s centered appropriately in the stock shroud. It does have a 50/50 mix with a four core radiator that is brand new. I can open up the cap and see coolant flowing when the thermostat opens up. The temperature here about sixty degrees when running these tests.
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[Steeveedee]

GENERALLY, heating at speed is due to coolant flow, and idling due to lack of air flow. My truck was running hot at idle and on the highway. After chasing my tail for awhile, I discovered that the standard thermostat didn't allow enough flow. I installed a high flow thermostat and the heating problem was solved.

I have a big block 400 and it would get up to 260º pulling a grade with the travel trailer. That won't kill a big block, but it isn't doing it any favors, either.

[Uncle Mike]

Here are some pictures of the motor. I didn’t realize I’ll hat there were different types of thermostats besides their temperature range. I’ve used various Napa thermostats including me adding a high flow water pump thinking that was the issue.
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[Uncle Mike]

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[The Rocknrod]

That looks like a long water pump, a pic of the fan in the shroud would tell a lot. I'm not sure how you wouldn't get 220 towing that trailer up a grade.

[MT65]

What type of mechanical fan…4 blade, auxiliary fan in front of radiator, transmission cooler in radiator or stand alone cooler?…
If using the radiator for transmission cooler, you are throwing that much more heat to your cooling system, personally I never use a radiator transmission cooler, there are many good stand alone coolers made, that makes the radiator only cooling the engine, not both. It too has to have good air flow.
The aforementioned high flow thermostat is a huge plus, they are not created equally, originally designed to let the motor warm up faster and then to slow the coolant down to absorb more heat in the engine and get rid of it in the radiator, think restrictor…its all a balance of flow, both air and coolant…ever wonder why the manufacturer started putting 4 corner water ports in the manifold,ask an old circle track racer….

[Uncle Mike]

Here a picture of the fan mounted in the shroud. Its got maybe a 1/8 inch outside of the shroud. I have a four blade 18” fixed fan on it. I have a pusher fan mounted on the front of the radiator in the core support. I only turn it on when I’m halfway up the hill and noticing that I’m overheating. I also have the transmission lines going through the cooler and the radiator. I can’t remember the size of the cooler but I picked one that was midsize for aftermarket applications. Are there any recommendations for a specific high flow thermostat? I know my efi requires at least a 180 degree one. Thanks guys for all the ideas!
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[Steeveedee]

I bought my 180 thermostat from NAPA. Don't worry about the search terms, that thermostat fits from ~1940 into the '80s.

https://www.napaonline.com/en/p/BK_8...&gclsrc=aw.ds&

[Desert dog]

Could it be timing? 38 degrees seems a bit much for an SBC, especially pulling a load.

[Bushman66]

Try running a 7 blade fixed fan (w/fan clutch), it pushes a LOT more air than the 4 blade fans, I snagged one and with the factory shroud, here in AZ, won't over heat even in traffic on a 115 degree day. Classic Industries has them p/n 3947772, but you can find a used one off a 67-79 truck with heavy duty cooling for about $25 in a wrecking yard.

Also agree with the comment that 38 degrees total timing seems a little excessive, especially for a tow vehicle. I'd back it down between 32-36 and try that...

[mikie 1954]

I had a 64 with a 327 that had a four blade fan that would over heat like yours , put on a 8 blade on it and problem solved. I could be wrong but isn't the fain supposed to be about half way in/ out of the shroud ?

[Steeveedee]

It looks like he has a 7-blade "baloney slicer" on there, atm. Lack of coupling due to the fan being too far in would show up as running hot at idle.

[urmyboyblue]

Are you sure the electric fan is pushing and not pulling? If the fans are fighting each other, it isn’t helping. Also go to a 160 degree thermostat will help as well as a thermostat controller on the electric fan.

[MikeN]

At 35-40mph or more, you don't even need a fan, the air is coming through the grille and radiator already. I don't think 38* timing is too much, but I would definitely add vacuum advance if you don't have it already. I would also look at carb tuning - you may be running lean under a heavy load.

[MikeN]

Can't see what type of carb that is, but try running it a little richer. Not with the idle mixture screws, but with power valve, main jets, or metering rods.

[SkinnyG]

If it's overheating when working at speed, I'd look at inadequate radiator, plugged (internally or externally) radiator. Possibly leaky headgaskets - there is a dye you can use to confirm that.

[The Rocknrod]

Originally Posted by SkinnyG

If it's overheating when working at speed, I'd look at inadequate radiator, plugged (internally or externally) radiator. . .

One reason I dont use an electric fan in front of the radiator.

[Uncle Mike]

I want to thank everybody for the input. I just got a high flow thermostat and will be trying that in the upcoming week. I have a brand new radiator in it. I know that doesn’t mean it works but I can see good coolant flow when I look in the radiator cap. I have 38 degrees and do have it hooked up for vacuum advance. I also have a Holley sniper efi unit so I can’t make it run richer without going deep into the tuning spectrum. I’m usually only turning on the electric fan if it hits 220. I know for that reason my cooling system isn’t adequate at the moment. I’ll even turn it on early and not see a noticeable difference.
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[Uncle Mike]

Well tried it with a high flow thermostat. It didn’t fix the issue. Almost 75 degrees here today and I hit 240 on top of the hill. Started at 180 at the bottom of the three mile hill.
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[Steeveedee]

I still think that is a coolant flow issue. It is extremely rare, but take a look at your upper hose and verify that it hasn't collapsed. You can feel along the hose for "soft" areas. I've only seen this once. The hose separates like a tire tread and coolant gets in between the inner and outer hose sections and restricts the flow. Also verify that when you rev it up that the lower hose doesn't collapse. It should be warmed up and the system pressurized for the lower hose check.

[val1gonzales]

You mentioned you'd installed a high flow water pump, have you checked to see if the lower radiator hose isn't collapsing from the water pump sucking the water into the engine. There's a spring inside the lower radiator hose that is there to prevent that from happening. Might need to check it. No spring, damaged or crushed spring could be collapsing when you're engine is in high rpms. Might have someone rev it while you watch the hose. Possibly even debris along spring and hose. Squeeze the hose by hand, not when hot, and it shouldn't go completely flat. Or, if it been a long time since changed just get a new one. I like Gates brand hoses are the best. Going old school here but you can also take out the thermostat to keep the water circulating and cooling all the time. Then reinstall it in the winter for the heater.