[Squidward]

Nylon fan and a 1" spacer are on the way.

Looking around my junk today. Found a little used 19" 7 blade fan from a 75 Chevy truck mounted on a fairly tight clutch. I might try that too for more comparison data. It's only 4 bolts and some bloody knuckles, right?

[Speargun]

I've chased cooling issues on my '67 Firebird over the years and have spent lots of money on fans, radiators, snake oil coolant, etc... and what I've learned boils down to this:

Large clutch fan & shroud* > SPAL electric fans > any chicom electric fan.
*(Although modern PWM brushless fans have pretty much caught up and may be the best choice)

Straight water is the best coolant, but you need an additive to prevent corrosion & lube the water pump.

The faster the water can flow, the better it will cool. I.e. No thermostat > thermostat > restrictor.
(The science behind it: heat transfer coefficient)

Here's a post I made a while back on cooling with a little more detail.

The Ultimate Cooling Thread

[RocktimusPryme]

2nd only to general cobbling, which is a problem on all old cars, I think the biggest problems is almost all of the 60s/early 70s era cars are under radiated from a size perspective. Which is why cooling is often an issue.

Per Cold Case a first gen F-body "Big Block" radiator has core measurements of 16.85 x 23 for a total frontal area of 387.55.

By comparison your basic run of the mill 5.3 99-2012 Silverado radiator from Cold Case is 17.25 x34 for a total area of 586.5 inches. By percentage of change, that's 51%

Thats a giant difference. And its reflective of sizes available for most of those common 60s cars. We talk about all the fan solutions etc, but if you just have more cooling area its going to solve most of your problems. Unfortuately that's easier said than done.

I disagree that a big clutch fan is the best solution. And I say that as someone who runs that setup. A well engineered electric fan setup is better. There really isn't an argument. Most peoples cooling issues with old cars are at idle and that's where the electric shines because its not RPM dependant. Plus less parasitic loss ETC.

Now I do agree that if we were to graph this out, the big clutch fan would probably be the equilibrium point where ease/value meets an effectiveness line. So I would also recommend the setup to most people, but I don't think the statement that it is the best is correct.

[Sirrotica]

Many things factor into cooling system efficiency, and not everything that solves one persons problem will necessarily solve someone else's problem. All the pieces have to be put together to form a system.

The first gen birds do have a limited frontal area same as the 67 GTOs did. In 68 GM widened the frame horn area to allow a larger frontal area for the radiator on A bodies, but F bodies didn't get a redesigned subframe until 70.

The narrow crossflow radiator did one other thing beside have vastly smaller frontal area, the small radiator also reduced the cooling system capacity. One of the things I learned when trying to make my oval track cars run cooler is additional capacity also helps. Ford used to use the reservoir expansion tanks in their systems as it added more capacity to the system.

GM/Detroit diesel 6.5 engines had problems with O/H usually pulling a load on long grades. Lots of warranty dollars got spent by GM because of the marginal cooling systems in those trucks.

The engineers made several modifications to the later truck engines to address the marginal cooling systems. Redesign the clutch fan to come on at a lower temp, and lock up more positively. A water pump impeller redesign to deliver approximately 40% more coolant, dubbed the HO pump. In conjunction with the water pump improvement they made a dual thermostat water crossover to allow the redesigned pump to not be restricted at the thermostat housing. These changes made a lot of difference in the cooling efficiency. Many of those changes on the 6.5 carried over to the 6.6 Dura-Max engines.

Picture of dual thermostat 6.5 water crossover:



Another thing is the whole cooling system in these 50 plus YO engines and cars have crud and sediment in them, that may or may not get addressed during restorations. Some of these cars are still using the OEM engines the car was built with. Lots of variables in every car/engine combination.

Chrysler had their K cars with 1.7 VW engines in them with a iron block, an aluminum cylinder head, and a brass radiator. Back in the 70s the cars would O/H on the highway due to the corrosion combination of these 3 metals in the cooling systems the radiators would scale on the inside effectively insulating the heat rejection of the radiator. It took place in under 5 years and around 40,000 miles.

Lots of old wives tales on the physics of how an engine cooling system works add to confusion when troubleshooting cooling system problems.

Lots of things that most people haven't a clue about that take place under the right conditions in older cars, any combination of some of these things can make you tear your hair out trying to solve an O/H problem.

[Squidward]

Originally Posted by RocktimusPryme

Per Cold Case a first gen F-body "Big Block" radiator has core measurements of 16.85 x 23 for a total frontal area of 387.55.

By comparison your basic run of the mill 5.3 99-2012 Silverado radiator from Cold Case is 17.25 x34 for a total area of 586.5 inches. By percentage of change, that's 51%

HaHa! My Sierra had a 28" wide core, which was MOSTLY adequate, until I went to a 34" HD sized core. It's a 2004. In 2005 GM went to a dual electric and never turned back. Hmm....

[Speargun]

Originally Posted by RocktimusPryme

...I think the biggest problems is almost all of the 60s/early 70s era cars are under radiated from a size perspective. Which is why cooling is often an issue.
.........
I disagree that a big clutch fan is the best solution. And I say that as someone who runs that setup. A well engineered electric fan setup is better. There really isn't an argument. Most peoples cooling issues with old cars are at idle and that's where the electric shines because its not RPM dependant. Plus less parasitic loss ETC.

Now I do agree that if we were to graph this out, the big clutch fan would probably be the equilibrium point where ease/value meets an effectiveness line. So I would also recommend the setup to most people, but I don't think the statement that it is the best is correct.

You hit the nail on the head!
From my experience with a Firebird, the radiator is way too small for a high performance engine. So when the cooling area is reduced, the only cure is to increase the airflow across that area since we're somewhat limited on what we can do to increase the coolant flow through the radiator.

When I say that a clutch fan is better, I'm referring to the ability to move a lot of air through the radiator. A good fan/clutch/shroud combo will move way more air than most* electric fans. ....Except at idle. This is where an electric fan, set up as a pusher, can help keep the temps down at idle.

You are correct when you say "A well engineered electric fan setup is better." but I would add, "When combined with an adequately sized cooling system", which, we don't have.

The other problem with electric fans is the fact that the manufacturers LIE. And people (generally) are going to buy the fan with the biggest CFM rating for the least amount of money that they can find. The problem is that most of these sellers just pick a random cfm number and have never actually tested the fan. I've seen the exact same, made in china, fan advertised as 2400 cfm all the way up to 3800 cfm, but it only draws 7 amps. I call BS. In reality, it's probably a 240 to 380 cfm fan once mounted to a radiator.

When I bought a Cold Case radiator for my bird, I also bought their 16" electric fan/shroud combo that was rated at 2500 CFM, but only pulls 6.85 amps. My car overheated before I left the yard.

Cold Case does make the best radiator that I have tested and their warranty/customer support is excellent, but they should add Spal fans to their inventory because the ones they sell now are junk.
SPAL is the only company that I'm aware of that publishes the actual flow ratings at different pressure drops and it's surprising at how much that cfm number plummets when pulling through a radiator.

Now I'm nowhere near being an expert on cooling systems, but I have tried multiple fans, shrouds, & radiators in my bird and these are the things that have worked, or not worked, for me. YMMV.

* Newer OEM, brushless, PWM, fans (Made by Spal btw) are close enough to pulling as much air through a radiator as a clutch fan that I would need to see actual test results to decide which one is better.

I have a 19" Camaro/Cadillac 850 watt PWM fan in my bird now and it does a pretty good job of keeping the IA2 cool; especially at idle. My temps climb when cruising, but when I pull up to a stop light, I can watch the temp drop from 210* +/- to 185* in less than a minute. It sounds like a turbo prop preparing for takeoff, but it does get the job done. The downside is it's not a direct fit so I had to fabricate a bit to make it work. It's expensive and requires a PWM controller. It can pull a steady 70 amps so a quality electrical system is a must.

A clutch fan & shroud did as good, or better, at cooling (for a lot less $$$), but big fans & serpentine systems DO NOT play well together so I had to move to electric.

[RocktimusPryme]

Originally Posted by Speargun

My temps climb when cruising, but when I pull up to a stop light, I can watch the temp drop from 210* +/- to 185* in less than a minute. It sounds like a turbo prop preparing for takeoff, but it does get the job done. The downside is it's not a direct fit so I had to fabricate a bit to make it work. It's expensive and requires a PWM controller. It can pull a steady 70 amps so a quality electrical system is a must.

A clutch fan & shroud did as good, or better, at cooling (for a lot less $$$), but big fans & serpentine systems DO NOT play well together so I had to move to electric.

Yeah I could see that being the trade off. Especially because big electric fans pressed right up against the back of the radiator are now restrcting air flow through at cruise.

But its the exact opposite scenario I have with the 19" clutch. Mine will sit right at 178-180 while moving but if I pull into a drive through I will watch it slowly climb. When it gets really hot in the summer, I actually adjust the idle RPM on my Terminator from 800 ish to more like 1000 because the extra fan RPM helps some at idle.


Im working on a 66 Fairlane gasser project with a 429 based 503 inch engine. I am likely just going to hack up the core support in that car to make it fit a far larger radiator than even the 390 FE Fairlanes would have gotten. Im going to be super limited in fan space on that ride so I want all the cooling area I can get. But like you said, the downside is time sunk into fabrication. And I tend to be more of a function over form guy. So Ill get it in there and working, but its highly unlikely Im going to expend the effort to make it look pretty.

[Squidward]

I was daydreaming last night about clearing out some of the stuff on my core support and behind it (coolant overflow bottle, battery, some electrical stuff) to stuff in a bigger (wider) radiator. The battery would be the biggest challenge unless I went trunk mounted. And I'm not ready for that.

I'm wondering if I could find a way to squeeze in a 28x17 core radiator. It would open up a whole new world of dual fan options, too. That would be an almost 20% increase in surface area. And that would bring radiator size in line with 2nd gens and other 70+ up platforms that realized the radiators were too small. Even the Nova realized this by 1975, and went bigger.

Thinking out loud.

Pulling my tsat gave me max coolant flow. My aftermarket ac has a heater hose throttle valve, so the timing cover recirc path and the radiator are the only two coolant flow paths in my setup. So I am thinking the coolant flow is maxed, no room to tweak this outside of exotic pumps.

The only two variables I can work with are airflow, and cooling area of the radiator. Insane airflow can crutch a poor surface area radiator, or a really big radiator could crutch lackluster airflow. Or crazy amounts of coolant flow could crutch a constraint on the other two.

Does the Chevy world fight the same battles on the first gen platform?

Thanks all, for the discussion. It makes me think back to my earlier adult life, doing arrow analysis with heat transfer equations for a reactor powered steam plant.

[Speargun]

At one point, I was considering daisy-chaining a bunch of oil/tranny coolers on the heater hose side and hang them under the front end to increase the cooling capacity.
I never got around to that one.

I did, however, build an inline tank to increase the coolant capacity by almost 2 gallons.




It helped a little, but I think the design was too blocky and caused too much back pressure. Throw in a 22-24 psi cap and I would regularly get zipper tears in the upper radiator hose when I made a hard run.



I picked up an inline water pump a few years ago, but never did install it. I talked to the guys at Stewart and they swore by it, but then again, it's their job to sell them.
It seems like a good idea and I would think that it would help with cooling at idle. Especially in combination with an electric fan to help out.
Has anyone tried one of these?

[RocktimusPryme]

Those are all interesting. Did you feel that the extra capacity made a difference? I think you could probably use a 2 gallon fuel cell and be 90% of the way to being there rather than building one from scratch.

That inline pump is interesting too. My firebird needs just a small bit of help. I just needs a touch of help at a long idle. Ive been considering an electric setup, just because I already have a Terminator setup and I feel like Im wasting potential because I already have a build in fan controller.

[Speargun]

Originally Posted by RocktimusPryme

Those are all interesting. Did you feel that the extra capacity made a difference? I think you could probably use a 2 gallon fuel cell and be 90% of the way to being there rather than building one from scratch.

I think that the extra capacity did make a bit of difference, but the design I used had too many hard turns in it and created too much back pressure. A fuel cell might work better if the flow isn't restricted. (In at the bottom, out at the top, with no divider plate.) The extra capacity has to help with spreading the thermal load, but I'm not sure that it will make enough difference to be worth the effort.
I think that if you put a fan on a large oil cooler or old heater core, plumbed it into the heater hose, and tucked it away in the fender or under the core support would be much more efficient at cooling than a little extra capacity.

That inline pump is interesting too. My firebird needs just a small bit of help. I just needs a touch of help at a long idle. Ive been considering an electric setup, just because I already have a Terminator setup and I feel like Im wasting potential because I already have a build in fan controller.

I'm in the process of installing the Terminator X in my bird right now so I'll be switching over to it for PWM fan control.
I would strongly recommend the fan I'm using if you decide to go that way. You can see all of the details in my The Ultimate Cooling Thread
I can sit in traffic all day with the AC on and it will stay cool with this thing running!
I just realized that, since this fan is so much bigger than the radiator and I had to fab up a cover plate for the bottom of it, if I still have cooling issues at cruise this summer, I may mount a cooler or two at the bottom and try the heater hose idea.

[Squidward]

Speargun, I just read your thread. Nice work. Interesting that you mentioned extra cooling capacity, a coworker and I were geeking out about this stuff last night, and he mentioned adding extra cooling volume. I didn't see how adding extra volume would help unless there was a corresponding heat sink that went with that volume, but I am glad you got some results out of it.

That fan in your thread is gnarly! I will keep that in mind. Good thread. I can't remember if I had seen it before, but I've only been back here on PY since 2024.

My nylon flex fan showed up today, the one that Sirrotica recommended. When you say the pitch of those blades is steep, you are NOT stretching the truth! The leading edge of each blade is flat, while the trailing edge flips up at about a 90* angle. I will install it this weekend and see how it performs against my baseline data from last week. I don't think I will see 67 degree night time temps for several months, but it should find itself in the 70's for a night cruise.

I am still going to look at the possibility of squeezing a radiator with a 28x17 core. Bigger radiator=more cooling surface area. This could also open the door for a bigger/better electric fan setup, maybe even a 28" wide Silverado dual fan from 2005+. Just 2.25 inches wider each side from what I have, based on seeing one of these: https://www.ebay.com/itm/256504481391

[RocktimusPryme]

I might try the cooler in the heater hose thing on my channel. Fun and relatively inexpensive.

Only downside is I hate opening the cooling system. Messy and I swear I can feel antifreeze on my skin for days after I touch it.

[Squidward]

Data...

I bolted on the nylon fan with a 1" spacer. It wasn't as deep in the shroud as desired, but the previous clutch fan setup was in a little deeper than half.

Took it for a drive, with outdoor temps in the 70's. It took a long time to heat up to 160. Stopping at a drive thru for several minutes at idle resulted in temps around 197. Getting back on the road to cruise speed brought things back down to 171, which was my previous cruise temp.

I got home, parked, and left the car idling for a good 10-15 minutes. Temp got up to 227. I didn't like that.

End result is that I saw roughly no improvement. I'm happy with 170-something while at cruise, but not being able to idle for an extended time is frustrating. And these aren't even the 115 degree summer months yet.

I have a few other fan combos I could try if I feel sassy. But I will be looking at other models and solutions, tho.

[Squidward]

Just finished a 20 mile drive. Outside temps 67 degrees. Cruise at 45-50 mph and 2500 rpm yielded 158-160 degree temps. Even a 4 mile zip down the interstate at 65-70 and 3600 rpm barely cracked the low 160's.

Comparing this with last week's drive in virtually identical conditions, with only change being new fan, it dropped 10 degrees. I'll take that.

I still don't trust the car at extended idle, but I am pleased that in the current configuration I have a little bit of extra cooling capacity.

[Gator67]

Originally Posted by Squidward

Just finished a 20 mile drive. Outside temps 67 degrees. Cruise at 45-50 mph and 2500 rpm yielded 158-160 degree temps. Even a 4 mile zip down the interstate at 65-70 and 3600 rpm barely cracked the low 160's.

Comparing this with last week's drive in virtually identical conditions, with only change being new fan, it dropped 10 degrees. I'll take that.

I still don't trust the car at extended idle, but I am pleased that in the current configuration I have a little bit of extra cooling capacity.

Was this with the same nylon fan and 1” spacer as yesterday?

[kingbuzzo]

how deep outside of the shroud?

[68 Firebird]

What size crank pulley & waterpump pulley.
Mine responded well to AC pulley setup that
Overdrives waterpump and fan.

Gerry

[Squidward]

Originally Posted by Gator67

Was this with the same nylon fan and 1” spacer as yesterday?

Yes. Maybe the 10 degree drop in ambient caused the 10 degree drop in operating temp, IDK. I didn't think it would be, but the numbers were the numbers.

[Squidward]

Originally Posted by kingbuzzo

how deep outside of the shroud?

Maybe 1/4 of the fan is in the shroud.