[Squidward]

There are those here whose cooling system is aces. Their cars never get off the thermostat, or they can idle in a drive thru for an hour with the AC on, in 110 degree heat.

I was wondering if anyone with these highly successful cooling systems would be able to share their formula with common criteria. Maybe even include stats on performance in various ambient temps. Looking to see what WORKS.

Platform (year and model):

Engine (mild to wild):

Water pump config (8 bolt, 11 bolt):

Water pump style (cast impeller, stamped impeller, special aftermarket):

Water pump pulley size (small/med/large diameter):

Lower hose spring:

Radiator (# rows, material, brand):

Tstat:

Cooling fan configuration (blades, clutch specs, electric, etc.):

Typical use factors, like ambient temp, AC, etc.:

Any special mods:


So I'll get the party started with the template, even tho I wouldn't consider my setup an example of highly successful. In fact, mine needs some help.

Platform (year and model): 1967 Firebird

Engine (mild to wild): mild 350P, I would put it at a 2 out of 4. Hotter than stock. FiTech.

Water pump config (8 bolt, 11 bolt): 11 bolt

Water pump style (cast impeller, stamped impeller, special aftermarket): Factory style cast

Water pump pulley size (small/med/large diameter): Small diameter

Lower hose spring: No, but have one arriving this week!

Radiator (# rows, material, brand): 4 core Champion, aluminum.

Tstat: 180

Cooling fan configuration (blades, clutch specs, electric, etc.): 19" GM, Hayden 2797 clutch

Typical use factors, like ambient temp, AC, etc.: Super hot summers. Car has AC, but is not used currently. Temps creep at idle, temps creep while cruising.

Any special mods: divider plate clearanced.

[kingbuzzo]

No secret formula here but scirrotica solved all my idle temp woes with this cheap flex fan:

https://www.summitracing.com/parts/DER-17019

[Squidward]

Will keep that in mind. I have a factory shroud, good fan depth. Maybe the system is fully coated with scum, or my divider plate rotted away unknowingly. I've always kept a good antifreeze mix. I have baffles between the bumper and core support to keep air going into the radiator. I can't imagine my open RA hood scoop inserts are drastically interrupting under hood air flow much.

It's not that mine DOESN'T work, but it definitely underperforms.

I'm hoping some others chime in with their cool setups.

[Sirrotica]

Originally Posted by kingbuzzo

No secret formula here but scirrotica solved all my idle temp woes with this cheap flex fan:

https://www.summitracing.com/parts/DER-17019

I'm glad that helped you out, I started using those composite fans in the late 70s and they have always been affordable to buy, and do away with all the extra weight, and mass hanging on the extreme end of the water pump shaft. If the car starts to get hot in an idling situation that fan will pull enough air if you rev it in neutral to bring the coolant back down quickly.

If you keep the basic principles of physics in mind and science out cooling system problems you can pinpoint and fix your woes.

Plenty of air through the radiator, no restrictions in the system and as much volume of coolant as possible in the system. Overdrive the pump to keep pressure high to minimize steam pockets and run the coolant as fast as possible through the system.

Thermostat, or a restrictor need to be in the system to keep water pressure high in the engine. Coolant rejects or takes on heat at the speed of electricity, so the old wives tale that you can run coolant too fast through a system is false.

GM had cooling woes in their 6.5 turbo diesels, one of the changes they made was to run a water crossover with dual thermostats converging into a single upper radiator hose. The purpose was to allow more volume of coolant through the engine and radiator. With 2 thermostats the flow was higher, but still had a restriction to keep water pressure in the engine high. Water pump was modified to pass a higher volume of coolant and the increased the size of the fan as well as reprogrammed the fan clutch to come in sooner at a lower temperature.

If you're running and automatic transmission. and you're borderline on overheating don't use the cooler in the radiator, use a separate cooler.

Keeping a dirt track Pontiac cool during the summer running for 20 laps in the features made me find answers to why they overheated, and what measures I could use to eliminate the O/H problems. Lots of experimenting and research went into the cooling system, at the end I could run 20 laps and never get the coolant above 180, no matter what the ambient temp was.

I hope this helps someone having cooling system problems..........

[Squidward]

If you're running and automatic transmission. and you're borderline on overheating don't use the cooler in the radiator, use a separate cooler.

Good point.

Personally, I run out of the trans, to external cooler, to radiator cooler, and back to trans. I've always reasoned that the external pre-cooler took load off the radiator, and if anything, the radiator could even add excess heat back IN to the trans fluid to get it to normal fluid temp in case it was cold outside.

[srmmmm]

I think I have the opposite problem of most posters, over cooled in town and under cooled on the highway. With a 180 degree thermostat, I barely see 165 in town or at steady idle. Running the A/C will get it up to 180.

At 70 mph though, it's running at 210 and will run 230 with the A/C.

1700 miles on Len Williams built engine. Original 1970 350 block stroked to 413, XE276HR cam, Torker-I intake and 800cfm Q-Jet, 6X-4 heads, 9.3 cr

TCI Turbo 350 with 2400rpm stall converter, 3.23 rear axle

Original 4 row radiator, has been "overhauled" twice with lower row replacements. Internal Turbo 350 transmission cooler used. 24 quart cooling capacity

Edelbrock 11 bolt water pump with CNC impeller

Original 7 blade fan with new Hayden H-duty clutch

CVF serpentine belt drive - appears to be at least a 10% overdrive from the crank pulley to the water pump pulley

14 degrees initial timing, 21 mechanical all in at 3200 rpm, MSD 8563 distributor vacuum advance connected

I'm beginning to think the radiator has been painted too heavily and can't dissipate heat fast enough at higher engine rpms.

[nUcLeArEnVoY]

1979 Trans Am W72 400/4-Speed; stock low-comp 400 with a mild camshaft and true dual exhaust; everything else more-or-less stock. I'm running an 11-bolt Flowkooler clearanced down to 0.050" w/ gasket; Oversized 1.25" 2-Row Cold case radiator; new copper/brass heater core; 160 degree thermostat (balanced sleeve type); all new hoses and lines with anti-collapse spring in lower hose; 15 PSI rad cap as original; stock fan shroud; stock 7-blade 10008888 19" clutch fan; Hayden #2747 heavy duty clutch; shroud sealed to radiator with weatherstripping; all factory baffles and seals in place; stock overdriven AC waterpump pulley; stock HEI with 18 degrees initial timing as per factory spec; vacuum advance metered through the factory modulator valve that supplies partial manifold vacuum to the distributor (around 17 degrees of the full 25 degrees the advance canister supplies), and so I'm making 35 degrees total advance to the distributor at idle. Mechanical advance around 34-35 BTDC by 3500 RPM. Cooling system jackets clean as far as I can tell, since every flush I've done has never revealed dirty coolant - it always comes out green. I use Napa 50/50 pre-mixed conventional green coolant and every couple years as part of a backflush and refill, I throw in a bottle of Rislone Super Coolant additive, cuz why not?

I live in SoFlo, and around town, my car struggles to reach operating temp and I can idle till' the cows come home and the needle will almost never reach that first tick on the temp gauge (which for 2nd gens, I've always interpreted as around 160 degrees), no matter the ambient temp. I can drive around town for an hour and literally grip my hand around the radiator hose and hold it without getting burnt while the car is running.

My temp will creep up to the first tick, maybe a little past it when I'm on the highway sustaining higher RPMs, and that's after roughly 10-15 minutes on the highway. I've never been on the highway long enough to see how high the engine temp will go since I have a driveline vibration above 60 MPH that I need to address, so I usually avoid taking the highway, anyway. I have the factory 3.23 gears, and so in 4th gear on the highway, I'm at around 2250 RPM at 55 MPH, so figure around 2800 RPM at 70 MPH.

The AC, however, will cause my engine temp to spike very quickly. I think something may be wrong with my compressor or AC system, because while it does blow cold air, it taxes the engine a lot and just sitting there idling, I've seen the temp needle creep to halfway between the first tick and 220 tick on the gauge within maybe 8 minutes before I freaked out and shut off the AC. It's been converted to R134A, but only had the lines and compressor replaced with a crappy reman unit, while the condenser and evap are still the originals. I usually drive the car in the evenings, so I don't use the AC.

Overall, I'm pretty happy with the performance of my cooling system for living in SoFlo. Leagues better than when I first got the car, even though even then, it has never overheated. I just wish I could more confidently use the air conditioning, since living in SoFlo without it is oppressive and you need to make a lot of concessions to be able to enjoy the car without it (i.e. driving it only at certain times of the day when it's not as hot out, or depending on what time of the year it is).

I also think that people's standards for how these cooling systems operate are a little high, especially in accordance to the factory specifications as shown in service and owner's manuals. People get awfully paranoid just seeing their car in the 190's-200's, when in reality those are totally normal operating temps which these cars regularly saw when new. So many of these overheating threads may not even be based in actual overheating, but rather, "car not running at a temp that I, the owner, personally like to see it at."

[kingbuzzo]

One sage here told me that if the temp goes up when it's idling then it's the fan/airflow.

My old non-stock fan was too small and didn't push enough air.

How far does your stock fan stick out of the shroud? Or does it?

[68 Firebird]

ok throw my 2 cents in on this topic

My cars setup is as follows.

-11 bolt waterpump with tight clearance to divider plates

-Cold Case aluminum radiator with TH400 cooling lines in use in rad
.
-all factory baffles to direct air into radiator and seal around core support

-original fan shroud my car was born with

-converted to AC pulley for crank and waterpump to speed up water pump and fan

-factory AC 7 blade fan from 76TA using a hayden STD duty fanclutch

-NOS AC Delco 170 degree thermostat. verified to crack open 165 and fully open 180.

-Q-jet 7028276 with proper recalibration done during rebuild and full RA pan setup

-factory HEI with 12 initial 32 total using heavy advance springs for conservative curve.
weird thing is my car idles butter smooth and has more toque off the line with slower
curve. also 12 degrees from VAC ADV and have tried both ported and FMV and neither
effected cooling. but I prefer exhaust note from FMV at idle(today anyway).

-with 3:08 on highway she is happy at 75 and runs just shy of 180 and then drops back down to 170 on backroads. never hear fan clutch engage and happy with cooling.

In my garage for wall art, are the original crank and WP pulleys and 5 blade. they worked
well for years but temp did creep up in traffic. All these changes occurred over 15 years.
biggest bang for my buck was to speed up WP but then factory 5 blade fan was too loud on
highway. thus, installed matching fan clutch and shortly after has to replace leaking radiator and Cold Case was installed. Gas mileage did improve with fan clutch change.

this is just what worked in my car. I have a collection of thermostats that worked and some that were crap. current Delco stat was installed with no additional holes or voodoo.
All original parts were saved if I ever wanted to go back to original setup.

Gerry

[burd]

Water pump divider has to be set, I didn’t do mine, a guy in Miami did it, I never overheat now. I use a 160 thermo too. I can have ac on in Dreamcruise, no issues.
Test your rad cap, even if it’s new. We tested 3-4 new ones at the natz last year, they didn’t hold rite out of the box.

[george kujanski]

Clearanced 11 bolt pump, Shroud, clutch fan, Cold Case radiator, 180 degree thermostat, 12 degrees BTDC, manifold vacuum.

George

[nUcLeArEnVoY]

The issue is, that restriction the thermostat provides allows for pressure buildup in the system to further protect from boiling the coolant in the event that you do start to run hot. Maybe try a balanced sleeve thermostat (the "hi-flow" ones you're seeing).

Also, what's your tune? Initial timing, are you using vacuum advance and if so, manifold or port vacuum to the distributor? Airflow is indeed the most important factor for idle temps, but ignition timing plays a big role, too.

[Squidward]

Originally Posted by nUcLeArEnVoY

The issue is, that restriction the thermostat provides allows for pressure buildup in the system to further protect from boiling the coolant in the event that you do start to run hot. Maybe try a balanced sleeve thermostat (the "hi-flow" ones you're seeing).

Also, what's your tune? Initial timing, are you using vacuum advance and if so, manifold or port vacuum to the distributor? Airflow is indeed the most important factor for idle temps, but ignition timing plays a big role, too.

14 initial, running somewhere around 12 degrees manifold vacuum advance. It likes a little more, but I wanted to be reasonable with the rest of the tune. I am a fan of manifold vacuum advance for the idle performance.

[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 68 Firebird

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

Gerry

I have a standard 67 ac crank pulley setup, with what I think is the smallest diameter wp pulley. I can't remember the part number. Yup, we are on the same page.

[Squidward]

Originally Posted by kingbuzzo

how deep outside of the shroud?

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

[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.