Cooling system tips from Stewart Mfg.

Tech Tip #1 - Water Pumps & Pulleys
In order to increase your cooling system's performance you must maximize BOTH the water flow AND air flow.
Water Pumps
• There are significant differences between a stock or OEM water pump, and Stewart Components water pumps. Most stock or OEM pumps
are built to meet standard performance requirements at relatively low RPM. Stewart pumps are designed and manufactured specifically for
high performance applications.
• Every pump is designed to exacting tolerances for reliable, long-term performance that meets the requirements for your application.
• In addition, all Stewart high-flow water pumps are designed to deliver maximum flow with minimum power consumption. Stewart high-flow
water pumps deliver up to180 GPM (gallons per minute) of coolant flow (at 8,000 RPM), yet can consume just 2.26 horsepower (at 4,000
RPM)!
Pulleys
• Using the proper pulleys and drive system is critical to matching water pump performance to your specific application. RACE applications
require a maximum water pump speed of 6,000-7,000 RPM. For STREET applications, the water pump speed must at least match crank
shaft RPM, to a maximum recommended 25% faster than crankshaft speed.
• Stewart Components does NOT recommend the use of underdrive pulleys on any application. Stewart high-flow water pumps consume
minimal horsepower, so the actual savings in parasitic loss through the use of underdrive pulleys is minimal. In addition, in a properly
designed cooling system, flow and efficiency are designed to operate at a given speed. In years of testing, Stewart has consistently proven
that the engine will lose more horsepower due to higher operating temperatures than any possible gain from underdrive pulleys.
Tech Tip #2 - Radiator Caps
Radiator Caps
• In a cooling system, higher pressure equates to a higher boiling point for the coolant. Higher coolant pressures also transfer heat from the
cylinder heads more efficiently. We recommend using a radiator cap with the highest pressure rating the radiator is designed to accept. In
general, performance radiators will accept 22-24 PSI, and professional racing radiators will accept 29-31 PSI.
• The coolant will typically only build to 16-18 PSI, due to expansion up to 200° F. However, if the engine does overheat due to external factors,
the pressure inside the cooling system could reach as high as 28 PSI. Once the radiator cap has opened and vented coolant, the
engine will not cool down until it has been turned off. The radiator cap is a "safety valve"; always use the highest pressure cap the radiator
will tolerate. If you are unsure of the pressure rating for your radiator, check with the manufacturer for the maximum recommended operating
pressure.
Radiator Cap Location
• The radiator cap should always be located at the highest point of the cooling system, and on the low pressure side (after the radiator core).
Cross flow radiators mounted higher than the engine are ideal because the cap is on the tank that s connected to the water pump inlet.
This configuration offers 3 advantages:
1. The cap is at the highest point of the system, allowing any air to migrate to the area just below the cap. In the event
the cap vents due to excessive pressure, the air will escape first.
2. This area has the lowest velocity within the system, allowing air to separate from coolant even at high engine RPM.
3. The cap is located on the low pressure (suction) side of the system, so it is unaffected by the generated pressure.
• For cooling systems NOT using a cross flow radiator, mounted higher than the engine, you must use a surge tank. A surge tank
is typically a 1 quart tank mounted at the highest point of the system, with the radiator cap on top. The bottom of the tank is connected to
the inlet side of the water pump with a 1/2" or 3/4" line. A 1/4" to 3/8" "bleed" line from the side of the surge tank is connected to the highest
point of the low pressure side of the radiator. The bleed line allows some circulation through the tank while the engine is running. The
surge tank is also large enough to allow the air to separate as the coolant flows through it. Air in the system will then migrate to the area
just below the radiator cap, so that it will be forced out first if system pressure exceeds the radiator cap's rating.
• In street car applications, an upright radiator (top and bottom tanks, with the cap on the top tank) represents a compromise that will work,
as long as the car is not operated at sustained high RPM, like those seen in racing.
• Any aftermarket thermostat housing that mounts the radiator cap directly above the thermostat location, or that mounts the radiator cap in
the top coolant hose, is NOT recommended. Both housing styles are poorly designed, and will push coolant out of the cap at high RPM.


Tech Tip #3 - Thermostats & Restrictors
Thermostats & Restrictors
• We strongly recommend NEVER using a restrictor; they decrease coolant flow and ultimately inhibit cooling.
• For applications requiring a thermostat to keep the engine at operating temperature, we recommend using a Stewart/Robert Shaw high
flow thermostat. This thermostat does not restrict flow when open. The Stewart/Robert shaw thermostat enhances the performance of the
cooling system, using any style of water pump. Stewart Components recommends using this thermostat with Stage 1 pumps. Stage 2, 3 &
4 pumps require a Stewart modified Robert Shaw thermostat, as these pumps have no internal bypasses.
• Stewart modifies its thermostat by machining three 3/16" bypass holes directly in the poppet valve, which allows some coolant to bypass
the thermostat even when closed. This modification does result in the engine taking slightly longer to reach operating temperature in cold
weather, but it allows the thermostat to function properly when using a high flow water pump at high engine RPM.
• A common misconception is that if coolant flows too quickly through the system, that it will not have time to cool properly. However, the
cooling system is a closed loop, so if you are keeping the coolant in the radiator longer to allow it to cool, you are also allowing it to stay in
the engine longer, which increases coolant temperatures. Coolant in the engine will actually boil away from critical heat areas within the
cooling system if not forced through the cooling system at a sufficiently high velocity. This situation is a common cause of so-called "hot
spots", which can lead to failures.
• Years ago, cars used low pressure radiator caps with upright-style radiators. At high RPM, the water pump pressure would over come the
radiator cap's rating and force coolant out, resulting in an overheated engine. Many enthusiasts mistakenly believed that these situations
were caused because the coolant was flowing through the radiator so quickly, that it did not have time to cool. Using restrictors or slowing
water pump speed prevented the coolant from being forced out, and allowed the engine to run cooler. However, cars built in the past thirty
years have used cross flow radiators that position the radiator cap on the low pressure (suction) side of the system. This type of system
does not subject the radiator cap to pressure from the water pump, so it benefits from maximizing coolant flow, not restricting it.
Tech Tip #4 - Coolant, Fans, and Hoses
Coolant
• UNEQUIVOCALLY, WATER IS THE BEST COOLANT! We recommend using a corrosion inhibitor comparable to Prestone Super Anti-Rust
when using pure water. If freezing is a concern, use the minimum amount of antifreeze required for your climate. Stewart Components has
extensively tested all of the popular "magic" cooling system additives, and found that none work better than water. In fact, some additives
have been found to swell the water pumps seals and contribute to pump failures.
• In static cooling situations, such as quenching metal during heat treating, softening agents (sometimes referred to as water wetting agents)
will allow the water to cool the quenched part more evenly and quickly. The part will cool quicker, and the water will heat up faster.
However, an automotive cooling system is not static. In fact, the velocities inside a cooling system are comparable to a fire hose forcing
coolant against the walls of the engine's water jackets. If the softening agents actually aided in cooling the engine, the temperature of the
coolant as it exited the engine would have to be higher because it would have absorbed more heat.
Fans
• Electric fans have improved tremendously in recent years, in both quality and reliability. Electric fans now outperform mechanical fans in
nearly every application, except towing and dirt oval track racing.
• When using a mechanical fan, a properly designed shroud must be used. Most mechanical fans are not designed for high RPM use — they
can have serious vibration problems, due to air turbulence, when run over 6,500 RPM. This is a turbulence problem, not a balance problem,
and will destroy the water pump and components in front of it. The large fans preferred by dirt oval track racers can consume up to 18
horsepower at 6,500 RPM. Do NOT run a mechanical fan that is any larger than required for the application.
• Flex fans are a poor design for performance applications. They move less air at higher RPM, and only consume a fraction less power than
standard fixed pitch fans.
• Clutch-style fans are inconsistent and we do not recommend their use for any application.
Hoses
• Standard full-size hoses should be used to ensure maximum flow. Smaller "AN style" hoses decrease flow and hence inhibit proper
cooling.

Tech Tip #5 - Radiators & External Plumbing
Radiators
• Thicker radiators do have slightly more airflow resistance than thinner radiators but the difference is minimal. A 4" radiator has only
approximately 10% more airflow resistance than a 2" radiator.
• In past years, hot rodders and racers would sometimes install a thicker radiator and actually notice decreased cooling. They erroneously
came to the conclusion that the air could not flow adequately through the thick radiator, and therefore became fully heat-saturated before
exiting the rear of the radiator core. The actual explanation for the decreased cooling was not the air flow, but the coolant flow. The older
radiators used the narrow tube design with larger cross section. Coolant must flow through a radiator tube at enough velocity to create
turbulence.
• The turbulence allows the water in the center of the tube to be forced against the outside of the tube, which allows for better thermal
transfer between the coolant and the tube surface. The coolant velocity decreases, and subsequently its ability to create the required
turbulence, increases in direct relation to the increase in thickness. If the thickness of the core is doubled, the coolant velocity is halved.
Modern radiators, using wide tubes and less cross section area, require less velocity to achieve optimum thermal transfer. The older radiators
benefited from baffling inside the tanks and forcing the coolant through a serpentine configuration. This increased velocity and thus the
required turbulence was restored.
• Radiators with a higher number of fins will cool better than a comparable radiator with less fins, assuming it is clean. However, a higher fin
count is very difficult to keep clean. Determining the best compromise depends on the actual conditions of operation.
• Double pass radiators require 8x more pressure to flow the same volume of coolant through them, as compared to a single pass radiator.
Triple pass radiators require 27x more pressure to maintain the same volume. Automotive water pumps are a centrifugal design, not positive
displacement, so with a double pass radiator, the pressure is doubled and flow is reduced by approximately 33%. Modern radiator
designs, using wide/thin cross sections tubes, seldom benefit from multiple pass configurations. The decrease in flow caused by multiple
passes offsets any benefits of a high-flow water pump.
• Cross flow radiators are superior to upright radiators because the radiator cap is positioned on the low pressure (suction) side of the system.
This prevents the pressure created by a high-flow water pump from forcing coolant past the radiator cap at high RPM. As mentioned
in the radiator cap section, an upright radiator should be equipped with the highest pressure radiator cap recommended by the manufacturer.
The system will still force coolant past the cap at sustained high RPM.
External Plumbing
• Street-driven vehicles seldom need auxiliary plumbing or coolant lines. SBC race engines with aluminum cylinder heads usually require
extensive external plumbing to address two design problems:
1. Aluminum heads have much smaller water jackets than cast-iron heads because the external dimensions are similar, but the
ports are usually larger, the deck is thicker, and the material near the rocker stands is thicker, all leaving less area in the
water jackets.
2. The siamese center exhaust ports are a design compromise that presents additional problems when aluminum heads are used.
The area near the center exhaust valves is thicker, thus allowing less surface area for cooling.
• We recommend installing a pair of AN10 lines that connect the rear of the aluminum cylinder heads to the thermostat housing crossover in
the front. This step will help offset the smaller water jackets. A pair of AN10 lines connecting the pressure side of the water pump with the
area in the center of the cylinder head (just below the exhaust ports) will offset the lack of surface area due to the extra material.

Looks like a LOT of good information there. It's rare these days to find a company go to the trouble to publish tech information. Most are preoccupied with selling stuff, not education.

Yep, we sell that stuff at C. I. I read that a while ago. Very interesting.:noworry:

Hey Bird, thanks for posting this. Lots of good info!

lots of good info.
a couple of items I don't agree with but overall a good source of information

How can you not agree? What they say is gospel.

Twin_Turbo said:

How can you not agree? What they say is gospel.

Click to expand...

I'll take very few things as gospel. If Lars or John Hinckley (JohnZ) or one or two other people tell me something I trust and respect them enough to take their info as gospel, but I don't blindly take ANYTHING from a vendor as gospel.

Stewart is known as a high quality vendor and like I said I agree with much of what was written, but there are a few points I don't.
They are a vendor and while I don't feel on those few points that it's 100 wrong, I feel they have slightly slanted the presentation of the info to help sell their products. They are a vendor so this is not surprising but it's the same as only telling half the story......

What don't you agree with?

We have this long list of thermodynamics laws, let NONE of them be MIST....


:yahoo::yahoo::hunter::hunter::shocking::1st:

mrvette said:

We have this long list of thermodynamics laws, let NONE of them be MIST....


:yahoo::yahoo::hunter::hunter::shocking::1st:

Click to expand...

Ok, could we see the list?:toothbrush:

Twin_Turbo said:

What don't you agree with?

Click to expand...

keep in mind that my perspective on this is from the point of view of a STREET car, not a race car. That's why I disagree with a few of their points. If the point of view was for a race car on these few points I'd agree with their write-up 100% but as I mentioned I felt their points were slanted towards their own products and they market most of their products to race applications.

point one:

• There are significant differences between a stock or OEM water pump, and Stewart Components water pumps. Most stock or OEM pumps
are built to meet standard performance requirements at relatively low RPM. Stewart pumps are designed and manufactured specifically for
high performance applications.

many, (most?) hi-flow or high performance water pumps are designed for racing application therefore are designed to work most efficiently at higher RPM's where race motors live the vast majority of the time. Many times this is in the 7,000-11,000rpm range. At lower rpms, especially idle and lower speed, driving these pumps are not as efficient as a stock style pump. In fact, a hi-flow waterpump designed to work best at high RPM's in most cases are LESS efficient than a stock waterpump at lower or mid rpm's where most street cars live at, being actually counterproductive to cooling.
For a street driven car this is not practical and not the most efficient type of part to put on a car.
They state a stock pump works as designed at relatively low RPM but many, many cars, such as my '65 L76 were designed with a 6,500rpm redline and I've had it for extended periods close to or at that speed (and a few times beyond it). The waterpump and cooling system worked flawlessly and never, not once, did the thought of the waterpump not being able to keep up or fail ever enter my mind as a concern. 6,500rpm for a STREET car with a vintage motor is considered pretty high rpm. (remember, we are not talking about a sports style motorcycle where 11,000-13,000rpm is normal).
You start looking at BB motors and most redlines are lower than my 6,500rpm.
GM designed and built these waterpumps to handle the rpm ranges their motors allowed.
I can see where a company that produces racing products would consider 6500rpm "low RPM" but on a street car that statement is not applicable and there is no need at all for a hi-flow or high performance waterpump to allow the cooling system to work properly.
In fact, on a street car, the only reason I see for changing out a stock waterpump to a nonn-OEM type would be to go with an aluminum unit simply for weight savings, not for any "performance" increase.

point 2 & 3: they are related so I'm putting them together

• When using a mechanical fan, a properly designed shroud must be used. Most mechanical fans are not designed for high RPM use — they
can have serious vibration problems, due to air turbulence, when run over 6,500 RPM. This is a turbulence problem, not a balance problem,
and will destroy the water pump and components in front of it.

• Clutch-style fans are inconsistent and we do not recommend their use for any application.

Again, I wouldn't disagree except most of us here on the various forums are looking to make sure our STREET Corvettes run properly and cool correctly. We aren't dealing with a race car. If we were talking race application I'd agree.
On a street car a stock style mechanical fan / fan clutch set-up works just fine and if everything else works correctly there is nothing wrong with a mechanical fan. Can electric fans work good? Of course, no question they do and if someone wants on on their car I see no problem with that and there are a few advantages such as giving the engine bay a "cleaner" look, but on a street car, even one with a fairly worked over motor making much more power than stock, a mechanical fan still works fine if we are only talking about cooling, not cleaning up the looks of an engine bay.
If someone claims that their motor wouldn't cool until they put on electric fans than in 99% of the cases I'd wager that there were other unresolved issues contributing to the problem and that the electric fans were just masking those issues.

As for their statement that clutch style fans are inconsistent and they don't recommend them for ANY application is a bit far fetched. Sorry, again, for a street driven car a stock fan clutch and fan is an excellent working set-up and was for over 50 years and more. It's efficient and it's reliable. It took 41 years for the original fanclutch to go on my '65 and when it did it only took 4 simple bolts to replace it with another unit which I have no reason to believe won't last another 41 years. It cools down my motor just fine same it they have for the MILLIONS AND MILLIONS of cars produced for over half a century with fanclutch/fan set-ups. To say they are inconsistent and not recommended for any application is a completely foolish statement on their part.
If they were to say not recommended for any racing application could be a different story and I would not disagree but again I'm looking at things from the perspective of a street driven car.

BarryK said:

Twin_Turbo said:

What don't you agree with?

Click to expand...

keep in mind that my perspective on this is from the point of view of a STREET car, not a race car. That's why I disagree with a few of their points. If the point of view was for a race car on these few points I'd agree with their write-up 100% but as I mentioned I felt their points were slanted towards their own products and they market most of their products to race applications.

point one:

• There are significant differences between a stock or OEM water pump, and Stewart Components water pumps. Most stock or OEM pumps
are built to meet standard performance requirements at relatively low RPM. Stewart pumps are designed and manufactured specifically for
high performance applications.

many, (most?) hi-flow or high performance water pumps are designed for racing application therefore are designed to work most efficiently at higher RPM's where race motors live the vast majority of the time. Many times this is in the 7,000-11,000rpm range. At lower rpms, especially idle and lower speed, driving these pumps are not as efficient as a stock style pump.
For a street driven car this is not practical and not the most efficient type of part to put on a car.
They state a stock pump works as designed at relatively low RPM but many, many cars, such as my '65 L76 were designed with a 6,500rpm redline and I've had it for extended periods close to or at that speed (and a few times beyond it). The waterpump and cooling system worked flawlessly and never, not once, did the thought of the waterpump not being able to keep up or fail ever enter my mind as a concern. 6,500rpm for a STREET car with a vintage motor is considered pretty high rpm. (remember, we are not talking about a sports style motorcycle where 11,000-13,000rpm is normal).
You start looking at BB motors and most redlines are lower than my 6,500rpm.
GM designed and built these waterpumps to handle the rpm ranges their motors allowed.
I can see where a company that produces racing products would consider 6500rpm "low RPM" but on a street car that statement is not applicable and there is no need at all for a hi-flow or high performance waterpump to allow the cooling system to work properly.
In fact, on a street car, the only reason I see for changing out a stock waterpump to a nonn-OEM type would be to go with an aluminum unit simply for weight savings, not for any "performance" increase.

point 2 & 3: they are related so I'm putting them together

• When using a mechanical fan, a properly designed shroud must be used. Most mechanical fans are not designed for high RPM use — they
can have serious vibration problems, due to air turbulence, when run over 6,500 RPM. This is a turbulence problem, not a balance problem,
and will destroy the water pump and components in front of it.

• Clutch-style fans are inconsistent and we do not recommend their use for any application.

Again, I wouldn't disagree except most of us here on the various forums are looking to make sure our STREET Corvettes run properly and cool correctly. We aren't dealing with a race car. If we were talking race application I'd agree.
On a street car a stock style mechanical fan / fan clutch set-up works just fine and if everything else works correctly there is nothing wrong with a mechanical fan. Can electric fans work good? Of course, no question they do and if someone wants on on their car I see no problem with that and there are a few advantages such as giving the engine bay a "cleaner" look, but on a street car, even one with a fairly worked over motor making much more power than stock, a mechanical fan still works fine if we are only talking about cooling, not cleaning up the looks of an engine bay.
If someone claims that their motor wouldn't cool until they put on electric fans than in 99% of the cases I'd wager that there were other unresolved issues contributing to the problem and that the electric fans were just masking those issues.

As for their statement that clutch style fans are inconsistent and they don't recommend them for ANY application is a bit far fetched. Sorry, again, for a street driven car a stock fan clutch and fan is an excellent working set-up and was for over 50 years and more. It's efficient and it's reliable. It took 41 years for the original fanclutch to go on my '65 and when it did it only took 4 simple bolts to replace it with another unit which I have no reason to believe won't last another 41 years. It cools down my motor just fine same it they have for the MILLIONS AND MILLIONS of cars produced for over half a century with fanclutch/fan set-ups. To say they are inconsistent and not recommended for any application is a completely foolish statement on their part.
If they were to say not recommended for any racing application could be a different story and I would not disagree but again I'm looking at things from the perspective of a street driven car.

Click to expand...

:thumbs:
Very good write up. I use many of your points, here, when our customers want the "latest race" cooling system.

My BIG old Pontiacs.....with LARGE radiators in the B body cars would run fine regardless of the fan condition....but the A body/GTO types ran hotter so had to have a super stiff clutch and a Caddy 7 blade aluminum fan on it to cure the problems....same radiator as the B body, so I conclude the space under the HUGE hoods help greatly with heat dissipation....freeking football field for a hood....

but when getting into vettes, the '87 had no problem with it's aluminum rad/fan combo....I ran a 180 stat and it was fine....this about 92-95 or so....

bought this '72 and being tired one of the first things to go was the OEM radiator....I bought a '89? F body radiator, same core size but only single 1.25 thick row....same thing in there now....but I used an '87 vette fan in the OEM shark shroud, cut the depth down and sealed it in....it was very marginal up north, and gave off freeway problems here in Florida.... driving as speed was fine though....even in 100f temps which makes all the spoiler comments moot to ME....but needing no front tag here is what made the most differance...popping that center tag and bracket off there made it much better.....for off freeway airflow....

then a couple years ago, I went to dual spals, properly and completely sealed to the total rad tank to tank and top to bottom, the fans draw air with NO leakage....

problem solved....I suggest from my Pontiac experiences that any shark with a stock mechanical fan setup and anything smaller than the largest BB AL radiator is in trouble....:fishing:

Barry makes some good points.:1st: