Overheating... SBC 350

[fieldsken1]

lol..

This is actually what I hear from them every time I walk in regardless of the complexity of the part.

That's how they are programmed like little robots

 

[chevurai]

A no cost test would be to remove the thermostat, temporarily, and see if that changes anything.

 

[Brian in Oregon]

Removing the thermostat may or may not tell you anything. If you have a high flow waterpump, the lack of a thermostat may push the water too fast through the radiator to allow complete heat exchange with the air.

 

[fieldsken1]

What he said

 

[LandCruiserPhil]

Looking back on your build you have been using electric fans since your 1st test drive in '09. Is your overheating a new problem or have you always had it?

 

[chevurai]

Do some reading on radiator heat exchange theory and you will find that moving the fluid through the radiator faster will cool the engine better. It's an old shade tree mechanic notion that coolent needs to move slowly to be effective. Fast moving, turbulent flowing coolent provides the greatest exchange of heat. Maby we should all install really small pumps so that the coolent has gobs of time to exchange heat? A lot of high flow water pumps are sold on the idea that faster moving coolent is better.

 

[jackbrad]

Looking back on your build you have been using electric fans since your 1st test drive in '09. Is your overheating a new problem or have you always had it?

I believe that is has always been an issue. I have really only been driving the last year and rarely when very far. Now that I am venturing further than I used to I think it is not showing itself.

Thanks for looking in the build and reviewing... means alot.

 

[jackbrad]

So far I have decided try a test on the thermostat and am considering moving up to and aluminum radiator.

1. I have often thought the thermostat was suspect.
2. I have heard and have been convinced that the Radiator at highspeeds is not performing enough exchange and I have not had any problems at idle.
3. I plan to add a spring to the lower hose in case the bottom hose is colapsing and I cant catch it.
4. Lastly I am going to check into a better fan but, have not decided what that means yet.

 

[DSRTRDR]

If your plan is to stick with an electric fan plan on overheating issues.

Basiclly the same set up as you just add AC A 70's BB fan with shroad does my cooling without issue in AZ.

I would listen to this guy - he knows what he is talking about

 

[saryon7]

Don't a ton of SBC engines use a 180 degree thermostat? The solution might just be that simple. Just something to think about.

 

['74 UA FJ]

I've used a taurus fan for 10 years and the highest temp I've seen is around 205.

 

[Brian in Oregon]

Do some reading on radiator heat exchange theory and you will find that moving the fluid through the radiator faster will cool the engine better. It's an old shade tree mechanic notion that coolent needs to move slowly to be effective. Fast moving, turbulent flowing coolent provides the greatest exchange of heat. Maby we should all install really small pumps so that the coolent has gobs of time to exchange heat? A lot of high flow water pumps are sold on the idea that faster moving coolent is better.

That's not entirely true. You've completely overlooked the optimal flow rate.

Why do you think thermostat eliminators for racing engines look like a giant washer? It's to restrict the water flow, even though they are using high volume water pumps. Flow rates are restricted depending on the size of the hole. This allows fine tuning of the flow rate, along with pump capacity, pulley sizes, engine rpm and road speed.

Why would you want to fine tune the flow rate?

Optimal cooling is with 6 to 8 cubic feet per second. If the rate is increase to 10 cubic feet per second or more, several problems crop up. Foaming and aeration of the coolant is one. Caviation of the pump is another. And radiators are only made for so much pressure before a weak spot is found.

Also, the primary purpose of a high volume water pump is not to increase flow speed per se, but to match flow rate when going to a larger radiator.

Let's assume you have a standard flow water pump and a three core radiator. Let's assume it is designed from the factory within the optimal flow rate of 6 to 8 cubic feet per second.

So you install a high capacity water pump to increase the flow rate. Now it's approaching 10 cubic feet per second, but due to foaming and aeration the engine is now running even hotter.

What the high volume pump works best at is maintaining the coolant flow rate when installing a larger radiator.

Taking the same scenario, which is the standard flow pump and a three core radiator, you upgrade to a four core radiator.

But now there is little or no improvement in the cooling. This is because the fourth row has added another cooling path. For arguments sake let's say it has slowed the flow rate through the radiator by 25%. Now the optimal flow rate may be at the low end, like 6 cubic feet per minute, or even lower, less than optimal.

The solution is to install a high capacity water pump to bring the flow rate back into the optimal range.

 

[Brian in Oregon]

Don't a ton of SBC engines use a 180 degree thermostat? The solution might just be that simple. Just something to think about.

That doesn't mean the coolant is going to be 180 degrees.

All a 180 degree thermostat does is open at 180 degrees. The system itself tends to balance based upon the heat output of the engine and a cooling system set up for optimal flow rate.

Believe it or not, the actual amount of cooling is based on radiator size and flow rate, not what the thermostat rating is. The main purposes of a thermostat is to provide a fast warm up of the engine to improve drivability, and to bring the engine into an optimal temperture range to reduce wear. I recall from an old chart that an engine run at 160 degrees has twice the wear rate as an engine run at 200 degrees. This is because the hotter engine expands more, providing more clearance and less metal on metal wear. A race engine gets around this by building more clearance into the engine. Some drag racing engines don't even have a cooling system, so they need a lot of clearance to prevent engine wear and galling. But I digress...

A radiator only has about a ten degree coolant temperatur drop between the top and bottom tank. Check it out for yourself with a cheap Harbor Freight laser temp reader.

Let's say we are running a SBC with a small radiator. The temp gauge says the coolant is at 220 degrees going into the top tank. There will be a 10 degree coolant drop in the radiator, so 210 degree coolant is being returned to the engine. In this case it doesn't matter if you put in a 165, 180 or 195 degree termostat. Any of these will always be full open. They will not contribute one iota to cooling. All the 15 degree thermostat will do it lengthen the warm up time.

Now you install a much larger radiator and a pump to match. The radiator is still only going to have a 10 degree drop between the top and bottom tank. BUT, the increased surface area of the radiator handles more total BTU load, so the cooling system now runs at, for example, 180 degrees. Meaning you have 180 degrees going into the top tank, and 170 degrees coming out of the bottom tank.

And this is where the thermostat comes into play. 180 degrees is on the low side for most engines from a wear and economy standpoint. Install a 195 degree thermostat and the system temp will be increased. The factory may install a 210 or even hotter thermostat.

So why do some SBCs seem to do OK with the OEM FJ40 cooling system and others don't? The more stock the engine is, the cooler it runs. (The burning fuel is roughly split into 1/2 power, 1/3 exhaust heat, and 1/3 engine heat.) Hot rod the engine and all three go up. Same for increasing the cubic inches. For a bone stock base motor, a 283, 305 ot 207 is going to produce less heat than a 350. The FJ40 radiator was designed with desert conditions in mind for the stock six. So it likely has ample capacity for a smaller SBC. It may be borderline for a 350, especially in the hot states, so installing a 4-core radiator and a higher capacity water pump will match the cooling system to the engine.

I know a few bone stock 350s are doing OK with the stock radiator, while others do not. This may be dependant upon the water pump specs plus pulley sizes, and condition of the radiator. I'm not aware of anyone with a hot rodded 350 or a 383 or 400 using a stock FJ40 radiator. If anyone did, I'll bet they upgraded pretty quickly.

 

[jackbrad]

BTW, space is an issue so this is one reason I am not sure I can go mechnical fan.

 

[fieldsken1]

If you have an electric in there you should be able to go manual no problem

 

[fieldsken1]

That doesn't mean the coolant is going to be 180 degrees.

All a 180 degree thermostat does is open at 180 degrees. The system itself tends to balance based upon the heat output of the engine and a cooling system set up for optimal flow rate.

Believe it or not, the actual amount of cooling is based on radiator size and flow rate, not what the thermostat rating is. The main purposes of a thermostat is to provide a fast warm up of the engine to improve drivability, and to bring the engine into an optimal temperture range to reduce wear. I recall from an old chart that an engine run at 160 degrees has twice the wear rate as an engine run at 200 degrees. This is because the hotter engine expands more, providing more clearance and less metal on metal wear. A race engine gets around this by building more clearance into the engine. Some drag racing engines don't even have a cooling system, so they need a lot of clearance to prevent engine wear and galling. But I digress...

A radiator only has about a ten degree coolant temperatur drop between the top and bottom tank. Check it out for yourself with a cheap Harbor Freight laser temp reader.

Let's say we are running a SBC with a small radiator. The temp gauge says the coolant is at 220 degrees going into the top tank. There will be a 10 degree coolant drop in the radiator, so 210 degree coolant is being returned to the engine. In this case it doesn't matter if you put in a 165, 180 or 195 degree termostat. Any of these will always be full open. They will not contribute one iota to cooling. All the 15 degree thermostat will do it lengthen the warm up time.

Now you install a much larger radiator and a pump to match. The radiator is still only going to have a 10 degree drop between the top and bottom tank. BUT, the increased surface area of the radiator handles more total BTU load, so the cooling system now runs at, for example, 180 degrees. Meaning you have 180 degrees going into the top tank, and 170 degrees coming out of the bottom tank.

And this is where the thermostat comes into play. 180 degrees is on the low side for most engines from a wear and economy standpoint. Install a 195 degree thermostat and the system temp will be increased. The factory may install a 210 or even hotter thermostat.

So why do some SBCs seem to do OK with the OEM FJ40 cooling system and others don't? The more stock the engine is, the cooler it runs. (The burning fuel is roughly split into 1/2 power, 1/3 exhaust heat, and 1/3 engine heat.) Hot rod the engine and all three go up. Same for increasing the cubic inches. For a bone stock base motor, a 283, 305 ot 207 is going to produce less heat than a 350. The FJ40 radiator was designed with desert conditions in mind for the stock six. So it likely has ample capacity for a smaller SBC. It may be borderline for a 350, especially in the hot states, so installing a 4-core radiator and a higher capacity water pump will match the cooling system to the engine.

I know a few bone stock 350s are doing OK with the stock radiator, while others do not. This may be dependant upon the water pump specs plus pulley sizes, and condition of the radiator. I'm not aware of anyone with a hot rodded 350 or a 383 or 400 using a stock FJ40 radiator. If anyone did, I'll bet they upgraded pretty quickly.

Long winded

 

[fieldsken1]

Long winded and to much spare time LOL

 

[fieldsken1]

Stewart Components Tech Tips
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/Robertshaw high flow thermostat. This thermostat does not restrict flow when open. The Stewart/ Robertshaw thermostat enhances the performance of the cooling system, using any style of water pump. However, the Stewart Stage 1 high-flow water pump may require this thermostat to operate properly, and Stewart Stage 2, 3, and 4 water pumps simply will NOT operate with a regular thermostat because these pumps have no internal bypasses.
Stewart further 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 overcome 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.


Next Tech Tip - Coolant, Fans, and Hoses

 

[fieldsken1]

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 vibrations 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, if possible.

 

[fieldsken1]

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 a velocity adequate 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 actually decreases, and subsequently its ability to create the required turbulence, 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 16x more pressure to flow the same volume of coolant through them, as compared to a single pass radiator. Triple pass radiators require 64x 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.

Gross 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 radiator cap with the highest pressure rating recommended by the manufacturer. The system will still force coolant past the cap at sustained high RPM.