Some radiator questions

[Bruce Dorsi]

I asked this question (and several others) on two posts which were lost the other day, when the RRT went down.   ....I don't know if anyone read them or replied to them.


While the high-flow pumps are rated in excess of 100 gpm, what flow rates are THERMOSTATS capable of supporting?

It seems to me that the thermostat is the "bottleneck" in the cooling circuit, negating the high-volume output of the pump.  

Are there flow rates advertised for any thermostats?

Steve, is that flow rate on your Chevy the rated pump output, or is that an actual measurement of flow through your system?

Thanks for all responses!

[HOTRODSRJ]

I asked this question (and several others) on two posts which were lost the other day, when the RRT went down.   ....I don't know if anyone read them or replied to them.

While the high-flow pumps are rated in excess of 100 gpm, what flow rates are THERMOSTATS capable of supporting?

It seems to me that the thermostat is the "bottleneck" in the cooling circuit, negating the high-volume output of the pump.  

Are there flow rates advertised for any thermostats?

Steve, is that flow rate on your Chevy the rated pump output, or is that an actual measurement of flow through your system?

Thanks for all responses!

Hey Bruce.......first the numbers from my pumps are measured as tested at a given pressure X.  But this is relative. If you have a stock at the same pressure X, because of the inefficiency of stock pumps, the high efficiency pumps will not "fade" due to the design issues.

Also, actually there are many other "bottlenecks" in the coolant jacket that are very restrictive and it's up to the ability of the water pump to "force" flow thru the restrictive manifolds.   The thermostat and upper hose are NOT the problem. In fact, you can have rear cylinders run hotter than the cylinders in front of them due to the pressure and volume division due to restriction.  The good analogy is the simple "garden" sprinkler/soaker hose.  The further away from the source the weaker the stream and so goes the very same thing in the block .....and therefore rear cylinders are less flow!

Look at these typical numbers from a cup engine and would be about the same for a street block as well.

Following is a typical Winston Cup engine at 100 GPM:

Lower radiator hose = 1.5 PSI
Block and cylinder head - each (at 50 GPM) = 8.5
Outlet manifolding = 1.25
Top radiator hose = 2.25
Radiator = 1.5
Total = 15.00 PSI

You can easily see that the block and cylinder heads drop the most pressure whereas this means that the resistance is the most.  The thermostat and outlet cavity drops only 1.5 at the outlet and 2.25 at the top radiator hose.  While I don't know what the actual numbers are for a standard or stock thermostat, I do know that the higher flowing thermostats are BETTER for three reasons.  One is that they support the higher flow rates within the design of the application(s) (ie, very high flowing (in excess of 100 gpm) applications) and two, is that IF they fail ...they fail OPEN...not shut which is  in and of itself reason enough to use them and lastly they are very accurate!

And.....you would NOT be negating any high flowing pump whereas the higher flowing/volume pumps would create more flow ....only at higher pressures as compared to their lesser brethern.

Let me tell you...and I have tested these beasts......the stock bodied and impellered water pumps are junk compared to today's aftermarket high volume/flowing pumps.  The intake and output cavities are "flow designed" and impellers are super tight tolerances compared to stock, which both breed less cavitation, eddy currents, by-passing, and suction issues.  What this all means is more efficient flow and less hp to do it.  As seen in above links the typical high efficiency water pump only takes about one hp plus at moderate engine speeds.

While I am sure that there are flow rates at certain pressures for some of these thermostats,  it's really moot because they are designed to work inside certain parameters of the application.  But, high flowing thermostats definitely flow alot more!

FWIW,..... IMO alot of "hotrodders or builders or whatever" never fully analyze their "cooling" situation for the use or upgrade to high flow/volume pumps, not withstanding the issues aforementioned.  Yes, I know they cost more than rebuilt (which I never suggest) or stock or even OEM ....but are worth the muster frankly.  I get about a dozen emails a week asking for cooling issues that are easily remedied by either higher flowing pumps and/or higher efficiency radiators. It's usually flow related.

For example, if you put aluminum heads (aftermarket, stock or factory) it is likely that the cooling manifold (internal casting) of the aluminum heads are in fact SMALLER to offset the propensity of aluminum to "heatsink" the combustion chambers.  This is very common design practice and the need for upgrading the waterpump is a must to offset the increase in pressure drops!  Also, the increase of hp of an engine due to whatever improvement(s) also creates more waste heat needing higher flow rates to compensate.  This needs an upgrade. If you add more connnections to the coolant stream or use smaller hoses or lengthen the coolant path, this also affects pressure drops and warrants upgrades as well.  If you run your engine at higher RPMs (even tho your pump supplies more flow), stock and/or older pumps simply will drop the efficiency down and/or cavitate more causing all kinds of issues.  These are all good issues to consider a high quality aftermarket water pumps.

Also, if you DO upgrade your pump.....you will need an upgrade in cap too.  Commonly these high flowing/volume pumps will create more pressure in the system which means a higher cap is needed......especially on downflow radiators where the combination of working pump pressure at high rpms will surpass the caps ability to hold pressure.  I recommend at least a 14lb cap!

I know........too much information so I will get off my soapbox!

[2buck]

I never realized it took more pumping power to circulate the water in a multipass radiator. You never know what you can learn by reading thru the posts. Thanks

[Bruce Dorsi]

Me again, the proverbial thorn-in-the-side, back with more questions!

Steve, I believe that you have said that a thermostat or restrictor provides necessary turbulence to promote cooling.

So, my questions are as follows:

(1) Is the location of the restrictor/thermostat important?

....Would it not be more beneficial if it were located at the inlet of the radiator?

(2) If the thermostat/restrictor creates turbulent flow, doesn't the flow pattern change back to laminar flow in the radiator hose?

(3) What happens to the flow pattern as the coolant enters the (larger) volume of the radiator tank?

(4) Does coolant flow become turbulent when it is forced to divide into the many small openings of the radiator tubes?

(5) Isn't the flow inside the radiator tubes primarily laminar flow?  ....Especially so with wide tubes??


Yeah, I know, lots of questions, but I'm here to learn!