LT5 Cooling and Radiators

[HAWAIIZR-1]

Originally Posted by Dynomite

One item not discussed in this thread of which I have since experimented with is Engine RPM effects on Water Pump Flow and Engine Cooling.



1. Conditions



A. Fans turn on at 205 deg F and OFF at 200 deg F (Haibeck Chip)

B. I use 180 deg Thermostats.

C. Ron Davis, Dewitt, and Fluidyne multi core Aluminum Radiators.



2. My experience with Engine RPM (depending on Gear Driven 6th, 5th, 4th) in all ambient temperatures.



A. In sixth gear running 65 mph (less than 2,000 rpm) the Coolant always gets a bit over 200 deg F. On Hot days the coolant will get a bit over 213 deg F. The key is the Water Pump is not pushing enough flow through the fully open thermostat to cool the engine to a Temperature where the Thermostat takes over (180 deg F).



B. If I shift to 5th gear at 65 mph (more than 2,000 rpm) the coolant temperature drops to Thermostat control (180 deg F) on cool days and drops to near 200 deg F on Hot days.







3. Findings.



My findings are simply that the stock water pump is a bit low on coolant flow rate at rpms under 2,000 rpm. As you can see there is a big jump in Coolant Pump Flow rate between 1,000 rpm and 2,000 rpm and it is in this area or engine RPM that the Coolant Flow Rate is not sufficient in HOT Climates. This is specifically the overheating issue when idling at a stop sign on HOT days (100 deg +). If you raise the rpm from 800 rpm to say 2,000 rpm, coolant temperature will drop appreciably even though you are not moving.



The Coolant Pump Flow at 800 rpm is 15 gpm. The Coolant Pump actually gets more efficient as the rpm increases from idle to 2,000 rpm.



4. Water Pump Flow Rates.



As Per Marc Haibeck graph provided to the ZR-1 Net email list by Graham Behan about ten years ago, the Coolant Pump flow rate is:

15 gpm at 800 rpm

18 gpm at 1,000 rpm,

44 gpm at 2,000 rpm,

65 gpm at 3,000 rpm,

90 gpm at 4.000 rpm,

120 gpm at 5,000 rpm at which time cavitation is starting.



A. The Dual Thermostat Bypass pressure is apparently 5 psi and block resistance at 100 gpm is approximately 20 psi. I am not sure what the radiator Head Loss is at various flow rates but definitely depends on the radiator type.

B. It would seem that the Coolant Pressure Relief Cap on top of the Coolant Reservoir in front of passenger side set at 15 psi would assure the radiator maximum pressure would be 15 psi plus the Bypass Pressure of 5 psi or 20 psi.



See Item #5 The 180 deg versus the 160 deg thermostat or no thermostat

Always a wealth of valuable details and info Cliff. You mention in other posts that you never drill any holes in the thermostat. Is there any reason why you feel 1 or 2 (or more) holes is not good or will make a difference in the lower rpms off idle or while stuck in traffic? The reason I ask is my area puts me in a lot of bumper to bumper until I can get to the expressway. Thanks!!! Craig


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[QB93Z]

Cliff, I agree completely with you analysis of the coolant flow at low engine RPM. I have observed that effect on many different ZR-1's.

With a brand new radiator, there is marginally enough coolant flow and air flow to maintain coolant temperature in the thermostat operating range. But as the radiator air flow is compromised due to fin blockage (ie age), the temperature of the coolant will rise until the larger coolant temp to air temp differential will allow more heat transfer and the coolant engine temperature will stabilized above 200 degrees.

Jim

[Dynomite]

Originally Posted by HAWAIIZR-1

Always a wealth of valuable details and info Cliff. You mention in other posts that you never drill any holes in the thermostat. Is there any reason why you feel 1 or 2 (or more) holes is not good or will make a difference in the lower rpms off idle or while stuck in traffic? The reason I ask is my area puts me in a lot of bumper to bumper until I can get to the expressway. Thanks!!! Craig


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As I calculated, 1/8 inch diameter holes just are way to small compared to the wide open area available when the thermostat is completely open to have any effect. However, a few 1/8 inch diameter holes would not hurt anything as far as too low a temperature for the same reason and......these small holes will allow some air to travel from the engine to the top side of radiator when thermostat is still completely closed. I just do not bother with the holes and have no issues with air as I have explained in my Coolant Filling techniques discussions.

Also.......Marc suggested at one time the older Stants will deteriorate (Decrease in FUll Open Area) by up to 15% as they age. A thermostat with over 50k miles generally opens 5 degrees later and opens about 85% and that far exceeds the additional Coolant Flow Area created by small 1/8 inch diameter holes. SO......along with replacing Original Injectors, Refurbishing Original Starter Solenoids, Installing Aluminum Radiators in ZR-1s and Replacing ALL Fluids as part of Reconditioning, I also Install New Stant 180 deg Thermostats in ALL ZR-1s. Oh....and I also Install the Starter Relay and Carter Bling as part of Reconditioning and some other things.

See Item #6 regarding additional holes in thermostats. The 180 deg versus the 160 deg thermostat or no thermostat

Originally Posted by QB93Z

Cliff, I agree completely with you analysis of the coolant flow at low engine RPM. I have observed that effect on many different ZR-1's.
With a brand new radiator, there is marginally enough coolant flow and air flow to maintain coolant temperature in the thermostat operating range. But as the radiator air flow is compromised due to fin blockage (ie age), the temperature of the coolant will rise until the larger coolant temp to air temp differential will allow more heat transfer and the coolant engine temperature will stabilized above 200 degrees.
Jim

Thank you Jim for the confirmation and I completely concur with your radiator cleaning techniques and discussions. There are many stock ZR-1 Radiators as well as relatively New Aluminum Radiators in ZR-1s compromised by leaves, plastic bags and Oil Cooler leakage creating an oily situation which collects dust on the Oil Cooler fins as well. There IS a reason for the Screen installation in front of the air flow opening on a ZR-1 as that will at least keep the leaves and plastics from stopping the air flow through a radiator. That additional screen is very accessible for inspection and very easy to clean of trash.

[A26B]

Originally Posted by Dynomite

As I calculated, 1/8 inch diameter holes just are way to small compared to the wide open area available when the thermostat is completely open to have any effect.

Empirical trumps theoretical. Over the years, there have been numerous, noted improvements in cooling efficiency as a direct result of drilling holes in the thermostat flange. A very few follow.

1. Source-My personal experience; with a new Woods 160F thermostat on the bench, I decided to drill 3 holes in my "old" stat. The results were so definitive, I never replaced it with the 160F. [415ci, Ron Woods Radiator].

2. Source-Memory, not verified ; Secondchance here on the forum, had 3 holes drilled. Ran too cool in winter, replaced with another t-stat, drilled 1 hole & achieved desired results for year-round driving. [385ci, stock radiator].

3. Source-Memory, not verified ; XFireZ51 here on the forum, has 1 hole drilled. Desired improvement noted & retained as effective aid to cooling. [stock displacement? radiator?]

There are more cases of drilled t-stat flanges out there, I simply never took the time or made the effort to document them. I answer quite a few tech questions from Jerrys Gaskets customers, including cooling issues. I have drilled new thermostats by request before shipping to customers.

I don't take exception to your mathematics. I just believe the the holes have a more dynamic effect than simple enlargement of. cross sectional area. This is a subject worthy of documentation. In that regard, keeping it simple such as number of holes drilled & results restrained to categories such as "no change," "slight improvement," effective" & "excessive cooling."
I think there are too many variables to try & pin it down so the factors can be quantified & calculated.

It would be useful to read posts from those who have drilled t-stat flanges.

[Demps]

I have a good problem to have...I guess. I'll give my experience today...if I get to it after injectors, brake bleed, then thermostat drill.

Ted

[HAWAIIZR-1]

[QUOTE=Dynomite;259697]As I calculated, 1/8 inch diameter holes just are way to small compared to the wide open area available when the thermostat is completely open to have any effect. However, a few 1/8 inch diameter holes would not hurt anything as far as too low a temperature for the same reason and......these small holes will allow some air to travel from the engine to the top side of radiator when thermostat is still completely closed. I just do not bother with the holes and have no issues with air as I have explained in my Coolant Filling techniques discussions.



Also.......Marc suggested at one time the older Stants will deteriorate (Decrease in FUll Open Area) by up to 15% as they age. A thermostat with over 50k miles generally opens 5 degrees later and opens about 85% and that far exceeds the additional Coolant Flow Area created by small 1/8 inch diameter holes. SO......along with replacing Original Injectors, Refurbishing Original Starter Solenoids, Installing Aluminum Radiators in ZR-1s and Replacing ALL Fluids as part of Reconditioning, I also Install New Stant 180 deg Thermostats in ALL ZR-1s. Oh....and I also Install the Starter Relay and Carter Bling as part of Reconditioning and some other things.



See Item #6 regarding additional holes in thermostats. The 180 deg versus the 160 deg thermostat or no thermostat

Cliff,

Thanks for your thoughts. I did not think the 1/8" hole was for air and thought just to aid a little more coolant flow despite how little. It is amazing to hear how 3 holes can be too much and cause the car to run too cool in certain conditions. I know you spend a lot of time in your analyses and it is valued for sure.


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[A26B]

Originally Posted by Dynomite

Thinking your 160 deg thermostat was going to offer greater cooling at high temperatures is suspect thinking.....was that theoretical thinking?

I never thought such a thing, knowing well that a cooler thermostat can only enable, not create.
Acquiring the 160F thermostat was not theoretical thinking, it was to be an experiment.

BTW I noticed several references in your posts pertaining to "up to 15% degradation" in thermostats as they age. That's a pretty broad range & doesn't actually state that any occurs at all. Details would really shine some light on this subject. Is it linear? does it always affect the range of the valve aperature?

[Hog]

OEM radiator
YEARS 1990-92 1993-1995 Core Thickness 1.34 in. Same Frontal Area 405 sq. in. Same Radiator Cap 17 psi. Same Thermostat Open 180 degree F Same Fully Open 195 degree - 200 degree F Same

Coolant pump
YEARS 1990-92 1993-1995 Type Centrifugal Same Capacity 12 gpm @ idle 85 gpm @ 7,000 rpm Same Supplier Ace (Casting) Same