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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