LT5 Cooling and Radiators

[Dynomite]

A lot of guys get caught in traffic on HOT 100 deg F days observing the temperature gauge move toward the cross hatch area (230 deg F +). That seems to be typical of the Cooling System for the LT5 in traffic with AC ON. And those High Engine Coolant temperatures often caused by trash between the AC Condenser, Oil Cooler or Radiator or trash on ALL three. Especially if there is any oil film on the Oil Cooler.

I am installing my third Ron Davis Radiator tomorrow in what was suppose to be my Stock 1990 in CA.....did the same to what was suppose to be my Stock 1990 in SD.

I will take the 1990 for a run when it is 100 deg F ambient today with stock radiator and then another run tomorrow in 100 deg F ambient with the Ron Davis. Including idling as in sitting at a stop light for both (Stock and Ron Davis) with air on and off to see what maximum coolant temperatures are like for both Stock and Ron Davis.

Originally Posted by XfireZ51

With both fans running, my Fluidyne is keeping coolant temps at 90C at idle in 95F weather.

Yesterday took a 1991 with Ron Davis Radiator for a cruise with 95 deg F ambient and Coolant stayed around 194 F cruise (60 mph) and rose to 206 F with Air On Idling. This using the Fan Controls for Digital Read Out of Coolant Temperatures.

This testing with the same identical AC Condenser, Same identical Oil Cooler, Same Identical Coolant Fans and same identical 180 deg Thermostat.

The objective here is to create a baseline of simple testing criteria to determine how ZR1 radiators (1990 and 1991) will function cruising and in traffic (idling). The simple baseline criteria are 100 deg ambient temperatures, 180 deg thermostat, and functioning AC.

If you want to test radiators....this is the time here in central CA
Jun 16
Hot with plenty of sunshine
98°Lo 61°
Jun 17
Blazing sunshine and hot
101°Lo 63° more
Jun 18
Blazing sunshine and hot
101°Lo 62° more
Jun 19
Hot with plenty of sunshine
100°Lo 64° more
Jun 20
Hot with blazing sunshine
103°Lo 66° more

Note:

Engine RPM.

My experience 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.

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 when the ZR-1 is moving in 6th gear at 65 mph.

The overheating issue when idling at a stop sign on HOT days (100 deg +) is more related to Fan Air Flow.
Tests at 50 deg F ambient.
Going 65 mph in 6th (1500 rpm) coolant temperature 205 deg F.
Going 65 mph in 5th (2200 rpm) coolant temperature 192 deg F.
Idling at 750 rpm coolant temperature 204 deg F.
Engine rpm 2000 rpm (not moving) coolant temperature rose to 213 deg F.

So...….At 65 mph it is the coolant flow. At 0 mph (Not moving with rpm at 2,000) it is the air flow.

If I could get the air flow higher while in traffic the issue would then be the coolant flow again where keeping rpm above 2,000 rpm would solve the High coolant temperatures on hot days in traffic.
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.
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 through the engine (not the radiator or thermostat) 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.

NOTE:

See the following post for a complete update regarding Engine RPM.

Post 7 - Thermostats, Fans, Water Pump, and Radiators