Cooling Question

[secondchance]

Originally Posted by KFoster

Dynamite is correct. All those extra holes in the thermo could delay opening a little. Prob wouldn't notice. A good thermo has a bleed hole. All you need is one hole and install it at the top to bleed any trapped air. 180 is the way to go. And it will help some to have a fan come on at 185-190 but coolant flow is more important. With ac the fans should be running anyway, but idle in hotter temps is still going to stress the system. Too cool a thermo will result in the engine staying in "choke mode" in colder weather.


Sent from my iPhone using ZR-1 Net Registry

Also, possibility of building up water in the oil pan due to inability to boil off condensation in cold weather.

[Hog]

Remember the purpose of the thermostat, to delay cooling until its required. An air bleed is fine, bypassing the thermostat isn't.

The a major concern of an over cooled engine is cylinder wear. Not sure how a Nikasil cylinder bore would work into this.

[XfireZ51]

Frankly, I thought a stock thermo w a Fluidyne rad would have been just fine, but it appears to me that the under drive pulley setup may require some help at low rpms i.e. < 1500. The coolant temps were not an issue w the previous thermo until ambient temps got below 60F. Then I couldn't keep any heat in the motor at cruise.
However, now cruise rpm below say 1300 or sitting at a 900rpm idle, the temps creep up, albeit not rapidly. Once rpms reach above 1300 or so, temps drop fairly quickly and stabilize at about 187-192F.

[Hog]

Originally Posted by XfireZ51

Frankly, I thought a stock thermo w a Fluidyne rad would have been just fine, but it appears to me that the under drive pulley setup may require some help at low rpms i.e. < 1500. The coolant temps were not an issue w the previous thermo until ambient temps got below 60F. Then I couldn't keep any heat in the motor at cruise.
However, now cruise rpm below say 1300 or sitting at a 900rpm idle, the temps creep up, albeit not rapidly. Once rpms reach above 1300 or so, temps drop fairly quickly and stabilize at about 187-192F.

Your old setup was a stock therm. with 5 holes and caused difficulty with keeping heat in the engine at low ambient temps.

Now a new stock therm. with zero holes was installed and now you are getting some temp increase creep at very low rpms

I'm guessing that since the LT5 system was designed for high rpm usage that if waterpump rpm is affected by the aftermarket underdrive pulley setup, the combined effects are causing low coolant flow, which is then causing poor heat rejection from the system.

The old therm wasn't allowing the thermostat to do its job and allow the engine coolant to build heat, it was like driving with an always partially open thermostat. Which would be most problematic the cooler the ambient air was.

Speeding up the waterpump should solve your issue. EDIT:A small hole in the therm would help as well.

I was having trouble understanding the pre and post thermostat configurations at first. Sorry.

[Dynomite]

I see no difference between a 160 deg F thermostat and a 180 deg thermostat (both with the same Full Open Head Loss) once the coolant temperature has reached 190 deg F? I know the 190 deg F will be reached slower with a 160 deg F Thermostat but that is the only difference in that you reach the same Coolant Temperature at different rates of temperature increase. Kind of like using light weight pulleys to save HP which HP is only realized on acceleration as the rotational velocity of the pulley changes. Nothing is gained in a constant velocity (constant speed) situation.



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.

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 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.

1. 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.
2. 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.

[Hog]

Dyno:When you say "head loss" what are you describing?

[Dynomite]

Originally Posted by Hog

Dyno:When you say "head loss" what are you describing?

That is the pressure required to push the Coolant through the engine block and Radiator (and associated hoses including the Thermostat). That is a Hydraulic term describing the pressure required to push fluid through a pipe. The more pressure you apply the greater the fluid flow.

Or if you google Head Loss To move a given volume of liquid through a pipe requires a certain amount of energy. An energy or pressure difference must exist to cause the liquid to move. A portion of that energy is lost to the resistance to flow. This resistance to flow is called head loss due to friction.

The First set of Calculations is for The Pressure Drop in Oil Lines and is a bit complex but the same calcluations can be done with Coolant Flow. In the Second set of Calculations below we already know the flow characteristics of the Coolant Pump and Marc suggested the block resistance at 100 gpm is approximately 20 psi (which is the Head Loss at 100 gpm Coolant Flow) ...so a lot simpler as we really do not need the pressure drop unless we want to calculate flow rates (which we already have by measurements). In Marc's suggestion above the Head Loss is 20 psi.

Tech Info - LT5 Pressure Drop In Oil Lines Calculations
Tech Info - LT5 Coolant Flow Calculations

[XfireZ51]

Big jump in flow from 1000-2000rpm. Which is what I am experiencing.

I'm thinking 1-2 small holes to stabilize temps at low flow.

[Hib Halverson]

LT5s at low highway speeds in sixth, will run warm because of marginal flow speed through the cooling system. Underdrive pulleys will make that worse.

While there might be an advantage in a drag racing application, 160-deg 'stats run the LT5 too cool for good durabilty on the street. You need to be at least 170 and prefarably 180.

When I owned Barney, the "Purple Thing", I ran a 170 'stat with no extra holes, 0-10% antofreeze, Red Line Water Wetter, Fluidyne Radiator and lower fan on temps. Sixth gear cruse at 60-70 was usually 180-185. If I sped up or downshifted to fifth, ECT was in the mid 170s. In traffic I might see 205. In aggressive driving on an uphill mountain road with A/C on, the highest observed ECT was 216.

[Dynomite]

Originally Posted by XfireZ51

Big jump in flow from 1000-2000rpm. Which is what I am experiencing.

I'm thinking 1-2 small holes to stabilize temps at low flow.

The Thermostat is fully open at those temperatures which are in the range of 200-210 deg F even on 50 deg days (moving 65 mph in sixth gear at less than 2,000 rpm). Hib Halverson describes that situation very well

I run this unmodified 180 deg F Thermostat on ALL ZR-1s. You will notice there is BUILT IN BYPASS on the lower brass flange (two slots) to make sure the Coolant reaches constant and even temperatures as quickly as possible as this allows coolant to circulate in and out of the block (Not Through The Radiator) before it reaches a bit less than 180 deg F . It IS Important to have those two slots on the Recirculating Flow end of the Thermostat for the LT5.

You want to INSTALL The Thermostat squarely in the Housing making sure the rubber gasket is not pinched or otherwise corrupted as the Slotted End of the Thermostat could end up bound from opening or closing if the Thermostat is not squarely seated. One event could blow your Stock Radiator at High RPMS and the other event could cause Over Heating as the flow through the radiator would not be maximized.



I doubt a couple holes in the thermostat will help increase the Coolant Flow through the Block from maybe 30 gpm to over 44 gpm as it does when you shift to fifth gear. It is the Head loss through the block not just the thermostat the Coolant Pump is creating pressure against to increase the Coolant Flow. Your two small holes in the Thermostat is negligible compared to that total restrictions within the Block Coolant Passages.

As the Coolant Temperature moves downward towards the Thermostat operational range the Thermostat will close but will now have to close just a tiny bit further to compensate for your two small holes to keep coolant at 180 deg F Temperatures. Recognizing the Thermostat may start opening at slightly less than 180 deg F and be fully open at say 190 deg F.

The 180 deg versus the 160 deg thermostat or no thermostat