180 degree coolant and 215 oil temperatures have to be optimum for power, says Marlan Davis
https://www.motortrend.com/how-to/hrdp-0910-piston-ring-tech/sample quote
Control windage with a sophisticated oil pan and windage-tray setup. With a now-tight bottom end, you won't have oil flooding the cylinder walls, so a power-robbing high-volume oil pump is no longer required. Marginal engine coolant systems will no longer cut it, either; consider coolant system enhancements. For a nonemissions performance application, shoot for 180-degree F coolant temperatures and 210- to 215-degree oil temps. Get your carb and ignition dialed in right; washing down the cylinder walls with fuel isn't good for ring longevity. Combine all the tricks and details and the result will be more power.
end quote
My fuzzy memory is that one of the Aircraft Engine Companies did the first scientific study of cylinder bore wall wear versus coolant temperature and found that 180 degree was the lower wear minimum. I seem to remember Continental, although today they most make air cooled engines.
I think the bore wear graph in the link below comes from that older study.
http://www.carnut.com/ramblin/cool3.htmlMy interest in the “best” coolant temperature comes from an old link about year 1997 on the Evans Cooling website where one of their customers wrote he had done both dyno and personal vehicle tests at 260 degrees F and found fuel economy gains. This customer claimed to be employed at Ford as an engineer.
I searched for and failed to find a thermostat higher than a Robertshaw “Balanced Flow” 212 degree to put in a 1995 Magnum 5.9 V8 using Evans NPG.
Two one day/next day back to back identical 200 mile tests over I-40 between 180 and 212 thermostats showed a tiny 0.3 MPG improvement at 212 F,
but I now realize wind speed, wind direction and air temperature changes make that statistically insignificant.
It would take two pickup trucks traveling “convoy style” in a TMC/SAE RP1109 Type IV Fuel Economy Test Procedure rules for a two vehicle fuel economy test over maybe even longer than 400 miles to detect the real “statistically significant” MPG difference.
Later that Robertshaw thermostat failed in the closed position with NPG as coolant and I had to drive about 12 miles with coolant temperature showing over 250 degrees, but had no detectable damage.
Later still with a new working thermostat installed I did experiments with no fan attached to the viscous clutch.
One of the first experiments was to idle the pickup in park with no fan for several hours.
The dash temperature gauge showed a bit over 250, and the interesting thing was that idle vibration became very very smooth- much better than stock.
While driving without the fan on I got stuck stopped in a huge traffic jam on I-75 in Atlanta in 80 degree F weather.
The coolant temp went way high, but the engine idle was smooth, and the air conditioner was still blowing cold air.
But... after about 20 minutes I “chickened out”.
I turned off the AC,
turned on the heater at full blast instead, ( like Cannonball Run movie)
and rolled the windows down.
Got rolling again about 2 hours later.
No detectable damage.
