Optimum oil and coolant temperatures - photo upgraded

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Guy Croft
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Optimum oil and coolant temperatures - photo upgraded

Post by Guy Croft » Tue Aug 08, 2006 3:04 pm

This is in another thread but I have posted here for accessibilty:

Here is the actual dyno data that my references in the GC book came from, StIV long oval TC Fiat 2 liter NHRA engine, tested direct back-to-back in summer 1995 at Warrior Automotive, Superflow rig, corrected BHP is shown against preset water and oil temps. I was unable to find out the effect from any book, that is why we did these tests. I should be interested in anyone else's results.

From these results of average water and oil temp deg C plotted against the power I concluded that best settings were:

Water: 70-75 deg C
Oil: above 85 deg C

The dyno cell was temperature controlled, the 'hot water power loss' is of course due to loss of charge density by heat transfer in the inlet tract.

The issue of oil temp is critical from a number of practical points of view.
Too cold - say below 81 deg C and there is a measurable power loss from drag. With dry sump and later engines with internal-external crescent gear pumps you can run the oil hotter than 85 deg C of course because hopefully the pressure stage of the pump can cope with the bearing bleed-out rate when the oil is going very thin; not so the early Fiat TC (and many other) twin mesh gear pumps used on engines like the one under discussion here, I would not advise that. 85 deg C is certainly not cold as far as power is concerned and is plenty hot enough to evaporate off any moisture - or anything else (like gasoline) that may be in the oil. Also it's important to check the operating temperature of the engine oil seals, if you exceed it they will start to vulcanise.

for what it's worth in this case, in all the tests I did at Warrior I never determined any power increase from going higher than 85-88 deg C.
I say rather vaguely '85-88' of course because as the power comes on the oil temperature tends to rocket, and the thermostatic control won't stabilise unless you give it time to react. These figures are taken from computer-controlled 500rpm step tests with 15 seconds stabilising in between, but even then there is a variation of a degree or so throughout the run, hence average temp figures are cited.

I do claim to be the absolute 'authority' on this, other experienced engine builders may have decided on other temperatures for good reason. This is what this forum is for.
Effect of water & oil temp on power.GIF
Showing the advantage of oil and water/engine temperature on power.
Effect of water & oil temp on power.GIF (18.67 KiB) Viewed 6466 times


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