The oil temperature, 180 F in your example, is measured where the oil enters the engine after the oil cooler. After working its' way through the engine, before entering the cooler, the oil is about 40 degrees warmer, say 220 F in your example. That's above the boiling point of water... that's how hot the oil gets on its way to the sump where it can evolve that water into vapor out the crankcase vent. Works pretty well, actually.
Well that’s enlightening info actually. Which makes me wonder other than cheaper sensors, why measure at the coldest point.
Also makes me wonder why the quote from the engine maker says the oil has to reach the low temp instead of the actual oil temp. Just laziness/convenience of where most people would be measuring? Their wording doesn’t really hint at a location or how to measure.
Which leads to the question again of why we aren’t more specific in these words.
They probably don’t say “indicated” temperature for a reason? Lawyers don’t trust indicators? Differing installations? Etc.
We sure get specific on turbines but these old ass tractor engines, we still do the 1930s and 40s vague stuff with 1970s car gauges.
Any modern engine the engineer just sticks the sensor exactly where they want it and the computer won’t let you harm it. But I know... too newfangled for light GA and piston power.
I think it’s funny that the top minds in piston power plant tech tell us all to get engine monitors. So yay. We’ll have 1/8 the sensors giving us data that my 20 year old car with an OBD port provides. Haha. Oh by the way... interpret it yourself. Why would we program a microcontroller to do that?
On the flip side, that same “abused” engine with vague data and just pouring fuel through it, will probably make it to TBO and beyond. They’re big sloppy motors that take an impressive amount of abuse, but they started as stuff that would survive great-grandpa beating them up on the farm. Rebuilt them on the farm, too.
We act like they’re really fussy but on the low compression ones at least, they’re not that fussy.
I just like seeing reasons behind the numbers. 180F being the lowest temp in the engine because we are measuring at the coolest point, works for me. That isn’t exactly the wording quoted from the manufacturers though.
I’d also like to see a 40F split measuring the other side of the cooler but haven’t seen anybody do it. Seems like one could even do that inaccurately with an IR gun these days since that plumbing is visible.
Ground idle with occasional blasts of full power. 200F below the metal damage point. If you see 40F delta between the intake of the oil cooler and output, are you really losing 200F from the damage point to the oil cooler?
Be fun to give one of our typical engines to a modern race team and instrument it up as much as they do theirs.
@Ted DuPuis probably came the closest of anybody here who’s talked about it. And of course the late Ben H.
It’s kinda like digging for the basis of the MP green arc on the O-470 182s.
“So what’s this based off of?”
“The POH.”
“So Cessna based that off of a recommendation from Continental?”
“No.”
“What did they base it off of?”
<Blink...> “Stuff...”
“Vibrations? Prop? Anything?”
“Not that anybody has found published anywhere.”
“Okay. Well we’ll teach ‘em to keep it in the green...”
Now there are engines and prop combos we can find real data on, but some... nope. So I’m just saying it’d be really cool if we had data.
How many decades did the oversquare garbage from radials stick around in the straight engine folklore?
Or here we go. Shots fired... Shock cooling” affecting every single installation and flight profile? Heh.
That said I do love my obnoxious 13-15 GPH lumbering six cylinder monstrosity and avoid the things the old folks say are bad for it. Just don’t have any real data to prove much of it.
The power table in the book is based off of some WWII guy saying identical numbers were good, basically. It took until the late 90s to debunk that.
