Scudrunners

I run Phillips 66 X/C 20w50 in the O-470.


I have a box of Aeroshell 100 wasting away by the Stinson.


I’m due for an oil change in 3 hours or so, so basically after this weekend. 


What’s the effect of draining and replacing during the next oil change?

well heck at this time of year, save that "thick stuff" for next summer. unless you fly a lot! get another case of the multigrade. otherwise you will head to november with w100 in the crankcase. I use w 100 for my june change, then i get to multi for my fall change.But you know all this already....

I hate that multi-grade shit, but you have to choose the
lesser of two evils ... and if you live up north where it gets
cold, thin base oil and plastic VI's is the lesser evil.

Straight grade is fantastic when it's warm outside.

Remember the pour point of W100 (SAE 50W) is only -20C
and that can congeal in your oil cooler in flight, regardless
of how much you preheat.

All that said, I have no idea why people run multi-grade
in the summer.  Makes no sense at all.

I run W100 year-round, but you already knew that  ;D

I suffer from Post Traumatic Snow Disorder.  I don't want
to see ice or snow or slush ever again.  Give me sunshine
and blue skies every day.

[quote author=Colonel Sanders link=topic=8997.msg24633#msg24633 date=1536416259]
All that said, I have no idea why people run multi-grade in the summer.  Makes no sense at all.
[/quote]
I’ve been thinking about that lately but as it pertains to my old truck.  It basically has an airplane engine in it: low RPM, almost comical torque (practically like a steam engine), and incredibly sloppy fits between moving parts inside.  For the sake of longevity and laziness in putting off an overhaul as long as possible I’ve been seeking the perfect oil and one thing I came across was that even for summer driving a multi grade may be better.  They may be advertised as acting like a thinner oil at low temperatures but the same applies at higher temps too.


Basically if you plot temperature versus viscosity, multi grade oils will have a flatter curve.  Is there a measurable benefit at high temperatures ?  Beats me, but it’s food for thought.

[quote]temperature versus viscosity, multi grade oils will have a flatter curve[/quote]

Sure, until the plastic VI's burn off, and then you've got
cat piss in your crankcase (thin base oil).

Sometime, change the oil hot in your aircraft engine.  If
you are running cat piss (20w50) it will run out like water.

W100 will run out much slower and thicker, at the same
temperature.

I worry about the cat piss running off an infrequently
flown engine, too.

[quote author=Colonel Sanders link=topic=8997.msg24644#msg24644 date=1536426117]
Sometime, change the oil hot in your aircraft engine.  If you are running cat piss (20w50) it will run out like water.
[/quote]
I’ll have to use my truck as the testbed, I only use single weight in the airplanes I care for as specified by the owner.  I think I have SAE30 in the truck right now and am probably due for an oil change in October.  Damn 500 mile intervals...