XJet
Posts: 3217
Joined: 3/31/2003
From: Tokoroa, NEW ZEALAND
Status: online
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quote:
ORIGINAL: pe reivers
yes, in fact, many have tried, and all went back to more oil.
In a car engine, the engine NEVER runs all out for longer than mere seconds, and then is throttled back again, relieving the loads on all parts. Due to the high rpm, lots of fuel passes the engine, so even with 10% mix lots of oil enters the engine as well.
Pe, it's been my experience with hi-performance 2-stroke engines (motorcycle racing) that high revs on a trailing throttle is the *worst* possible thing for engines running a pre-mixed fuel.
The problem is that when you close the throttle the supply of essential oil is effectively stopped -- but the friction continues because the revs are high.
Just about every hi-performance 2-stroke I've seen that's suffered sudden failure due to lube failure has done so during or shortly after a period of running on a trailing throttle like this.
From this, you'd expect that model cars would actually need *more* oil in their fuel than a model aircraft. When you snap the throttle closed on a model car, the inertia of the car and the effectively direct connection between engine and wheels (ie: the clutch is engaged) means that the engine is being turned at high RPMs by the wheels, but with no fuel/oil passing through it. On an aircraft, prop-slip means that snapping the throttle close results in a very rapid decay in engine-revs -- pretty much in proportion to the amount of fuel/oil passing through the engine.
quote:
In an airplane, the engine hardly ever runs at idle, but it uses full power most of the time at about 16,000 rpm.
That may have been the case 20 years ago -- but today I'd wager that things have changed somewhat.
For a start, most non-competition engines these days are propped for 12K-14K RPMs and many types of application (scale, 3D, aerobatic, etc) don't actually require protracted periods of full-throttle operation.
quote:
A customer runs MVVS engines with 10% oil, and is happy with it. He does mini tractor pulling, revving up to 30,000. I checked his engines, and they look like they still have at least ten years of hard service to go before anything wears out.
What oil is he running?
It's as much (or more) about the performance of the oil as it is about the quantity.
quote:
When I inspect my combat plane engines, running at 22% oil mix, I see a lot more grueling use. I have tried to run them at 10%, and they survived, but did not feel good at all.
Can you define "did not feel good"?
I have deliberately *tried* to destroy engines running with 12% lube and failed. This has included *very* lean runs (without castor) and protracted periods of hi-RPMs at full throttle.
While I'm sure there may well be a marginally increased rate of wear under such torture, no wear was measurable over the test period so I suspect that the amount of money you saved by using less oil would more than pay for the difference in engine life.
In fact, when you look at the price of oil, you'd probably find that the use of 22% is costing you the price of several *new* engines during the lifetime of one.
Just think -- if you ran less oil (and banked the money you'd have otherwise spent on that oil), you could probably afford replace that engine twice -- even though you probably wouldn't need to) over the same period of time.
What people seem to forget is that we used to run 20% oil back in the 1960s when engine design, construction and metalurgy were a *lot* worse than they are today.
How far did your car go between sets of rings, valve-grinds or new bearings back in the 1960s? You were probably lucky to get 80,000 miles before the engine needed reconditioning.
Now look at today's modern cars. It's not uncommon to go 200,000 miles+ before any significant engine work is required.
Why is that?
Better design, better manufacturing, better metalurgy and better lubrication.
Well guess what -- all that also applies to our model engines.
Use a *good quality* modern oil in your model engine and you *can* safely go down to 12% or lower without sacrificing a thing. Plus, you'll have more money in your pocket as well.
The only caveat to this is -- don't try and cut back on the percentage of oil if you're using one of the older US-made synthetics (such as those commonly found in US fuels). They're 1980s technology and not quite up to the task. There's no way I'd run 12% Klotz for instance!
The European ester-based synthetics and Coopers in the USA are a whole different (better) animal to the PAG-based oils used by most US fuel-blenders.
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All Forums >> Glow Engines, Gas Engines, Fuel & Mfg Support Forums >> RC Fuels >> Too much oil. 
Too much oil. - 
RE: Too much oil. - 
as the same stock engines using 25% nitro he gets 8 minutes per tank compared to 6 minutes for the others. That means his oil flow rate is roughly the same as the nitro fuel with 15% oil.
