Run two strokes a gallon of oil low to curb oil useage. Myth or fact?

[gus]

Yes, the drop in pressure is due to the decrease in sump volume of oil. That is when I know for sure to add more!!

If an oil pump draws air the needle will jump around. Had that happen in an airplane once and had to keep the nose level, pressure dropped every time I lowered the nose.

30-40 psi oil pressure is never going to result in any problems at moderate speeds (60-65mph) and probably not even at slightly higher speeds in a non-turbo DD.

The oil may get hotter but my engine runs so cool I don't worry about that.



The best way to check a dip stick is when you refill it after you change the oil and know exactly how much you have added. Check it as you fill it.

[belfert]

Somewhat related, but I worked summers at a fairgrounds that used a very old Farmall tractor to cut grass.  The oil pressure gauge was reading zero one summer and we assumed the gauge was bad.  It turned out the operator of the tractor hadn't checked the oil ever that summer and the oil level was WAY down!  Once the oil was filled the gauge started reading the oil pressure properly

The engine didn't seem to be hurt by zero oil pressure and it was used 40 hours a week for another 10 or 15 years before it was replaced by a new John Deere.

The moral is if you see zero pressure on a oil gauge, don't assume it is broken!

[akbusguy2000]

On the GM coaches that have the torus fan drive you will find that oil level is very critical at times.  On my 4106 with V730 here's what I have occasionally noticed when driving uphill, and especially in hot weather: 

Over time the oil pressure would gradually but slowly degrade to about 35 or 40 psi, and the coolant temp would rise to 200 or so at the same time.  Each time this happened the oil showed a gallon or more low.  I then added enough oil to bring it up to the full mark and the oil pressure returned to 45 or more and stayed there, and the temperature went back to 175 to 185 and stayed there.

Some folks argued that it's natural for oil pressure to fall in an overheat situation, but I believe it's equally likely for a low-oil situation to cause overheating.  However in my case I have concluded that when conditions dictate, the torus drive gobbles up and holds a gallon of oil or so, robbing it from the engine lubrication and cooling functions.  So, if the oil level is below full, overheating and pressure drop may occur.

I once thought about solving this little problem by installing a separate oil tank and isolating the torus from the engine, using the old manual transmission oil pump to supply the torus.  But more recently I have changed my mind.  The engine now has about 19000 miles on it after a major out of frame rebuild and the problem did not recur on the last two trips, totaling about 3000 miles during which the oil level remained at the full mark.

Thus I think the problem only showed up during the break-in period.  But it should also be noted that the same problem would llikely occur equally or more so in a tired engine.

tg

[Damn Yankee]

When I had my 4104 it would loose a gallon (from the full mark) within a few hours while driving. A gallon low seemed to be the sweet spot for the oil level. The 8v71 in my MCI will only loose maybe 1 qt every 3000 mi from the full mark. I think the biggest factor is the condition of your engine and how well it's sealed.

[BG6]

The oil dipstick markings are determined by stand testing of one of the first production engines.  They put the engine on a test stand and run it at various throttle settings, while they keep an eye on the oil level.  First they find "Test Low," the minimum level which will keep the oil pump inlet fully immersed at all RPM settings, then they find "Test High," the level which keeps the top of the oil below the bottom of the pistons at all RPM settings.  Remember, there is a hurricane in the oil pan, as the pistons move up and down (every CC of displacement in the combustion chamber is also a CC of displacement in the engine bottom end), return oil flows back into the pan, and the crankshaft splatters oil up into the cylinders.

Once they have Test Low and Test High, they move the ADD mark up and the FULL mark down, to make up for ullage (change in level due to sloshing, tilting, etc).

This means that the marks on the dipstick are not precise levels, they are based on a combination of testing and SWAG (Scientific Wild-@$# Guess).  Each individual engine has its own sweet spot for oil level, and when you find yours (the way the Johnny Deere guys said to do it), take a file and put a small nick in the side of the dipstick right at that level.  As long as your level is between there and ADD, you're okay.  As long as you're at or under FULL, you're safe from slapped pistons.

[zimtok]

The marks on my dipstick (no not that dipstick) are about 2 gallons apart. If the oil gets down to the low mark it takes almost 2 gallons to get it up to the full mark.

When full it will drop down to about the middle of the marks really quick, then it wil take longer to drop down to the low mark. I keep the level in the middle.


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