Overfill = More oil pressure....explanation?

[Phishin]

My final viscosity in the pump is all over the place.

I put a quart of MMO in the sump not too long ago, and then topped off twice using 2 quarts total of 20w50. She was getting hard to start in the morning (cranking was a chore) but I wasn't that low on the dipstick, and added another quart of MMO anyhow. That's how I got over filled.

Your guess is as good as mine what the effective viscosity in my truck is.....It has 5000 miles since the last complete oil change. It started with 5 quarts of Valvoline 10w40 conventional. In those 5000 miles, I've had 3-5 quarts of MMO through her and 5-7 quart of various oils I have laying around, including 2-3 quarts of 20w50. I'm always adding oil/MMO to the sump.

 

[LeakySeals]

Ok. My guess is running with a brew consisting mainly of 10w40's and 20w50's in 4-8F weather is causing increased friction/increased oil pressure at the sending unit. But not in other parts of the engine where oil is likely bypassing the pump. Leading to increased ticking, engine wear, etc. The price to be paid using thick oil with poor flow to slow oil consumption.

 

[Phishin]

Originally Posted By: LeakySeals
oil is likely bypassing the pump. Leading to increased ticking, engine wear, etc. The price to be paid using thick oil with poor flow to slow oil consumption.


Actually, the truck always sounds the best in the winter. This is my second winter owning the truck. Yeah, it's got 10w40's and 20w50's in it.....but there is always a quart of MMO in there as well. The truck doesn't tick in the winter. Only in the hot summer. This summer, I'm gonna try a sump full of 20w50 and see if that gives me the same results that winter does.

 

[dailydriver]

Originally Posted By: INDYMAC
Maybe it's colder outside than you're normally used to.


^^^THIS.

Hasen't it been like near 0*F there during the day recently with this Arctic Circle cold front we're experiencing now??

 

[toneydoc]

Personally I would not use MMO in my crankcase, EVER. If I need to thin the oil, I will use thinner oil to start with and as a make up oil. And I never use 10w40 or 20w50 in the winter months or summer months, come to think of it. Probably your oil is too thick and therefore higher pressures

 

[widman]

Originally Posted By: TFB1
Originally Posted By: widman
Actually, adding too much oil (amount of "too much" varies by engine) causes foaming from being beaten by the counterweights and bearing caps. Foam is like pumping mayonnaise. It does not want to flow, especially through the filter, so the pump creates pressure instead of flow.

Adding more than the fill line is bad.

I got to call ya on that one, oil will aerate and become full of bubbles, loosing pressure but it will recover when the motion is stopped... If it turns into the kind of mayonnaise I'm imagining, there's moisture involved...



It takes quite a while for air bubbles to get out of motor oil. Turbine oils are designed for that. Motor oil to a certain extent. I said foam is like mayonnaise. I didn't say that this amount of air would turn the oil completely to that consistency. But as you noted, the moisture in the combustion chamber will also be incorporated into that foam.

 

[dailydriver]

Originally Posted By: toneydoc
Personally I would not use MMO in my crankcase, EVER. If I need to thin the oil, I will use thinner oil to start with and as a make up oil.



I am not going to get into the whole MMO flame war/conflict/polarization on here, BUT, I DO agree with using thinner, very high quality, high VI, OIL to 'thin out' a sump mixture.

(Same with 'thickening up' the sump contents using a higher HTHSV, but high quality/high VI oil.)