I apparently don't understand oil weights

[LouNY]

Every manufacture has a different suggested oil weight for different temperatures,
that particular manufacturer in that specific application decided that 5w-30 would not be the recommended oil for operation
in temperatures above 50F.
Your specfic application from your particular manufacture desires a synthetic 5W-30 for all temperatures.

 

[deezler]

Another thing to keep in mind might be the quality of residual oil film for "cold" starting.

The last number on a multigrade oil is the HOT rating, at 100C. But on a hot summer day you are still only starting the engine at 30 or 40C max. A 5w30 oil is still thinner than a 10w30 oil at 40C - they really only converge to the same 30W rating at truly hot temps (100C).

Tried to find a good image to represent what I am saying, but it was surprisingly difficult.

 

[LouNY]

It has always amazed me how similar the viscosity of gear lube and motor oil are,
that a 75W-90 gear lube isn't really much heavier then a 10W-30 motor oil,
untill you get to higher temps then the motor oil is actually more viscous.

 

[RalphVa]

This is from my generator Install (left) and Operator's (right) manuals. If 5W30 is supposedly only good below 50F, why are they spec'ing it for all temperature ranges?

Also note, they supply 'organic' oil, but recommend synthetic.

View attachment 689323

5w30 is good for the 212 F it sees against your thermostatically control cooling water typically at 190 F.

 

[RalphVa]

Another thing to keep in mind might be the quality of residual oil film for "cold" starting.

The last number on a multigrade oil is the HOT rating, at 100C. But on a hot summer day you are still only starting the engine at 30 or 40C max. A 5w30 oil is still thinner than a 10w30 oil at 40C - they really only converge to the same 30W rating at truly hot temps (100C).

Tried to find a good image to represent what I am saying, but it was surprisingly difficult.

The plots are a straight line when fitted against log of viscosity vs. 1/T. Here's a graph of the crankcase and transmission/diff oil ranges. The transmission/diff oils are just rated at 40 C vs. 100 C for engine oils.

 

[grsthegreat]

This is from my generator Install (left) and Operator's (right) manuals. If 5W30 is supposedly only good below 50F, why are they spec'ing it for all temperature ranges?

Also note, they supply 'organic' oil, but recommend synthetic.

View attachment 689323

they want engine to break in with non-synthetic oils is the only reason. they recommend swapping to synthetic after 25 run hours.

 

[bcp]

I worked for over 3 years in the 1960's as a petroleum lab technician, and this thread really shows how much I've forgotten. Or how much things have changed.

Bruce

 

[Username Taken]

Bob Is The Oil Guy

Bob Is The Oil Guy

bobistheoilguy.com

 

[Sberry]

It isn't the hot rating. It's the cold so to speak. If the ambient is below the hi number they suggest a lower weight oil. Got nothing to do with it's hot performance. They are saying when the ambient is cooler use lighter. It's still about cold starts.

 

[RalphVa]

It isn't the hot rating. It's the cold so to speak. If the ambient is below the hi number they suggest a lower weight oil. Got nothing to do with it's hot performance. They are saying when the ambient is cooler use lighter. It's still about cold starts.

That makes sense. I tried to find someone to talk to who made those charts and could not find out how.