40 weight in OPE that specs 30 weight

[Oldtom]

I have been reading that a lot of folks use multigrade with a top weight of 40 in OPE that specs 10 W 30 or straight 30 weight. A lot of small engines are splash lubed and the oil has to get into the bearing by capillary action. Would a heavier oil not wick into the bearing as well? Not downing anyone's favorite OPE oil, just trying to understand the logic behind using heavier than spec oils.

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Thanks in advance for your reply

 

[Jetronic]

the multigrade only becomes thicker than the SAE 30 around 80°C (around 175°F). But once in the bearings, the situation is reversed, the multigrade will temporary shear down in viscosity and the SAE 30 not. To get similar viscosity in the bearings at operational temps, you need to go up a bit with a multigrade.

When you start the engine and the oil is barely 75°F, the SAE 30 will be more viscous than the multigrade and about 5 times the viscosity at operating temps. Are you running with improperly lubricated bearings until that time?

 

[gfh77665]

I always run SAE 40 wt.

 

[BrocLuno]

It also depends on how hot the daytime temps are that you are operating in. A lot of us use Rotella T6 5W-40 for OPE and that is a bit on the thin side for a 40.

 

[IndyIan]

I like T6 5W40 as a year round oil for everything but the cars and the 2 strokes. Starts well enough in our cold and may offer some additional protection over a 30wt oil in high temps? I don't run my OPE except the ATV when it get really hot so maybe it doesn't matter. I also extend the OCI a little with T6 for the cheaper stuff.

 

[Lubener]

I have used 40 weight with oil burners and "loose" engines.