Oil Weights?

[DatDudeMIC]

I forgot what weight to use during the spring time. Actually what weights are best for the different seasons?

[Oracle427]

A modern multi weight oil is just fine. 20W-50 gives you good lubrication in temps found your average temperate zone.

A heavier weight oil may be considered in particularly hot climates, and I believe there are some lighter weights around for the extreme cold climates.

I think this was once a problem years ago, but the viscosity modifiers have come a long way in recent years. There may be engine model specific considerations, but on the IO-360, I have used 20W-50 with Camguard in temps from -10C to 35C with no issues at start with oil pressure being slow to rise or going too high.

The lubricant properties always come out normal during the oil analysis, so I'm not seeing evidence that it is breaking down between 50hr changes and our engine made it to 2400 hours before we opted to overhaul it.

[AKar]

Unless one specifically wants to simulate something else, I'd simply apply 20W-50 (or 15W-50 if using AeroShell for instance) and forget about the grade. It works throughout the temperature range one normally meets, and one runs into starting issues anyway in temperatures where the oil would start to show problems.

Recommended oil grades for different temperatures can be found from the Servicing chapters of the relevant manuals (POH, AMM...):



Interestingly, the latest revision of Lycoming Service Bulletin No. 480 from where these guidelines for oil change interval origin from, allows for increased oil change interval as detailed in the Service Letter No. 270, dated April, 2017. This specifies an extended oil change interval of 100 hours for engines that use unleaded fuel, and a transition procedure to apply. The 4-month calendar limit still applies. As an added bonus, an improved condition of spark plugs is expected.

This supports what Oracle mentioned about viscosity index improvers. The classic source of concern in use of multi-grade oils has been mechanical and thermal breakdown of the polymers that make up the viscosity index improvers. How the referred Service Letter words it, the main reason to limit the oil change to 50 hours would be the leaded combustion byproducts contaminating the oil, not the degradation of the oil itself. This is precisely as expected, due to still relatively short oil change interval and probably comparatively low mechanical stresses the oil is subjected to.

-Esa