Volvo 740: 5W30 vs. 10W30 upper temp limit

[dnastrau]

Hi everyone:

I have a '91 Volvo 740 and I am curious about something: The owner's manual does not recommend that 5W30 oil be used in the summertime (temps above 60F I believe), but 10W30 is OK. After all that I have read here, this does not make sense as 5W30 and 10W30 should behave the same way in warm temperatures, shouldn't they? Does anyone know what Volvo's reasoning behind this was? Was 5W30 oil from 1991 too unstable at higher temps? I currently use 5W40 Rotella Synthetic with excellent results, but am still curious about this. Any thoughts?

Thanks,

Andrew S.

 

[Pablo]

You nailed it - some conventional 5w30's were not so great.

New wave 5w-40 is fine in your red block.

 

[TeeDub]

The chart in your owners manual is for conventional oils and has little or no relevance for modern synthetics....

Many of the other European manufacturers also had similar viscosity/temp charts and SAE 15w40 used to be the thinnest petroleum oil they'd recommend for high temp use. Even the 5w-40/10w-40 grades were restricted to temps < 20C/68F as I recall and 5w30 was typically only recommended for temps < 0C/32F.

 

[dnastrau]

Thanks, guys - you confirmed my suspicions.

Andrew S.