GlennRMK

Opinions on what oil to use in Montana in the winter?

Seen temps in the -30 range a few times. But not always. Around 0 is quite common though.

Should I put the Mobil 5w40 Truck and SUV in next oil change?

Have Premium Blue 15w40 Valvoline in now. Only 35k on her.

Marine

I am going to go with a 10w30 this winter.

Mike

RowJ

Bill, You and I have disagreed on the topic of synthetics before...and I guess we still do.
There are two reasons, IMO, why synthetics will go more miles than dyno...without changing filters & adding oil.
1-Ozidation -Dyno oil is much more prone to oxidation which will attack petroleum fluids and lead to thickening (viscosity increase) and deposit formations. Synthetics are, for the most part, impervious to oxidation brought on by heat, pressure, moisture, acids & metal catalysts.

2- Synthetic additive packages tend to be a higher quality level...to last longer and allow for longer change intervals. for example, Amsoil, Royal Purple, and a few others use a "harder" TBN additive, that depletes more slowly...allowing longer useful life.

I ran Delo 400, 15w-40 (IMO, the best dyno oil available today) for 7500 miles...and analysis showed TBN dropped from 12 to 6.9. Oil should be changed at 1/2 the starting TBN #.
I ran Amsoil 15w-40 for 10,000 miles. TBN only went from 12 to 8.4

RJ

infidel

I run Delo 15w40 year round but plug in. Seems to have worked fine for 400k plus and 10 years.
I'm in western Montana though, our below zero temps rarely last over a few days and it's not unusual to have periods of 50-60° for days at a time in the winter.
If my temps were similar to eastern MT I would most likely use a oil pan heater during the few below zero days just because our temps swing so much in the winter. If I couldn't plug in would use a 10w30.

Quote:

I ran Amsoil 15w-40 for 10,000 miles. TBN only went from 12 to 8.4

Yes, but did you change the filter mid way through and add make up oil?

RowJ

No....Fleetguard Stratapore went the distance in both cases.

RJ