What grade of oil do you use in the winter time?
 

Ive always used Rotella 15-40 through out the year here in Houston ,have now come across some harder starting issues once 40 or below temps come into the area.Ive have done all the necesary upkeep on the glow plug system but have never thought about oil viscosity as being the issue.

I would keep that in your car and just leave the glow plugs connected for 45 seconds... just leave the key there... no restarts... time it... this is recommendation from the FSM..

What car do you have?

I use 15w40 year round, down to about the coldest temps we get here in Tucson (which can be subfreezing, down in to the 20's, overnight) and haven't had any issues starting.

If your glow plugs are indeed pretty fresh, and working well, you might look in to the health of your battery, the condition of the battery cable (can be hard to discern since it's wrapped in insulation, but if it's of unknown age, it would be worth looking at as closely as possible), and the health of your starter. If your engine is not spinning fast enough under cranking, good glow plugs won't be enough.

If you've been using the same viscosity oil for multiple years and are only now having a problem, I'd look at something else. Old battery? When's the last time you adjusted your valves?

I run 5w-40 during the winter, temps in the teens.

You might need a starter,I bought my starter,and alternator at Advanced Auto Parts,they work fine.Forget the BS about buying Bosch,and save your hard earned money.

I run the Shell Rotella T6 5W40 year round.

Today there is no good reason to use different oil in the summer than in the winter. Todays multi-vis oils cover a wide range of temperatures, and the synthetics such as 0W40, cover even arctic conditions. Of course, a heating device may be needed in true arctic conditions. Your oil should be fine year around in your location. A problem starting is an indication that something else is going on, in my opinion.

Lubro Moly 5w40 Full Synthetic (what I use year round)

Temps around here range from 7°F in the winter to 110°F in the summer.

If you are having trouble at that temperature with 15w40 in the crankcase, I would second the remark about your starter and/or the battery, but also ask when the valves were last adjusted.

I use 5w40 Rotella but around here it gets COLD in the winter and 15w40 is fudge in those conditions.

I use 5w40 year round.

-J

Delo 400 15w40 all year in both 300SDs. I glow longer when it gets below freezing.

Synthetic. I think 5W40. Going to synthetic makes a difference in the winter so I just switched for all diesels. Valves are adjusted.

Used rosmella for years but have now switched to NAPA 15-50 Full Synthetic caught the sale in Oct.
Been working Great here in St. Louis, also rebuilt my starter and have the valves adjusted and glow plugs cleaned.

Once it gets warm I will go back to Valvoline Blue, started that this past summer and Alfred loves it, got a sale at Rule King $10.88 gal so bought a case.
greazer2b

Delo synthetic 5 - 40 in the SDL.