William Davidson Posted January 30, 2015 Share Posted January 30, 2015 I've got an '85 DM688 and I was wondering if it was OK to run 10W-30 in the winter (or all year round). I've always run 15W40 in everything but a couple weeks ago my Dodge Cummins spun a bearing and when we drained the 15w40 it was like grease not oil and I suspect that is why the Cummins had trouble. I don't want to repeat this mishap with another engine. The temperatures are running +15 during the day and 10-15 below at night. Thanks for any advice. Quote Link to comment Share on other sites More sharing options...
farmer52 Posted January 30, 2015 Share Posted January 30, 2015 The first number is the cold or winter number. There is not much difference in the viscosity between 10W and 15W. The best thing to do in the winter (extreme cold) is switch to a full synthetic oil, either a 5W-40 or 10W-30. You may experience some oil consumption with the lighter oils. So check the oil level regularly. It is okay to use 15W-40 during the spring/summer/fall months. Make sure it is a CJ-4 Diesel oil.As for the Cummins...likely a lot of soot causing the thickness. Quote Ken PRR Country and Charter member of the "Mack Pack" Link to comment Share on other sites More sharing options...
William Davidson Posted January 30, 2015 Author Share Posted January 30, 2015 The Cummins had an oil and filter change only about 500 miles before the problem so it wouldn't seem that soot would be the problem but who knows? Quote Link to comment Share on other sites More sharing options...
DodgeMan Posted January 30, 2015 Share Posted January 30, 2015 What type of filter are you running? Quote Link to comment Share on other sites More sharing options...
farmer52 Posted January 30, 2015 Share Posted January 30, 2015 What brand oil did you have in the Cummins? Most oils will flow like "honey" at cold temps. Quote Ken PRR Country and Charter member of the "Mack Pack" Link to comment Share on other sites More sharing options...
85snowdog Posted January 30, 2015 Share Posted January 30, 2015 This is out of a Mack maintenance and lubrication handbook from 1986.I use 15w40 myself (with a bit of lucas ). But our winter temps are not consistently below 0 F . I think if you click on it, it will be clearer Quote Keith Link to comment Share on other sites More sharing options...
Ezrider Posted January 30, 2015 Share Posted January 30, 2015 i am running 5/40 synthetic. first number is the cold flow number second is the hot viscosity so 5/40 is the same as 15/40 when everything is warmed up but flows better cold. Quote Link to comment Share on other sites More sharing options...
William Davidson Posted February 2, 2015 Author Share Posted February 2, 2015 Thanks for all the replies. I've been using Napa Gold filters on both vehicles. I bought the oil in bulk from Bay Oil Company and I've used their products for years both engine oil and hydraulic oil. I have been wondering if the motor oil deteriorated from sitting since I've had that particular drum for a couple of years.I'm planning to switch to Rotella 10w30 for the winter and change back to 15w40 next summer. I plan to use the remainder of that old drum of engine oil for bar and chain oil. I can't afford to ruin any more engines! Quote Link to comment Share on other sites More sharing options...
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