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Mixing synthetic with standard engine oil

I am using Chevron Delo 400 15-40 motor oil in my ISX Cummins engine. I just had my rod and main bearings replaced because of metal in my oil sample and wanted to go with a synthetic blend 10-30 but my shop put the 15-40 back in. When I need to add oil can I add the 10-30 or the full synthetic Chevron to make it a synthetic blend? I have an Amsoil bypass filtration system and don't anticipate a total oil change for a good while.

I do enjoy your radio program and have gotten many good tips with both mechanical and business issues. I replaced my vibration dampner and added the crank shaft balancer from Pittsburgh Power and this Cummins has never run so smooth!

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You can add the 10W30 full synthetic as makeup oil. There is no problem in blending oils. You will just be creating your own blend. No problem at all especially if your doing oil samples too.

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Agreed. Makeup 10w30 will not affect things significantly. I would recommend staying with the same brand though. Additive packages of oils in the same brand are usually similar.

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I agree the only problem I have with 10W/30 is the fact that 10W/30 tops out at amibent temperature of 95 degrees

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Then why is 10w30 the recommended viscosity for all the current crop of engines year round.... Cummins, Volvo/Mack, Detroit. It would make a difference in a air cooled engine, but a water cooled engine with oil cooler, that argument falls on its face. I can recall in my younger days using 30w oils in Cat earth moving equipment in the heat of summer.

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Well Cliff I just purchased 2017 Ford f350 diesel and Ford inform me once outside temps reaches 100 degrees then 10W/30 has to be replaced with 15W/40 or 5W/40 in order to retain my warranty and I am sure that Detroit, Cummins and all the rest of motor manufactures I am sure has the similar requirements

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Ford made a broo ha ha about CK-4 saying it didn't meet their standard. But the latest Ford oil list has a stack of CK-4 oils, including 10w30. Not sure I would trust much of what Ford has to say about things outside of their own engines, they can't seem to get their own act together. But Cummins, Volvo/Mack, Detroit, Navistar, Paccar all recommend 10w30 year round. And have for several years now. I would think that they probably have it all worked out over those years. I know of several individuals with both Cummins and Detroit engines that have been using 10w30 year round for over 3 years. Even in my Detroit 60 12.7 pre-EGR, I am using a Schaeffer 10w30 syn blend, and all this year it has been CK-4 variety. It is a factory reman engine with 768,000 miles on the reman and it still only uses about 1 quart of oil each 11,000 miles. And UOA's look as good as they did when the engine only had 50,000 miles on it. So one is going to be hard pressed to convince me that 10w30 will not work.

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I am glad this is working for you but I've got warranty to protect. Ford only allows 10W30 providing its below 100 degrees

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