After trying both a full synthetic and a conventional 15W-40 in my old 7.3 Powerstroke, the synthetic's cold start performance in our Wisconsin winters was the clear winner.

The conventional oil took over 5 seconds to build decent pressure below 20 degrees, while the synthetic was under 3, so what's your go-to winter oil for older high-mileage engines?

3 comments

3 Comments

wadea531mo ago

Full synthetic 5W-40 is the only way to go for winter starts on these old diesels. I ran conventional 15W-40 in my 7.3 for years and it just got too thick below 20 degrees, sounded like a bag of marbles until oil pressure came up. Switched to 5W-40 full synthetic and it cranks easy, pressure builds quick, and no more rattle on cold mornings. If you've got an older high-mileage engine, that thinner winter grade is what saves the bearings and turbo from dry starts. Just make sure it still meets the older API specs your engine needs, most quality synthetics cover that.

wells.brooke2mo ago

Yeah, that cold start difference is huge for engine wear. I was just reading a forum thread where a guy with a high-mileage Cummins had the same result, even after switching to a synthetic blend. He said the main thing was finding an oil that met the old specs but still had modern additives. For my own truck, I stick with a full synthetic 5W-40 once the temp drops, it just seems to crank easier and get oil moving faster on those first cold mornings.

sullivan.nina2mo ago

@wells.brooke You're not wrong about the cold starts. My old truck sounded like a coffee can full of rocks until the oil warmed up. That forum guy hunting for the perfect old-spec oil is basically doing alchemy at this point. Just run the good synthetic and save yourself the headache. Watching people overthink oil is a full time hobby for some folks.