We own a 2002 F-350 crewcab dually 4x4 with the 7.3 PS, 6 speed manual. Bought the truck new. It now has 69K miles on it. The truck goes to the dealer for repairs which have been few and far between. I do all of the fluid changes and minor stuff. I use the Motorcraft diesel oil and Motorcraft filters. I run Optilube XPD in the fuel and one quart of Optilube oil fortifier in with the oil. Air filter and fuel filter are changed every 15 K miles, and usually look clean. We have an 11 foot slide in camper that stays on the truck most of the time, and we tow a 22 foot sport boat. The truck rarely sees in town driving. It mostly spends it's time on the interstates. I start the engine weekly and run it for 30-45 minutes. In the winter the truck never leaves the mountain we live on. It stays parked inside a garage when not in use. I have been changing the oil and filter every 6 months or 3K which ever comes first. Sometimes it will have 2500 miles on the oil, and other times just a few hundred. My question is will it hurt anything to go longer on the time if the truck hasn't been driven much? Is 9 months or a year too long if the mileage hasn't gone over 3K? The dealer says I change it too often and am wasting money. I don't plan to ever buy another truck. The truck goes to my son when I am gone. Thanks in advance!
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