Originally Posted by
axistr
I change my mineral base oils every 5,000km and where synthetic oil is used every 7,500km, basically half of what the manufacturer recommends, probably a bit of an overkill. I use Shell Rimular X in most of my vehicles. Its a diesel engine oil but I still use it in my petrol and diesel engines and have done so for the last thirty years.
Some people will tell you that diesel oil will wash out old petrol engines and use more oil. Old wise tale that isn't necessarily correct. Diesel oil has more detergent in the oil to stop sludge build-up. Due to diesel engines having higher compression ratio, more soot will naturally pass by the rings. All engines will use oil new or used, but its the carbon, fuel and soot that passes over time into the oil that raises the level and minus the oil usage that keeps the oil at a constant level on the dip stick. Oil never wears out its the contaminants from the combustion process that slowly adds to the oil and when there is more contaminants floating around than the original oil the contaminants leach out and sludge forms on internal parts, building up and can't be drained out during an oil change. Much worse and earlier when using a real bad cheap manufactured oils. I never used cheap oils.
I found the opposite In just about all cases, when I switched customers vehicles that had been using oil to Shell Rimular it dramatically reduced the oil burn after around 3,000km. It cleaned out and freed up rings that were previously gummed up in the piston ring lands not allowing the rigs to seal in the bore.
Most diesel engine oils have Zink added to the oil during manufacture to better help lubricate camshafts and lifters which is also a bonus for standard or performance petrol engines, especially Holden V8 engines which have had cam issues over the years. I use full synthetic oils in my beamer and Ranger only because the manufacturers state they must be used or warranty is void. I use Shell helix ultra (full synthetic) for these vehicles. Quality full synthetic oil do have a lot of detergent in them and suspend contaminants for longer and will have longer oil life intervals. Most later model cars now come with larger capacity oil sumps, the more oil the longer it takes for the oil to contamination ratio to reach its limit. Its for this reason large diesel trucks commonly come with 50lt sumps and 25-35,000 km oil change intervals.
Hope this helps some of the myths about oil changes.
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