OCI Recommendations

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46
Location
KY
Just found this site and have to say A+… I have been lurking for a couple of days and had a question… I have three vehicles that are nearly identical, and I am considering an extended oil change interval. What is the community’s suggestion? DETAILS 1995 GMC Suburban 4x4, 5.7L engine (225 hp), auto transmission, 120,000 miles,15MPG, throttle body injection, weighs 8,000 lbs, turns 1850 rpm at 60 mph, uses 1.5 qts of oil in a 3,000 mile oil change. Average trip is 20 to 40 miles twice a day. 1997 GMC extended cab truck 2 wheel drive, 5.7L engine (250 hp), SFI, auto transmission, 16 MPG, 148,000 miles, weighs 4,400 lbs, turns 1850 rpm at 60 mph, uses no oil. Average trip is 5 to 40 miles twice a day. 1998 Chevy extended cab truck 4x4, 5.7L engine (250 hp), SFI, 5 speed transmission, 18 MPG, 142,000 miles, weighs 4,400 lbs, turns 1500 rpm at 60 mph, uses 1 qt in a 3,000 mile oil change. Average trip is 20 to 40 miles twice a day. I use Havoline 10W-40 in the summer (average low = 65F, average high = 90F) and Havoline 10W-30 in the winter (average low = 20F, average high = 35F) and along with AC Delco oil filters. Is it safe to go 4,000 miles on the oil in each vehicle? What about the suburban? It is twice as heavy as the other vehicles, so the engine has to work harder?
 
Messages
1,183
Location
Vermont
pburchett, [Welcome!] - The more minds to share thoughts on the same topic, the more diverse the responses, and a better likelihood of finding a well rounded answer...in good time! I don't have any first-hand experiences with these vehicles, but as far as 4000 miles being considered extended, well that's something. What are the "regular" service intervals for engine oil and filter per manufacturer recommendations, as well as grade? 10w-40 for summer and 10w-30 for winter sounds reasonable to me. So far I only feel confortible with bringing up synthetics for over the coldest winter months for the vehicles that are to be driven the least per drive (GMC ext. cab 2wd truck), as the oil is likely to not heat enough to remove any condensation that might develop in the crankcase. H2O + combustion blow-by gases = acids = drop in oil TBN...oil oxidation/aging. I may be wrong in thinking that a synthetic (PAO rather than G3) with it's inherent oxidation resistance over standard petro bases, would be a good consideration solely on this merit. Perhaps someone else could correct me here (that's the great thing about forums like this). If the synthetic approach isn't the ideal in the overall scope of things, than I would think that those vehicles that are driven for short, infrequient trips during the cold winter months, would be less of a candidate for extended OCI's, using a good quality petrol-base lube (often heard: motorcraft, chevron supreme/havoline...). "Is there anybody out there?" Again, welcome aboard.
 
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