I have always done 3,000 mile OCI on everything I drive with syn or dino oil. It get -40F winter here, +105F summer. I use XD3 0-30 Esso Syn oil, POA group 1V for $3.71 litre or quart, Can. (a premium dino 5-30 oil is about $3.00 per litre on most shelves now, on 4 litres it costs me $3.00 more for a syn oil change)
My brother owns a 1982 Honda Civic, 420K miles, I once owned this Honda with my OCI schedule, he has done the same OCI schedule too, keep in mind this Honda also has been operated in the same harsh weather conditions. The body is nearly rusted off, the engine doesnot burn oil, he has never opened it up, he still takes it on long trips on work commutes up north. This Honda has seen harsh weather in -40, not 420K California miles.
My brother uses my 0-30 XD3 3K waste oil with new filter in this Honda, this syn oil doesn't get wasted, this oil does go 6K miles in two engines. In a new engine I run 3K with syn, once I get 340,000 miles it owes me nothing, I then will probably do the same then, I will use full syn in whatever I buy new then and put it's 3K waste oil in this 05 X-TRail then.
If you have someone with a junker with excessive miles and this beater owes them nothing, see if they will use your 3K waste oil on it, or use it on your junker if you have one.
Many will suggest I change my filter after 3K and keep the oil in it, I wont do that, changing a filter is 85% the work in an oil change, if I have to change the filter, then I will change the oil too. I dont do 80% work for nothing. For $3.00 more total on OCI for this XD3 syn oil over a premium dino, I am not going to run 6K OCI in my new engine.
The cost for syn oil to me is for piece of mind on -40 starts, long 105F highway trips, and my hard working engines like the QR25DE with a counter shaft. I cant risk or afford a new engine falling short of life span because I go against all that works for me in past 27 years, $70 per hour garage rates or premature new engines are not acceptable to me. "If it aint broke, dont fix it," I stay wit 3K oci.
Dont be a sheep and extend your OCI on syn oil if it does not seem right to you Gilitar, what ever you put into a vehicle in maintenance will pay 4 fold in saving garage and new engine costs if you have long term plans on the vehicle, this is IMO.
Please keep in mind my harsh weather guys and the fact this 3K syn oil gets reused, not wasted, and my total extra POA syn cost on 4 litre OCI is $3.00 over a premium shelved dino 5-30.
Cyprs