WobblyElvis - I did not believe you either. However, I looked for a bread and butter 1970 Chevy owners manual.
Findings below.
For normal passenger car service: Change oil every 6,000 miles or 4 months whichever comes first.
Change the oil filter at first oil change and every second oil change thereafter.
For certain types of service (dusty, trailer hauling, excessive idling, short trips engine not warmed up and commercial use): Change oil every 3,000 miles or 2 months whichever comes first.
Change the oil filter at first oil change and every second oil change thereafter.
They also had a 200 hour cap on idling.
So, if you were running easy highway miles you could run 12,000 miles or 8 months whichever comes first on a filter by the Chevy recommendation. Otherwise, 6,000 miles or 4 months or 200 hours whichever comes first.
Filters of that era had large filters with good capacity.
That is one of the big 3.
If 7,500 mile OCI were common I would think Chevrolet would have been in the mix.
Findings below.
For normal passenger car service: Change oil every 6,000 miles or 4 months whichever comes first.
Change the oil filter at first oil change and every second oil change thereafter.
For certain types of service (dusty, trailer hauling, excessive idling, short trips engine not warmed up and commercial use): Change oil every 3,000 miles or 2 months whichever comes first.
Change the oil filter at first oil change and every second oil change thereafter.
They also had a 200 hour cap on idling.
So, if you were running easy highway miles you could run 12,000 miles or 8 months whichever comes first on a filter by the Chevy recommendation. Otherwise, 6,000 miles or 4 months or 200 hours whichever comes first.
Filters of that era had large filters with good capacity.
That is one of the big 3.
If 7,500 mile OCI were common I would think Chevrolet would have been in the mix.