I take a bit of a different perspective on this...and with Engine Break-in
While much of the engine components are seated, there are some (such as piston rings) that can take up to 1,000 miles to fully seat. Here's what I do with every new OEM vehicle...for the 1st 1,000 miles
1. I lock out overdrive and drive normally (city & hwy)- this keeps the rpm's constantly varied...do not beat on the engine
2. At 500 miles, I change the oil & filter to remove any mfg contaminents that may exist.
3. At 800-1,000 miles.....we go for a long trip....something in the 2-4 hour driving range, running 70-80 mph with the overdrive off.
4. Upon my return, I change oil & filter.
I guarantee you engine will have a much different, smoother "feel" to it. Max mpg's though are typically seen at around 10k miles.
Some items that I will just refer to as "of interest" to me.....
1. The timing chain tensioners are hydraulically operated, cleanliness of the oil is imperative to keep the actuators functioning.
2. Most of the oil filter mfgs conceed, that after about 90 days of use, the bypass valve in the filter opens to some degree. While the stored/caught particulates do not escape, the oil is allowed to flow straight through to prevent starvation. I change filters every 3 months in my daily drivers....going back to the 90's.
3. With the extended oil changes 5,000 up to 10,000 miles, with the reduced ZDDP and the longer exposure to periodic oil filter bypass activation, this is another parallel to the hydraulic timing chain actuators failing at around 100k miles as compared to their design specs which say they should be good for 150K+ miles. Thos who have experienced these specific failures, the majority report they are on extended oil drain frequencies- most of the Ford Master Techs i have spoken diretly too regarding this, agree their gut instint says there is a relationship between the two.
4. I too do extended coolant & oil changes on my vehicles. I use cathodic protection installed in each of the vehicle coolant reserve containers, the ph and ehtylene glycol levels of the water is checked annually and the fluid is removed, filtered (3 ppm), the system is flushed and then refilled with the same fluid every 5 years. The oil on my 65 300 hp mustang (which has been inthe family since new), has only seen 3 oil changes since its ground up rebuild (and of course after the engine break-in period) since the mid 1980's......but I do change the oem filter annually and i run a bypass filter (filters down to 5 ppm) and on the last oil change (which was recent) I did add one bottle of ZDDP per after discussing this indetail with Ron Eskenderian (yes, Isky Racing Cams), and I add 1/3 of a bottle to my mod motors as well (1997 Cougar Sport 4.6 & 2006 Lincoln Mark LT 5.4)- IIRR it is a 9 oz bottle.
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Flatheads ain't so bad!
Certified backyard mechanic I & II