What Engine Oil Viscosity During break-in ?

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I had my 2F professionally rebuilt. It's no longer in warranty due to the extensive rebuild time of the tub.
Nevertheless,the warranty instructed to have 1st oil change at 100 miles (now 85 miles), 500 miles after that, and 1000 miles after that and to replace it with straight 40W oil which is currently in engine.
That seems a little heavy to me for this week's approaching 45 degree weather. I browsed through a parts store after work today and looked at the 40W Castrol Oil. It said to use in temps above 65 degrees. The shop that rebuilt the motor is closed today so I ask you fellow 'Cruiser-heads what viscosity oil to use during the initial break-in?....and afterward? Did the '78 FJ40 originally use 40W oil?
 
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I have no experience with breaking in a rebuilt 2f, but im going to use 15-40w non syn.. The original owners manual for my '78 40 calls for 10-40w from 0-100 deg F under normal use. After a couple oil changes and 3k miles I'm going to switch to a full synthetic.
 
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Don't go too crazy on a big spread between viscosity numbers. Apparently the modifiers or additives which give the larger viscosity range are not all that stable or good. I'd go with 10w-30 in the winter and something thicker in the summer.
 
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Go with 10-30 or 10-40 in winter. 20-50 in summer if it is hot there. I have run 20-50 year round with no issue. I would get it running with 10-30. Make sure you run the pump to pressure prior to starting the motor. Once you get it running and some hours of non driving but messing with time on it I would change it again. Drive it 3-4 hundred miles change it. Drive 1000 more and change. After that normal interval.
 
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10w30, 10w40, 15w40, 20w50 any off them will serve you well during breakin. The first 2 or 3 changes are important as the engine makes a fair amount of metal during this time. Warm it up before puting any loads to it. dont beat the snot out of it but dont baby it either. Run 2500 mile intervals to 10k then change to synthetic if you are inclined to. 10K on dino oil will assure a proper breakin. Synthetics are very slick. You might not be very well broken after only 3000K and a synthetic at that time might prevent further breakin of the engine.
If it was me I'd use either the shell rotela or mobil delvac 15w40 with a quart of Marvel Mystery Oil during the first 10,000 miles. Available at wallmarts cheap( the high grade dino diesel oils are arguably the best out there.If its good enough to get diesel engine last between 500K and a million miles it aint gonna hurt a 2F)The MMO will prevent any galling, scuffing, or glazing of the cylinders during the first few cold starts and hot runs.
I recomend 2500 mile intervals because regular petroleum oil starts to sublimate after 2500 miles leaving a varnish in the engine.
Just my two cents and I've been screwing around with this stuff for almost 30 years now. :beer:
 

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