I'm sure this topic has been posted before but couldn't find one and thought I'd ask for a few opinions.

Would it be ok to run 40w in a rebuild with no miles? Or maybe lighter weight till after the break in?

 

I just rebuild my motor with new bearings. It is still on the engine stand waiting for me to swap the intake manifold and accessories over.

I plan on using HD 30 wt. oil for the first few hours (30-45 minutes of idle then around 50 miles of driving. Then I will switch to some 40 wt. for another hundred miles or so then to my regular 10w30. I will change the oil again at around 600 then 1000 miles. From there it will be normal 3000 mile oil changes.

Why 30 wt.? Good question. I seem to remember reading that 30wt was recommended weight of oil from one of the major rotary engine builders (Mazdatrix?). And it is the break in oil that a friend of mine uses in his shop in piston engines.

 

GRRRRR... My first double post. I got an error page and hit reload.. Boom... 2 posts! I then tried to delete it and got a message saying I did not have permission to.

 

Irun 20-50 in all my engines, used or rebuilt, year around with no problems.

 

Some guys start off with the lighter 30 or 40 for the first 2 changes then switch to the heavier 20-50 from there on out. Im sure your going to get a lot of feed back but it basically comes down to preference.....if you look in previous oil posts you will see what i mean.

 

i used 20-50
its really hot here in the summer and i figured that that would be fine

 

In the couple of motors I have rebuilt now, I have always used 20W50 on first start and run.

 

Mazda Motorsports recommendation: Low-ash content mineral-based (non-synthetic) 20w or 30w.

Racing Beat recommendation: Mineral-based (non-synthetic) 20w.

 

hmm 40w lol don't know where I got that from lol....I've actually got castrol 20W-40 and if it's safe to run in a fresh rebuild I'll probably just use that. Just wanted to be sure a light weight wasn't more highly recommended