ok as the title states is it bad to mix oils. like 10w-30 with 10w-40 or 20w-40? smple question just needs simple answer thanks

 

I can't see it being bad as long as they are the same type ( Castrol, Mobil 1, etc. ) and the same make-up. Conventional or synthetic. Curious, WHY are you mixing ?

 

no problems, with mixing weights or brands as long as you don't mix dino with synthetic

 

No problem mixing different weights and types. No Penzoil or Quaker state however. 2qt. Syntec plus 3 qts GTX makes a good mix for a 5000 mile change interval in a piston engine. You get the additive package of the synthetic at lower cost. For a rotary you may only want 1 qt since our oil stays cleaner than a typical piston engine's. Ideally consider feeding the OMP with 2 stroke oil instead of crankcase oil as well.

 

there is no problem with mixing any synthetic with and dino oil. You won't get the protection of a full synthetic, but your engines not gonna lock up or some other thought up BS story.

 

If you've been running petroleum based oils and then switch to a synthetic, you will begin to loosen the varnish and deposits left by the regular oils (synthetics are better detergants). All the loosened "crap" may or may not cause you problems. Most times they end up some where they shouldn't and cause a problem. I'd stay with dino juice here.

On a complete rebuild, break in on regular oil (10000 - 12000 miles), change at least every 3000 mi - 500 on the first go, and then switch over to synthetic.

I've read on synthetic in rotaries - seems to be 2 schools, one pro, one con. I haven't made up my mind yet. After my 12a rebuild (probably next fall), I'll run synthetic unless I find a good reason not to.