Recently rebuilt motor with less than 2000 miles on it. The guy who did the rebuild is a mechanic by trade - so I assume that he knew what he was doing...
He did the rebuild for himself so he used quality MIJ parts (Aisin, etc)

I noticed this engine is using about 1/2 quart of oil every 300 miles... he put in full synthetic 5W-30 despite mfg saying this engine should run 10W-30. Could that be part of the problem? I intend to do conventional oil 10W-30 to see if oil use subsides.

Engine runs great with no knocks/leaks/smoke.

 

I am sure that the oil is your problem. I made the same mistake on my first engine rebuild (350 chevy V-8), full synthetic right from the start thinking "I'll give it the good stuff". It took forever for the rings to properly seat and for it to stop burning oil.
synthetic oil is too slick to allow proper break in and even if you go with the exact same weight of oil the synthetic is slightly thinner, so a leaking engine will leak faster, oil blowing by the rings will blow by faster. It will also clean passages, so it will clean the gaps where the leaks or blow-by are and make it worse. The 5W-30 isn't helping anything either.
The punch line is, don't use synthetic if your engine leaks or is freshly rebuilt.
Your best bet is to drain the oil, put in some break-in oil of the proper weight and put 1000 miles on it before switching back to synthetic, or whatever instructions say on the break-in oil.

 

I used to run 20W-50 conventional with a quart of Lucas Oil stabilizer in my high mileage 3VZE (over 300,000 miles) and didn't burn or leak a drop. After about 330K I switched to 15W-40 full synthetic (scored on a next to free deal through work) and noticed I was consistently a quart low every 3,000 after that and nearly every seal and gasket began leaking.

 

Thanks for the info guys! I'll definitely get that synthetic 5W-30 out of there this weekend... will be going conventional 10W-30 with the Lucas "Break-In Oil Additive - TB Zinc Plus."
Will probably just stick with conventional oil after break in period.

 

Just so you know, I've been using Castrol SynTec 5W30 in my 4Runner since I moved up to Oregon 15 years ago with no trouble. Before that, it was the SynTec 10W30. Same for my pickup, with it's 22R engine. Been using the same oil for 30 years in both trucks. Only reason I went to the 5W30 in the 4Runner, is that I mostly drive it in the winter, and our winters can get pretty cold. It makes a difference in the Runner's initial start when it's very cold out.

I wish you all the best!
Pat☺

 

Isn't SynTec kind of a different synthetic though? I seem to remember it being classified differently than other more common 'full synthetic' oils.

 

Not that I'm aware off. It SAYS it's a full synthetic on the bottles. Honest, it does!
I'll see if I can get a picture of the bottle. Worst case, just take a look next time you're in the auto parts store that carries it.

From the Castrol site...

This is what I use in both trucks I have.
Does this help at all?
Pat☺

 

I believe you. I think it has a different chemical makeup than classic full synthetic, or something along those lines... I haven't seen anything but Schaeffer's for the last 10 years so I'm a little rusty. Maybe SynTec is much better!

 

I have no idea. Never even heard of Schaeffer's.

I started using this stuff when I rode my '73 KZ1000P Police Special motorcycle in a Memorial Day Parade in Yuma, Az. back in 90. It was a normal Yuma day, about 105°F, and the parade wasn't moving much. A lot of us with air cooled motorcycles were starting to have overheat troubles. I had just gotten my bike's oil changed, and the SynTec is what the shop used.
Since we were getting hot, just sitting in the parade, we started driving around in our little area, doing some fancy riding. Anything to move air over the engines and cool them down. The Parade announcers made a big deal out of us having done months of practise for the maneuvers we were doing. Half of us had never even met each other before the parade, we were just trying to cool our bikes off!
Anywho, after all this, when I got the bike home, I pulled the filler cap, and sniffed. No burnt smell I could detect. I dipped a stick in to get a little oil out, and rubbed it with my fingers, to see if there was any break-down, or whatever. Felt exactly the same as new oil out of the bottle. I know, scientific as heck, right?

After that, I started using it in my trucks, and have never looked back. It's never let me down, not even when a "friend" overheated my 4Runner after dropping the water pump belt. Long story. I had to replace the head. Twice. Got a cracked head from the shop I bought from. They did replace it. Anyway, the oil didn't seem bad in any way when I went to rebuild the top end. My "friend" had driven the truck until it overheated, let it cool, driven it till it overheated, let it cool, etc all the way to my house. Jerk...

Convinced me I was using the right stuff in my engines. At least for me!
Just my little story about why I use this stuff in my engines....
Pat☺

 

You know, "synthetic" is a marketing term. https://en.wikipedia.org/wiki/Synthetic_oil There is no API definition of what "synthetic oil" even is. What we do know is that every manufacturer of such oils uses a different proprietary formula. And you're as likely to learn what's actually in a particular "synthetic" oil as your are to learn what's in Classic Coca Cola.

Does anyone know a particular manufacturer or reputable journal that says "Whoa! Don't ever use the oil we call "synthetic" in a newly-rebuilt engine"?

There is no shortage of internet sites run by self-proclaimed engine experts who will say all sorts of contradictory things about engine "break-in." Some of what is said is probably correct, some almost certainly not. One of great strengths of YotaTech is getting the experience of other Toyota users. But not so much when the comment is limited to something like "I've always used Frankie's Yam Lube in all my engines, and I've never had a problem."

Me, I change my oil at 7,500 miles, and change the filter at the same time. I use the cheapest (reputable) 30w [oops! actually 10w30] I can get. There. I said it.

 

do you truly use 30w, instead of multi-grade such as 10w-30 or 5w-30? afaik, toyota recommended either 10w-30 or 5w-30 in these 80's and 90's engines, instead of 30w, even in warmer climes. fwiw, i tend to change the oil in my vehicles a bit earlier, around 3500 to 4000 miles with a filter, but i invariably drive a significant amount of time on dirt and gravel roads with the accompanying dust.

 

You are correct, I mis-remembered. I checked the containers in the garage: 10w30. Just like the Owner's Manual says.