Thanks for the info - I just **assumed** that Mobil 1 was only synthetic and not conventional oil. I've used Pennzoil, Castrol and Valvoline and I suspect any good quality brand name would be fine.

Ted

as you should use that oil. Working & living in Mammoth Mountain for a season, I've heard some oil horror stories.

Thanks for all the replies - I greatly appreciate the info! I've had the good fortune of having a few 3rd gens, and put a lot of miles on my '98 in particular. I guess with all the information available these days, I started over thinking things. :0 I've mostly used Mobil 1 oils in my 4Runners - and always 5w-30 - and after reading the specs pertaining to the various 5w-30 variants currently offered by Mobil, thought I'd research a little further to see if there was one in particular which was ideal for use in the 5VZ.

Me...

Mobil 1 IS only Synthetic, however, Mobil as a brand offers conventional oil's as well but it is called Mobil Super.

I run Amsoil Signature Series 5w-30 Full Synthetic and an extended Filter Purlator Pure One PL20195 it's about 1 inch longer than the intended filter.

I had a slight valve cover leak maybe 1 drop per minute after the first oil change to synthetic, it dropped onto the exhaust on the left side of the motor at the back but the valve cover gaskets were in need of being changed regardless.

Absolutely NO issues after changing the valve cover gaskets aside from gaining 1mpg and having a quieter engine but I wouldn't really call that an issue.

Well there's your problem, you NEVER flush an auto trans, a series of drain and fill is fine, but once auto's get over 100k if they haven't been religiously flushed at their intervals or earlier than recommended every time (And it's possible even if they have) then the gunk you flush out and off the clutches is what was holding everything together. I learned this after I lost a high mile car to a trans flush. I hated that car anyway and am glad it's gone, me and Auto's have never gotten along, switched back to manual after that but I know MT isn't a viable or desired option for everyone.

Irregardless, Synth Oil is just fine in these trucks and highly recommended by my old 35y+ experience Toyota and ASE Certified Mechanic mentor in his experience he's never seen an engine in better condition as last as long by using Dino over Synth.

I don't think this is written in stone.
@slapdappy and I flushed our auto transes with 16 qts. Holding up fine so far... And I did mine when I had over 200k miles without a flush.

fwiw i use amsoil 10 40 signature in my 01 t4r with 137k and rotella 15 40 dino in my wifes 99 limited with 266k miles no issues thus far no leaks either and since I live in Florida where it is warmer than the northern states I use thicker oil also the higher miles on the 99 mean she needs a thicker oil for sure however if I l lived up north I would not use oils this thick.

Yeah, I don't think this is canon.

I had really dark red (nearly brown) trans fluid when I bought mine @155k, had it flushed passively with 12qts and have put 3k miles on it since then with no slippage or problems whatsoever. In fact, it shifts smoother than it did before.

Not saying it won't take a dump tomorrow, but there aren't any obvious trans problems rearing their head--especially in the month and a half since the flush.

"flushing" a transmission can be bad if it's a power flush, not just a fluid exchange type of flush. Some repair shops will call it a flush when it is in fact just a fluid exchange.

To stay on topic, I use mobile super 10w-30 here in AZ, temps never get below 32F, and summer has long stretches of 110F+. Also being at 260k miles seems to run a bit better with the thicker oil.

Veering off topic...

the friction material is cellulose (paper). my research (couple hours googling) tells me you are correct re friction material loss in high mileage vehicles that have not been flushed.
Everything You Need To Know About Automatic Transmission Clutch Disks
Transmission Flush, When and when not to flush transmission | MDH MOTORS
Powerflush | Best Western Transmission

my new favorite word.

yeah.
Mine had already been machine flushed by previous owner (2nd/3rd owner) at 173,000. No idea about original owner but I'll assume it was given the classic drain and refill at recommended interval. this removes some of the old fluid and leaves most behind.
mine was shifting kinda clunky so I went ahead and did the full home depot bucket style flush last year, including dropping the pan and wiping all the grey gunk (friction material mixed with metal?) out of the pan and off the magnets (metal, duh). Cannot say if shifting improved. Thought so but may have been self delusion.
Actually re-flushed recently after using a "miracle" additive, which required driving for 4000 miles then replacing. Put "miracle" on a bottle and add a few anecdotal testimonials and I'm likely to buy in. Maybe it was detergents and friction material? No idea.
About the same time I removed the rear drive shaft and cleaned the gunk (old grease) from the sleeves and seals. Pretty simple. This most likely fixed the shift clunk (reverse to drive/drive to reverse) and hard/harsh shift 1st to 2nd.
Subsequently shifts smoother, especially first to second and drive to reverse. Not perfect but no longer clunky. Def improvement.
So, reality based advice is don't do the full flush above ????? miles.
Anecdotal experience for me and amalik is positive, but we don't know the full maintenance history of our second hand vehicles.

It's funny how we ended up steering towards a discussion on ATF fluids. Coincidentally, that'll be my next research project. The fluid in my '99 Auto is is dire need of replacement...

Think I'll start a new Mobil ATF thread....

Thanks for the info Woody - I think I'll just keep on doing what I've been doing

Next time I need filters I'll get the larger one. I usually r&r the filter through the fender flap...with the skid plate on it hard to reach from below.

Ted