Ive always ran Valvoline high millage 10w30 in my vehicles from my 3.9 to my 318 mag and my la318 also in my 3.7. thats just what i like to use
but i will never use synthetic because my uncle (a mechanic since forever) absolutely hates synthetic motor oil. he tells me its because if you blow the engine after using synthetic its more likely to damage the cylinder wall worse (less likely to be rebuildable) as apposed to non-synthetic it would be more likely to be rebuildable.
But you can take that how you will.

 

I have heard of engines leaking really bad when switched to synthetic if you have any existing leaks. Haven't heard about engine cylinder walls getting damaged if it blows up though. Personally, I think running good synthetic oil can be a preventative measure though to blowing your engine up. But that being said, everyone has their opinion and when it comes to synthetic vs. conventional it seems to be one of those hotly debated topics.

 

Currently I use Pennzoil High Mileage 10w30 and a can of Restore or Wynns Friction proofing when I can find it. I've heard that it's not good to convert over to synthetic if you've been using regular oil, unless you're rebuilding the engine. That may just be an urban myth but, I'll wait til I rebuild my 318 Mag before I switch to synthetic.

Has anyone had any experience with that Z-Max I always see on TV?

 

I agree and could see switching from reg oil to synthetic being a problem and from synthetic to reg.

 

i use Pennzoil 10w30 in my 318 and its got over 350000+ miles on it and still run strong dont use any Oil Stabilizer just transmission is the only thing that is going out of my truck and im not easy on it drive it every day like i say i dont drive it easy

 

i have a 89 dodge d 250 with 411 rear and a auto 3 speed motor is real strong

 

The new "conventional" oils, according to people who know a lot more about oil than I do, are actually more synthetic than the old "synthetic" oils...

I used to care, then I stopped doing that. Now I buy a case of Mobil Super 10-40 whenever it goes on sale at Kragen. I use that to change the oil in the Dakota (145k miles), the Audi S4 (210k miles), the Mazda RX-7 (99k miles), the Range Rover (180k miles), the Tacoma (150k miles) and the Land Cruiser (120k miles). None of them have ever had any oil pressure issues, none of them burn more than a quart between changes, and the oil comes out looking clean after 5000 miles. I should also add that every engine listed above is "virgin", having never been taken down lower than the heads. And I am HARD on my cars. All of them have been over 100mph, and the Audi regularly gets tossed through turns at full throttle and bounced off the rev limiter.

Edit to add: The fleet I currently have is the youngest fleet I've ever owned, miles-wise. My Porsche had 210k and a giant turbocharger and my 1970 BMW had 950k on the original block, many of those miles raced in BMWCCA events.

 

I use 10w30 Valvoline Max Life conventional in the winter and the same in 10w40 in the summer.

My 3.9 has 161K on it now. I ran Mobil 1 synthetic in it about a year ago for around 5,000 miles....while it ran great, I did notice a bit more seepage from the rear main. With conventional oil, I can go 2K to 2500 mi. before I have to add a half quart or so. It was more often with the synthetic. The truck doesn't 'burn' any at all. No smoke at start-up or under WOT. Plugs are always clean.

It was basically 'raised' on conventional oil with regular changes from the previous owner and I. Seems to really like it so, I'll stick with it.

 

I did a major repair job to replace rear main seal and plenum gaskets, valley pan, & hoses (the truck was marking its territory in the carport.) So my 230xxx mile 5.2 is fairly dry now. 'cept for the leak on the junction between the trannie and the x-fer case. When it cools off here in the gateway to Hell, Tucson, I'll be changing the valve cover gaskets.

I'm currently running Rotella T3 sythetic--it's what I had in the cabinet when I did the work. When oil change time comes, I'll probably change back to dyno Rotella T, 15w40. It's what I use in my KLR, it's great oil, takes a likkin' and keeps on tikkin'. And it's pretty economical.

Modern standard oils are (imho) at least as good as earlier generations of synthetics.

 

http://www.widman.biz/uploads/Modern...tion_Guide.pdf
Modern car means roller tappets not flat tappets
if you want the details
http://www.widman.biz/uploads/Corvair_oil.pdf
an essential read if you are running a flat tappet cam and informative for all
if you are running a stick shift (synchromesh)
http://www.widman.biz/Corvair/Englis...Transaxle.html