synthetic oil?

Viscosity is more of a "what's the weather like" kind of decision. If it's cold out then a thick oil like 20-50 is really not the best choice. I run a 10-30 Amsoil all year long in most of my stuff.
Ideally...you want to run as light a weight oil as you can (within reason of course)...Lighter weight oils increase efficiency and HP. You want it heavy enough to have a nice "film" on the bearings...but light enough not to cause a massive amount of parasitic loss....Now that I've rambled out all that mumbo jumbo...my advice to you is to run the exact viscosity of oil, for the temperature outside that the manufacture recommends. I'm not sure what is recommended for the 258...probably around a 10-30 or 10-40 for your (and my) climate. Oil viscosity can be made a little heavier if you have a very high mileage engine as well....In general though...I say "stick to the book".

 

Well I just ordered a case of 20/50 Amsoil, I mostly wheel out in the Mojave desert where the temp is usually 80+. Thank you for all the advice and knowledge.:stout:

 

Synthetic is good stuff, especially for extreme heat or cold, very expensive engines, etc. That being said, I don't recommend running Synthetic gear oil in a manual transmission that was designed for dinosaur oil. It can create issues with the blocking rings not able to grab the cone on the gear so then it grinds going into gear. Had this happen on 3 fresh rebuilt transmissions. Flushed the transmissions out and put in the PROPER oil and they worked fine. The first we had a problem with was a Wide ratio T-19 about 12 years ago and it's still running fine with no issues on the recommended oil, regular old 85w-90 dino oil. On Manual transmissions, PUT IN WHAT IS RECOMMENDED BY THE MANUFACTURER OF THE TRANSMISSION! Save yourself some headaches.... Nickmil

 

I have seen something similar happen...it is rare...but I have seen it...The syn is so slick...that the syncro won't work like they are supposed to...and it can cause gear grinding...and difficulty to get in gear...I have never personally had it happen...As a matter of fact...syn has actually cleared up problems like that for me a couple times....Either way...Amsoil has addressed the whole "too slippery syncro" deal and they have this....
http://www.amsoil.com/StoreFront/mtf.aspx
While I have had nothing but great luck with the original...I will use this the next time.

 

How soon after a fresh motor rebuild would you want to start using synthetic oil? Right off the bat or after some break in time?

 

As you can imagine...there are some different opinions regarding that. I have heard quite a number of guys refer to that as an old Wives's tail..and they use syn right off the bat on a new engine. There is even a synthetic company that says it's okay to use it on a fresh motor.

The theory behind not using it on a brand new engine (or rebuild) is that synthetic oil works "too well"...In other words, it makes parts too slippery to break in and seat properly. So your engine won't really seal and "match up" like it should.

On the other side of the fence...guys will say "yeah...it's slippery, but not that slippery...put it in...it won't hurt a thing".

Now...I have not done a lot of "testing" involving these theories...So my opinion on this is more of a gut instinct...so take that for what it's worth.
Three years ago...Two close friends of mine (two Brothers) bought two of the exact same crate engines for their trucks...They were both the 502 horsepower 502 cubic inch big block Chevys. Since these are roller cam engines...they do not require that 20 minute break in at 2000 rpm. Rob put Amsoil in his right out of the box...but Rick decided to use Rotella until he had a few miles on it. Two weeks later, I met up with both of them at a friend's Birthday party...After a bit...we work our way outside to the trucks. After listening to both of them run...Rick's truck sounded like an entirely different engine...They both sounded good...but Rob's just did not seem to have the same sound...Of course...this could be pretty much anything...Some motors are just better than others...even though they are the same thing...I run into that all the time.
A couple more weeks go by and I meet up with them again...This time Rob's truck has the same hard hitting nasty sound as Rick's. Rob said he went for a 900 mile round trip in it...and it just kept getting stronger and healthy sounding as the trip went on.
This is FAR, FAR, FAR from any kind of accurate test....It's more like one of those "I once new a guy who had a friend who said..." kind of tests.
My own personal thoughts on it are this...I think that synthetic oil will delay the break in of an engine to some degree. So what I do myself is I put at lest 1000 to 1500 on an "non race" engine before switch to Amsoil....There are two reasons for this though...One....is the whole break in thing...and two, regular oil is much cheaper...and I change the oil very often during the break in of a new engine...This is to keeps the amount of metal running through my new engine to as little as I can. So I change it like some obsessive compulsive with reg oil for the first 1500...then I switch to Amsoil and change it normally.

 

On our fleet and service vehicles we switch to syn at first oil change. Run for 2,000 miles and change, then change every 10,000 after that. We avg anywhere from 40k to 70k a year on our trucks.

 

Im not trying to be partial or paranoid here. I think synthetics are great. Especially synthetic grease. But IMO Im shocked that no one has mentioned running rotella in their engines. Our old engines were designed to run with oil that had manganese difluoride, manganese trifluoride, zinc etc. Oil manufacturers used these metals to help ease the metal on metal friction inside the engine. EPA has put a stop to this some years back. So far the only oils that have these supplements in it are rotella diesel (which can be used on light truck engines) and Reliant. STP has an oil treatment bottle that you can add to your engine oil and has some of these ingredients in it. As for me I mix Rotella with the STP to help reduce as much wear as possible. I also threw some STP Treatment along with rotella gearoil in my tranny. Does anyone feel the same way or am I being too extreme here? Again I think synthetics are amazing. I just feel our old jeep engines were designed to run oils with these supplements, and should be added to your synthetics.

 

First...I would like to say that I have ran Delo (pretty much same as Rotella) in many engines...good stuff. I would like you to clear up one particular statement that you made... When you say our old engine were "designed to run on this oil"...specifically what in our engine is designed to run on a certain type of oil molecule? In case this comes across as me being "snide"...I'm not...but I know that sometimes things sound wrong when in print.

 

It is good on the cams and lifters. Most modern engines are roller tappets or overhead cam. Withou this lubricant the cams wear out prematurely due to the load that is put on them. Competition cams and Crane both had warnings a year or 2 ago on there websites about this very thing in older engines with modern oils.

 

That warning was (and still is) for camshaft break in. And it was not about synthetics...it was about (as you say) modern oil...it was the lack of Zinc & manganese needed for proper lube during break in...This was especially true with Chevy V8s. Once everything was ground uniform...it was okay to switch back to regular modern oil (if you wanted). And trying to break in anything with synthetic is never a great idea.
Unfortunately...I am PAINFULLY aware of new oils (not synthetic) and there destructive nature to camshafts. This is because I have been grinding custom camshafts for quite a number of years...and a while back...had a few of them go flat...even with a proper break in. It took a bit for the info to come out about modern oils..So I lost a few...not to mention..probably took a hit or two in the reputation.
Here is what I suggest to my customers....
Run Shell or Delo for break in...Then switch to Amsoil, If they don't want...or can't offord Amsoil, I tell them to stick with the shell or delo for the life of the car or until they want to switch to amsoil. When I sell a roller camshaft...none of this is really necassary...

Here is a link to that comp cams bulliten about new oil.
http://www.compcams.com/information/whatsnew/NewsDetails.asp?ListHistoryID=1985582846

 

Wanted to add this to the thread. Thought it was pretty informative as well: http://www.motorists.org/blog/technology/warning-if-you-have-an-older-vehicle-choose-your-oil-carefully/

 

Thanks for the link........some great info.

Next time I'm at the parts store, I'll take a look at the Shell Rotella T.

 

I broke my 45 MB in on Synthetic oil (Castol syntec 10W-30) and the rings had still not seated after 2000 miles.Switched to Rotella 10W-30 for 500 miles and then switched back to syntheticand it does not burn a drop.So I am a believer in breaking engines in on conventional oil and then switching over to full synthetic.