I know this has been discussed, under various terms, for a while, but simply put: would I expect to have any issues (mainly leaks) if I switched from regular old dino oil, which I think the car has had its whole life, to synthetic?

Also, if doing so, better to use one of the specific higher mileage blends or anything similar to help prevent issues?

Not saying that this is even a definate thing I'll be doing, but am wondering if it will really be worth it...as long as there's no issues switching over with 117k already on regular stuff.

I might also do a blend, as we used that in the '93 FWB once and it did well...and didn't cost as much as full synthetic.

My personal opinion is you are wasting your money in normal usage conditions. I use synthetic occassionally but only when I get it cheap. (I got a bunch of Mobil 1 for $7 a 5qt jug a while back). Otherwise quality dino is the way to go.

That's basically what I'm thinking, just wanted to get some opinions on possible issues if I DID switch over.

We run all 4 cars on the same dino oil and have never had a single issue, so I think I'll keep it that way. Or go with a blend, as we've sometimes used from time to time.

Zonie,

Are you sure that wasn't a 4qt. jug? The Mobil 1 I get comes in 4qt. jugs, or 6qt cases of 1qt. bottles. You know, the marketeers would never sell us an even 5 qt. container.

I think if you keep your oil clean with regular changes, and use a quality name of the correct viscosity, it doesn't really matter.

Yup, leaks are VERY common with synthetic. The detergent nature of the ester and diester base stocks has high detergent properties. So any sludge plugging up a hole will be cleaned.

If you have some oil usage due to rings fluttering or just plain ring wear, synthetic might help reduce that.

Personally, I would use a quality 15W40 like Delo, Delvac or Rotella T. Been running it all last year, including the winter on my Suburban and Cadillac since January. No issues in the winter and the fuel economy has been virtually the same. There is more anti wear additives in CI-4 Plus diesel oil than any gaoline oils. Note no gas oils like 5W30, 10W30, 10W40, 20W50 don't meet the CI-4 Spec. There is a higher base proper to the oils, and the oil handles soot and acid formation much better than most any other oils.

My local SW MI Meyer chain sells the Mobile 1 5-quart jug for $20+.

Like already said, this topic has been kicked around countless times on the B-body forums. I am no expert on oil so I go off of the veteran members that put tons of time into research and belong to forums like bobtheoilguy and theoildrop (or something like that) where there are chemists and gurus abound.
They go as far as sending in their used oil to labs and get a used oil analysis that tells them the best/worst wear factors and all kinds of details on different weights, brands, etc.

Here is a quote from a guru on a b-body forum referring to the iron-head LT1 engines. I converted my 98K mile Fleetwood to M1 synthetic and my 96 Caprice (38K miles) to the below recommended weights. I picked M1 since it is the most readily available. His info is based on used oil analysis by other gurus.
If you want to use M1 then just switch to 0w-40 or 5w-40.
Only problem with M1 is the most commonly used grades the 10w-30 and 5w-30 are too thin for this engine, this is specific to M1 other oils are fine in these weights and CASTROL syntec 0w-30 "made in Germany" has proven to be about the best for this engine, though most of the Syntec line is not worthwhile this one and the Belgian 5w-40 are returning good reports.

As far as detergents and causing leaks, I forgot the details but there is in-depth conversation on this as well. Basically there should be no worry on getting leaks from high-mileage swap-overs to synth oil. Research www.impalaclub.com for details.
When you do switch, however, it is recommended that you change your oil filter after a 1000 or 2000 miles since the detergents will clean out a lot of crud and fill the filter up after the synth changeover. Then you can run the rest of the oil period (5K miles or whatever), just be sure to change the filter one more time at this occasion as well since there could be more crud.

But for me, if it is not CI-4 or CI-4 Plus, it won't go in any of my vehicles. Mobil1 makes no oils that can meet the CI-4 spec.

People can say how much they think it is good, the lack of ZDDP makes it a loser. Especially in the SM spec forumula. Get SL while you can still find it. You WILL expecience more wear with the SM spec formula.

Check out the lastest Hot Rod, the article about flat tappet cams and oil. And why not to use car oil in your flat tappet ride. I guess Bob was right.... Forget SM spec'd oil.

"Cam Info You Need
Why are flat-tappet cams getting wasted more frequently these days? You'll be surprised by the answer."

But for me, if it is not CI-4 or CI-4 Plus, it won't go in any of my vehicles. Mobil1 makes no oils that can meet the CI-4 spec.

People can say how much they think it is good, the lack of ZDDP makes it a loser. Especially in the SM spec forumula. Get SL while you can still find it. You WILL expecience more wear with the SM spec formula.

Check out the lastest Hot Rod, the article about flat tappet cams and oil. And why not to use car oil in your flat tappet ride. I guess Bob was right.... Forget SM spec'd oil.

"Cam Info You Need
Why are flat-tappet cams getting wasted more frequently these days? You'll be surprised by the answer."

I know you posted a similar thread in the other forum...but could you please "decode" some of the terms you mentioned:)

Flat tappet I get, but what are all the other "letters"?

Chevelle might know better, I think he has some small experience with it.

But, the CI-4 spec is the oil that is rated with the addtional ZDDP (anti-wear additives). If you notice, it has been a LONG time since a S (gasoline, aka, "Service" class) rated oil has met the CI (Commerical/Industrial) spec. SL to SM was a significant reduction of ZDDP. Almost 1/2 the amount.

If we can get our resident oil guru's to post the spec (I'll see what I can find) to see if it is in english for us....

Sorta off topic...
I did contact Amsoil directly on the thoughts of using Amsoil oils with E85 and the cyl wall washings. They do NOT recommend the extended drain intervals with it, std only with E85. I am curious what GM and Ford spec with the E85 OEM vehicles. Does the OLM adjust accordingly?

Good reading:
http://www.highperformancepontiac.com/tech/hppp_0606_understanding_motor_oil/index2.html

http://www.ford-trucks.com/forums/showthread.php?t=269596

Synthetics are good when you start out with them in a new engine, in my opinion only. I wouldn't switch the type of oil that you have been successfully been using for the last 117,000 miles. Just keep on doing regular oil and filter changes and save the extra money that synthetics cost.

They are fine to switch to after high miles, just expect it to leak. My dad's 85 Cutlass at 155K to synthetic did not, my 4.0L Aerostart @ 225K, did. The van went to the boneyard at >280K with not a single problem in the engine. Trans was dying and the body was almost rusted away. But ran great.

My LT1 rear main is now leaking a little, not enough to worry about for me. I'll fix someday, but I am not terribly worried. Put synthetic in at 160K or so.

My 1996 Suburban hasn't seen it yet, 232K, but will soon. Already has some very minor leaks.

My 1980 Turbo T/A with a rebuilt 400, will probably get it now that I have flat tappet cam and can't get good oil anymore, so it will only get CI-4 oil from now on. No leaks. But engine is only 5K miles old or so. Don't expect any....

My 1991 Bonneville got Amsoil 10W30 @ 60K, never did leak, and has 250-300K now. Still runs strong, has been on and off again diet of synthetic. None in the latter years with new owner.