Ive always ran Mobil Super High mileage, and still changed oil and filters every 3000 miles. I ran that in my beat up s-10 and my blazer and both worked fine. I do know people that throw generic oil in and crappy filters in and it still runs perfect. like chris015 said, 4.3's dont care what they got in em.

 

ive ran cheap 5 quart jugs of walmarts "universal" fluid as long as it says its good for dexron,run it. No issues from that,i do replace 1 quart with a bottle of lucas trans slip. great stuff. Dont do a flush,ONLY a pan change (5 quarts and filter) flushes on high mileage transmissions thats been avoided most of its life is worse then never touching it imo. bad stuff usually happens.

 

I've heard this as well. IIRC, something to do with the friction material degrading off the bands and clutches and the old fluid keeping it in suspension. Thereby giving the fluid more "grip"? Viscosity? Something. Point being, the old fluid is keeping the transmission from slipping. New, fresh oil will not have pieces of friction material in it, and will be "slicker" and let the old worn out transmission slip, causing heat and wear, and will ruin an old transmission fairly quickly.

I can't remember where I read that, or if that is even how it was explained. Without totally hi-jacking the thread, can anybody shine any light on that?

 

Yes you have to be careful flushing high mileage trannys but If they have been maintained properly there whole life there less chance the clutches will even been worn as much. Yes if you neglect it the fluid breaks down and the clutches friction material wears off. If there so worn the cluth material is floating around the fluid and that's the only thing keeping it going you will notice it doesn't work the same. The newest dextron 4 is synthetic awesome stuff. Under easy conditions gm says you can go like 60k before a change and about 40k under normal/ hard conditions

 

I planned on just dropping the pan, changing the filter, installing a different pan with a drain plug and filling with fresh fluid.

 

do some research,i remember something about the pans on the newer silverados have a drain plug. I found a thread with part #s a while back but cant find it now

just make sure its a 4l60.

 

For the engine: Stay away from Fram filters. Wix, (NAPA & Carquest) and Purolator pure one are the best available, use a name brand oil, and change it every 3K to 4K miles. Syn oil can go longer. It'll be fine.

For the trans: You can buy pans made by Dorman with a plug in them, or you can get a kit to add a drain plug, (also Dorman) to your existing pan. It avoids a trans fluid bath when draining Dexron VI is the latest, (fully synthetic) trans fluid. If all you're doing is dropping the pan and replacing the filter, it'll take ~5 quarts. Keep in mind that it holds almost 11 quarts, so you're only changing about half of the fluid. Change it every 36K miles, don't beat on it, don't tow more than 1500 pounds, install a trans cooler, and it will last well over 200K. Customer of mine has 388K on the original 4L60E and the engine, using those guidelines.

 

im one who doesnt believe in synthetic or any of these other high mileage oils.

i worked in the garage of a limo company for 9 years. every car that ever came through there got oil changes about every 8000-10000 miles (yes the boss was that cheap) with sam's club certified oil 10-30. never had one engine failure or issue due to high mileage.

most the cars got traded in for new ones around 150k but two 1997 town cars actually reached 600,000 miles. the little sedan sold on ebay for 2k with 617,000. dang thing actually ran great just would smoke at idle

also use that oil in everything ive ever owned, again no issues. my daily driver has 197,000 and im at about 5000 miles since my last oil change

 

I like synthetic oils. They are the best, especially in extreme temp.s like starting a cold engine on a sub freezing morning. However, I don't think the syn.s are up to driving for extended oil change intervals as some drive. I am sure they are trying to cost justify the additional per quart expense. The BITOG forum usually rec. 7k to 7.5K for syn. and 3K to 3.5K for petroleum oil. Remember a good quality oil filter is an essential part of this oil formula.
B & M also makes a oil pan drain kit you can install on you existing oil pan.