I run synthetic just for the little extra HP (2-5). I got the chance to talk to a ashland guy once off the record, and he said they put synthetic oil in there fleet trucks when they are new and dont change em for 100k if the truck lasts that long( not due to engine failure, either they get sold off, or smashed, or do not hit 100k before they are depriciated off the books and something else goes wrong). Because he told me this I soaked my lifters in synthetic before install, but broke her in on reg. oil, changed it at 50 miles, 300 miles, and at 500 miles I switched to synthetic.

Here is a thought on runing synthetic in high milage motors: What about a syn blend? You would still get the better cold start up protection, better cold flow, probably no performance increase. Do you think the seals would leak with a blend?

 

Big trucks (18 wheelers and such) can get 100k on an oil change because they never shut them off and they hold 20 something quarts with a 3 quart filter.

I remember a s-10 blazer come in with a locked up block. 24k miles on synthetic oil. looked like yellow slimy silly puddy.
Really nasty job, cleaning that block out.

 

On a high mile motor, if it's leaking, it's gonna keep leaking till the seal or gasket is repaired. If it's worn it's worn there is no mechanic in a bottle. I don't understand why people fall for that ploy. The guy I bought my Z from was using Valvoline Max life in it, Guess what, it still leaks more than it burns. She's got 230k on the origional motor (not rebuilt) so what do you expect. On a high mile engine, it's not going to care what you put in it, you won't gain sqwat.

 

I know that this is an older post but I thought I could add some information about this topic. I recently took out the stock LT1 that had 39,994 original miles on it. I am the second owner and the car has run Mobile One synthetic since its first oil change. The engine was perfectly clean when taken out of the car. To my surprise there was no build up of any kind under the intake, valve covers, or in the bottom end. I used Mobile One syn but sometimes it would go over on the alapsed time in between oil changes. I would deploy to Iraq and come back six to 12 months later and have to change the oil. I can say that with the Mobile one syn that I am a true believer and will always use it.

 

Thats all that engine had run in it since it was new, thats why. My K20 had 70 miles on the motor when I bought it, I just put head gasketts on it 3 weeks ago. At 42,000 miles on conventional valvoline 10w40 the motor was as clean as the day it was built. no buildup or deposites of any kind.

 

Just change the oil frequently (every 3K miles or so) and use the right grade, and the engine will last a long time regardless of oil type. Don't change the oil and all the grit and dirt will grind away at the engine. Syntethics are better lubricants, but they need to be clean. Change the filter at every change. As for seal leaks due to syntethics, that is no longer the case. It was common when they first came out, but improved additive packages have resolved the problem. However, the reputation remains.

 

Gotta put my 2 cents in. As for you ppl saying u lose oil pressure with syn you are full of crap. i have mobile 10-30 in my car since i bought it at 64,000 miles and it runs great, doesnt leak anywhere and i have between 40 and 60 psi of pressure depending on how hard im on it. But i will also say that conventional motor oil is fine just make sure u change it every 3 thousand, better yet just keep an eye on it and change it when you think its getting to dirty. different driving conditions have different outcomes on how quick your oil wears down. And as for another prop to synthetics, iw ork in a lube shop and i saw one of my customers push a 5.3 liter in a tahoe to 14.000 miles in one oil change, i dont recommend it but there was still oil on the stick and it still runs to this day.

 

I drove the same service truck ('77 chevy C10 305 2bbl) for 4 years at my first job. never once changed the oil, no lie. just topped of with whatever Motomart had cheapest, and I can tell you it was'nt synthetic. It went another 3 yrs. after I quit. I was 16 do you think I was kind to that truck? lol. what's wierd is that truck always ran great never had a mis or a tick like the small blocks get when they get that abused.

 

Back to back I have seen an LS1 in sound condition dropo about 4 lbs at idle going to MObil1 synthetic from a normal oil of the same weight. But oil pressure is still good. If you look into the specs this is because the Mobil1 is actually thinner: not all 10W30s are exactly the same.

My vette was built "loose" by my engine builder, who said it would not hurt a thing (and I sort of believe him, he's built some real Nascar winners including one Daytona winner in the mid 90s), and it has piston centered rods which reduce oil pressure a few pounds, and an oil cooler which takes about 3 more lbs, yet with a 50/50 mix of 0-40 and 15/50 Mobil1 (that works out to equivalent of about 5-44, mixing does not average the numbers), it holds 34 lbs at idle with oil temp at 210 degrees and does over 55 lbs (pressure spring setting) at RPM about 2500. I have roller rockers which show no signs of oil starvation so far (only 5000 miles on the engine) and they'd be the things to starve first, I think).

 

I got an 01 Explorer sport and i have a numerical pressure gauge. I actually picked up 8 lbs of pressure with Amsoil. It flows easier and more consistant than petrolium.