Is synthetic oil bad for engines with over 100,000 miles on it? I was going to buy royal purple and see how my car reacts but figured I should ask you guys first. I'll just get a high mileage oil if it won't work for my car. I heard thicker oil is better for high mileage motors and synthetic is thinner than conventional oil. Thanks for the help

I personally wouldn't run synthetic in a high mileage engine that isn't used to synthetic oil. The thinner oil will increase the clearance between bearings and can cause serious damage. I've had two higher mileage engines that died due to spun rod bearings, both shortly after switching to synthetic.

well i have a 133k lo3 that i bought from my next door neighbor . i used a syn. blend . from the get go , no problems , i now use a 50/50 blend ( mix it myself ) no problems . anyway , clean eng. , fix oil lks. , and go with what you feel best . in regular hwy. cruising i get 27-29 m.p.g. . also check out bobistheoilguy . more info than you can ever need . i also do an eng. flush with a qt. of mineral spirits/solvent before each oil change . put it in and let it idle for about 5mins. before drain . has worked for me for many years . i do have a lift , so i do my own oil changes .

Synthetic was DESIGNED for high mileage engines! Use regular after a rebuild so the parts can wear in, then switch to synthetic.

I switched to synthetic a while ago and noticed a) smoother running, b) better mileage, c) less engine noise and d) no more oil consumption for some reason! Perhaps the higher viscosity was making it harder for the oil to leak...

TheDude has a point and I wouldn't want to destroy my only motor. I'll give the 50/50 mix a shot and see what happens. What oils do you use and what mineral spirit solvents UncleTom and you only use one quart?(I probably get the worst gas mileage for a 305 on the board........14-15 cough...thats with keeping the revs under 2000rpm and it's only a 305 with small energy cam) My brother is getting his q jet rebuilt for his firebird so I'll see how that works out) My motor has 102,000 miles on it so I want to give it the right oil it needs. I change the oil every 2 and half months outside and it is always thick black when it comes out.


Thanks

You think that your LO3 got bad milage? Mine (before I switched to a L98) averaged about 8 all city mpg, completely stock!!!!

Now with the L98 has gotten me about 15 all city.

Would a synthetic oil be a good choice for a 600 mile remanufactured long block? Or should I stick with regular for now and go synthetic later?

Thanks,

-Tim-

thick and black???? wen its comes out?....you proli have engine sluge and thats why you get very bad gas mpg....i would buy that stop sluge oil...deff

Does it leak oil anywhere? Switch it to synthetic's and keep an eye on it. Remember, the synthetic oil is going to do a real good job of cleaning the seals and will seek out any and all potential exits.

i used valveoline high mileage synthetic oil at 75k , runs alot smoother , the leaks are the same as they were before i switched i have not noticed any leaks getting worse i barely lose 1/2 a quart before a 4k oil change , it burns oil slightly less and i have the LB9 motor and it gets id say about 14-17 mpg also a lil key to look at even on some bottles of synthetic motor oil they dont say ENERGY CONSERVING on there starburst label u always want to buy ones with energy conserving on the label , also a good can of restore every other oil change has made noticeable changes for the mileage gained about 2 mpg w/ restore but some say is it worth paying 8 bucks for 2 mpg ? depends on your driving habits and how much you care about your car , thats my lil 2 cents

Synthetics can cause high mileage engines to burn oil, something with how they break up deposits on valve seats I think. Id just run a thicker oil if its burning,10w40 or 20w50.

My car doesn't burn any oil. It leaks a couple drops once in a blue moon. But it seems that there is a split decision with running synthetic or thicker oil. Still not sure if to go ahead and get the royal purple or just get high mileage thick oil. The 50/50 souds like a good idea. I know a lot of circle track racers do that, but then again my car isn't a race car. As of now I have read that synthetic will break your motor because it will increase the clearance between bearings and can cause serious damage, and that it breaks up deposits causing oil to burn, and was designed for high mileage motors, and is going to do a real good job of cleaning the seals and will seek out any and all potential exits. On the other hand thicker oil will reduce bearing clearnce, not clean engine sludge, and make my car run smoother. What should I do? I am in the direct center of a pickle and don't know what to do now.

Options:
-Run 50/50 mix
-Use High mileage oil
-Put in mineral spirits solvent
-Put in Engine restore
-Use one of those oil filtermag's
-Use synthetic
-Somebody said diesel oil is good for high mileage. don't know?
-Take off my manifold down the road and see what kind of garbage is in there and clean it out

I'd just run regular oil, my fav is castrol GTX, i haven't tried the high mileage one but im sure its good. That an an ac delco filter. I wouldnt bother with synthetic, way too much $$$ not worth it unless you have a low mileage engine and always run it.

Edit: don't even think about engine flushes, thats just asking for trouble. If you want to clean it add a quart of ATF for the last 500 miles b/c ATF is full of detergents and itll help clean it out. Don't use diesel oil either.

remember they also have thicker weights of syn oil too , but if your worried just get a regular oil , syn blends are horseshXX ,

synthetic oil has alot of advantages.....

don't listen to all the BULL about not using it in high mileage engines......

it has superior lubrication properties over time.......basically the biggest benefit of a synthetic oil is it lasts alot longer before it loses its lubricity and viscosity properities......

the MYTH, thats right i said MYTH about synthetic oils being lighter is garbage.......that stems from the fact that people are accustomed to seeing synth oils in newer cars.....which typically use a lighter oil in the 1st place (like 5w30) Synthetic oil is available in all weights and multi grades, and the weight of the oil on the container, is the weight of the oil......a synthetic
20w50 is the same weight and thickness as a conventional 20w50 etc.

the reason for not using it in a new engine supposedly is that it lubes so well the rings won't seat.......and thats only a theory anyways......

the biggest reason for not using it in a new engine is you have to change the oil like 3 times very quickly, so you'll be throwing away a ton of extra money on synthetic oil thats unnecessary.

Personally I use conventional oil.....because i change my oil so often i'll never see the benefit of a synthetic.

this is wrong........its only correct if you use the wrong weight oil. The only possible correlation between your rod bearing failure and the synthetic is if the inside of your oil galleys had tons of crap built up, which the synthetic oil disolved, and then that material got into your bearings and cause them to touch.

changing your oil has NOTHING to do with oil clearance......your oil clearance is the difference in the OD of the journal and the ID of the bearing......which most of the time on a rod bearing its around .002

newer engines use lighter oils because they have tighter oil clearances than the engines of old.

I just changed my oil today. First i put in a quart of ATF in the motor and ran it for 4-5 minutes. Then I dumped it out and put in castrol syntec blend with a new oil filter. I have to say the results for me were pretty staggering. My car now idles between 550-600 rpm compared to 1000. even on the highway i can cruise at 1300 rpm. My idle is very smooth and quiet now. Almost runs like a new car. I have to say thanks for the help guys! My gas mileage should be better now.

what aftermarket product are we reviewing

The original poster, IROCJoyce, was wondering about switching to Royal Purple synthetic oil, but this topic is also well suited for the Tech / General Engine forum.

That, by far, is the most important thing to do. That is where the biggest benefit to your engine can be found.

I began using synthetic at 63,000 miles no problem yet.

I have stated it before and I will say it again

1992 RS 305 156,xxx miles and switched to Royal Purple and still have zero problems or leaks.

im new to TGO. but i work at a pennzoil oil change. i use the pennzoil platinum. its there full synthetic. but there is a lady that has a 1996 firebird that has a 3.8 in it. she was using regular oil. at 100k she switch to the full synthetic and now it has 433k. and stock and it dont take oil.

How many sets of intake gaskets has it gone through? Does it only leak coolant at the intakes?

it leaks nothing. she gets her oil changed 6 weeks because she 5000 miles in that time. but all her fuilds are full every time and and nothing leaks. the gaskets are all original. the only thing that she had replace was the clutch last fall.

I switched to synthetic 5k miles ago, has around106k now, no problems at all. Another good idea is to add BG MOA at every oil change, great stuff...all BG products are great.Can only be bought from a shop though, almost all the shops I've worked use it...I've used it for years.

i switched to using royal purple 5w30 like a year ago and the car has never been happier...i just switched out to royal purple's max gear in the diff, and it actually got my posi working again...(http://www.thirdgen.org/techboard/tr...-end-help.html (Rear end help))

Understanding this thread is over a year old, I have to say there's no such thing as a "quick oil question" on this Board. The misinformation is rampant, and in this case started with the very first reply.

Most of the cars I've switched over to synthetic had more than 100k miles on them. The most mileage was the '95 2500HD 6.5TD Silverado that had 284k miles on it when I switched it over 2 years ago (has 300,430 on it now). The only leak is the oil cooler lines, they were leaking (and had been replaced once before due to leakage) before the switch, and they're a common leak item on those vehicles.

There is no way synthetic can "hurt" an engine. It can only improve it. If it dies after being switched over, it was going to die, anyway.

Debunking all the myths and misinformation out there about synthetic oil is practically a full time job. It's a dirty job, but somebody has to do it.

It's really a question of how well was the car taken care of. If it wasn't reamed on and run with cheap oil or cheap oil with few oil changes along with poor mantainance; (which sludges up the innards and eats away at the gaskets).

There is a certain amount of fuel and vapor that gets past the piston rings. If someone lets the oil stay contaminated with fuel and water vapor, it eats away at the gaskets. Mine had 145k miles on it when I bought it. It didn't have any sludge build up, but it did have cheap non detergent oil that was heavily contaminated. When I changed out to Royal Purple, after flushing the engine really good, she ran SIGNIFICANTLTY smoother, reved quicker, mileage increased approx. 17%, and also ran cooler.
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However; as has been mentioned prior:
Quote:
I personally wouldn't run synthetic in a high mileage engine that isn't used to synthetic oil. The thinner oil will increase the clearance between bearings and can cause serious damage. I've had two higher mileage engines that died due to spun rod bearings, both shortly after switching to synthetic.
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I did pick up a slight rod knock within 1k miles and had to switch back to a higher viscosity dinosour oil. Three years later, I've had an increase in the rod bang but have a new engine pieced together out in the garage.

I did NOT have any oil leakage due to the synthetic switch. I would not have tempted fate with the Royal Purple if there had been any sludge build up underneath the oil cap or on the rockers. So think about the 'big picture' before going to synthetic OR staying with dinosourus oil....Nitro