i like using castrol gtx oil.

for my 5.0 305 v8 fuel injected tpi enigne what is a good safe choice of oil for it???

it has over 100,000 miles

5w 30?
10w 30?
10w 40??

i keep hearing its too late to go full synthetic but how about synthetic blend?

this is just a summer car so dont take winter into consideration


anybody have any suggestions?

 

Has the GTX oil sludged up the engine in those 100k miles? (I've seen it more than once.) Does the engine leak oil? Does the engine burn oil? Do you want the engine to wear out sooner?

If the answers to those questions is "No", then there's no reason not to go to a full synthetic.

I would advise going to a "real" synthetic, but it won't start with "C" if you do. Starting with a blend isn't a bad idea to help clean up some of the crud that has built up in the engine by using petroleum-based oil.

10W-30 is fine for summer operation.

 

i would love to go full synthetic but wouldnt do more harm then good on worn rings and create leaks in those old gaskets?

im not sure. it doesnt leak now. and i use additives to help clean n lubricate

and i used the high milage castrol stuff so far.


I just keep hearing its too late for full synthetic. if it was a brand new engine id totally agree.

also isnt bad to start full synthetic cold turkey? if i did do a switch should i start with a blend first then do the full synthetic?

 

Borrowed from another recent thread on the topic (I would have linked it, but there's a bunch of other confusing stuff in there):

In our own time, synthetic motor oils have been the object of numerous misconceptions held by the general public. Many people, including some mechanics, have been misled by these persistent myths.

PARAMETERS OF THE DEBATE

Synthetic motor oils are fuel efficient, extended life lubricants manufactured from select base stocks and special purpose additives. Synthetic oil base stocks are made from organic compounds or synthetic hydrocarbons using a process that re-arranges the structure so all the molecules are uniform in size, shape and weight, a phenomenon that does not occur in nature. In contrast to petroleum oils which are pumped from the earth and refined, synthetics are custom-designed to produce, in effect, the ideal lubricant.

In responding to the objections most commonly raised against synthetics it is important to establish the parameters of the debate. When speaking of synthetic motor oils, this article is defending the lubricants which have been formulated to meet the performance standards set by the American Petroleum Institute (API). (The first such synthetic motor oil independently tested and confirmed to meet these industry-accepted tests for defining engine oil properties and performance characteristics was AMSOIL 100% Synthetic 10W-40 in 1972.)

Many people with questions about synthetics haven't known where to turn to get correct information. Is it super oil or snake oil? Some enthusiasts will swear that synthetics are capable of raising your car from the dead. On the other hand, the next fellow asserts that synthetics will send your beloved car to an early grave. Where's the truth in all this?

In an effort to set the record straight, we've assembled here ten of the more persistent myths about synthetic motor oils to see how they stack up against the facts.

Myth #1: Synthetic motor oils damage seals.

Untrue. It would be foolhardy for lubricant manufacturers to build a product that is incompatible with seals. The composition of seals presents problems that both petroleum oils and synthetics must overcome. Made from elastomers, seals are inherently difficult to standardize.

Ultimately it is the additive mix in oil that counts. Additives to control seal swell, shrinkage and hardening are required, whether it be a synthetic or petroleum product that is being produced.

Myth #2: Synthetics are too thin to stay in the engine.

Untrue. In order for a lubricant to be classified in any SAE grade (10W-30, 10W-40, etc.) it has to meet certain guidelines with regard to viscosity ("thickness").

For example, it makes no difference whether it's 10W-40 petroleum or 10W-40 synthetic, at -25 degrees centigrade (-13F) and 100 degrees centigrade (212 degrees F) the oil has to maintain a standardized viscosity or it can't be rated a 10W-40.

Myth #3: Synthetics cause cars to use more oil.

Untrue. Synthetic motor oils are intended for use in mechanically sound engines, that is, engines that don't leak. In such engines, oil consumption will actually be reduced. First, because of the lower volatility of synlubes. Second, because of the better sealing characteristics between piston rings and cylinder walls. And finally, because of the superior oxidation stability (i.e. resistance of synthetics against reacting with oxygen at high temperatures.)

Myth #4: Synthetic lubricants are not compatible with petroleum.

Untrue. The synthesized hydrocarbons, polyalphaolefins, diesters and other materials that form the base stocks of high-quality name brand synthetics are fully compatible with petroleum oils. In the old days, some companies used ingredients that were not compatible, causing quality synlubes to suffer a bum rap. Fortunately, those days are long gone.

Compatibility is something to keep in mind, however, whether using petroleum oils or synthetics. It is usually best to use the same oil for topping off that you have been running in the engine. That is, it is preferable to not mix your oils, even if it is Valvoline or Quaker State you are using. The reason is this: the functions of additives blended for specific characteristics can be offset when oils with different additive packages are put together. For optimal performance, it is better to use the same oil throughout.

Myth #5: Synthetic lubricants are not readily available.

Untrue. This may have been the case two decades ago when AMSOIL and Mobil 1 were the only real choices, but today nearly every major oil company has added a synthetic product to their lines. This in itself is a testament to the value synthetics offer.

Myth #6: Synthetic lubricants produce sludge.

Untrue. In point of fact, synthetic motor oils are more sludge resistant than their petroleum counterparts, resisting the effects of high temperature and oxidation. In the presence of high temperatures, two things can happen. First, an oil's lighter ingredients boil off, making the oil thicker. Second, many of the complex chemicals found naturally in petroleum base stocks begin to react with each other, forming sludge, gum and varnish. One result is a loss of fluidity at low temperatures, slowing the timely flow of oil to the engine for vital component protection.

Further negative effects of thickened oil include the restriction of oil flow into critical areas, greater wear and loss of fuel economy.

Because of their higher flash points, and their ability to withstand evaporation loss and oxidation, synthetics are much more resistant to sludge development.

Two other causes of sludge -- ingested dirt and water dilution -- can be a problem in any kind of oil, whether petroleum or synthetic. These are problems with the air filtration system and the cooling system respectively, not the oil.

Myth #7: Synthetics can't be used with catalytic converters or oxygen sensors.

Untrue. There is no difference between synthetic and petroleum oils in regards to these components. Both synthetic and petroleum motor oils are similar compounds and neither is damaging to catalytic converters or oxygen sensors. In fact, because engines tend to run cleaner with synthetics, sensors and emission control systems run more efficiently and with less contamination.

Myth#8: Synthetics void warranties.

Untrue. Major engine manufacturers specifically recommend the use of synthetic lubricants. In point of fact, increasing numbers of high performance cars are arriving on showroom floors with synthetic motor oils as factory fill.

New vehicle warranties are based upon the use of oils meeting specific API Service Classifications (for example, SJ/CF). Synthetic lubricants which meet current API Service requirements are perfectly suited for use in any vehicle without affecting the validity of the new car warranty.

In point of fact, in the twenty-eight years that AMSOIL Synthetic Lubricants have been used in extended service situations, over billions of miles of actual driving, these oils have not been faulted once for voiding an automaker's warranty.

Myth #9: Synthetics last forever.

Untrue. Although some experts feel that synthetic base stocks themselves can be used forever, it is well known that eventually the additives will falter and cause the oil to require changing. Moisture, fuel dilution, and the by-products of combustion (acids and soot) tend to use up additives in an oil, allowing degradation to occur.

However, by "topping off", additives can be replenished. Through good filtration and periodic oil analysis, synthetic engine oils protect an engine for lengths of time far beyond the capability of non-synthetics.

Myth #10: Synthetics are too expensive.

Untrue. Tests and experience have proven that synthetics can greatly extend drain intervals, provide better fuel economy, reduce engine wear and enable vehicles to operate with greater reliability. This more than offsets initial price differences. All these elements combine to make synthetic engine oils more economical than conventional non-synthetics.

In Europe, synthetics have enjoyed increasing acceptance as car buyers look first to performance and long term value rather than initial price. As more sophisticated technology places greater demands on today's motor oils, we will no doubt see an increasing re-evaluation of oil buying habits in this country as well.

CONCLUSIONS

Since their inception, manufacturers of synthetic motor oils have sought to educate the public about the facts regarding synthetics, and the need for consumers to make their lubrication purchasing decisions based on quality rather than price. As was the case with microwave ovens or electric lights, a highly technological improvement must often overcome a fair amount of public skepticism and consumer inertia before it is embraced by the general population.

But the word is getting out as a growing number of motorists worldwide experience the benefits of synthetic lubrication. The wave of the future, in auto lubes, is well under way.


About The Author

Ed Newman is Marketing Manager for AMSOIL INC., manufacturer of the original synthetic motor oil for automotive applications. He has published more than 200 articles as a freelance writer on a wide range of important topics.

As pointed out in the other thread, not all synthetics are created equal. The better ones on the market right now are Group IV PAO. By U.S. regulatory fiat, Group III lubricants, hydro-cracked refined petroleum, can also be called "synthetic" on the label, although technically they are not synthesized (another example of the general dumbing-down going on in this country). The really sad part is you can't tell from the label which type a particular product is, because they aren't required to tell you what they made the stuff out of.

If your rings are worn, synthetic won't make that worse, but you will continue to use oil which will cost more to make up between changes. However, the two most common cause of oil use in high-mileage small block Chevy engines are worn/hard/cracked valve stem seals, and rings stuck in the piston grooves by accumulated sludge/varnish. Using synthetic won't cure the valve seal problem, but a quality crankcase flush, followed by use of a synthetic or synthetic-blend oil will eventually clean up the sludge and varnish.

One old tried-&-true method of converting to synthetic is to change your oil & filter and use one quart of synthetic in place of one quart of petroleum. The next oil & filter change, use two quarts of synthetic in place of two quarts of petroleum; next change 3, etc., until the entire change is all synthetic. That brings up the issue of additive package mixing mentioned above, but that's minor compared to the continued wear and deposit build-up you'll get with only using petroleum oil. As already mentioned, a few changes of synthetic blend will help clean things up before going to full synthetic. I do like AMSOIL's crankcase flush, though - it really gets the cleaning show on the road.

Almost all of the cars I've switched over to synthetic had more than 80k miles on them, with most of them over 100k. I've had several people get AMSOIL from me with fairly new vehicles as well. As long as the engine doesn't have major wear (usually meaning neglect or abuse), you'll be fine switching over.

 

New
Clean
Often (on schedule)
Synthetic

Some of those "old wives' tales" that just won't go away.

Bad idea. Use good oil in the first place. Diluting inferior and inadequate oil, i.e. non-synthetic, with all that other stuff doesn't do any good. Running modern oil instead of all that is the way to go.

More of the "old wives' tales"..... there's no such thing as "too late". The need for effective lubrication of the metal parts, doesn't decrease with use.

Can you figure out what this is more of?

Use Mobil1 10W-30. It'll be fine.

I'd suggest though, flushing out some of the gunk that the dinosaur juice has allowed to accumulate in the engine, so that your new better oil doesn't immediately become contaminated with it and have to be changed out too soon ANYWAY. Run a quart of ATF in your oil for 1000 miles or so, and then change it. You won't BELIEVE how much schmutz the Neanderthal stuff has left in there, the old oil will probably come out black and thick and chunky from it all. Like I said, no point in corrupting new high-quality oil with all that. Get it out first.

 

ok thanks guys

what is ATF? only asking so i know what im asking for when i buy it and anything else i can do like a engine flush?

anything i can do to just flush n clean the system instead of driving it before i switch?

 

ATF = Automatic Transmission Fluid

Not really.... that gunk has been building up in there for 20 years or whatever; it won't come all out in an instant, without creating more trouble than it solves.

 

Like I said, the AMSOIL crankcase flush is a good start. But, I wouldn't say it's a guarantee to get it all the first time. That splash pan under the intake tends to catch a bunch of crud (could argue it creates it), which is almost impossible to flush out by running something through the crankcase.

 

You keep hearing wrong. You can go to full synthetic anytime you want.

 

would doing a sythetic blend to start be a bad idea or shoudlnt be a problem?

 

Not a problem.

Already said that.

 

The only issue is seating new rings. The syn will not hurt, it will just take a little longer. I usually wait 5000 miles. Then use syn.