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Like fordgt, I've always run Castrol 20W50 in mine during the warmer season. In winter I switch to Castrol 10W40. I may try the Castrol synthetic this summer. Are you able to see any difference running the synthetic oil fordgt??

...All New Engine, Tighter Tolerences, I will 'Break it in' with a thinner oil. I use 10W30 Castrol GTX Turbo. After 10,000 to 20,000 Miles, I may go to 20W40 then 20W50 (much later and then over 90 Degrees Ambient temps). 'Oil Experts' I have talked to, would never put the 'Thicker' Oil in a Brand-New Engine, it just would not get through the .001" clearences; not 'In-Time' anyway...
The best oil to use is typically the same oil you have been using. Problems arise from changing oils (unless it's a new engine). The worst thing you can do is go from a non detergent to a detergent oil. It will break up particles that were built up (originally un-disturbed). Some times peopel will use one type for break in then switch to another to run through out the engine life which is ok. Basically, pick one and stick with it.

Experts have quoted the pure synthetics as the ultimate if you can afford them. Many an aircraft engine has been bought by synthetic oil companies after they tore them up. They do well but cannot absorb everything the petrolium based oild can. When they get saturated they start gumming up stuff. Many aircraft and car manufacturers will not longer warrent their engines if you use PURE synthetic oils. If you do, change it OFTEN (which is in oposition of what they say). The minute it gets dirty, you'll start getting deposits on things such as pistons, etc.

I am no expert here, just repeating what I have been reading in aircraft journals.
the 351C was originally spec'd for 20W40, 20W50 became the viscosity of choice when 20W40 was no longer available off the shelf. Living in a climate that is much colder in the winter and much warmer in the summer, I would advise you to run a lower viscosity oil in the winter, higher viscosity in the summer.

Having been inside many engines over the years I can generalize and say that Valvoline leaves a grey residue inside engines, Pennzoil leaves a gummy brown varnish, Castrol leaves the engine clean (assuming regular oil changes).

Synthetic make sense for new or rebuilt engines, if you want to avoid wear. I have seen bearings come out of engines running sythetic oil that looked like they were new, out of the box. Synthetics also leave the engine clean inside and are far superior at elevated temperatures. Running synthetics in my own vehicle, I have seen oil consumption get better with mileage, a 100,000 mile car getting better oil consumption than it did when it was new! There is less or no carbon build up in the piston ring grooves.

Viscosity stabilizers tend to break down with use, I prefer to use oil with less viscosity stabilizer (10W30 as opposed to 10W40). Amsoil marketed a 20W50 synthetic oil that had no viscosity stabilizer in it, it was "naturally" 20W50.

Byproducts of combustion pollute synthetic oils at the same rate as mineral oils, so the idea that synthetic oils don't require changing as often as mineral oil is bogus.

Finally, if you're going to spend the bucks on synthetics, buy one that uses a synthetic base (100% synthetic), not one that uses synthetic additives to a mineral oil base. Mobil 1 sued Castrol in Federal court about a decade ago because Castrol was claiming their oil was 100% synthetic when in reality it used a mineral oil base.

First, a meaningful discourse on this issue is best held with a chemical engineer, which I am not.

I believe the ester based synthetics are better at high temps & prevention of deposits. PAOs were noteworthy for their low temp peformance & resistance to oxidation. Most synthetics these days have a large amount of highly distilled mineral oil in them known as group III oil.The entire "synthetic" issue was muddied when Mobil 1 lost it's court battle with Castrol. Oils containing group III bases can be referred to as "synthetic". Most synthetic oils today contain a mixture of products in their bases, and they are not readily advertised, so its hard to say what you're buying.

From an earlier post, I know you use Red Line. Red Line is a poly-ester, due to its high temp characteristics it is a great oil for use in air cooled engines, perhaps the best oil for air cooled engines used in competition.

Amsoil & Mobil 1 are both good recommendations. Amsoil switches back & forth between PAOs & ester, depending upon the application. Mobil 1 advertises its motor oil as a "tri-synthetic", its base is not pure PAO.

If I can make one point clear, the semi-synthetics cost the oil companies 15% more to manufacture, yet they charge twice as much as for their pure mineral oil products. In other words, caveat emptor.

Originally posted by george pence:

George, intersting stuff, being around airplanes, full sythetics are the devils fluid. The Class actions suits against Mobil Oil:

Open the door to the problems with synthetics. Albiet this effects aircraft more severely. They can not disolve the lead deposits (in aircraft fuel) and other deposits which remain in suspention. After discovering these sorts of problems I read about test where they could not get brand new engines to go to 2000 hours with 3000 hour overhaul intervals. With the concentrated sludge it was also damaging propeller systems which pump oil through them.

I am not doubting the high temp and lubrication benifits but the word in avaiation is "PURE" synthetics are as good as water; which is why they are none in aviation oils any more. Very few in automobile oil which contributes to the high price.

Obviously car engines do not have as much lead in the fuel but it's not just lead it cannot disolve. On top of that, the synthetic car oils boast longer oil changes which with it's unability to disolve combustion bi-products, oil changes should be more often.

It is not against any warenty (and amosole is constantly telling people that) because of the Magnuson-Moss act which basically says oils are judged by Viscosity not by brand.

I did a search for articles on oil changes. Found many by Amasol and many others touting long oil change periods, trying to tell people it doesn't void their warenty, trying to dispel comon myths, etc then found many articles about car companies with longer oil change intervals and people finding a lot more sludge in their oil, maintenance guys telling them to go back to the 3000 mile oil change and car companies backing off the use of pure synthetics. The corvette did but I don't know if it still does. I had heard they stopped but don't know.

Modern oils are pretty good and are not going to break down in 3000 miles. If you get 150,000K on pure synthetics, would love to see the info, compresion test, oil change history, would be good info. It's an absolute no no for aircraft.

On the other hand the synthetic blends are still held in high reguard because the blends can disolve the deposits.

The bigest concern with oils is dirty oil. Good fiters, and good oil changes. If a car sits, water is absorbed in the oil and it should be changed at least yearly reguardless of mileage. Dirty oil (especially for older engines with more blow by) acts like sand paper and needs to be clean. I always thought the guys with double oil filters were a good idea.


the aeronautic issues are not duplicated in automobiles. Perhaps because the fuels are significantly different.

There are no despoits inside the engines of autos running synthetics. My last 3 autos improved oil consumption and fuel economy with age. It is amazing. I change oil every 5000 miles. My last work car, a '92 T-Bird, had 200,000 miles on it when I donated it, still not burning any noticeable oil between oil changes. My current work car, a 2001 Taurus, is getting about 7% better gas mileage than it did when it was new, it has 108,000 miles on the odo.

I pulled the top end off a little Honda motorcycle a couple of years ago (1989 XR100 dirt bike) that had been fed a diet of Amsoil 20W50. The cross hatch marks were still visible on the cylinder walls. The engine had no varninsh or deposits of any kind. It was spotless, like new inside. The bike had been abused, frame cracking, rims bent, obviously ridden hard & put away wet. But the motor was like new. Impressive.

Back in the '80s I pulled apart a Cleveland motor that had been driven hard in a Mustang, running Cleveite bearings & synthetic oil. The motor had about 20,000 hard miles on it. The bearings looked like they did the day they came out of their box.

As I mentioned in my first post, I don't agree with the concept of extended oil changes, that's pure non-sense. The byproducts of combustion build up in synthetics at the same rate as they do in mineral oils.

With perhaps the exception of Amsoil & Red Line, all current automotive synthetic oils claiming to be pure synthetic have a base of blended chemicals, most composed of a large percentage of group III mineral oil. These "cocktails" are blended to accomplish certain goals, perhaps to improve profit, but just as likely to improve the ability of the oil to contend with problems like the dissolving of combustion by-products you mentioned. A blend of PAO & ester provides the benefits of both, the cold flow benefits & resistance to oxidation of PAO, the high temp & deposit control of esters.

The semi synthetics are a rip-off because they are priced way beyond the difference in manufacturing costs & have very little synthetic chemical in them (less than 30% by definition), they do not even have to use group III mineral oil in the base.

In the automotive world, the "pure" synthetics are superior to mineral oil based lubricants due to their superior high temp oxidation resistance, high film strength, very low tendency to form deposits, stable viscosity of the base and low temp flow characteristics. Amsoil, Mobil 1 & Spectro are the synthetic oils normally given the highest ratings in these areas.

the article seems to validate what we guessed, that its the lead in av-gas thats the problem.

interestingly, synthetic automotive lubricants did not become readily available until after the switch to unleaded fuels.

the author of your article also agrees with me that extending the oil change intervals when using synthetic lubricants is bunk.

...About using Synthetic oil in a 'Brand-New' Built engine. Where part of the Breaking-in Process is to 'Seat' the piston rings; I have (only) read that Synthetic Oil does not allow the 'wear-in' that is needed to properly seat the rings. I imagine one would break-in an engine(seat the rings), on a mineral based oil, and then switch to a Synthetic. Any other comments?...

I would agree too. Dirty oil is dirty oil even when the oil is not broken down. I had heard of an experiment with cabs that were using huge Semi truck filters in the trunk and going 10,000 with out oil changes. The oil was still clean because of the huge filters. Saved them a lot of down time and frequent oil changes.
I used to run mineral oil for the first couple of oil changes (10,000 miles) before switching to synthetic oil.

My oldest son attended the Motorcycle Mechanics Institute a few years ago & passed on what he learned about breaking engines in to his dad.

I realize now that an engine broken-in properly can have the mineral oil used for break-in drained immediately afterwards and begin running synthetics. The rings should be seated after the first running of the motor. For practical purposes, I would recommend 500 miles on mineral oil, drain it & begin using synthetic.

Have you ever noticed how break-in oil drains out with a green color? That's the metal left behind from machining. Don't leave that oil in long. (Motorcycle trans oil also takes on a green color due to the wet clutch)

Marlin, my mother lives in Escalon, I'm familiar with your area.


I've been out of town, logged onto a friends computer this AM, sorry I haven't responded sooner.

Ash content is still a measured "spec" for motor oil, but it is not listed on the bottle. Ash content may be specified in the ILSAC or API oil rating systems. In general ash content is better than in decades past, the high ash content oils run around 1% I think. The oils with high ash content, by the way, are Valvoline, Halvoline, Shell.

Detergent content is not advertised either, although most oils have "detergent" or additives that take the place of detergent. Modern oils have an extensive additive package. The exception is the oil you mix in gasoline for 2 cycle engines, that oil contains no detergents, and may say "non-detergent" on the label.

The bigest thing we were taught in college was you could go from detergent to non-detergent but NOT non-detergent to detergent. Detergent will break up deposits otherwise undisturbed by non detergent. The problem being most automotive oils do not put on their detergent qualities. I would gather from this that all have some detergent qualities but differ some what based on the type of additives used. For this reason it is important to pick one oil and stick with it as a different oil can cause problems down the road. This is not to say one oil is better than another, just that swapping oils can caause problems.
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