Synthetic Oil

[Lou Boffa]

I accidentally picked up some Castrol GTX synthetic oil the other day. I normally use GTX--but not the synthetic stuff. Is it ok to use on my 91K 350? Any concerns?

[cleszkie]

You may notice some seals start leaking (rear main, front crank seal). I think the synthetic stuff is generally thinner that the organic stuff. I was always told never to switch from conventional to synthetic. Not sure what other pitfalls there may be, but why chance it. Return the synthetic and get conventional.

[Lou Boffa]

Originally Posted by cleszkie

You may notice some seals start leaking (rear main, front crank seal). I think the synthetic stuff is generally thinner that the organic stuff. I was always told never to switch from conventional to synthetic. Not sure what other pitfalls there may be, but why chance it. Return the synthetic and get conventional.

I think you are right. Thats what I'll do.

[Thanos]

I always go full synthetic , you just have to be ready to replace warn out seals and gaskets. I swapped to mobile 1 in the IMO crappy 454 it started to leak around the pan.

I'm swapping in another motor anyway however I have had GREAT luck with using "The right stuff" gasket maker on things like that over a new gasket.

[1970chevc101994]

I did a reasearch powerpoint on conventional vs. synthetic oil awhile back for a school project and what i found is that synthetic is a better oil due too it being lab-created and that is has different "additives" in it. I run Amsoil in my DD which has 140,000 miles with awesome oil pressure. The old synthetics were hard on seals because they were made of esters. New synthetics are not. I would say they wont hurt your seals but because the molecules are smaller it may leak from any cracks that there may be.

[summitflier]

I've ran both natural oil and synthetic in many vehicles over the years.
I actually have better luck with the synthetic, but with one caveat.

I never go directly from natural to synthetic. I always run a blend for a while
before switching completely one way or the other. In fact sometimes, I just run
a blend all the time. The thing about blends is... "How much of a blend"?

Some oil companies will state "80% synthetic". But many do not.
So you don't always know what you're getting with a blend.

[Alex V.]

Yeah, I'd return it and get the right stuff. While IMHO a full-synthetic is overkill for any halfway tame small block (short of engines that rack up a lot of highway miles and could use an extended drain interval) if I was going to synthetic I'd stick with it. Syn blends, on the other hand, is what I run in all my pushrod engines with change intervals around 3,500 miles; If I put more highway miles on them I might extend it to 4K.

[Z10]

You might find this helpful "540 Rat".

https://540ratblog.wordpress.com/201...-test-ranking/

As for me......I run Mobil 1 in all of my engines for a lot of reasons and this study pretty much supports my decision.

Full disclosure, all of my cars, both old and new have newer engines which I run synthetic. The only exception is my 1979 Mazda RX7 which runs dino oil. I tried synthetics in it, but it leaked like a sieve. If you're running an engine built in the 80's or later you should be fine running synthetic.

[In The Ten Ring]

Everything I've read here seems to be completely opposite of what the "experts" I've heard say. LOL

Some things are like that.

My truck has only ever had conventional oil. Now that it has sat for 11 years I guess I'll put conventional back into it along with 1 quart of Marvel's Mystery Oil. Apparently that stuff is some kind of miracle mix.

My Honda Accord does great with conventional, I have been told if an engine begins to leak at the seals or smoke to then start using synthetic as the "molecules are longer and thus, fills in voids better like scratches in the cylinder walls." I don't know. I do know that even with synthetic my Accord manual states changes must still occur every 3,000 miles so one isn't saving any money switching.

If I had been running something and I got something different, I'd take it back and try and get what I had been running before. But it's oil....the job is to lubricate....how much difference can it make?

[Mr Handy]

My understanding to why you may not want to switch to synthetic in an older engine is that the synthetic oil has detergent additives in it to help keep the engine clean. If your engine is dirty this is can actually be a problem if it starts knocking junk loose... the oil filter should take care of it, but some of that grunge may be acting to help old seals seal and the engine may begin to leak. There is nothing I hate more than oil leaks... except maybe an engine that runs hot.

Other than this there really should not be a reason to not switch in this day and age, unless you are using an oil without the proper amount of ZDDP (zinc/phosphorous) to properly protect your cam and lifters.
This is why some companies like Amsoil and royal purple offer synthetic oils designed for flat tappet engines

ZDDP is an additive that was in oil for a long time and when emissions regulations came about and the catalytic converter rose in power the ZDDP was removed from oil because it burns in the cat and creates a black soot at the end of the tail pipe. Modern roller cams have much lower need for the ZDDP so it makes sense from a modern standpoint. ZDDP was removed from conventional and synthetic oil, and I believe has now also been removed from Diesel oils, so the Rotella 15/40 probably is not what is was a few years ago...

[In The Ten Ring]

Originally Posted by Mr Handy

My understanding to why you may not want to switch to synthetic in an older engine is that the synthetic oil has detergent additives in it to help keep the engine clean. If your engine is dirty this is can actually be a problem if it starts knocking junk loose... the oil filter should take care of it, but some of that grunge may be acting to help old seals seal and the engine may begin to leak. There is nothing I hate more than oil leaks... except maybe an engine that runs hot.

Other than this there really should not be a reason to not switch in this day and age, unless you are using an oil without the proper amount of ZDDP (zinc/phosphorous) to properly protect your cam and lifters.
This is why some companies like Amsoil and royal purple offer synthetic oils designed for flat tappet engines

ZDDP is an additive that was in oil for a long time and when emissions regulations came about and the catalytic converter rose in power the ZDDP was removed from oil because it burns in the cat and creates a black soot at the end of the tail pipe. Modern roller cams have much lower need for the ZDDP so it makes sense from a modern standpoint. ZDDP was removed from conventional and synthetic oil, and I believe has now also been removed from Diesel oils, so the Rotella 15/40 probably is not what is was a few years ago...

Now that was an interesting reply! Always much more knowledge here than I could ever attain.

[Z10]

Originally Posted by Mr Handy

My understanding to why you may not want to switch to synthetic in an older engine is that the synthetic oil has detergent additives in it to help keep the engine clean. If your engine is dirty this is can actually be a problem if it starts knocking junk loose... the oil filter should take care of it, but some of that grunge may be acting to help old seals seal and the engine may begin to leak. There is nothing I hate more than oil leaks... except maybe an engine that runs hot.

Other than this there really should not be a reason to not switch in this day and age, unless you are using an oil without the proper amount of ZDDP (zinc/phosphorous) to properly protect your cam and lifters.
This is why some companies like Amsoil and royal purple offer synthetic oils designed for flat tappet engines

ZDDP is an additive that was in oil for a long time and when emissions regulations came about and the catalytic converter rose in power the ZDDP was removed from oil because it burns in the cat and creates a black soot at the end of the tail pipe. Modern roller cams have much lower need for the ZDDP so it makes sense from a modern standpoint. ZDDP was removed from conventional and synthetic oil, and I believe has now also been removed from Diesel oils, so the Rotella 15/40 probably is not what is was a few years ago...

Take the time to read through the 540 Rat's tech article. A lot of myth surrounding ZDDP. Quote from his research:

"In recent years there have been entirely too many wiped cam lobes and ruined lifter failures in traditional American flat tappet engines, even though a variety of well respected brand name parts were typically used. These failures involved people using various high zinc oils, various high zinc Break-In oils, various Diesel oils, and various oils with aftermarket zinc additives added to the oil. They believed that any high zinc oil concoction is all they needed for wear protection during flat tappet engine break-in and after break-in. But, all of those failures have proven over and over again, that their belief in high zinc was nothing more than a MYTH, just as my test data has shown.

.
A high level of zinc/phos is simply no guarantee of providing sufficient wear protection. And to make matters even worse, excessively high levels of zinc/phos can actually “cause” DAMAGE your engine, rather than “prevent” it. Motor Oil Industry testing has found that motor oils with more than 1,400 ppm ZDDP, INCREASED long-term wear. And it was also found that motor oils with more than 2,000 ppm ZDDP started attacking the grain boundaries in the iron, resulting in camshaft spalling (pitting and flaking). The ZDDP value is simply the average of the zinc and the phosphorus values, then rounded down to the nearest 100 ppm (parts per million)."

[fwayne]

I have gone full synthetic on many older cars and trucks. On my SBF it actually stopped leaks! Synthetic is miles ahead of the old school oils. It's not going to break down at high temps, it keeps its viscosity much longer and think about this...all of your rubber inside is already synthetic. In some cases synthetic oil actually rejuvenates rubber parts. Thats one reason modern engines rarely leak.

The viscosity of both are the same for any given rating...30w is 30w regardless however synthetics are much more stable when using lower weights, so you can use a 5W-30 and not burn up an engine compared to old school oils that broke down after a coupe thousand miles. Synthetics have no impact on metal parts at all, but may reduce varnish and oil sludge which may require a quick oil change for the first attempt.

[Mr Handy]

Originally Posted by Z10

Take the time to read through the 540 Rat's tech article. A lot of myth surrounding ZDDP. Quote from his research:

"In recent years there have been entirely too many wiped cam lobes and ruined lifter failures in traditional American flat tappet engines, even though a variety of well respected brand name parts were typically used. These failures involved people using various high zinc oils, various high zinc Break-In oils, various Diesel oils, and various oils with aftermarket zinc additives added to the oil. They believed that any high zinc oil concoction is all they needed for wear protection during flat tappet engine break-in and after break-in. But, all of those failures have proven over and over again, that their belief in high zinc was nothing more than a MYTH, just as my test data has shown.

.
A high level of zinc/phos is simply no guarantee of providing sufficient wear protection. And to make matters even worse, excessively high levels of zinc/phos can actually “cause” DAMAGE your engine, rather than “prevent” it. Motor Oil Industry testing has found that motor oils with more than 1,400 ppm ZDDP, INCREASED long-term wear. And it was also found that motor oils with more than 2,000 ppm ZDDP started attacking the grain boundaries in the iron, resulting in camshaft spalling (pitting and flaking). The ZDDP value is simply the average of the zinc and the phosphorus values, then rounded down to the nearest 100 ppm (parts per million)."

There looks like that RAT guy has some good data and appears to have done the work. But if I was actually going to do all that work and stand behind it, I would be inclined to sign my name to it. He says you can't argue with science in like 5 different places that I counted as I scrolled,but half of science is documentation so that others can duplicate tests.
I'm not saying he is wrong, but I would not take his word as law either.

[mike16]

no problems at all,I bought my 72 307 c10 with 71k miles on it. begane emediatly to use mobile 1 and no problems at all in fact it stopped burning oil.

the leaking sels myth is just that...a myth. some chemicals in some early off brand oils desolved sludge and unclogged leaks that already existed. but that was like 25 30 years ago.

I work on aircraft engines built in 1963 that use mobile one. they dont leak.

its a persistant myth ,,,,,a myth none the less.

as for the other concerns, throw a couple of quarts of rotella in there.