So my girlfriend was telling me that a relative of hers had the argument the other day that once you use synthetic you can't go back to regular. This obviously isn't true, but he was insistent. I know from the oil journals here that going back to minoil after being on synoil is fine.

Anyways, readin the oil journals I could not find any specifics on where the myth comes from and any technical information to debunk it. I'm hoping to get a good solid answer here and maybe then it can be placed as an addendum to the oil journals FAQ under "switching from synthetic back to mineral".

 

Untill you have specifics of what happened to the engine, what type of car etc. etc. It's way to early to blame switching back to synthetic.

Diagnosing the failure is the 1st step to eliminating synthetic oil as a cause.

 

How can you expect a solid answer when you provide so little info about the car? Saying that the engine 'blew' or 'went' means nothing. It's like saying, 'Hey, I picked up my date last night and after I drove 10 miles, my engine blew. Do you think that she caused the engine to blow'? I don't mean to be a smartass, but if you want to do a cause/effect determination, you need much more info. Personally, I doubt that switching back to non-synthetic oil is the culprit. If you've read the oil journals, you know how good present-day mineral oils are. Blaming the engine failure on the oil is probably wrong.

 

The point of the thread was NOT to diagnose the engine. To my understanding that is irrelevant, since going from synthetic to mineral will NOT cause an engine to die in any way shape or form.

I was simply trying to get some technical information dispelling the myth that you CANT go back to mineral after using synthetic. THAT is the purpose of this thread. Not to diagnose the problem of the old car.

 

See? this phrase in my original post? THIS is the purpose of this thread.

 

PM Road Rage, he's the only one on the board who is a oil engineer.


I still think it's easier to diagnose the failure at hand than disprove a unrelated theory.

 

Total coincedence. An engine is not going to get "addicted" to synthetic and then when you put conventional back in it.

 

Hey Matt are we talking about a GM product? I have seen lots of problem with GM's blowing motors after doing intake gaskets. Intake leaks cause coolant oil mix washing the main and rod bearings. Due to the lubricant ability of Synoil maybe switching to a conventional oil may have been the death of it. Let us know.

But to answer you question switching oil should not cause a motor to blow. I have seen switch from on oil to another can cause problems since some oils run wax additives and when switching from one to another the detergent in an oil can cause the wax additives to be washed out and glogging oil passages etc. But switching from Synoil to Regular NO!


P.S. seen this happen to fords V6's too

 

i'm going to edit my original post to remove the unrelated story. it was really just kind of a side story vs the real topic i had started.

will i'm not sure on the GM product. i'll find out and PM you.

 

This is one of those synoil myths that hangs around forever. I found a 20 year-old article in my archives that had this, and about 9 more, synboil myths.

As best i have been able to determine, looking at my 30 years of info on the topic, the "warning" never has had anything to do with a failed engine, or any engine mechanical failure for that matter. It likely was made up by a salesman or seller of a synoil mfr, hoping to "scare" clientele into staying the course.
************************************************** ****************

Switching TO synoil on a very old engine is a different matter.I often do not recommend it, esdp for engines with questionable maintenance history, or ones that are 10 years old older. A look into the oil fill will often show a lot of varnish and/or sludge.

I believe it originates from the high detergency of synoils vs the older minoils. Oxidation and sludging were common with old minoils, and in many cases, it was sludge that was keeping seals/gaskets from leaking - valve cover gaskets, even some oil stem seals. Using synoil in an engine with sludge often caused leaks, and it certainly caused the synoil to get very dirty very fast, reqruiring more frequent oil changes than a synoil should require, at elast until the cleaning was completed.