I own a shop that does normal repairs but never have come across this question.

Can you mix regular oil with synthetic oil?
I have always been lead to believe that you can go from regular oil to synthetic if you do a engine flush, but I have heard that once you go synthetic it is not a good idea to go back to regular.

Is this just a myth?

I know on some cars you can run regular during the hotter months and then go to a synthetic in the colder ones because it does not break down as quickly but what about my dsm?

Info on the car:

1995 Eagle Talon TSI, guy I got it from said he was running synthetic so I have been doing the same but I have a pretty decent leak and dont have time to fix it right now and it is getting pretty costly.

Thanks in advance DSM guru's!!!!!!! The force is strong with you all.

 

It does not really matter if you switch back and forth.

And where was the literature saying that synthetic breaks down faster in hotter temperatures? I run AMSOIL 10W-40 w/zinc additives and has great viscosity values.

 

it is just what I have heard about the way oil breaks down, and I said that synthetic does not break down as fast, but what I said about using different types of oil in different weather climates is that if it is hot outside like in the southern states then most people will go with a cheaper oil, not meaning a cheaper grade but we all know that synthetic is alot more expensive and I know me personally I like to change my oil more times when it is the dead of summer because not only do you have engine heat but also when the temp outside is hot, like day before yesterday it was 106 at 12:30 in the afternoon then the oil is staying hotter then in the colder months, and just makes it break down faster.

So my question is that if I have lets say 3.5 qts. of synthetic in the pan can I put in regular 10/40 for the extra quart that I need?

 

u dont want to mix the oils at the same time. it dosent matter if u got from full syn to standard at any time. they are made by law to be compatible these days. its not like the old days when u couldnt. if u switch all the time u dont get the benifits of the syn. there for u are just wasting money going back and forth.

as far as break down in oil the syn wont break down as fast as standard oil. the additive package will break down inside the syn oil faster then the oil will break down

 

If you plan to change it often, go for the cheaper oil. No sense in wasting money on the expensive juice.

 

even buying the good stuff helps the motor when u switch it all the time. i use full syn and change mine every 3000-3500