4A-GE and syntethic oil

[Mux213]

Nookie,

From what I've understood from reading is basically what Nohachi sais, most oils that you buy in the store that claim to be synthetic really aren't, they are semi-synth meaning they are plain old normal oil but with synthetic additives that improve the oil in one way or another.

The thing with these additives is that they often improve the oil in ways like enabling the oil to desolve polutents, making sure the oil does not leave any residue, making sure the oil lasts longer so you need less frequent oil changes before the oil goes bad etc.

Now this all sounds very good and indeed it is but with an old engine there is a drawback which is why people tent to say that you shouldn't use (semi-)synth oils in these engines. If you have an engine that has run with mineral oils for its whole life its run with oils that has deposited gunk, this gunk tends to build up around seals and that sorta thing. No problem at all, these engines are designed with it in mind, its often is just a few microns of the stuff anyways.

When you switch to the newer oils they tent to start to 'clean' your engine and slowly break the gunk away. Two results in this. First, the gunk starts to move around in your engine and if not filtered out quick enough by your filter (and if not clogging up your filter in no time) it is possible it may end up clogging up the smaller oil channels within your engine with bad lubrication of specific parts in your engine as a result.
Second, with the gunk being resolved on very old engines this can actually cause small oil leaks where the gunk has actually damaged the seals a bit.

Whether this is all true or not, or just and urban myth? No idea, but it always sounded logical to me. Its always been the reason for me to tell people not to switch to (semi) synth on old engines until you've rebuild your engine because in that case, with all new seals and a cleaned engine I do believe running (semi) synth has added value for money.

My mean reason for not switching to (semi) synth though is a different one, a simple matter of numbers.
I can go to the store and buy enough mineral oil for an oil change for 5 to 10 euro's. If I buy the right type of oil and I drive my car nicely warm before I abuse it, 4AGs last well over 300k before they need a rebuild. Just look around at the cars we have on the forum, we have MANY +200k km cars on the board and almost all of them run mineral oils.

I can also go to the store and buy semi synth oil for 20 to 30 euro's.
WHY?!?!?! WHY spend 4 times as much money just so I can say I use oil in my car that is slightly better??? Sure I might be able to do oil change every 15k km instead of every 10k km or whatever oil change scheme you use but then still its 2 to 3 times as expensive and still its questionable if my engine will really outlive my future wishes. I'm probably going to rebuild and tune my engine way before it brakes down anyways!

So I ask you, WHY in heavens name buy expensive oil if it only is slightly better.
Yes for a new rebuild engine I can understand. But for an older engine, it just doesn't serve a purpose!