BrutFord!
That's the best description of synthetic oil I've ever heard! So it's the composition of the seals in older vehicles that just doesn't hold up to synthetic oil?

 

Thank you and pretty much, that and wear. Older Chevy's for example, for a long time Chevy didn't machine the valve cover surface and used a cork gasket. Those suckers can leak like crazy with synthetic. Pretty much any engine with a multi piece cork oil pan gasket. Also 2 piece rear main seals and umbrella type valve seals are more susceptible.

All of these and other sources of leaks are also either solved or made worse by a much neglected part of the engine, the PCV system. A properly modified PCV system can stop just about any leak that occurs while the engine is running.

I've never seen a Ford engine without a well machined gasket surface and Fords tend to have more rubber and one piece gaskets. This is tossed on it's head with FE engines and there heads, but that's not a subject here. Pretty much leaks are easily dealt with on these engines if they occur. If a switch to synthetic "causes" a leak, it's not really causing it, it's showing it, the path for the leak already existed, the synthetic just took more advantage of it.

There's two places ALL engines consume some oil. Even a brand new engine with dino oil will consume some oil, it may be too little to notice but it does. Those two places are the cylinder walls and the valve stems/guide. These two places are metal on metal and in contact with combustion gasses. Synthetic in these two places has it's ups and downs. Yes it will tend to stay on the cylinder wall and creep down the valve stem, and this will tend to cause the engine to consume more of it. This will also tend to make those parts last A LOT longer. More important cause of the nature of synthetic on these parts it tends to stay in the little imperfections, stick to the part, and isn't as flammable, the later tends to offset consumption.

If you have an engine that leaks while it's parked and blows blue smoke when decelerating then absolutely do not switch to synthetic. If you have an engine that only leaks when running, and doesn't blow blue smoke then fix/modify your PCV system and consider switching to synthetic. If you don't leak or blow but are concerned try starting with either a cheap synthetic or a blend. They're makeup will tend to leak/consume less.

A word on change intervals, two things are cause for oil changes, the break down of viscosity index improvers(VII) and contaminants. Both of these turn oil black, so change it when it turns black. This of course doesn't work on oils that are already dark. Just yet another reason to stay away from snake oil like royal purple, I hate royal purple they are just marketing crappy oil. Anyway, synthetic oils don't use as much if any VII, so if the contaminants can be kept under control you can go potentially much longer between intervals. If when you open the oil cap while it's running it puffs out visible smoke, don't bother trying to extend intervals, contamination is your issue and you should work on your PCV. If not consider paying attention to a good or better oil filter, try synthetic and watch the color.


EDIT.. A word on gaskets while I'm at it, on the market now for most engines and most valve cover and oil pan gaskets are silicone gaskets with a frame, they are AWESOME. If you ever replace one of these gaskets use them. Most oil pan and valve cover leaks aren't gasket issues, they are actually caused by over tightening the sheet metal. this bends it distorting the surface. If you take these parts off flatten these surfaces again and only tighten to the spec. One hand and a stubby ratchet is enough.

 

Another Bravo! Great reading! I have defiantly learned something about oil today.
Now...That PVC thing your talking about. PM me if you decide to talk about it in another post. I want in!
My 7.3 has no leaks, doesn't use oil either. The guy I bought it from just recently with 200K on the clock used Rotella all it;s life with regular oil changes. I'm going to continue...

 

Thanks, I've done several PCV posts, people disagree but my thoughts are out there. The search on this site has a great advanced feature to search the posts of one user, give that a try. However these wouldn't apply to your 7.3, diesels don't make vacuum and thus have no PCV in the same since as a gas engine. Some of the theory can be applied to the system they do use but it's not the same.


I use Rotella T6 5W40 synthetic in four of my engines. Both of my 7.3IDIs and both of my carbed 460s. In the other two I use Mobil 1 0W30.

 

Thanks! I'll check it out!!