El Commandante

Ok, so since I'm pretty much going to be tearing my engine apart (I'm doing the belts, seals, rollers, water pump, and painting, powder coating, or polishing my cam tower and intake), i am thinking about replacing gaskets which will be prone to leaking if i switch to synthetic oil. Can anyone tell me which gaskets would be prone to leaking on a 150k mile engine after switching?

Thanks

Wipeout

May be the smartass in me, but none of them should if you bolt it all back together correctly.

It sounds like you're doing top end stuff...I'd think the stuff that's prone to leakage would be if you did the oil cooler seals or some such. Cam tower gaskets really shouldn't leak if you get them tightened down correctly. At least, that's been my experience.

El Commandante

Yeah, i've just heard that alot of old gaskets tend to leak if you change from dino oil to synthetic. I'm guessing the oil pan gasket is a no brainer, but are there any other ones i should replace while I'm at it?

Spidey944

Here is what I learned in my days with Valvoline. Granted this was 10 years ago, and some synthetics have changed, as well as the additive packages and requirements for manufacturers.

Synthetic oil molecules are all the same length, Semi-syns are mostly the same, and conventional oils are a mix of short, mid, and long chain molecules. It is the short chain molecules that leak out the fastest, and this is why on high milage engines, with minor/no leakage could start to leak after switching to a syn. oil.

I witnessed this myself when I switched to a syn oil on my 1986 Mustang GT back in 1997, 84k miles, after running a conventional oil for the entire previous year. It was not a leaker by any means, maybe a slight rear main seal, but that is it. When I decided to try the synthetic 10w30, (maybe 10w40) I burnt up 2 quarts in 3 weeks, when previously I had no issues ever. I went back to the conventional oil after that, and only had to add a quart after 2000-2500 miles.

So that being said, one could deduct that with good seals on the engine, good piston rings, etc. A syn oil should not make any difference, and if it does, it's an easy switch back to conventional oils. I will probably get bashed for the info i just provided, but again, this is what I was taught by Valvoline.

Yummybud924

I use synthetic on my high milliage 944 and no leaks. I have replaced the oil pan gasket and all front seals but that's it. Depends on the engine I guess.

most oil seals aren't too hard to replace if they do start leaking, other than the rear main seal or oil pan gasket.

LeMans71

Doug, that is interesting info. I have been looking into this, as I am researching synthetics for use in my 100K S2, which does not leak (knock on wood) but (I assume - no records) has been run with conventional oil during its life until now. I have discovered that there is a "high mileage" version of Mobil 1 pure synthetic, and I have also been looking at Valvoline Max Life, or whatever they call their synthetic blend for higher mileage vehicles. Any insight into those formulas, and whether either is a good/better choice?

Thanks,
Scott

indyryder3x

Being a fan of synthetics myself, in a high mileage motor, there is no advantage to running a synthetic. Not even referring to leaks, but as far as wear. If your planning on stretching your oil change interval thats one thing but if you do the 3000 and change, your wasting money. Many synthetics also leave a residue on the cylinder walls and if the engine has been run on conventional oils, this will actually decrease the effectiveness of the oil control ring and many owners and engine builders have noticed increased blow by on the pistons.

On a brand new motor this is a completely different story. Being consistent with an oil type and change intervals far outweighs the advantage of a longer change interval.

Funn944

I have well over 170K on my engine. switched to Royal Purple in engine and tranny.
I was afraid it might leak also, but has not developed any.

Spidey944

Scott,

The main difference in the "high-milage" oils is a detergent package that they add to the base oil stock after refining. It he a bit stronger than your normal synthetic oils and is supposed to help remove sludge/deposits by using said detergent package. You could technicaly run a high milage oil, or a synthetic on a brand new car and probably get the same results after 100k of wear.

Just remember this. 80% of statistics can be made up, 50% of the time.