Synthetic Oil Change Interval

[Dr. 240Z]

My Z's engine has been recently rebuilt and after the break in oil was replaced, synthetic oil was chosen.

My question: Under average use, how often should I change the synthetic oil?

Thanks

[djwarner]

IMHO, this is problematic for our engines that were designed to have more blowby than modern engines.

On the plus side synthetics have more detergent, less ash, tend to be more uniform in chemical composition and so resist breakdown and sludging.

On the negative side is cost and the circulation of suspended combustion products in higher concentrations as we extend change intervals.

If you change oil yourself, changing oil every 3K and filter every 6K, your engine will be quite happy and you will end up saving substantial money over synthetics.

If you really want to dote on your ride, and don't mind the cost of synthetic, there are oil analysis services that will track the wear of the oil and various metal components from the engine that will tell you when to change the oil more accurately than a mechanic. Many owners of small aircraft, where engine overhauls can run north of $20,000, use there services routinely. You might even get 25,000 miles between oil changes.

Today's standard oils are much higher quality than those produced when our cars were new. However, the combustion products bypassing the rings are still the same. Datsun says a $5 oil filter should last 6K, while my wife's new Infiniti G25 says the $12 filter should be changed every 7.5K under ideal driving conditions.

[Gary in NJ]

How much do you drive the car and how is it stored?

My Z get's about 1,000 miles per year. At that rate I change my oil by calendar time vs. miles. My car is in a dry garage and I change the oil every spring. The filter gets changed every 3,000 miles. This rate of usage doesn't justify the use of a synthetic oil. In fact, in certain circumstances synthetic oils can do more damage then dino oil. In my experience in aviation, cams can get sprawled from low usage as synthetic oil doesn't "stick" to surfaces the way good old dino oil can. As a result every start is a dry start.

[siteunseen]

Just to add to what you don't want to hear, my mechanic says "No synthetic oil in the L motors".

[Dr. 240Z]

Thanks for your responses...I'm a ltttle confused by distilling them, however...Perhaps, I should return to what I started using in her 41+ years ago: Castrol GTX - changed every 2k miles

[EuroDat]

When the Z's first came out, oil had ZDDP (zinc). That greatly reduced in new oils, but still availably in Valvoline VR1 en Mobile 1. The zinc helps protect old engines. They were designed for before the EPA cracked down on emmisions in the 80's. http://www.valvoline.com/pdf/vr1_racing.pdf

Chas

[Bonzi Lon]

I use a synthetic blend of dino oil with a dose of ZDDP supplied by www.cam-shield.com and change it with a Nissan filter every 3K miles.

Bonzi Lon

[gogriz91]

Mine says Mobil 1, he swears by it and has for a ling time. I'm willing to spend the money and use it in my '05 Pathfinder too, cheap insurance?

[Wade Nelson]

It's not so much that oil WEARS out as it gets contaminated by blow-by, and condensation of water. The latter is a greater problem in vehicles that sit parked a lot. The former, in high-mileage cars with worn rings.

Aside from the Toyota sludge motors, oil-related failures are rare, rare, rare. The only ones I've EVER seen as a mechanic were where people with cars that consumed oil let it get too low, it started knocking, they added oil, and 50 miles later a bearing seized.

[Gary in NJ]

...oil-related failures are rare, rare, rare...

Way back when my Mom had a '78 Granada (5.0l V8) that she purchased new. She drove that car until 1988 until the frame was so badly rusted that it could no longer be driven. The car had somewhere between 80,000 and 100,000...I don't remember. But what I do remember is that car only had a handful of oil changes, about every 25,000 miles; whether it needed it or not While the car suffered from chronic neglect, the engine always ran perfectly. It didn't burn a drop of oil...good thing because she would have run it without.

[LeonV]

It's not so much that oil WEARS out as it gets contaminated by blow-by, and condensation of water. The latter is a greater problem in vehicles that sit parked a lot. The former, in high-mileage cars with worn rings.

Aside from the Toyota sludge motors, oil-related failures are rare, rare, rare. The only ones I've EVER seen as a mechanic were where people with cars that consumed oil let it get too low, it started knocking, they added oil, and 50 miles later a bearing seized.

Agreed.

I use Mobile 1 synthetic with no worries. I've been using it for 2 years now. I change it once a year as the Z doesn't see too many miles, maybe 5k/year.

[Pomorza]

Here's my two cents

I personally think the actual oil you use doens't matter but how often you change it. I've religiously done oil changes at 3 months or 3,000 miles (usually three months as I don't really drive that often). I was debating switching to a synthetic oil but figured since I change it so often I should just stick to dyno oil. That being said, I've used mobile 5000 (10W40) for the past couple of years with lucas oil stabil added. I've had not problems to speak of and I'm still running the original engine. I know people that use basic 20W50 from the parts store as oil and haven't had issue with it either.

Just my comments

Jan