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

[conedodger]

All flat tappet engines apparently need zinc additive ZDDP. A few of the synth oil alternatives have this in appropriate quantity. Royal Purple being one. In the dinosaur oil category, Brad Penn, which is named for Bradford Pennsylvania and used to be the Castrol GT green oil before that plant was shut down has the appropriate ZDDP content. Now having said this, I think the most important time for this ZDDP additive is when the engine is breaking in the cam. This happens in the first 20 minutes at 2000 RPM. I have seen Porsche motors eat their own cams when not appropriately broken in, this in the first 1000 miles.

Changing oil every 3000 miles is very old-school and not necessary. Oil has changed. It is better and worse. The old stories about synth causing leaks while true, have been eliminated by changing the formulation of the synth oil. The ZDDP was taken out of most oils to increase the life of catalytic converters.

I change my oil twice a year. This frequency increases when I do track days with one or the other cars but I would guess miles to be about 750 - 1000 between changes. I do this only because oil that sits in low mileage cars can form acids that cause damage. I am allowed with my 'Historic Plates' and by my classic car insurance to drive 2500 miles a year each. I'm doing maybe half with each the 914 and the Z.

A friend who runs a performance shop and does routine maintenance on BMW, Audi, Porsche and Ferrari and such, uses 1000 miles per quart capacity with modern oils. He uses and recommends a Swepco Synth blend I think...

[Dr. 240Z]

I just spoke with a Quaker State 'Fluids Rep' about their synthetic, 'Ultimate Durability', and its use in older engines. Basically, he stated that it does contain ZDDP (800ppm) and that the addition of more ZDDP might be appropiate. That said, he did caution that the addition of excessive amounts of ZDDP can destroy certain types of catalytic converters.

I have learned a lot on this topic via your comments - Many Thanks

[71Nissan240Z]

valvoline vr1 racing oil is pretty good stuff.

[siteunseen]

Valvoline VR1 for the rebuilt 280, Castrol 10W30 GTX in everything else. 297,000 on a '87 Nissan Hardbody pickup, 240,000 on a 2000 Toyota Camry, 1000 hours on Briggs & Stratton Vanguard powered Exmark mower. Replaced timing belt on the Camry at 175,000, timing chain will hopefully get done this winter on my truck. No other problems just maintenance stuff. I don't like to buy new cars. Just bragging a little bit, thanks!

[ta240]

I personally think the actual oil you use doens't matter but how often you change it.

Years ago I worked at a farm that sent off oil out of every truck and tractor to be analyzed at every oil change. I talked to the guy that ran the testing place one time for quite some time on the phone when we were looking at different types of oils and additives and his recommendation was the same as yours. It isn't as important what you put in it, just as long as you change it frequently.

And it was for the same reasons listed here, oil gets a lot of bad stuff in it when you run the engine and you don't want the concentrations of that to get too high.

We had a late 80s Pontiac that I pulled the valve cover on at around 120,000 miles (we got it at around 110,000) and it had layers and layers of cooked on crud on all the insider surfaces. I have no idea what they used in it or how long they left it but it was ugly.

When we got our first brand new car it had a little tiny oil filter and only took about 2.5 qts or oil per change and it got a lot of in town driving and not a lot of miles overall so I changed it every 3,000 miles and did use synthetic but here is the top end of it after 100,000 miles:

and I never ran any sort of flush or cleaner through that engine. That kept me a fan of the regular change.

I just run the GTX 20-50 in my Z but it is old and original. And I change it twice a year and average about 7,000 miles a year on it.