I have toured the Internet looking for opinions on the best oil for my 1994 300ZX NA. The consensus is I should use Mobil 1 synthetic for High Mileage engines. OK so I did use it. Anybody have an opinion on how often I should change it? The car is stored in the winter and I drive it every two or three weeks until it comes up to temp. Should I change it in the spring and then again in six months?

Personal opinion, as you requested:

Synthetic oils boast the ability to endure higher mileage btwn changes than fossil oils, because they don't break down as easily nor are they as susceptible to excessive heat. Under normal driving conditions they outlast every fossil oil ever made. If you routinely warm your car to full operating temperature in clean "driveway" conditions, you shouldn't have to change the oil even half as much as with regular oils.

There's a difference btwn using an oil for "engine hours" instead of for "highway miles". Long-idling Police cars, taxis, delivery trucks etc get far more engine hours than miles, so they put different demands on their oil than the family cars do. Race cars, on the other hand, place extreme demands on their oil in a brief period, so mechanics change their synthetic oil each race.

I run synthetics in my 240, which hasn't left the driveway since arriving. I warm it routinely and I monitor the oil each time for signs of anything unusual. Your car during the winter is experiencing the same idle time mine is. I recommend making your wintertime decision based upon how the oil looks, feels and smells to you when you check it. After a full year of being warmed every week but with less than a mile of travel, my oil is still clear, smells fresh and has no tangible grit.

As soon as any of that changes, so will the oil.

Bryan Little did some really good explanations about synthetics in his Datsun Z Garage Website. You can link to it from our Homepage.

Frank

normal oils...3000 miles
synthetic oils....4500 miles

anally retentive mechanics with synthetic oils...3000


I've done tooooooo many oil changes...but from my experience... I've had one engine that I rebuilt, fly 3000 hours....with the oil replaced every 50 hours, and I rebuilt it again...and it's prolly been rebuilt 4 times since I rebuilt it...but we were using Aeroshell oil. (aircraft non synthetic oil) and I've rebuilt another engine that was a PT-6 turboprop...and never changed the oil for 200 hours, ..and it will be 9000 more hours before another rebuild would be needed, but the oil lasts for about 200 hours. (jet engine full synthetic)... and 200 hours on a jet engine (turbo prop) would be about...uhmm 80,000 miles... 50 hours on a piston aircraft engine would be about 10,000 miles...and when I was working on F-15's (turboJet)....well...that math is out of my league...

Just don't do what I did twice in a day, and run a car on a racetrack with a quart or two low while beating the crap out of it on a loooong sweeper.

That was a fun day, and I'm glad I had AAA.

_________________


Also Known As Clayton Pace

I'm wondering if Mike should consider changing his oil a little sooner since this is the first time running synthetic in it. My understanding is that the synthetic oil will break up and clean some of the oil residue from the fossil oil he's used for years (though I can't imagine anything dirty about his beauty!!). Also, keep an eye out for new oil leaks. The molecules that make up synthetic oil are smaller then fossil oil and sometimes find their way through some gaskets that fossil fuel did not.

BTW, I've run Mobil 1 in my Z for the past seven years. I put on less then 2,000 miles a year but change it every fall before I put it away. My understanding is that the contaminants in used oil can be corrosive when left sitting for extended periods of time. Probably a waste of oil, but it makes me feel better and allows for some good quality time with my Z before I put her away.

Phil

Personal opinion: I don't believe in synthetics, and from my understanding it still contains fossile oil, but has synthetic compounds. (you may correct if I'm wrong) Changing the oil when it's needed seems to work, and has for many years. using bargain brand oils and changing it when you feel like it, when it's b l a c k , now that's the wrong thing to do. I change mine when it starts to turn brown. Not by miles or hours, and in the fall is a good thing if it's going to sit. I use 10/30 from NAPA, because I get a discount, and it's Valvoline, the same oil I used when working at the machine shop in Arizona, so why not, my boss trusted his business with it. Other major brands are good to, but pick a brand and stick with it. Combining different brands can contaminate, because they have different chemicle make ups, and I use no additives, just oil. just like my french fries, nice and oily. (so all the slt can stick)

Personally, I miss the smell of burning Castrol from the 1960s, but those days are gone now, and in the Past they Must Remain....

The technical functions of any motor oil are to:

Seal (forms seal btwn rings & cylinders to prevent blowby, etc);
Cool (removes heat from moving engine parts);
Clean (washes particles from moving internal parts)(and sometimes external parts, if your gaskets leak:lol:);
Absorb shock (btwn bearings and moving parts);
Reduce friction (to reduce wear and prevent horsepower loss);
Reduce heat (to prevent mechanical failure).

Synthetics outperform fossil oils in nearly every category, and maintain their viscosity better than fossil oils do under extreme conditions. The best non-synthetic oils seem to come from Pennsylvania crude (such as Quaker State or PennZoil), and I fully agree ~ you should find the oil which does the best for your engine and stick with it, at least until your engine wear changes the requirements.

Because of a "street rumor" during the 1960s I never used additives such as STP, which was said to gum up rings and require constant re-use or elevate the risk of blow-by.

*(And Paul, you're probably referring to Semi-Syn oils, which are about 1/3 ester synthetics mixed into 2/3 petro crude oils. I think they were called PAOs, or PolyAlpha oils).

*(And Phil, that's right ~ because synthetics break up old carbon deposits better than petro-fossil oils did, there can be an initial detergent effect with the first use of a synthetic, which indeed can lead to small dribbles here and there. Also, today's modern engines are so vastly different from the engines in our classic Z cars, that some older synthetics can actually harm the materials modern engines are made from. Weird!)

And now you know everything about oils that I do.

Poor Mike! He only asked a simple question and all us SnowBound Cabin Fever claustrophobes buried him in theory he never asked for!

my 2 cents...I use Mobil 1 or Shell Rotella Synthetic available at BJ's, I use the Moble 1 oil filter too. Change every 5K miles and/or when I put it away for a few months. My first year with the Z, I drove 10K so I am changing it about twice per year. The previous owner was using Mobil 1.

*I heard if you talk to an Amsoil salesman, and you may switch to it. Anybody have any interest hearing what an Amsoil saleman has to say? We could invite the CT Rep to come present to us at a meeting. Or Not. They'll do a free oil analysis on your car. One of my co-workers was sold on Amsoil motor oil and tranny fluid and is trying to convert me.

_________________
Keith Hultmark
2009 370Z Touring - Sold (5 years owned)
1993 300ZX - Sold (5 years owned)
1976 Porsche 912E. #163 of 2200 - SOLD (3 years owned)
2018 BMW 330i GT xdrive daily driver
2004 BMW Z4 3.0i ….it is a Z

Red Line fluids is what you want in your tranny and differential.

Phil

It bothers me for some reason that synthetic motor oil is more expensive then fossil oils.....guess I'll get over it.

And yes Frank, a believe we are all under a severe case of cabin fever.....

Phil

I'll bet our first monthly meeting is gonna be PACKED.

Ok, full synthetics I could understand, but like said, why is it more money? I'll stick with Valvoline for now, but am open minded to better products, for the buck of course. Well, changing it when it's needed is at least not hurting nothing. Plus I don't fuss much on an engine built so well.

All valid pointz ~ in other words, "if it ain't broke, don't fix it".

The internal combustion engine has survived just fine for more than 100 years on dinosaur juice. Only when aircraft became so advanced that they could reach extreme altitudes and speeds (subjecting their engines to CRAZY differences in temperature, pressure and G-forces), did Synthetics start looking necessary. Then the car racing community (named Andy Granatelli) began putting synthetics in Indy 500 cars. They won, but it probably had more to do with his driving than with his oil.

But salesmanship being the Art it is in the USA, we became convinced that by putting synthetics in our cars we could "drive better" or something.

Synthetics do almost everything better than fossil oils. But what fossil oils do ain't bad!

Let's hold a moment of silence in respect for Poor Old Mike, who stepped blindly into this cross-fire by innocently asking a simple question

I thought it was a complicated question.

Another reason I use synthetic oil is that they handle the heat of turbo's better then fossil oils.

Phil