The following is the a distilled version of the Frequently Asked Questions and discussions (FAQ) about

Z-Car Oil FAQ

as discussed by the Internet Z car club.

All information published here is the property of the original authors who are members of The IZCC and may not be reproduced for commercial purposes Everything stated here is based on the experiences and opinions of the original authors. The authors and editor accept no responsibility for any damages arising from use of this information. Always consult your workshop manual and take appropriate precautions when working on the car. If in doubt consult a specialist. Specific information about synthetic oils and lubes can be found at various web sites by searching using a brand name or "synthetic+oil".


Q: My oil pressure gauge shows fluctuating oil pressure (often readings near zero, which make me nervous). What could be the problem?

A: Almost invariably, the culprit is the oil pressure sending unit having gone defective. This is a common problem on Zs. Replacing the sender is simple, and should solve the problem instantly.

The normal mode of failure is for the internal diaphragm to develop leaks. This may lead to external leakage where the wiring connects to the sender. It was also mentioned in the Motorweek show that the little hole that admits oil on the unit can get plugged very easily and creates the problem.

Oil pressure sending units cost around US $40.00 at the dealer. Aftermarket units seem to be cheaper, but last no longer. There have been reports that the sending unit is physically sensitive to shocks or impacts, and thus should be treated carefully while installing (and when working near it in the engine compartment, changing oil filters, etc). The oil pressure sending unit is located on the right (passenger) side of the block just forward of the oil filter. Special large sockets are available to deal with such senders (a slip joint pliers, etc, will work in a pinch). So long as the engine is *not* running, the oil does not need to be drained before changing the sending unit.

If your oil pressure *really* drops to near zero while running, you'll know it! (screeeeeeeechhhhchchhc clunk screeeeecccchhh, etc.)

If the sender is defective, it is important it be replaced. The fuel pump relay in earlier Z's is keyed to the oil pressure (IE. loss of pressure, fuel pump shuts off, engine shuts off).

If it will set your mind at ease, check the pressure with a shop gauge if it is available, otherwise, replace the sensor and go from there. If the gauge seems to check out ok, it could be the pressure regulator spring in the oil pump. Simple and cheap to replace.

Q: I see constantly higher than specification oil pressure readings. What does this mean? Isn't more pressure better?

A: You have to watch this logic on street engines. Better than a pump that gives lots of pressure is an oil pump that gives good pressure across the entire rpm range. This is achieved by using a high volume pump. Having too high an oil pressure at best wastes HP and at worst I've heard some series of Ford engines can get bearing wipe. On my car (91) and from talking to other Z people it is clear that Z's typically show a pressure near 15-20 psi at idle and around 60+ psi at higher rpms. If all the engines do this and nobody is reporting oil related failures then accept this pressure range as good and only worry when the pressure deviates from this range.

BTW, yes, you can move the pressure around by playing with the oil's viscosity but why ? The Nissan engineers spent some time figuring out what viscosity is best in their engines for a given temp range; take advantage or their research.

My 240Z oil gauge would be completely pegged at 3000 RPM. It would run 45psi at idle-1000 rpm and ramp on up. I replaced the sending unit; same results. I then bought the oil valve assembly ($6), and replaced the spring, valve washers in the oil pump. I noticed the old spring was about 3/16" or more shorter than the new one, and that it definitely had more "K" spring constant; it resisted the installation much more than the old one. Additionally, the valve was pretty well worn. Everything looks good now.

Q: What about "magic" oil additives like SLICK 50?

A: There is a MUST READ article in the August 1992 issue of Road Rider magazine. The article is entitled, "Snake Oil! Is That Additive Really a Negative?" I will not retype the whole article here as it is rather lengthy, however, suffice it to say that after reading the article I will not let the stuff anywhere near ANY of my engines.

The article bases its statements on test results from the following very reputable research institutions: University of Nevada Desert Research Centre, Avco Lycoming (aircraft engine manufacturers), Dupont Chemical Company (the creator of PTFE which is the main ingredient in Slick 50 and other similar products), North Dakota State University, Briggs and Stratton (of lawn mower engine fame), the University of Utah Engineering Experiment Station, California State Polytechnic College and NASA Lewis Research Centre. Quite an impressive list. Each of these institutions spoke out AGAINST using Slick 50 in your engine. In fact, ROAD RIDER was unable to find any independent testing organization that would support the findings that Slick 50 brags about.

When you ask the Slick 50 folks about who did their testing, they will not tell you. Here's one quote from the article I think you'll want to read, "... By far the most damning testimonial against these products originally came from the DuPont Chemical Corporation, inventor of PTFE and holder of the patents and trademarks for Teflon. In a statement issued about ten years ago, DuPont's Fluoropolymers Division Product Specialist, J.F. Imbalzano said, "Teflon is not useful as an ingredient in oil additives or oils used for internal combustion engines."

At the time, DuPont threatened legal action against anyone who used the name "Teflon" on any oil product destined for use in an internal combustion engine, and refused to sell its PTFE powders to anyone who intended to use them for such purposes. "After a flurry of lawsuits >from oil additive makers, claiming DuPont could not prove the PTFE was harmful to engines, DuPont was forced to once again begin selling their PTFE to the additive producers." - ROAD RIDER/August 1992

Here are a few of the things mentioned in two articles as possible failure modes for Slick 50 style products:

  1. PTFE is a solid. The additive makers claim this solid "coats" the moving parts in an engine. The article states, however, that, "such solids seem even more inclined to coat non-moving parts, like oil passages and filters. After all, if it can build up under the pressures and friction exerted on a cylinder wall, then it stands to reason it should build up even better in places with low pressures and virtually no friction."

  2. Additive manufacturers will claim that they use "sub-micron" sized particles that will pass through your oil filter. The only problem is that, "PTFE expands radically when exposed to heat." So when your engine reaches normal operating temperatures, the particles may not longer pass through your filter, but instead will clog it!

  3. At least one military study was conducted which showed that PTFE matter may tend to clump together in cold weather and actually block the oil pump inlet screen. Portions of this study were published in a national automotive newsletter called "Nutz & Boltz" in 1993.

The above quotes and data are just small titbits from articles filled with such information. Briggs and Stratton has done testing on it's engines with and without the stuff and found the an engine using the stuff actually showed more wear than an engine using conventional motor oil. Do read the article. It does not come out and tell you that you should not use Slick 50 and other products like it, but it gives you lots of data for you to make your own decisions.

For example, if I were someone with a racing motor that was torn down and rebuilt after each race, I might consider using the product as there are some results that have shown there to be less friction within the engine, thus resulting in an increase in horsepower. Again, read the article and make your own conclusions. More than one author contributing to this FAQ agrees that they will not use any Slick 50 style products in their engines, but that is just their conclusion after reading the articles referenced.

[Authors: Michael Jue, Al Powell]

Q: I get really dirty working on my Z, any good hand cleaners that really work?

A: One of the best hand cleaners I've ever found is ordinary high detergent motor oil. I keep a can of Quaker State (wouldn't dare put it in anything that burns gas :-) right next to my can of dishwashing soap. Works better than GoJo, Lava, or any of the other hand cleaners I've tried.

I start out with about a tablespoon full of oil in my palm. I massage the oil into both hands for a couple of minutes. I use a parts cleaning toothbrush on my fingernails. Then I mix in about a tablespoon of liquid soap. Massage some more and then add water a few drops at a time. Rinse and then apply liquid soap one more time. Rinse and dry. Voila! You are now ready to assume the role of corporate geek again.

For light grease & oil, use standard baby wipes. They contain ethylene glycol, and will do an amazing job of cleaning hands if the dirt and grease are not terribly ground in. They're handy to carry in the trunk in case of unscheduled tire changes or roadside "fixums" because you can get them in small, sealed containers.

Q: I hear a lot about synthetic oils and gear lubes. Are they really any better than regular oils? [Synthoil Q&A by Al Powell.]

This is a substantial question, so let's tackle it in stages.

Basic properties of synthoils
Synthetic oils differ from "regular" petroleum oils in that they are engineered from specific base stock to have superior performance. Their polymer chains (the parts which provide the actual lubrication) are stronger and resist breakdown much longer then petro- oils under conditions of mechanical wear, high heat, and contamination by foreign elements - all of which are found inside car engines.

Synthoils will simply last much, much longer inside an engine because they don't break down as fast at petro-oils. Semis have reported running over 100,000 miles on a single oil change while having the oil chemically analyzed at regular intervals to assure it is still capable of performing its functions. However, running oil to this distance requires superior filtration and regular analysis.

Another issue is volatile elements. Petro-oils and synthoils both have heavier and lighter (more volatile) elements. Under heat, the petro-oils "volatilize" (give off the lighter components much faster). This increases the oil's viscosity and contributes to its breakdown. Synthoils are much superior in this respect as well.

It is very important that synthoils (unlike petro-oils) leave a lubricant film on metal surfaces, providing better lubrication at start-up. They also are much less affected by low temperatures than petro-oils, making it much easier for your engine to turn over and start on cold days.

Not all "synthetic oils" are totally synthetic. Many brands combine part petro-oil and part synthetic stock to hold the cost down. These oils cost less than true synthetics and are superior to regular petro-oil, but inferior to pure synthetic oils. Check the labels to be sure what you're getting; it may make sense to use a blend if you're short on money, if your car has high oil consumption or if you insist on frequent oil changes, but want some of the advantages of a synthetic oil. The leaders in pure synthoils are Amsoil, Red Line and Mobil 1, although many others have entered the market recently. However, many of the late entries are blends.

New Cars/break-in period
Synthetic oils are more "slippery" than standard oils. Because of this, no manufacturer I am aware of recommends running synthoil during break-in, as it can actually prevent the wear necessary to keep piston rings from seating. The best tactic according to "common wisdom" is to run a good grade of petroleum oil (whatever the manufacturer recommends for your car and climate - it's in the manual...) for at least 1000 miles, preferably longer, before switching to synthetic oil. This allows the rings to seat fully. During the break-in, I like to change oil and filter at 500 miles, 1500 miles, and again at about 5000 miles, switching to synthoil at the 5K mark.

Be aware that if you change to synthoil in a new car, you must still change oil and filter at least as often as the manufacturer recommends in order to keep your new car warranty in force. Since this interval is 7500 miles in most cases, you at least will get your money's worth out of the synthoil and can feel good about being able to run 7500 miles with confidence your oil will hold up well. (Most car aficionados do not run petroleum oil more than about 3K miles between oil/filter changes.)

Used cars/changing to synthoil
The decision whether to run synthoil in a used car is primarily economic, based on oil consumption. (Sludge buildup is also a factor - more on that later.) If your car burns a quart every 500 miles, it's not a candidate for synthoil because it's just too far gone. Change over after a rebuild. However, IMHO, if the car goes 1000 or more miles between quarts, it is a candidate for synthoil. Many high performance cars, especially V8s, will burn a quart at 1K intervals and it may not indicate engine problems (my '66 GTO comes to mind...). Whenever you change to synthoil, you can usually expect that your oil consumption will stay at its current level and not increase for a long time, as the engine will generally not wear very fast on synthoil.

To change over a car: first, pull a rocker arm cover and look to make sure it does not have a heavy sludge buildup. All synthetic oils are very highly detergent and will break up any sludge or deposits in the engine. For this reason, heavily sludged or very old engines with deposits are not good candidates, as you really don't want to break all that stuff loose to plug up your oil passages.

Having determined that the car does not have sludge, add a quart of a good "engine clean-out" treatment and use it as per the instructions. The goal is to get the inside of the engine as clean as possible before changing over. After the treatment, change the oil and filter containing the cleaning agent.

Install a new filter and synthetic oil. If you can buy a filter superior to standard ones (aftermarket filters are available which offer better filtration than standard filters) do so, because it will allow you more protection during your extended change intervals. It's a good idea to run the first change of synthoil for no more than 3,000 miles, then change oil and filter again, because it's sure to dissolve deposits your engine cleaning treatment did not get.

Oil change intervals
This is the most controversial aspect of using synthoils. Because most of them cost $5 per quart or more, it gets very expensive to change them as often as petro-oil, and it's not really necessary. However, car engines are subject to condensation and accumulate particulate matter, both of which contaminate the oil. If you want to extend your oil change intervals, do your homework on both air and oil filtration. Air filtration affects the particulates which enter the engine, and the oil filter is your only defense against particulates and contaminants. Major aftermarket brand names in filtration include Amsoil and K&N, and web searches will provide information for you. (This is not a brand pitch - but you have to know what to look for.) Amsoil says you can run their synthetic oil one year if you also use their oil and air filtration; they also sell kits you can use to have their lab test your oil if you want to see how far you can run it before it actually needs to be changed.

For many years, I have run each change of synthetic oil for a year, changing the filter at six-month intervals. That's my own guess at what's reasonable for me, running a used car about 10K miles a year.

Gear lubes
Gear lubricants for automatic and manual transmissions and rear ends are superior to their petro-oil counterparts in two ways. First, they offer less mechanical resistance to gear movement, especially in cold weather, where they are vastly superior. This results in easier shifting in the cold, and some users report improved gas mileage (both from oil and from gear lube...). Second, they break down more slowly, so they provide good lubrication longer.

In automatics, synthetic ATF's highly detergent qualities keep varnish from building up, extending transmission life. The ATF also resist breakdown under heat better than petro-ATF, giving you more "grace period" to discover mechanical problems.

In manual transmissions, synthetic lube makes shifting easier and reduces mechanical resistance to the gears moving. Note: you must put the correct synthetic gear lube in a manual transmission or it may grate when shifting gears. The synchros in your transmission are brass rings which require a certain amount of friction to function. If you put in a synth-lube not made for transmissions, the synchros may not be able to work properly due to their friction being reduced too much...resulting in grating gears when you shift. A synth-lube made specifically for transmissons has friction agents designed to allow proper shifting. This is a case in which transmission gear oil and rear end gear oil are NOT created equal.

In front wheel drive transaxles, synth-lube has been the standard for years. Make sure to get the right lube for yours. If you doubt the wisdom of using it in transaxles, ask an Audi mechanic. Enough said.

Situations indicating use and non-use

When to use synthetics:

When not to use synthetics:

Why doesn't everyone use synthoils?

But in the last five years, almost every major oil manufacturer has brought out a synthetic oil, and in the near future, cars will be designed to run on them exclusively. Example: Since the 1993 model year, the Corvette has required owners to use synthoil to keep the warranty in force!