Synthetic lubricants

[Ray D]

While I was getting my oil changed, I was thumbing through a hot rod magazine.  In the ask the expert section, one asked about using synthetics.  I don't remember much specifics or his sources, but this is his final line.  If you bought a new car and were going to keep it the rest of you're life, yes synthetic oils would probably help you out "some".  But if you are buying a used car or only plan on keeping it for a few years, there is no advantage to this expense.  You are really better off to use the extra money for added total preventative maintenance.  I can not argue this point as I am not an expert, just passing on what I read. 

Ray D

[JohnEd]

Sean,

John, I've been wrong many times, even on this board -- just check the archives.    I'm not sure, though, what you're referring to in this thread.

You must have seen my tongue pushing out my cheek in this.   You simply must have.  NOBODY is always right, I am sure.  With you the wait seems to be longer than with most and you spread yourself over an unusually wide spectrum of topics.  Now "accusing" someone of being always right is either a snide remark about another"s ego or a note on their consistent reliability and intellect.   Pick one of those!   I'm still a fan, so there!

Well, maybe and maybe not.

Now there is the engineer that I just knew was lurking in there somewhere. Had to be!

The engine is designed for the oil to run at a certain temperature, so you don't really want it to be below that design threshold.

I don't think you believe that or you wouldn't be committed to Syn in your TX.  They, transmissions, are designed to run best at a specific temp as well as an engine.  The engine temp is controlled by the thermostat and I mention that to confirm to you that I know that.  Lots of engines have oil coolers that are not thermo controlled so they just dump all the heat they can at the given ambient.  My 440 engine oil runs slightly below the coolant temp till I hit 50 and then it goes slightly over.  Hills take it WAY over coolant.  Notice there aren't any numbers here!  It is happy at 250 F and 180 F and has pushed 15K lbs down the road at 60 for the past 70 K miles and with one bearing change that it didn't need at 30 K my bearings show no wear....Amaazing.  Still if the ambient drops to 32 F they want me to run a multi grade but I have never run anything but 40W and I carefully warm the engine in cold weather.  But I have to agree that "they" want the engine to run within the design limits, and , again notice I have no numbers here.

Along those lines I installed a trans cooler and didn't connect it cause I knew that if I ran it cold (below 180 F) it would rob me of MPG.  The first Mt. out of SD going east is Vejas Grade.  Not all that bad but really long.  I pulled over that first night at 10 PM to connect the cooler cause the TX hit 290 F as indicated by my "brandy knew" oil temp gauge.  Ambient was 60 F so that Hayden has been on and cooling since 1990 and 50K miles and usually runs at 180 F.

DD tried, for a while, to spec 15W-40 for the 2-strokes, with poor results.  If anything, a synthetic will exacerbate this problem, not help it.

I think Syns are adding new definition to oil performance.  Apparently RP's 15W40 has higher viscosity at high temp than their straight 40W. ?  I don't quite understand that but then I am more easily confused than I used to be and even then it wasn't all that difficult to do.

Thank you for all your comments Sean.  They all help...really.

John

[Sean]

The engine is designed for the oil to run at a certain temperature, so you don't really want it to be below that design threshold.

I don't think you believe that or you wouldn't be committed to Syn in your TX.  They, transmissions, are designed to run best at a specific temp as well as an engine.

Well, yes, "but."  These are two very different applications.  If an engineer could design a transmission that didn't heat up at all under stress, she would.  A transmission is a hydraulic device, and the performance of hydraulic fluid generally only goes down as temperature goes up.  Yes, there is a flip side, which is that at extremely low temperatures, the fluid might be so viscous as to increase stress on the components, but synthetic oils generally have better low-temperature characteristics as well

By contrast, engines require heat to be efficient.  If an engineer could design and engine to run hotter, he would.  Generally, the higher the temperature of the combustion chamber (piston, block, liners, valves, etc.) the more complete and efficient the combustion process will be.  The only reason that engines have cooling systems is that the materials they are made from will melt, distort, or break above certain temperatures.  So "design" engine temperature is a compromise -- hot enough for relatively good combustion, but low enough to keep things from breaking.  This is precisely why engines have thermostats -- you want the heat to stay in the engine when it is below that design temperature, and to leave the engine when it is above.

The engine temp is controlled by the thermostat and I mention that to confirm to you that I know that.  Lots of engines have oil coolers that are not thermo controlled so they just dump all the heat they can at the given ambient.

Again, yes "but."

First, engine temperature, as I am sure you know, is only coarsely controlled by the thermostat.  Like many things, it is a compromise between engine complexity (and therefore cost) and performance.  In a more perfect world, you would prefer to monitor the temperature of each cylinder at key points, and direct specific cooling only to the places that needed it.  You'd want to turn the cooling on and off instantly.  In practice, it's "good enough" to circulate coolant through the entire engine, monitor the outflow temperature of that coolant, and direct the coolant to an external heat exchanger (the radiator) as needed.  Note that the coolant temperature is not nearly the same as the cylinder temperature -- the engineer has to determine the thermostat opening temperature based on how much cylinder heat ends up in the coolant versus going out the exhaust, or into the oil, or radiated directly from the block.

If one merely takes the "some cooling is good, so more is better" approach, they would be tempted to put in, say, cooler thermostats, and that would probably be a poor choice.  (Increasing radiator capacity or fan speed, OTOH, provides more cooling "capacity" without messing up the engineers' design goals, because the thermostat will still keep needed heat in the engine where it belongs.)

When you look at oil coolers, if the balance of the system is such that the oil is getting hotter than it needs to be, and the coolant is having to shed excess oil heat (heat is exchanged in the block, where oil and cooling passages are close together), then an external oil cooler will help reduce the heat load on the cooling system at high engine temps.  If, OTOH, the oil is already at or below optimum temperature, then an external oil cooler will do more harm than good.

This is particularly an issue with 2-stroke diesels, due to the sheer volume of oil being dumped onto the liners.  Cold oil can actually reduce the temperature inside the cylinder, interfering with combustion.  So, again, in a perfect world, if you had an external oil cooler, it would be bypassed until the oil was up to design temperature, whatever that is (and it is almost certainly different than the coolant design temperature).

Bear in mind that I am not saying that either synthetic oil or external oil coolers are bad for DD 2-strokes.  All I am saying is that I don't know, one way or the other, because the engineering is complex and I haven't done it.  Maybe somebody has, but I am always wary of marketing claims that are not backed up by solid, independent engineering.

I think Syns are adding new definition to oil performance.  Apparently RP's 15W40 has higher viscosity at high temp than their straight 40W. ?  I don't quite understand that but then I am more easily confused than I used to be and even then it wasn't all that difficult to do.

Here again, I'm not a tribologist so the science behind multi-vis oils is way above my head.  I just try to stick with the engine manufacturer's recommendations to be safe.  In this regard, my Detroit guidance (publication 7SE270) says that only straight 40 or 50 is allowed, no multi-vis*, and for synthetic oils, "For two-stroke cycle engines, only synthetic oils which do not contain viscosity improver additives may be used."

*There is an exception for below-freezing starting conditions:

At ambient temperatures below freezing (32° F or 0° C), sufficient starter cranking speed may not be achieved to start the engine with SAE 40 grade oils. Where starting aids are not available or at very cold temperatures (0° F to -25° F or -18° C to -32° C) even if starting aids are available, the use of multigrade SAE 15W-40 or monograde lubricant SAE 30 will improve startability. These lubricants must possess a High Temperature – High Shear Rate Viscosity (measured by ASTM D 4741 or equivalent) of 3.70 cP minimum. These oils must be replaced with monograde SAE 40 lubricants as soon as ambient conditions permit.

(emphasis theirs).

We have a "starting aid" (we can pre-heat the block with our Webasto), so we stick with the 40-weight, which is preferred in all cases once the engine is running -- it is only "startability" that is being addressed by this exception.

-Sean
http://ourodyssey.blogspot.com

[BG6]

Umm, folks, "synthetic" oils are petroleum-based.  So I'm not sure what the reference to "dino" oil is supposed to mean.  It all comes out of the ground.  FWIW.

Dino oil is refined mineral petroleum, as opposed to synthetic, which contains compounds which are created through other processes.

[Sean]

Dino oil is refined mineral petroleum, as opposed to synthetic, which contains compounds which are created through other processes.

...from petroleum.

So if you believe that "normal" oil come from dinosaurs (a stereotype propagated by Sinclair, I'm pretty sure), then synthetic motor oil does, too.

There are processes to completely synthesize oil from other substances, such as the oft-touted Fischer-Tropsch process (although even then, it is not uncommon for natural gas, another "dinosaur" byproduct, to be the required methane source), but it is generally not cost-effective to produce synthetic lubricants this way.  Most "synthetic" motor oils are API group III, which starts as highly refined mineral (petroleum) oil processed through hydrocracking, and/or API group IV, which are polyalphaolefins (PAO's).  Note that, while PAO's are truly engineered synthetics, they are made almost exclusively from petrochemicals -- there's that dinosaur again.

BTW, I can not tell from the Ro-Quip Asia Pacific cut sheet cited earlier on Royal Purple whether this is a Group III, IV, or V synthetic.

Again, not a tribologist, yada, yada.  But I have stayed in a Holiday Inn Express.

-Sean
http://ourodyssey.blogspot.com