Will switching from Synthetic to Dyno oil harm my engine?

EVERYBODY is reluctant to qualify THEMSELVES first. Sure it's easy to call
the other guy who makes errors an idiot but ... are you better qualified or
better experienced? Be honest. Why did you sublet the repair in the first
place?

 

Are you NATRUALLY stupid, or stupid by FORCED INDUCTION?


All together, class: "What does static compression ratio have to do with
the peak pressure achieved during combustion?"

NOTHING!

Post again if you can't figure out why.

 

I think it is not important. My Nissan IDI turbo engines deposit far less
soot in the oil per mile than my NA Land Rover diesel ever did. In fact I
don't see much difference between the Nissan turbo's and the small
Ishikawajima NA indirect.
My Toyota direct injection turbo keeps oil very clean for a diesel.

Huw

 

I know this is getting far afield, but the question is a good one.

I had started subletting larger part replacements because sometimes the time
and frustration are more important than the money, and I lacked air tools.
Now that I have air tools, there are more I do at home - although a lift
would be nice

I have let out exactly one diagnostic since about 1987. I had an '84 Dodge
with a Mitsubishi power train (live and learn). It failed emissions on
cruise CO, and I didn't feel up to troubleshooting that new-fangled feedback
carburetor so I took it to the dealer. The dealer said it needed a new
carburetor - $660, please - but couldn't say what was wrong with the
carburetor. I took the car back and determined the problem was the
mechanical fuel pump - it couldn't keep up with demand and when it caught up
the carb was still trying to enrich the mixture. $20 and an hour and a half
later the problem was solved.

Since then I once had to take my turbo Volvo to the dealer because it ran
like a dog after I replaced the injectors (longer story, but that's the gist
of it.) The mechanic spent most of the day swapping parts, and was baffled
until he put in new injectors (although the flow rates on the ones I put in
were on the money). Problem solved. But the engine still wouldn't run in
turbo boost, and he blamed the $500 ignition control module. I had to find
the problem in a sensor connector myself.

The question is one of batting average - nobody bats 1000, but I like my
average (with the help of my friends, local and on-line) better than any
shop I've found.

In addition, professional and DIY approaches are necessarily different. When
I find an electric motor misbehaving, I always tear it down to see if
brushes, lube or cleaning will take care of the problem - it usually does. A
pro can't afford to do that, because if it fails the cost falls on him, not
the customer. If the part has to be replaced, he is out the labor for
trying. Ditto with the time the A/C clutch failed in the Volvo - no pro
would replace the clutch because the compressor lifetime was about the same
as the clutch. I replaced my own clutch and sure enough, a year later the
compressor failed. Didn't cost me any more that way, but a pro couldn't do
business like that.

Mike

 

I can't figure out why. By your logic, mechanical compression ratio would be
meaningless.

Ignition timing (injection timing for a conventional diesel) and induction
charge affect the combustion chamber temperature/pressure, but so does
mechanical compression ratio. For gasoline engines, that is why compression
ratios were reduced when NOx limits were imposed - to reduce peak combustion
temperatures. EGR (to reduce effective induction charge) and changes in
ignition timing were part of the solution, but mechanical compression ratio
was an important key.

Recall that the pressure is the result of the addition of heat, and the
Carnot efficiency of the engine - any heat engine - is the ratio of the
temperature at which heat is added to the engine to the temperature at which
heat is exhausted from the engine. Higher temperatures/pressures mean more
efficiency, so the modern design goals emphasize higher temperatures.
Controlling NOx is the trick.

Mike

 

Huw. Are you saying the presence of a turbo is not relevant to soot
production? All else being equal, Cummins and Caterpillar would laugh you
off into the liquid abyss that surrounds your island.

 

Mike: Your closing paragraph hits the nail on the head. "Diagnosing" a
problem down to a specific point within an assembly has not been profitable
for the line mechanic for many years now. All the shop or manufacturer
warranty will pay for is diagnosis down to the most relevant assembly. You
don't get to replace intermediate sprag clutches in Hydramatics ... you just
swap out the entire transmission for a factory authorized rebuilt.
Baddabing, baddaboom. Get the thing off your lift ASAP and move on.

 

It is hardly relevant in the simple way I think you mean. Today's road
diesel engines produce less exhaust soot, which is representative of total
soot production, than ever before and I cannot think of one car diesel that
is not turbocharged offhand. It is interesting that in parallel to the
dominance of turbo diesels the service intervals have also increased
substantially and so have power output verses swept volume and specific fuel
efficiency.
You have shown a disturbing trend towards a lack of understanding on this
topic Philip. Nothing is black and white, but are mostly shades of grey.
That is, all systems interact in a complex way and no particular is fixed
because technology in all areas advance continuously but is applied in steps
as is convenient for each manufacturing process.

Huw

 

Steve: That you have attempted to bluster bully when you are short on
knowledge is evident.

"We" know that turbochargers increase air density within the cylinder and
therefor ... dynamic compression. This readily evident to everyone but you
that turbo charged engines running significant boost pressures will always
have different pistons to reduce cranking compression. "We" also know that
all else being equal, having brake mean effective pressure close to TDC will
result in higher combustion chamber pressures than with BMEP further from
TDC.

Do read up on your subject if you really wish to be conversant.

 

In the grand scheme of things, it is rather meaningless. Two normally
aspirated gasoline engines with a given compression ratio (mechanical)
can have drastically different peak combustion pressures depending on
things like cam profile, cam timing, and ignition timing. Similarly, a
turbocharged DI diesel like a Cummins B5.9 can reach astronomical
(comparatively) combustion pressures compared to a normally aspirated
IDI (or even DI) diesel, not only because the turbocharger can supply
all the boost that the connecting rods can withstand (detonation is not
a limiting factor as it is in a turbo spark-ignition engine) but also
because of the cam profile (practically non-existent overlap) and
injection timing that can be used in a DI forced-induction 4-stroke diesel.

Yes, both do have an effect. But refuting my statement that a modern
Cummins has higher peak combustion pressures than a 40-year old Nissan
simply because the Nissan has a higher static CR is laughable.

Exactly. But think of it this way: a gas turbine engine has a
"mechanical" compression ratio of zero, yet still has a high FUNCTIONING
compression ratio. A turbo-diesel is rather like a gas turbine engine
wherein part of the compression is due to the turbocharger's compressor,
and the rest is due to the pistons in the diesel itself, and the
turbocharger is like the "free turbine" of a 2-stage turbine engine.

 

..Philip. wrote:

And that has precisely WHAT to do with the static CR of a Nissan SD22
vice a Cummins B5.9 and their comparative peak chamber pressures? And
why are you seemingly using the term "BMEP" to represent a pressure at a
single point in the cycle, when in fact the "mean" in the term "brake
mean effective pressure" makes the measurement at a single point in time
nonsensical?

You really should take your own advice, Philip.

 

PV = nRT. heating is adiabaic. the above sounds like constant volume
which clearly is not the case.

ie. combustion temperature

T1 - T2 / T2, where T1 is combustion, T2 is exhaust, in Kelvins.

because it's hard to get T2 lower.

 

good points mike! i've had similar experiences to yours, and often do
stuff myself if i have the time or inclination. but, like you, there's
stuff i can't do because i don't have the tools or won't do because i
don't have the time. i don't do alignment or crank regrinds for
instance. while it can be apita, and if you call enough people, you can
find people that know their business.

as for replacement vs. repair, replacement makes perfect economic sense
/if/ and only if the diagnosis is good. just bought a car from someone
after they'd spent a fortune on trying to get it to start properly. it
still wouldn't so they gave up. new distributor, new plug leads, new
injectors, new starter, new battery, the works. turns out, incredibly,
that the morons at the garage had not bothered to change the plugs for
what looked like over 100k, so of course, absent electrodes, the plugs
weren't much good! if it /had/ been a distributor problem, as you say,
the labor of repair vs. replace with the uncertainty of subsequent
reliability means that replacement is definitely the way to go. all
about the quality of the diagnosis.

 

BMEP is the highest pressure attained during combustion. This is affected
by numerous factors, not the least of which is the mechancial compression
ratio and boost pressure. All else being equal and with natural aspiration,
do you disagree that BMEP with 24:1 is going to be higher than BMEP with
17:1?

 

Rapidly rising pressure results in heat. You can have pressure but without
heat ... no ignition.

 

EVERYBODY is reluctant to qualify THEMSELVES first. Sure it's easy to
call

Maybe I'm just big headed, but in actual fact I trust my own diagnosis
first, then i ask around for advice and filter out the crap, which is almost
always from dealers and 'specialists' and people I know have no idea. As far
as I can remember I've not been wrong yet, except for in the hunt for a
knock on the rear susp of a pug 306, which i dont thing was ever found lol.

I never complained about lack of candidates?

And believe it or not, I know enough people in medical areas to know the
number of mistakes (that are generally covered up) are actually scarily
high, and YES I do worry about the guy checking the bolts on the wings -
being an engineer has instilled into me a complete lack of trust of anyone i
dont *know* personally and know the quality of their work.

I know an aircraft technician, and I know the quality of his work is good,
I've seen it with my own eyes. I'd have him help me on my car, but I'd be
double checking everything myself.

I DO qualify them myself, and I've yet to meet someone i trust to do a
better job than me. I know that i may take longer, I may have to buy an
extra tool, but I know what im doing and i know i do it right - im not
leaving it to whether or not someone forgot to torque something up when the
finished for their coffee break. I'm also not trusting someone who gets paid
more for the more work they fit into a day. Or for finding more things to
replace - tis a totally backwards thing to do in my view. Why trust someone
to do something I can do myself. And when i have to, say i needed a block
honing or turbo rebuild, yes i am very untrusting and dislike being put in
that position.

I've seen a lot of these places, and worked in a few. Worked in a few
scientific labs, seen the shortcuts people make. Unless I can see the work
being done, or know the person who is doing it personally it aint being
done.

The vast majority of main/little/big end seizures are oil starvation
related. There are few other things capable of causing it, but if i had
symptoms of low pressure I'd have the bottom off the engine to check the
lot. Job done properly, not either a)guessed at or b)replaced sequentially
like a dealer would.
Couple of my mates have worked as spanner monkeys in dealerships, ive seen
how they work, and I've also seen how they take fast cars like mine and rag
the crackers off it while its left there. Main dealers, more so specialists.
Trust yourself, if you dont know - learn.

J

 

Since a 17:1 is likely to be direct injection and the over-twenty to one
will be indirect, then it is likely that the 17: 1 will have the higher peak
pressure, not least because the pressure rises so suddenly to the peak. This
is why direct injection engines are more noisy. Of course technology
advances and it is now possible to limit the peak pressure by injecting
sequentially in up to five stages for each power stroke and each cylinder
can be adjusted dynamically in real time using individual knock sensors to
adjust the fuel volume for each injector. Modern fuel injectors of the
piezzo controlled type each have a bar code which is read by a laptop which
informs the ECU which setting to apply to match it to each other injector in
the system. With this constant then everything can be controlled with
unbelievable accuracy.

Huw

 

Sorry Huw. You do not get to rewrite the question via your answer. The
passage "All else being equal" is germane.

Agreed. But this gracious contribution of yours is beyond the current scope.
But we'll get to it soon! LOL You know how these threads evolve.

 

You inferred on the simple level. I know my audience.

Yes Huw, all this is appreciated but a dodge from the question I posed to
you.

See the comment I made just moments ago. Shades of gray represent the
superficial understanding. ;-) From a very qualified Cummins source, I've
been told I a good grasp of the interdependent variables. How the fuel
delivery basics can be electronically manipulated is an ongoing education.

 

But they cannot be equal because there are no IDI engines running 17:1 and
no DI running remotely near to 24:1. You may know that IDI engines do not
incorporate the combustion chamber, as such, within a recess in the piston
crown which is the case with all DI diesels.

Huw