Simply re-read what I wrote, quoted below. Don't worry, I'll explain it again when we get down there....
I for one never said or implied a word about NOx.
Ring sealing technology has improved since 1960, but only very slightly compared to improvements in other areas, such as fuel delivery management and forced induction pressures. Combustion pressures tend to be much higher with direct injection, hence there's a bit more blow-by. So even though the combustion gasses may be cleaner, more volume (albeit of cleaner gas) passes through the crankcase. Also, the higher pressures result in higher piston underside temperatures, and that too stresses a lubricating oil.
Nissan SD22 (debuted in 1964), indirect injection, advertised compression
21:1, non turbo. and oil cooled pistons Ford and Dodge Cummins of late ... direct injection, advertised comp 17.5:1 with turbo, 21.5:1 without, and oil cooled pistons.
From these stats, your claim of "Combustion pressures tend to be much higher with direct injection" is not supported. Perhaps you'll clarify.
In the case of the SD22, there are pistons with three compression rings and those with two compression rings. Depends on application.
It is known that indirect injection while quieter, does result in more soot production.
AS I see it, less soot production due to chamber design and better fuel management ... MORE than off sets your claim of greater oil contamination due to compression ring blow-by so far as oil service life is concerned. Is there disagreement?
"Since rapid fuel autoignition requires a certain air temperature, an IDI engine needs a higher compression ratio to achieve the desired air temperature in the prechamber. IDI engines operate at compression ratios of about 20:1 to 24:1; while DI engines operate at ratios of about 15:1 to 18:1. The heat losses that necessitate these higher compression ratios have another, more important effect: they decrease the efficiency of the engine. IDI engines typically achieve fuel efficiencies that are
10% to 20% lower, on a relative basis, than comparable DI engines."
this text appears to be from the bosch automotive handbook - a superb publication.
I do have interest in them, but as I repeat - at what point would I take the decision to do something about it? Thats a decision I'd not make by oil analysis but by my own pretty capable decision making processes.
The day you stop trusting everyone who is supposedly qualified is the day you free yourself from the stinging tail of trust. I have NEVER met anyone I trust to make a decision about my car. I also know how easy it is to screw up this kind of test proceedure, contaminate things etc and how sloppy labs can get, and how it makes no difference to the guy who is doing the testing whereas it does to me. Other fields, yes, I've met plenty I trust and respect more than my own, but having seen dealers, 'specialists' and many others making totally stupid mistakes and assumptions costing friends and family large sums of money for no reason, at least I know if something goes wrong I only have myself to blame, and being pretty good at this stuff things dont generally go wrong.
I'd never have let it get to that stage, the moment the oil light flickered I'd have had all *my* test equipment on the car and sorted the problem myself. But I pretty much guarantee I'd have spotted a change in engine note before the light started flickering - and would have had it out to inspect.
i'm not saying you should trust everybody, i'm saying that it's possible to differentiate the good from the bad if you learn how to qualify them. if you withdraw from the qualification process, you can't complain about lack of candidates.
and some people you /have/ to trust, whether you like it or not. you're in the emergency operating theater after a crash. you going to worry about the competency of the blood group testing that was done on you before the transfusion? how about the last time you flew? did you worry about the competency of the person that signed off on the wing root bolt torque certificates? admittedly, the car world has very low barriers to entry, but that doesn't mean everyone is a fool. qualify them!
if siezure was simply a function of oil pressure, life would be simple.
Caterpillar were worldwide pioneers of oil analysis and service schedule prediction. I have had my oil analysed be Shell and even small blenders like Ovolene do it. One analysis is not representative of anything. A particular engine needs a series of analysis for a meaningful interpretation.
This is now a well established procedure and interpretation of long drain interval oil is reliable. Mobil can provide information IIRC.
No, I believe your point was that it is not appropriate to *you*, which obviously I can't comment on. It may well be cost effective and a useful management tool for others. In fact a form of analysis and optimised flexible servicing is now so cost effective that it is built-in to many fleet and private cars, i.e. family hatchbacks and saloons, as standard fit.
INdeed. I've read a fair number of Bosch SAE, and Cummins publications on the subject. I have opined that IDI diesels are more soot prone. Is there a particular point that you are supporting or disagreeing with? For comparisons of IDI vs. DI diesel, the presence (or absence) of a turbocharger must be consistant.
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?
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.
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.
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.
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.
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.
To append: The lower compression pistons fitted to a turbocharged engine also help prevent excessive peak dynamic compression levels, Steve. Known fact that higher cranking compression reduces the amount of boost you can safely run ... gasoline or diesel.
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.
MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.