A Question for John Kennedy

[OC_DMAX]

John,

Everyone on the forum greatly respects your opinions and judgement on diesels and the GM products in particular. On a previous topic "Another Oil Question" you made the statement "I will not run any oil past 10k, and have been changing mine at 4k even with synthetic".

My question: What has led you to change the synthetic oil in your Duramax at 4k miles?

The reason I ask the question is I am about ready to switch to Mobil Delvac 1 5W-40. (I am waiting for my oil analysis reports to stabilize; silicon and wear metals -- I anticipate that occuring on the next sample.) I am trying to determine what oil change interval I could expect to get out of a synthetic (like Mobil Delvac 1). My original thoughts were every 6 to 7K. However, I may have to modify that thought based on you input above.

Other forum contributors and I would appreciate any detailed insight you could provide on this subject.

Regards,
Alan

[Kent Tuttle]

Alan,

I just had an oil analysis done with 5K miles on the oil. Canme back back with no corrective action required and only recommended to change the oil. So for now I'm going to go with this. The truck has been on the Amsoil 15W-40 since about 6K miles and it now has 25K.

[mdrag]

OC-DMAX,

Have you ever noticed those disclaimers, written in small print, at the bottom of most ads for performance products?

"Do not try this at home, professional driver on a closed track...etc"

Kennedy ignores them....Me thinks that is the reason he needs to change his oil every 3-4K ;)

King of THE HILL comes to mind... :D

[csimo]

This wasn't addressed to me, but I'll put my two cents in anyway.

Motor oil has several jobs inside your engine other than lubrication. Your motor oil is a major source of engine cooling, and another very important job of motor oil is to maintain all contaminants in suspension that are not filtered out by your oil filter. These contaminants are bad things, acids, abrasives, etc. If the oil does not do its job and keep them in suspension you end up with sludge. No motor oil in the world can keep these contaminants from entering your crankcase, and none that I'm aware of have ever made the claim that they can. As your engine ages these contaminants increase.

First let's say you use an average dino oil (15w40 CH-4) at the manufacturer's recommended drain interval (say 7500 miles). We know from thousands of tests that under normal operating conditions the LUBRICATING properties of all major motor oils is not an issue. No measurable difference over the life of the engine.

Now let's say you use a synthetic motor oil (5w40 CH-4) and use some kind of extended drain interval. We know two facts... first that at the end of the 7500 miles there is no measurable difference in the wear of the engine, and secondly we know that both motor oils are equally contaminated.

In the first scenario you will have drained out the contaminated motor oil and replaced it with fresh motor oil that is able to start holding all those contaminants in suspension again.

In the second scenario you will continue to recirculate all the contaminants throughout your crankcase for a much longer period of time. Through oil analysis you will finally discover when the motor oil is finally too contaminated to continue, but you could have done that with any good motor oil as well.

Am I saying dino is better than synthetic? No! I use synthetic myself. I know that dino will be just as good as synthetic under NORMAL operating conditions, but I sometimes run my engine harder than the "normal" dirver would. I prefer the added safety that synthetic offers in those "not normal" conditions that somethime exist.

What I am saying is that extended drain intervals don't make sense. You don't change your oil because the oil itself is "worn out". You change it because its dirty.... contaminated. It doesn't matter if it's the cheapest oil on the market or the most expensive the fact is that at the end of 7500 miles they are both holding the same amount of dirt in suspension. I want that out of my engine.

What about oil analysis? Yes, you can use oil analysis to determine when you have reached the limits of the motor oil. This is not something exclusive to synthetic oils... you could do the same exact thing with dino oils and get similar results. No a dino won't test out as long as a synthetic, but I believe you would only find a 10% or so variation.

I don't want to run my oil until it is completely saturated with contaminants... dino or synthetic.

[MountainMax]

Good point.

I don't change my underwear each day because they're wornout or won't work any more,....I change em so they'll be clean and no suspended particles. :D

[WillowCreekStable]

Now there's a vision........

[mackin]

Moutain Max

Exactly.....Imagine extended WEAR intervals !!!!!! Due to some second party analysis..... :eek:

MAC tongue.gif

[kerry witherspoon]

Well as a mechanic oil and grease are the best spent money. Never herd of engine going bad from too many oil changes.

[OilMan]

One thing any engine loves is fresh, clean oil!
Whatever you run, dino for us public road drivers, or syn for the race road drivers, change your oil often - your engine will thank you for it.

[HDLD]

Mountain Max

That's one of the funniest analogies I've heard in a long time! Good one.

I'm not sure I agree though I'm really torn on this one. I've read a number of articles on the topic, even subscribe to a lubrication newsletter. I don't think many would argue that synthetic is the way to go under more extreme use or in gears and many other applications.

If you have a dual-stage filter (down to 1 micron), then in theory, the only suspended particles running about and causing havoc would be less than 1 micron in size. Given the long term testing on Freightliners and such, it would appear the engines are up to the extended drain intervals with no consequences when using this type of filtration (which is changed regularly). Certainly many fleet owners like the concept/savings and you can't argue the environmental benefits.

Then again, if you plan on trading your vehicle regularly, it probably doesn't matter that much what you do in which case I'd go with synthetic or a high quality dino and change at about 10k intervals. I was doing this on my Y2K Silverado 4.8L, sold it at 90k miles with no issues whatsoever and I drove the sh** out of it.

I'm hoping to have the D/A for at least 300k miles, perhaps many more. At 6500 miles, I'm getting ready to switch from dino to synth on what will be my 2nd change (1st at about 2500mi).

I will likely either go with an Amsoil dual-stage system and regular analysis (have one of the best labs around in town) but am also considering the KISS paradigm and going with the Delvac 1 and 4k intervals. decisions decisions...

[Kennedy]

What more can I say? I haven't decided on what I want to run for bypass filtration yet, but am considering resurrecting the old Como QCDA system. The one time I extended my drain intervals was on the Rendezvous III trip. What better time than a road trip of all highway miles and no significant (3k# of engine cores in bed) load? I went 10 k, and my ferrography said that was a no-no.

Suffice to say, and George ahs proven this to me, that ferrography is the way to find out what REALLY is in your oil. A spectro analysis looks past the big stuff to see the "fines"...

[OC_DMAX]

Everyone,

Thank you all for the replies. I had been reading all the oil analysis reports that were previously posted on the forum by different members and trying to correlate them with my own oil analysis results (just a novice at this myself, but trying to learn). I had also seen in a couple posts where John K. mentioned that 4K miles was what he was using as an oil change interval with synthetics. My intent is not to run the oil to its absolute last useful mile, but instead to determine a reasonably safe oil change interval (and there are probably a hundred opinions on that).

So,,, my conclusion here is that running a heavily modified truck (JK), the lower bound is around 4K miles. Looks like a good plan going forward would be to run to 4k-5K miles, then drain an oil sample to have Avlube perform a ferrographic analysis (Avlube has done my spectrographic oil analysis tests, and I am pleased with their product/customer service). Then, proceed from there at the advise of the experts (at Avlube).

One last thing, on various posts that I have seen people mention contaminants in oil, but nobody really mentions the additive packages. These are consumed (depleted) as the miles build up on the oil and that also limits the life of the oil. So no matter how well you filter the oil (bypass filters, etc), you still need to worry about the conditions of the additives.

Once again, thanks for the replies. You have answered my questions.

Alan

Kent Tuttle - how did you survive the winds last week where you live in La Verne? My property got really trashed. I lost several trees, had a fence get crushed by another falling tree plus some roof tiles were destroyed by flying plywood (who knows where that came from). Had gusts in the Santa Ana Canyon area clocked at 94 mph on Monday morning around 5:00am. Just got through cleaning the mess up. Hope you survived better. Alan

[ 01-12-2003: Message edited by: OC_DMAX ]</p>

[Kent Tuttle]

Alan,

Sorry about your damage. Everything is OK except the pool. The soot from the fires we had and everything else being blown around did a number on it. I also thought my canopy for my trailer was going to hammered watching it get blown around but some how it survived. I hope we don't see winds like that for a while. Thanks for asking. Kent