Engine Cleanliness

In general, doesn't using a less viscous oil than required (for the given load), eventually lead to more deposits? Once the oil is under stress including long oci, bad stuff can happen.

ad pack can't help Noack and oxidation ... isn't that why a good syn with better base oil wins the cleanliness test? Less impurities , thickens less slowly, less deposits, burns cleaner, resisting breakdown better, handling higher temps better, higher flash/fire point ... Isn't it all about the base oil baby?
grin2
 
I've run name brand synthetic only in several engines only to see varnish form. It's definitely not all synthetics that keep varnish from building up.
 
Engine oils are designed to leave a film bonded to the internal engine surfaces, something about "tribology" I guess :D I see light and medium varnish as a normal part of this tribology, not a problem. But if it's sludged or caked/baked carbon, that is a problem.
 
Engine oils are designed to leave a film bonded to the internal engine surfaces, something about "tribology" I guess :D I see light and medium varnish as a normal part of this tribology, not a problem. But if it's sludged or caked/baked carbon, that is a problem.
Varnish is not part of that process, varnish is oxidization that has settled out of the oil carrier and plated the metal, it is in no way desirable despite being common enough to perhaps be considered "normal" by some.
 
So, is the tendency to develop varnish proportional with the oil's oxidation, that grows over the service life of the oil?
Or is it when TAN>TBN?

I get the impression from this thread thus far that TBN>TAN doesn't well prevent or inhibit varnish... just severe sludging.
 
So, is the tendency to develop varnish proportional with the oil's oxidation, that grows over the service life of the oil?
Or is it when TAN>TBN?

I get the impression from this thread thus far that TBN>TAN doesn't well prevent or inhibit varnish... just severe sludging.

I've posted this in the past, but this is the basic cycle:
SludgeVarnish.JPG


The TBN/TAN relationship is more about the oil's ability to neutralize acids. Depending on the design and propensity toward contaminants (blow-by for example) your posit is quite correct, that it may meet its saturation point with contaminants before the TBN is depleted at which point those contaminants will fall out of suspension and plate on parts, creating varnish. You add moisture to that mix and you'll get sludge.
 
for term ownership I like the idea of severe service OCI lengths. Antioxidants are often added to oils and this helps extend useful life, but all additives can eventually lose effectiveness or be overwhelmed. to me it is easier not to eeek out every last drop of life out of the oil, especially with DI increasing soot in the oil. So instead of 10 k I run 5-7 k Miles, and I don’t freak out when I leave the truck running at curbside pickup to keep my wife and dogs cool.
 
So what is the conclusion for having a relatively clean engine?
  • Shorter OCI.
  • Even shorter with engines that run hot (e.g. Small Turbo)
  • Even shorter OCI with dino.
Maybe the old 3K miles OCI is still valid and relevant. :unsure: :alien:

Get under your cars gentlemen. lol
 
So what is the conclusion for having a relatively clean engine?
  • Shorter OCI.
  • Even shorter with engines that run hot (e.g. Small Turbo)
  • Even shorter OCI with dino.
Maybe the old 3K miles OCI is still valid and relevant. :unsure: :alien:

Get under your cars gentlemen. lol


None of the above
 
Too long of OCI for the lube or condition of the engine. He said SS and XL, XL is just your Joe Average Group III oil. I certainly wouldn't be happy with that much varnish in my engine.
Why? If the engine runs fine when the rest of the vehicle is ready for the junk yard who cares.
 
Why? If the engine runs fine when the rest of the vehicle is ready for the junk yard who cares.
I mean, if people don't care about varnish and the results that come from it, then running their OCI based off of UOA wear and TBN trends is way to go for them.

Also, I do think that engines can tolerate a certain small level of varnish without any influence to the movement of the engine's parts nor oil flow. But, I don't know that exact threshold of varnish it can tolerate. I don't think anyone knows that exact threshold; one day they know it went too far because they have mechanical problems (minor or major) or it starts consuming oil.
 
But how do you properly measure varnish is the question?
Is observation of the cams sufficient (as is often the easiest observation point), or is that totally misleading and not representative of the areas where varnish would be an issue?
 
So what is the conclusion for having a relatively clean engine?
  • Shorter OCI.
  • Even shorter with engines that run hot (e.g. Small Turbo)
  • Even shorter OCI with dino.
Maybe the old 3K miles OCI is still valid and relevant. :unsure: :alien:

Get under your cars gentlemen. lol

Oh man
 
Why? If the engine runs fine when the rest of the vehicle is ready for the junk yard who cares.

Define "running fine". Not misfiring? What about being down on power? What about a VCT system that has laggy response now? It would still "run fine". You ever see the ring pack area of an engine that's heavily varnished? Oil control rings baked into their grooves, sticking 2nd ring. Compression is down, blowby substantial, gas mileage is down, but hey, it "runs fine" right? :/

Sure, if you are a few steps from the nursing home and your idea of an exciting drive is taking your Camry through a 50 turn at 45, maybe "running fine" is all you need. If you value efficiency and peak performance on the other hand, varnish is something to be concerned about.
 
I have never had those problems.

Would you know if you had though? Typically it's a very slow progression, you aren't going to lose 20HP over night, it's more like over the course of years and you'll have zero memory of what it felt like before that point so you'll have no idea that you lost it. I've torn down heavily varnished engines and observed what I described, that's why I stated what I did and why I noted that the definition of "running fine" can be pretty broad.

Personal anecdote ( 😁 ) When I got my '88 F-250 with the 300 I6 it ran fine. By running fine, it was pretty slow but idled smooth and drove around well enough, just didn't have very much get up and go. My grandfather had always complained about it but had assumed nothing was wrong with it; it was just the way it was. My aunt, who I bought it from after he passed was of the same mind, that it was just a truck and that's the way it was.

I had owned it for a couple of months and one cool fall morning I noted that the steam coming from the exhaust was, well, it didn't look right. There wasn't enough of it. My Mustang threw a good plume on those fall days and there was barely a wisp coming out of the tailpipe of that truck. I had my wife rev it, the plume did not change. Lightbulb! There was an impediment in the exhaust! Being a multi-cat system, it had a large 2nd cat that both manifolds terminated into. I hacked off the pipe behind the cat, took a prybar to the inside of it and fire it up. It blew cat material way behind the truck and immediately you could tell it was much freer. Installed a section of pipe to hook the rest of the exhaust system back up and it was just like the Mustang with a big old cloud of steam coming out of the pipe that grew in size when rev'd. It was like a whole new truck! Picked up a massive amount of power (relatively speaking).

A good friend of mine, his Mustang (stock) never trapped anywhere near as high as mine did. Mine was clean inside with factory-spec oil pressure, despite high mileage, his was lucky to show 15psi and was UGLY, had lots of varnish. I was cutting close to 100Mph stock, he was down around 88-90. We eventually tore his engine apart and observed what I described to you. We knew it had some blow-by, but the oil control rings were stuck on almost all the pistons, the rings lands had heavy varnish and the rings were sticking. Bearings in it didn't look too hot either (showing copper) but that's unrelated to the varnish. But again, the car "ran fine", if you didn't take it to the track, you'd never have known it had lost enough power to be so much slower than another stock example and his is not the only example I can think of, another good friend of mine had a very similar experience, car was a lighter notch and I think the best trap he ever got out of it was 92. Normally was running 87-88Mph. Engine had probably half the mileage on it that mine did but wasn't as well maintained.
 
Define "running fine". Not misfiring? What about being down on power? What about a VCT system that has laggy response now? It would still "run fine". You ever see the ring pack area of an engine that's heavily varnished? Oil control rings baked into their grooves, sticking 2nd ring. Compression is down, blowby substantial, gas mileage is down, but hey, it "runs fine" right? :/

Sure, if you are a few steps from the nursing home and your idea of an exciting drive is taking your Camry through a 50 turn at 45, maybe "running fine" is all you need. If you value efficiency and peak performance on the other hand, varnish is something to be concerned about.

In a heavy duty engine I define "fine" as minimal oil use while still getting 7 mpg + at 65 mph while grossing 80,000 lb after 1 Million Miles.

So far that seems to require oil changes at 30,000 - 40,000 mi with conventional (and now blend).

Now if someone that runs a large fleet of passenger vehicles will just step in and tell us the equivalent in passenger vehicles with miles and service intervals.
 
In a heavy duty engine I define "fine" as minimal oil use while still getting 7 mpg + at 65 mph while grossing 80,000 lb after 1 Million Miles.

So far that seems to require oil changes at 30,000 - 40,000 mi with conventional (and now blend).

Now if someone that runs a large fleet of passenger vehicles will just step in and tell us the equivalent in passenger vehicles with miles and service intervals.

Serious question: Is varnish as prevalent in heavy diesel engines with massive sumps as it is in small sumped passenger vehicles? My diesel experience is limited, but I don't think I've ever seen a varnished up diesel. I've seen some pretty ugly soot and sludge messes but not varnish 🤷‍♂️
 
A quick chime-in here.. I though varnish was a light layer, discoloration of engine parts that was left behind on said engine parts (see through fill hole, over everything else if you were to take engine apart) that poorer quality oils left behind even if you did short OCIs, but the layer itself - if it even is that - is thin.

Sludge is the hard cruddy baked-on mess like bacon or something that has been in a pot or pan on a stove for too long etc

But can varnish ever get that thick? Or is sludge.. Thick varnish. ?
 
A quick chime-in here.. I though varnish was a light layer, discoloration of engine parts that was left behind on said engine parts (see through fill hole, over everything else if you were to take engine apart) that poorer quality oils left behind even if you did short OCIs, but the layer itself - if it even is that - is thin.

Sludge is the hard cruddy baked-on mess like bacon or something that has been in a pot or pan on a stove for too long etc

But can varnish ever get that thick? Or is sludge.. Thick varnish. ?

Per the diagram I posted earlier, varnish is comprised of oxidative byproducts that plate-out and are deposited on surfaces. These can be of varying thickness but the common theme is that it is tacky or hard like what you'd expect from a varnish or lacquer product you'd use on wood and not in any way gooey like a grease. Sludge, as shown in the chart, has a moisture component so, when mixed with the same byproducts that have fallen out of suspension you end up with something that can be more like a grease or emulsion.

So, you can have thin to extremely heavy varnish, depending on the engine, OCI length and quality of lubricant used. Two personal examples:

1. This is my sister's 2003 330i, you'll note the light varnish, which gets a bit thicker on top of the VANOS solenoids:
2003330ivcg03.jpg


2. This is the 2000 328i we owned for a stint, you'll note the heavy varnish, with carbonaceous deposits on the top of the VANOS solenoids:
338iengine03.jpg

338iengine04.jpg
 
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