Engine Cleanliness

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 🤷‍♂️
In my 30 years of diesel wrenching I never saw varnish. Not much sludge either. Lots of soot in exhaust ports from tired engines.
 
RP's API oil was only ever marketed as good for OEM intervals AFAIK. XL "up to" should probably have been followed with UOA's, as in this case obviously there was oxidation taking place. Certain applications just are not good with longer drain intervals, mechanical issues can also cause premature degradation.

@OVERKILL - Like all extended oil marketing, RP API says it is good for 1yr/12K but to use the manufacturer's interval during warranty period.
 
Here's my experience. No matter what the OCI is if engine has a problem rather check engine light or not it will sludge up. Had a Caprice first year of throttle body came in with 200k and ran all interstate still changed at 3k with Castrol so we were wondering why she wanted engine change which she replied lots of miles love for it to get another 200k and she drove alot. We I pulled it apart only thing holding it together was sludge so much so that covers left imprint. Another had Toyota 22r that I changed timing chain at 350k and oil change was 7500 Valvoline white bottle with engine so clean you could eat off it. Caprice engine had EGR problem that I attribute to the problem and Toyota owner had all maintenance done as well as problems fixed as it broke. Seen it more times with people who thought an engine light on was ok as it ran fine with sludge and ones who fixed them not have sludge.
 
In my 30 years of diesel wrenching I never saw varnish. Not much sludge either. Lots of soot in exhaust ports from tired engines.

curious, is that because of a typically bigger sump or the oil type (high zddp?) or the fuel (e.g. dilution factor)?
Do diesel engines run cooler than typical gas engines?
 
curious, is that because of a typically bigger sump or the oil type (high zddp?) or the fuel (e.g. dilution factor)?
Do diesel engines run cooler than typical gas engines?
I'm going back 30 years with my experience with class 8 diesel trucks. The oil back then was well developed to run in a diesel engine. Never in a million years would you use it in a gas engine. It was designed for the high sulfur diesel fuel of the day. Also this was pre-emission days for large trucks. Detroit Diesel tried emission devices on their 2 stroke engines with little success. So I suppose oil was a contributor. I suppose the large sump helped to keep oil contamination in check. Large diesel engines don't run a lot of oil pressure (6-10psi at idle and 40psi at speed) but they pump a huge volume of oil through the engine.

Fuel dilution wasn't a factor until the rings were shot and the engine was spent.

Back then, yes, they ran cooler. The Detroit's used a 140dF thermostat in the lower 48 and a 160 in the Arctic.

With fuel economy and emission demands on trucks today it's a much different story.
 
I've posted this in the past, but this is the basic cycle:
View attachment 29349

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.
*Does oil oxidation with heat play a role in varnish / sludge creation ?
 
Quick shot of my old E39 M5 through the fill hole which I think would meet your tight engine bay, physically large engine criteria. I have no idea was the previous owner ran, this was M1 0w-40:
View attachment 29077
View attachment 29078
The oil looks dirty, but the engine does not. props to you and the previous owner for keeping up with maintenance.
 
Is in any way different additive packages from different oil companies related to varnish? This came out discussing varnish with some friends today and one told me that in a Petrobras oil lecture someone from the company came out with this. That changing from one brand to another, could be a cause for some varnish. Any thoughts on this?
 
Is in any way different additive packages from different oil companies related to varnish? This came out discussing varnish with some friends today and one told me that in a Petrobras oil lecture someone from the company came out with this. That changing from one brand to another, could be a cause for some varnish. Any thoughts on this?
Sounds a bit out there, given what causes varnish.
 
Every engine I've run synthetic only in has had varnish too. Pennzoil and Castrol mostly. I can say without a doubt those two create varnish. Not saying it's bad, just saying it was there.
 
Every engine I've run synthetic only in has had varnish too. Pennzoil and Castrol mostly. I can say without a doubt those two create varnish. Not saying it's bad, just saying it was there.
What were the intervals?
 
5k - 7k

Do you think generally speaking a longer interval will form more varnish? Not sludge... but varnish?

If an oil reaches its saturation point and starts laying down what's suspended in it, yes, you'll get varnish. Varnish and sludge are products of the same process, the difference is that sludge involves moisture whilst varnish does not.
 
IMG_20191125_204139.jpg

My 1988 Ford Escort XR3i, this is what happens with cheap Group 1 Dino and few and far inbetween oil changes.
 
5k - 7k

Do you think generally speaking a longer interval will form more varnish? Not sludge... but varnish?
Interesting. Honestly, I am not sure what to think of your experience. I have never used either of those brands for the duration of an engine's lifetime nor have I seen an engine that has only used either of those brands.
 
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