oil viscosity seems to drop quickly

[Woofythewolf]

I have an Isuzu NPR-HD, with the 4HE1-TC 4.8 I4 diesel engine.
I replaced the engine with a used running takeout (129k miles) which I used shell rotella T triple protection in.

https://www.walmart.com/ip/Shell-Rotella-T-15W-40-Heavy-Duty-Diesel-Oil-5-gal./14958329 (although I got it for $60 instead of $103, cheapness was the whole reason for buying it lol) it doesn't say whether its the t4, t5, or t6, just a generic walmart diesel edition maybe.

I changed the oil after 100 miles (used generic cheap 15w-40 diesel oil from napa for the first fill), and now i'm about to do it again at 600 miles, this time with delo 400 ck-4 instead.

THE ISSUE:
the oil gets THIN. like feels really thin compared to the stuff I take out. possibly even thinner than 5w-30.

At first I thought it was either a solvent that they put in the engine to clean it before shipping it to me, or it was just cheap stuff that couldn't hold its viscosity when it got heated in the undersized turbo (although the turbo is watercooled so I don't see how that could be an issue), but now I've noticed that the shell also got thin. Any idea what would cause this?

Delo 400 ck-4 (and all ck-4 oils I suppose) is supposed to be good at maintaining viscosity at higher temperatures, so maybe that'll solve it if its the oil getting overheated. If that's not it I'm not I'm not sure what it could be.

When I do the oil change to the delo-400 I'll do a flow comparison of the used rotella, some new rotella of the same kind (I keep a 1 qt bottle in the truck) and the new delo-400 ck-4. (just drip some on a slanted metal sheet and take a pic after 1 minute). This'll tell me if it's all in my head or if I actually have an issue.

 

[HangFire]

Unless you get a UOA to confirm it, what you feel is meaningless.

Most people using their fingertips are comparing warm used oil to cold new oil.

 

[fdcg27]

Originally Posted By: HangFire
Unless you get a UOA to confirm it, what you feel is meaningless.

Most people using their fingertips are comparing warm used oil to cold new oil.


Exactly!
Oil viscosity is entirely temperature dependent. Oil drained warm will always seem quite thin.
The only other cause of reduced viscosity would be fuel dilution.
A UOA may have few real uses, but one valid one is identifying excess fuel in the oil.
You swapped the engine, but did you switch over the same injection pump and governor?

 

[Woofythewolf]

The engine was a whole complete unit (everything from injection pump and lift pump to the turbo, etc).

the fuel dilution is something I hadn't considered. especially being that the injection pump is oil lubricated and I suppose any fuel that goes past the plungers would get into the oil. (I don't know the exact inner functions, but its an inline pump using a camshaft and plungers).

I'll do the drop test (and ensure that they are all at the same temperature, preferably 210f in boiling water so it's close to operating temperature), and if one really is thinner I'll send it in for an analysis to see if I am having fuel dilution problems.

 

[Woofythewolf]

looked up fuel dilution, and I'm a textbook case:
common causes are lugging the engine, excessive idling, overcooled operation, and then the obvious bed injector spray patterns etc.

Thermostat stuck open: check (overcooled operation)
in town driving 90%: check (also overcooled operation since I drive like a granny)
excessive idling: check (high idle no load for 10 minutes to at least reach the bottom of the temp guage before gently driving 5 miles to school)
lugging the engine: check (just replaced the computer this weekend, but the old engine had a coarse tooth geartrain for the injection pump, while the new one has a fine tooth
(twice as many) geartrain which means the rpm sensor read twice as high, and as a result the auto trans was up-shifting at 1500 rpm at the highest)

I'm replacing the thermostats (and all the hoses and changing to a 5 year coolant) this week so that should solve the cool running, the lugging is solved as of yesterday, and also the thermostats should help me warm up faster to reduce idling time by a LOT.

I think the low rpm especially increases the fuel dilation becuase the plungers aren't going as fast, resulting in poor fuel atomization. The VSS was designed to prevent this (variable swirl system) but it was also disabled because the old computer thought it was at high rpm and didn't activate the system.

oddly enough, that never caused any problems associated with unburnt fuel like black smoke or anything like that.

 

[901Memphis]

Can't tell what the viscosity is without proper test

 

[demarpaint]

As already mentioned, you can't determine viscosity w/o testing for it. If you're concerned get a UOA, then you'll know for sure what's going on with the oil.

 

[kschachn]

As others have mentioned already, you neither know you have low viscosity nor do you know if you have fuel dilution.

 

[umungus1122]

There is no "generic walmart diesel edition" of Rotella. It's first rate, regular Rotella. Super-tech 15w-40 is fine also.

 

[Linctex]

Originally Posted By: Woofythewolf

I think the low rpm especially increases the fuel dilation because the plungers aren't going as fast, resulting in poor fuel atomization.


RPM has zero effect on atomization.

Fuel injector "pop off pressure" controls that.
No fuel flow occurs until the minimum pressure is reached for the injector to "pop"

 

[ARCOgraphite]

you can heat a used sample on a hot plate for an hour (220-230 degF) and see who much boils off , that will give you a rough indication of % fuel. Don't do this inside the house!

don't forget you can use a paint viscometer to check relative thickness of oil. They should be same temp.

You can make a contraption by punching a hole on a can bottom. Maybe a D nail size. Time on how long it take maybe 3oz to drain.

 

[CourierDriver]

Feel good mindset over our oils, cleaners, seal conditioners is a never ending story,,, I get that feeling when I add my all time fav,,, yep, good ole Marvel Mystery Oil to the gas or oil,,,yep, it's a man thing I guess............IMHO.

 

[A_Harman]

Get a UOA. It's better than the guesswork methods you're talking about.
Then you'll get real numbers on viscosity and fuel dilution.
It's also nice to baseline the new engine.