How to tell if an oil is sludging up from UOA?

[nobb]

I just did a 8000km OCI on my 1998 4Runner with 325,000kms on the engine on 5W30 Quaker State Defy. Im not 100% sure, but the oil coming out did seem thicker than normal. It might be because the engine wasn't warm when I drained the oil but I'm not entirely sure.

I plan on sending a sample to Blackstone for analysis. Out of curiosity, what would be the point in which an oil sample is considered sludging? Do you look for viscosity being out of spec? High insolubles?

 

[Oil Changer]

You'll have to spend extra so you can see the TBN/TAN relationship.

 

[Olas]

Draining cold will see thicker oil than draining warm, that's normal.
Aside from the UOA, did you notice any chunks when you drained it? 5k miles isn't exactly an extended drain for QSD, maybe you should have a look down the fill hole? If that's inconclusive drop the sump and you'll know in seconds if you're sludges or not..

 

[spasm3]

I'd expect to see a low tbn high tan , and oxdative thickening of the oil.

 

[The_Eric]

A modern, healthy engine will not sludge on those short intervals.

Now of course if you've got coolant leaking into the oil, or a bad fuel dilution problem then it could sludge up at those, or an even shorter interval.

 

[WobblyElvis]

Last year I sent an oil sample to blackstone labs and asked how and if, they could detect sludge. This was their response.

"Yes, we can detect sludge -- kind of. If it's washes out when you're changing the oil, then we
can see sludge in the insolubles reading. Insolubles are oxidized solids that form as the oil is exposed to
heat, use, and blow-by. Your readings are fine, but if there's sludge forming in the engine and not washing
out, then no, we can't see/read that stuff."

 

[KrisZ]

How is the engine running overall? How did the old oil look like when drained? Jet black or brown when put on a rag or finger? As mentioned earlier did you see any chunks of carbon floating around?

I don't see how a car with over 300k kilometers is worth all this hassle if it runs fine otherwise.

 

[CentAmDL650]

Older engines with oil consumption typically suffer from some degree of sludging. Increased blowby around worn or stuck ring packs will oxidise and nitrate the engine oil, which is main cause of sludging. So if your UOA could measure the oxidation and nitration levels in the oil you'd have a better picture of the potential to cause sludge. As mentioned above, looking at the insolubles reading will show how much sludge has drained out into the UOA sample.

My opinion is it's less expensive to once every 4 - 5 OCI's to run a cleaner like MMO in the oil for the last half of an OCI that will loosen and dissolve the sludge. And to counter the critics' complaints that it lowers your oil's viscosity, run the cleaner in the winter cold weather when viscosity is less vital to maintaining adequate protection. Or replace one quart of oil with a thicker grade, ie take 1 quart of 5W-30 out and replace with 5W-40 for instance.

 

[nobb]

The truck in general is running great, including the engine. I'm also getting good fuel economy, don't hear any weird noises, nor do I have to top up the oil on a 8000km OCI.

It was my mistake draining the engine cold, but the oil seemed to flow out fine until near the end which appeared "thicker". No chunks or anything being held up...just thickness. It still drained out fine. I figure a 5W30 oil should flow like water @ 10C, but this felt more like thick mushroom soup.

I've only had this truck for ~1 year. My very first OCI on this truck was with Pennzoil Platinum, then Quaker State Defy, and now running Pennzoil Platinum again (for the winter).

 

[BigCahuna]

The po might have loaded it up with STP or Motor Honey before you bought it. If you dump it in a cold motor, it just slides to the bottom of the oil pan and stays there. Thick goo sliding out at the end of an oil change is not a good thing.,,