Please Educate Me.

[Al Swearengen]

I'm new to all this but I want to learn. When looking at oil data sheets, what consitutes a good number? For example: Specific Gravity - is the higher the number better, a lower number better, or is it best to be in a specific range, say .850-.900 (as an example)? Same goes for these criteria like flash point, pour point, viscosity index, etc...

I come from the healthcare industry - we judge data like this by clinical improvement or clinical decline. So can anyone (in laymans terms) describe for me "good" #'s vs. "bad" numbers for the typical engine oil data sheet tests.

Gravity, °API ASTM D-287
Specific Gravity @ 60°F(15.6°C) ASTM D-287
Viscosity
@ 40°C, cSt ASTM D-
@ 100°C, cSt ASTM D-445
Viscosity Index ASTM D-2270
Flash Point, °C ASTM D-93
Pour Point, °C ASTM D-97
CCS Viscosity, cP (°C) ASTM D-5293
Viscosity, cP (°C) ASTM D-4684 15,200
HT/HS Viscosity , cP ASTM D-4683
Noack Volatility, % ASTM

Thanks for any help.

 

[ekpolk]

Al:

As in the health care business, there are a great number of variables that come into play in deciding what's "best" or "bad" in a given situation. A great place to start is in the Used Oil Analysis section. From those results, you'll get an idea about what's important generally and what's good or bad for particular types of engines. Some engines definitely like thicker oils, some like thin. In some instances, high temp high shear viscosity (HT/HS) may be a critical factor. I'd recommend that you focus on the types of vehicles you're driving, and build some knowledge from there. What's important to the owner of an old big block V-8 is going to be quite different than what interests the owner of a new high-revving DOHC I-4.

This site is a tremendous resource. I'm 44 and I've owned one car or another since I was 16. In my younger years, availability of the sort of info you'll find here was almost non-existent. In those days, I was flying blind. Now, in an evening of perusing BITOG, you can learn more than I could have found in a year when I was 22. Prowl around here for a while and you'll see what I mean. Bust some myths, learn some things you've never heard of and enjoy the company.

 

[Al Swearengen]

ekpolk: Thanks for the reply. You make a very valid point - I'm sure there are a number variables depending on the engine type.

I'm fairly easy, both my vehicles are Jeeps with 4.0L I6 engines (04 Grand Cherokee and 05 Rubicon Unlimited). This is an excellent engine and from past experience will easily do over 200k mi with regular conventional 10w30 with routine oil changes.

This site, however, has piqued my interest in oil and I'm eager to evaluate different oils.

Based on my vehicle/engine type - which of these criteria are most important to focus on?

 

[rpn453]

Flash Point, °C ASTM D-93
- Higher is better.

Pour Point, °C ASTM D-97
CCS Viscosity, cP (°C) ASTM D-5293
Viscosity, cP (°C) ASTM D-4684 15,200
- Lower is better.

HT/HS Viscosity , cP ASTM D-4683
- Higher is better.

Noack Volatility, % ASTM
- Lower is better.

Not that it matters a lot once you reach a certain point, which for most people would be that it can pass the required tests (API or otherwise) and is a suitable grade for your climate and vehicle.

The ideal values for the rest of the properties will vary depending on the engine, climate, and driving conditions.

 

[AEHaas]

I would like to expound here. A higher flash point and a lower volatility is useful if the engine is run under a higher load. For example, driving at 70 MPH down the highway is the least load on a car and results in the least wear. Any API SL or SM oil will be good enough regardless of the rated flash point or volatility.

However, pulling a 5,000 lb. load at 85 MPH up a long Virginia mountain grade or just driving at a constant 130 MPH is a higher load and a higher flash point and lower volatility will result in less oil consumption by the engine. Still, current rated oils would all fair well.

The lowest pour point is always best in all circumstances.

Although many engines require a HTHS of 2 or higher, more is not necessarily better. More is only needed for high loads again and generally for higher output engines. This is however a generalization. For example, a HTHS of 2.6 (0W-20 Mobil 1) is fine in my Ferrari Maranello for my driving situations. This has been proven by multiple modalities.

aehaas

 

[ekpolk]

I've never owned or operated a Jeep straight six, but there are a fair number of folks here who have. I'll defer to them, but from what I've heard, this engine seems to produce the best used oil analysis results when fed an xw-40 oil, most usually 10w-40. Dr. Haas, who just chimed in, generally seems to favor the use of lighter oils (and he has some pretty convincing info to back up his position). Doctor, forgive me if I'm overgeneralizing what you've said here before. This particular engine does raise an interesting question -- it's a particular example of an engine that, unlike many which thrive on thinner oils, really seems to do better with thicker stuff. So, while there are some interesting general arguments about the advantages of thin oils, we still have some engines like this that don't "go with the flow."

A parting fun shot: Dr. Haas has brought some terrfific insight to BITOG, but don't be afraid to disagree with him -- he can't get at you with the rubber gloves on over the internet!

 

[Al Swearengen]

Regarding these UOA: In a practical application, how useful are they?

 

[ekpolk]

I find them useful. There's so much brainwashing about how frequently to change oil, and virtually all of it is based upon generalities that may or may not apply to you and your car. You don't have to do a used oil analysis with every cycle of oil. Use them to find out which oil works well for you and how long that oil will last in your car, driven by you, in your environment. Then, run one periodically to check on the overall health of your engine and catch possible problem issues before they become destructive. Of course, you're not likely going to catch a "quick kill" problem with one or two used oil analysis per year, but you can pick up things like a slow coolant leak, a poorly sealed intake, etc.

I find them entertaining too. It's fun (for me) to take the challenge of keeping my vehicles in the very best possible condition.

 

[AEHaas]

UOA are very useful but generally over read. In general they are best to detect major problems and to follow trends.

If most UOA of a certain engine are slightly better with say a 40 wt. oil instead of a 30 wt. oil then one should feel comfortable using the thicker oil.

If an engine specs. 40 wt. but people are getting good UOA results by using 30 and 20 wt. oils then you should feel very comfortable using the 30 wt. oil.

I live on the edge but follow things closely. Thinner oils are easier on every engine component if there is no unusual wear of the metals. Benefits include more BHP and gas milage. I also feel comfortable stepping on the gas sooner after start up with an oil that does not begin so thick.

aehaas

 

[Al Swearengen]

Jeep recommends using 10w30 for all applications, however 5w30 is acceptable in cold weather situations.

I'm confused as to why Jeep wouldn't suggest a 40 weight oil if this was the better choice.

 

[AEHaas]

Read this, it may clarify some things:

http://theoildrop.server101.com/ubb/ultimatebb.php?ubb=get_topic;f=4;t=000427

This is the API service sheet that states that one of the purposes of SM oils is better low temperature performance:

http://api-ep.api.org/filelibrary/API_MotorOilGuide_2004.pdf

aehaas

 

[Gary Allan]

quote:

---

Jeep recommends using 10w30 for all applications, however 5w30 is acceptable in cold weather situations.

I'm confused as to why Jeep wouldn't suggest a 40 weight oil if this was the better choice.

---

I believe that your manual has a "preferred" after the 10w30.

The reasons for the 30 weight spec has probably more to do with availability than some other factors (there is no economical jeep engine). Although they had an EPA rating, I don't think jeeps were under the CAFE umbrella (until recently

) Although they could spec a 10w-40 ..it would be a 30 weight soon into an OCI of that length due to shearing (they can't assume that you're going to use HDEO or synths). They strongly suggest AGAINST a 5w30 for the same reasons. The higher anticipated VII (visc index improvers) would reduce it to a 20 weight over the recommended OCI and that would be unacceptable in their life cycle formula in this engine.

The same engine, basically unchanged except for head design, spec'd a 20w-50 to 32F, in the 70's, IIRC.

Just put "jeep" into the search engine in this forum and in the used oil analysis forum and you'll get a decent amount of stuff to read. Some do well with 30 weight oils ..others, like myself, have better indicated performance with 40 weights.

 

[ekpolk]

What Gary said. Read the stuff you unearth with a few searches, and then begin the process of trying the choices in your particular engine. And then, of course, let the rest of us know what works best for you.

 

[G-MAN]

quote:

---

The same engine, basically unchanged except for head design, spec'd a 20w-50 to 32F, in the 70's, IIRC.

---

Sorry, but the 4.0 I6 used in the Jeep wasn't around in any form in the 70s. It was AMC/Jeep's last totally new engine design just before Chrysler bought them in the early 90s.

 

[Al Swearengen]

The 4.0L I6 is a derivative of the 258 which was offered in the 1971 model year (when AMC took over for Kaiser - 1970) in the CJ model lineup and Commando. In 1987, Jeep changed the bore/stroke design configuration of the 258 (4.2L)engine and added multi-port electronic fuel injection. At the time it was launched in the XJ cherokee and from 1991 forward was offered in all wranglers and zj/wj grand cherokees. 2004 was the last year it was offered in a Grand Cherokee and 2006 will very likely be the last time it is offered in a Wrangler.

EDIT: Also, AMC sold Jeep to the Chrysler on August 5, 1987 - not the 90's.

Jeep education is always free!

[ November 09, 2005, 10:35 AM: Message edited by: Al Swearengen ]

 

[Al Swearengen]

Dr. Haas: I'm going to need a little extra time to read the articles, but I can certainly say that the API pdf was very helpful. Thanks.