Additive Pack vs. Evaporative Rate

[BrianWC]

This is something I have been pondering for a while. We know the purpose of the additive pack is to combat things like sludge formation and oxidation etc. We all also know that highway driving is very easy on the oil b/c it keeps it warm and helps the nasty stuff evaporate out.

Well, my question is, how fast is that process? In other words, do the chemicals in the additive pack immediately combat things like water or oil in the gas (resulting in the depletion of the additive pack) or does the heat of the oil evaporate the stuff out before it settles in. I'm inclined to think the later b/c otherwise why would highway miles be so much better on the oil. But then again, I don't really have a clue as to the actual chemistry of the situation.


Anyone?

Or does anyone even understand what I'm asking?

 

[Bryanccfshr]

I think you are asking why oil is depleted at a slower rate during constant hi-way driving?
If so it is because at steady temperature there is less blowby, less fuel getting past the rings and evaporation of fuel and H2O is optimal.
During short trips fuel and moisture get introduced to the oil and do no burn off.
The exact chemistry is complex but acids are formed from moisture and fuel in the oil and as a product of sulfur in fuel. Thiiese acids deplete the acid neutralizing additives.


In addition many of these additives work better or are not active until they reach certain temperatures.

 

[pitzel]

Theres little additive chemistry can actually do to fight actual ingress of water or fuel. Only proper combustion optimization, and operation 'at temperature' is effective against those measures.

Steady state conditions provide an environment where optimization can be made 'optimal' by the car's ECU or mechanical fuel metering systems. The 'stop and go' driving cycle involves many rapid changes of power setting, open-loop operation in some instances, and much higher peak power settings than highway driving. While a typical car on the highway doing 70mph only requires 20-40 horsepower constantly, the stop-and-go driving cycle can see horsepower peaks much closer to the engine's nameplate rating.

 

[Ken2]

Water and gasoline must be evaporated out of engine oil. Diesel fuel won't evaporate out.

I've seen a diagram of the operation of GM's oil life monitor (OLM) that tracks engine starts, engine temperature, engine load, etc., and gives a good estimate of remaining oil life. The OLM has a bell-shaped curve...low miles for the oil for short, cool trips, high miles for the oil for highway driving, low miles for very heavy loads like towing.


Ken

 

[BrianWC]

Yeah, I know WHY. I also knew that there still is blow by at constant speed (at least in my engine). So that's why I was wondering.

So you're saying that there is little in additive chemistry that combats water and fuel? I thought one of the standard lines in explanation of sludge formation was that it occured when additive packs were depleated.

Hmmm, the plot (and the oil) thickens.

 

[GMorg]

In the presence of water and oxygen, many metals (including Fe and Cu) can act as catalysts to oxidize organic compounds (like oil). The anti-oxidants in the add-package are deal with this until they are exhausted.

Also, in the presence of water and metals (particularly cooper), organic esters (including polyol esters) can undergo hydrolysis to produce acids. The resulting acids can then attack engine metals if the add-package is exhausted (total base in this case).

Personally, I think that you need to have a great additive package on top of a darn good base blend if you are going to use esters heavily. Especially in cooler, moist areas of the country. (paranoia ?)

 

[BrianWC]

Warning to Redline users? Course, A lot of oils have an ester component to their base stock, don't they?

 

[Blue99]

quote:

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Personally, I think that you need to have a great additive package on top of a darn good base blend if you are going to use esters heavily. Especially in cooler, moist areas of the country. (paranoia ?)

---

Yes, paranoia.

Here is a recent Redline 5W-20 used oil analysis run in a 5.3L Chevy Suburban, which spec's a 5w30 motor oil.

http://theoildrop.server101.com/cgi/ultimatebb.cgi?ubb=get_topic;f=3;t=003216

Excellent ppm's for Iron, any oxidation or corrosive effects would have put Iron much higher than low thirty's for a 10K OCI.

Sorry, but hydroscopic effects are a non-issue with the polyol base oils in current use by companies such as Redline.

 

[BrianWC]

Yeah, I knew that from MolaKule's posts, I guess. I recommend them for anyone who wants to learn the science behind esters. It's diesters that have a problem, right?

Anyway, I was just curious about the science.