I took an eight hundred mile trip, and burned 3 quarts of oil. 2 on the way and 1 on the way back. I had just changed the oil to 5/30 synthetic, I do not know what had been used before, the engine had not been run in several years. I used 5/30 because that's what GM recommended for my other cars.

I changed the oil and thought, there was an excessive amount of carbon in the bottom of the drain pan. I had changed the valve cover gaskets and the top of the engine was pretty clean. So did the carbon come from the trip or was it in the oil pan?

I went back to conventional oil and changed viscosity to 10/40. Whats the verdict?

Probably going to be pretty hard to know for sure where the deposits came from. But, when first switching to synthetic after many years of running conventional oil, I've heard that increased deposits or even a bit of oil leakage can occur. The synthetic oil molecules are smaller than conventional, and may leak through small openings (talking microscopic size) in the various engine oil seals. Still, I think the benefit of synthetic oil are worth adding a little between oil changes.

I wouldn't use an oil weight just because it is common in other GM vehicles. It is based on engine needs. I believe the standard weight for the Chevy 454 in your motorhome would be 10w-30. That's what I use in my 3/4-ton Suburban that pulls my 32' travel trailer, and what I used in my previous 35' Class A motorhome with the Ford 460.

Engines have changed and so have oils. The modern engines all have roller cams so very little sliding friction.

Extreme Pressure additives were used with the older slider cams to prevent scuffing. The EP additives had high metallic content and are not needed for the roller camshafts so are not as abundant in modern oils. The move toward lower friction drove the trend to lower viscosity oils.

The old loose 454s can use all the antiscuff EP additives. In older engines higher vis will help also.

In my old OEM 454 (~100,000 miles) I used Rotella 15w-40. Robust additive package, lots of detergent. Used about 1 qt in 1500 miles.

When I put the 454HO roller cam motor in I switched to the recommended 5w-30 synthetic. Even at 3000 rpm I got about 4000 miles to the qt!

Since it used less on the way back, sounds like the rings were sticky and may have loosened up. Hopefully it will continue to improve. The carbon in the pan just shows the previous oil no longer had the junk in suspension. A few oil changes with good detergent oil and you will see less I bet.

I had read from Rusty's post on oil to use the Rotella product and I did with this oil change. Will not get much use this winter and I will change it again in the spring.

I think I detect a bit of lifter noise so we shall see!!!

Engines of that vintage should not be run on less than 10W40. The detergency of Rotella T should clean up and sticky lifters.

In fact, before shear-stable viscosity index improvers were developed, the rule was straight SAE 30 or 40.

....the rule was straight SAE 30 or 40

So given that my 1982 MCC 8.2 diesel
is "living" up in Canada
should we be using which/what oil yearly??

RotellaT 15W40 will be fine year round.

I have heard of big block GM engines going 400,000 to 500,000 miles in trucks. Seems in RV's not so much. I wonder why. Any thoughts?

Motorhomes are almost always built right to gross weight. Engines are heavily loaded and relatively poorly cooled.

Some of the older industrial GM V8 big block engines had so-called "tall deck" blocks and used pistons with 4 rings. They may have had roller cams, too. These were the heavy duty version but I never saw one in a motorhome. They probably ran longer.

Motorhomes get waay too little use to get optimum life. Too much sitting. Trucks run steady and not always at full gross.

quote:

Originally posted by Steve VW:

Motorhomes get way too little use to get optimum life. Too much sitting. Trucks run steady and not always at full gross.

Well said Steve! When I say I have 281K miles most guys will say, great you should get 500K miles at least, my Dodge Cummins diesel-blah blah blah. 98% of the time their Dodges run out at less then 5000 lbs. 99% of the time I run out at 22,000 lbs. Of course, mine does not sit very long! Even if I had to do a complete engine/trans rebuild now I wouldn't be terribly upset. I run it hard!

So what about these synthetic/conventional oil blends? Like Rotella T5 any advantage to using that in a gas engine of the 454 vintage models?

If I were planning to run the oil in extremely cold conditions or for extended miles between changes I would consider synthetic base the best bet.

OTOH for normal use with standard oil change intervals, the extra money might be a moot. I am more interested in the additive package than the type of base stock.

Modern trends toward clean air etc have driven many of the traditional metallic EP oil additives into virtual hiding. This does not necessarily mean the oils are better, just more eco-friendly. The trend toward lower viscosity does not mean lower wear or lower oil consumption, just lower friction when cold and marginally improved mileage. All depends on your priorities.

Modern engines can use lower ash, lower vis oils with little problem. Older engines may see higher piston wear, oil consumption and lower oil presure. Flat tappet cam engines need more antiscuff additives than some modern oils provide. Older engines had more blowby and need more detergent than new engines.

Major additives over the years have changed. The industry term is "detergent-dispersant" (DD)

As SteveVW noted, in the past, metallic ash (usually fines of barium or calcium salts) was the predominant DD. Ashless DDs were developed first for reciprocating aircraft engines.

The two types of DD work entirely differently.

Metallic ash DDs are attracted to and chemically neutralize contaminants (in the "olde days", this was usually sulfuric acid, the sulfur having been delivered from the fuel in blow-by to the crankcase). Obviously, LSD and ULSD fuel has minimized that problem. The result of the reaction was a particle large enough to be trapped by the oil filter and a bit of water, which is held in suspension by the remaining DD until evaporated. A small advantage of metallic ashes was the slight additional wear resistance.

Ashless DDs are liquid, and are attracted chemically to contaminant particles and surround them, keeping them from contact with engine parts. Ashless DDs also, over time, coat the engine parts, aiding further in protection.

The most robust diesel engine oils in the past had a combination of both types of DD, were the ashless dispersant would surround a contaminant particle until encountered an ash DD particle, which neutralized it, freeing the ashless DD.

The effectiveness of the combo oils is illustrated by Shell's rebranding its Series III as "metal coating oil".

BTW, the Society of Automotive Engineers (SAE) and the American Petroleum Institute (API) provide key info for motor oils users. SAE issues the specs for viscosity. API determines Service Class (usage) criteria, such as SH (gasoline) or CJ (diesel).

Again as SteveVW mentioned, metallic anti-wear additives (predominately zinc dithiophosphate) and others (like tricresylphosphate - the famous gaso additive "TCP") have been phased out.

While it's true that lower viscosity oils are more energy efficient, their use required engineers and engine builders to redesign and build to tighter tolerances.

Along with better engine materials and build processes, many other improvements, such as throttle-body injection, ported fuel injection, direct fuel injection, and computer-controlled variables have lessened the need for some additives, while increasing the need for others.

Fantastic, the amount of actual knowledge floating around here. As an engineer myself, spending most of my years in management and not actual engineer work, I am amazed you guys seem so current. If a recent graduate engineer were to come up and want me to update him/her on the current state of aeronautics, I think I would stammer and turn bright red. You guys however would give him/her a great lesson. Nice to have folks like you here to get valuable information. Thanks