Why are diesel oils "heavy duty?"

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I'm somewhat of a newbie but I was wondering tonight why diesel engines would require a HDEO. Diesel engines should be easier on oil than gas engines according to my understanding. Diesels run at a lower RPM and I think they run cooler if I'm not mistaken. Also, we all hear of OTR trucks logging hundreds of thousands of miles and some even reach a million. Rarely do I hear of a gas engine making it to 300,000 miles let a alone a million. So why would a diesel engine need a HDEO?
 
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Not only fuel but and soot as well... Diesel engines run at a lower RPM yes, but have a lot more torque output, which is harder on the oil at the bearings. Turbos are also present on almost every diesel nowadays, those run over 1000F on the hot side..A couple hundred in the bearings. Then you have Older Caterpillars and Internationals with HEUI running the secondary HP oil in the quadruple digit PSI range.
 
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Im sure the fact the big truck Diesels are 10x the mass of a gasoline engine alone, that has something to do with it. Pistons the size of a small dinner plate.. Ive worked on some bigass engines (I have training as a truck mechanic) and the sheer size and materials used are definitely a factor in the longevity of the big diesels. I learned to do a top end set for example on a CAT 3406. The engine is something like 3,000 lbs. Engine hoist and heavy chains to remove the cyl. head. I really just assume that this is a factor in why they last for so many miles...
 
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diesels also run much higher compression than gas engines. their longevity is a combination of the lower rpm's; better metalurgy; and the duty cycle (more continuous use with fewer cold starts); and also oil capacity. diesel trucks hold 40 or more quarts of oil.
 
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Sulfur levels traditionally have been <i>much</i> higher in diesel fuel than in petrol. The major difference between petrol and diesel-rated motor oils has traditionally been the additive package -- obviously far higher levels of H2SO4-neutralizing additives in diesel-rated oils than the petrol-rated oils.
 

dnewton3

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HDEO is just a moniker that got placed upon the products many, many years ago. You might even question the breakdown of the wording, because you can view it a few different ways. 1) Heavy-duty-engine oil; meaning an oil for heavy-duty designed engines 2) Heavy-duty engine-oil; meaning an oil that is designed above the "norm" of "typical" oils That's splitting hairs, for sure. Just accept it for what it means; HDEO is an abreviation for products that are rated for compression-ignition engines. Regarding the need for HDEO in a diesel engine, they typically are run for longer OCIs; they often see more extreme environments (such as off road equipment); they often have turbo chargers; etc. EGR is now as prominenet in diesel engines as it has been for years in gas engines. Soot loads are higher in diesel fueled engines. This list is long.
 
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 Originally Posted By: Jaymus
HDEO = twice the additives, half the price PCMO = half the additives, twice the price ;-)
\:\!
 
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 Originally Posted By: Jaymus
HDEO = twice the additives, half the price PCMO = half the additives, twice the price ;-)
Try this. HD truck battery Size 31 120 AHr $85 Canadian. 12N16-3B Motorcycle battery 16 AHr $95 Canadian. This motorcycle battery is about 1/6 the size of the truck battery and it only gives me three years of service life on my BMW.
 
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 Originally Posted By: dnewton3
Yup; if the big three (Delo, Delvac, Rotella) were available in 5w-30 dino HDEO, it'd likely be the only oil my garage ...
Hey D, Rotella makes a 5W30...but I don't know if it meets your current requirement for specs. ;\)
 

dsmith41

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 Originally Posted By: D-Roc
Hey D, Rotella makes a 5W30...
Really? It's not on their website as far as I can see. Is this like an inside joke or something?
 
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Hi, dsmith41 - The HD notation was once thought to mean "High Detergency" but has been taken as "Heavy Duty" for several decades It is almost entirely to do with the combustion processes (two & four stroke, direct & pre-chamber etc.) used in diesel engines (especially prior to electronics). This of course embraces fuel quality as well! Diesel engines also have a variety of components of a different type and concept to petrol engines, the metallurgy can be different and the use/applications are wide and varied - from constant speed to all else. Of particular concern is internal deposits (cumbustion area & engine components) which until a decade or three back required frequent OCIs The move to electronics in small high speed diesel engines has greatly reduced the need for "HD" lubricants as can be seen from many Manufacturer Approvals - "CF" being a common multi Quality rating used often with present lubricant recommendations (eg SM/CF) Euro diesel engine design philosophies have let to enormous advances in engine refinement starting in the 1970s. This was caused by the price of crude oil and its availability! I have used HD lubricants in my petrol engines now for around 50 years! I hope this helps you
 
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 Originally Posted By: dsmith41
 Originally Posted By: D-Roc
Hey D, Rotella makes a 5W30...
Really? It's not on their website as far as I can see. Is this like an inside joke or something?
Yeah, you called me on it....I was just yanking yer chain.
 

dsmith41

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 Originally Posted By: D-Roc
Yeah, you called me on it....I was just yanking yer chain.
You had me all excited there for a second! Don't do that to a guy. Okay, I am an oil nerd. I think I fit in here though.
 
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 Originally Posted By: SLCraig
Im sure the fact the big truck Diesels are 10x the mass of a gasoline engine alone, that has something to do with it. Pistons the size of a small dinner plate.. Ive worked on some bigass engines (I have training as a truck mechanic) and the sheer size and materials used are definitely a factor in the longevity of the big diesels. I learned to do a top end set for example on a CAT 3406. The engine is something like 3,000 lbs. Engine hoist and heavy chains to remove the cyl. head. I really just assume that this is a factor in why they last for so many miles...
That is a small diesel engine. Locomotive engines are medium sized. Ships' engines (100,000+ hp) are big diesels. I can get my head & shoulders in the crankcase access ports on a medium diesel. I get into the cylinder with a ladder in a big diesel and get into the crankcase with a crew of men. We use chain hoists to lift bearing shells and gantry hoists to lift 7-ton individual cylinder heads. The loads inside diesel engines are higher than inside gasoline engines. Thus the need for stouter engine construction and more robust oils, plus the contamination from soot, acid, and the need for longer drain intervals.
 
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