The 250,000 Mile Engine
03-09-2008, 10:22 AM
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2008 GL 320, 2007 Silverado LTZ C3500 Duramax Turbo Diesel
The 250,000 Mile Engine
I found this Popular Mechanics article posted on the ML forums. This is one excerpt but it is a pretty good read.
The 250,000-Mile Engine
ULSD fuel and the new exhaust systems receive most of diesel’s accolades, but they aren’t the only advances to set today’s diesels apart from their predecessors. Advanced electronic engine control modules regulate functions, from fuel injection to timing, more precisely than old mechanical control systems, further minimizing emissions and maximizing fuel economy. Turbochargers pump more air into the engines, helping to overcome diesel’s former sluggishness at higher rpm. And improved engine isolation strategies, such as the incorporation of active mounts, has quieted the knocking noises typically associated with diesel-powered vehicles.
Meanwhile, diesel’s core virtues remain unchanged. The fuel contains more energy per unit volume than gasoline, and diesel engines operate at higher compression ratios than gasoline engines—typically 14:1 to 25:1, compared to 8:1 to 12:1. (The compression ratio is the relationship between the volume of the cylinder when the piston is at the bottom of its stroke and the volume when it’s at the top.) The higher the compression ratio, the more mechanical energy an engine can squeeze from its fuel/air mixture. So each time the mixture in a diesel engine’s cylinder ignites, the car gets a slightly bigger push than it would in a gasoline engine. That means it takes less fuel to move the car down the road. It also means that the engine generates a lot of power even when it isn’t cycling fast—and that’s the source of the beefy low-end torque these vehicles are famous for.
The high compression ratios also explain why diesel engines tend to last so long. “Diesel engines need to be built stronger,” explains Tony Molla, author of Chilton’s Diesel Engine Service Manual. “The crankshaft and connecting rods are quite a bit heavier than those in gasoline engines.” And because diesel has a low coefficient of friction, it also happens to be a good lubricant that provides protection to the cylinder walls. The result? It’s not unusual to see diesel engines still chugging along at 250,000 miles.
ULSD fuel and the new exhaust systems receive most of diesel’s accolades, but they aren’t the only advances to set today’s diesels apart from their predecessors. Advanced electronic engine control modules regulate functions, from fuel injection to timing, more precisely than old mechanical control systems, further minimizing emissions and maximizing fuel economy. Turbochargers pump more air into the engines, helping to overcome diesel’s former sluggishness at higher rpm. And improved engine isolation strategies, such as the incorporation of active mounts, has quieted the knocking noises typically associated with diesel-powered vehicles.
Meanwhile, diesel’s core virtues remain unchanged. The fuel contains more energy per unit volume than gasoline, and diesel engines operate at higher compression ratios than gasoline engines—typically 14:1 to 25:1, compared to 8:1 to 12:1. (The compression ratio is the relationship between the volume of the cylinder when the piston is at the bottom of its stroke and the volume when it’s at the top.) The higher the compression ratio, the more mechanical energy an engine can squeeze from its fuel/air mixture. So each time the mixture in a diesel engine’s cylinder ignites, the car gets a slightly bigger push than it would in a gasoline engine. That means it takes less fuel to move the car down the road. It also means that the engine generates a lot of power even when it isn’t cycling fast—and that’s the source of the beefy low-end torque these vehicles are famous for.
The high compression ratios also explain why diesel engines tend to last so long. “Diesel engines need to be built stronger,” explains Tony Molla, author of Chilton’s Diesel Engine Service Manual. “The crankshaft and connecting rods are quite a bit heavier than those in gasoline engines.” And because diesel has a low coefficient of friction, it also happens to be a good lubricant that provides protection to the cylinder walls. The result? It’s not unusual to see diesel engines still chugging along at 250,000 miles.
03-09-2008, 11:37 AM
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Thanks Scotty, great article. I had a diesel in 1984 that oozed oil, black smoke and rattled so loud that your teeth chattered, but I drove it for 190,000 miles. Today's diesels are fantastic. I notice you have a duramax also Do you know how reliable the tdiVW engines perform?
03-09-2008, 03:46 PM
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2008 GL 320, 2007 Silverado LTZ C3500 Duramax Turbo Diesel
Thanks Scotty, great article. I had a diesel in 1984 that oozed oil, black smoke and rattled so loud that your teeth chattered, but I drove it for 190,000 miles. Today's diesels are fantastic. I notice you have a duramax also Do you know how reliable the tdiVW engines perform?
03-09-2008, 10:45 PM
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The lack of understanding of simple mechanics is mind boggling.
First thing necessary when compression pressures are high is enough beef to make the engine last as long as a low compression engine.
Whether even more beef is added is up to the manufacturer based on the market the engine is designed for.
Diesel = 250K miles is NOT cause/effect.
First thing necessary when compression pressures are high is enough beef to make the engine last as long as a low compression engine.
Whether even more beef is added is up to the manufacturer based on the market the engine is designed for.
Diesel = 250K miles is NOT cause/effect.
03-13-2008, 03:56 PM
#5
somewhat misleading article- i agree....
diesel engines last longer for one simple reason- lower revs required to accomplish the same amount of work (due to higher compression and usually forced intake).
the higher compression is actually an enemy to longevity because worn piston rings have much greater negative effect on high-compression engine than on low-compression one...
overbuilding of diesel engines is not because of higher compression requirements, but because of the lugging nature of their work- they do their work at low rpms where the load on the reciprocating assembly is greater.
alex
few cars
diesel engines last longer for one simple reason- lower revs required to accomplish the same amount of work (due to higher compression and usually forced intake).
the higher compression is actually an enemy to longevity because worn piston rings have much greater negative effect on high-compression engine than on low-compression one...
overbuilding of diesel engines is not because of higher compression requirements, but because of the lugging nature of their work- they do their work at low rpms where the load on the reciprocating assembly is greater.
alex
few cars
03-13-2008, 04:13 PM
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somewhat misleading article- i agree....
diesel engines last longer for one simple reason- lower revs required to accomplish the same amount of work (due to higher compression and usually forced intake).
the higher compression is actually an enemy to longevity because worn piston rings have much greater negative effect on high-compression engine than on low-compression one...
overbuilding of diesel engines is not because of higher compression requirements, but because of the lugging nature of their work- they do their work at low rpms where the load on the reciprocating assembly is greater.
alex
few cars
diesel engines last longer for one simple reason- lower revs required to accomplish the same amount of work (due to higher compression and usually forced intake).
the higher compression is actually an enemy to longevity because worn piston rings have much greater negative effect on high-compression engine than on low-compression one...
overbuilding of diesel engines is not because of higher compression requirements, but because of the lugging nature of their work- they do their work at low rpms where the load on the reciprocating assembly is greater.
alex
few cars
The bottom line is they are definitely built heavier than gas engines, even today. If not, they would eat themselves and would be a very low mile engine. You are correct in that worn rings, which cuase "blow by," is amplified by higher compression. I also agree that low RPM's, due to longer strokes, due to a higher energy slower burning fuel, results in greater longevity.
03-13-2008, 04:58 PM
#7
yes, i was thinking the same thing... could not quite piece which was the cause and which was the effect... 
however, one thing is for sure - one of the diesel engine design requirements was to produce maximum torque and low rpms since the sole purpose for the engine was so farmers can use it in farm equipment and manufacture their own fuel...
alex
few cars
however, one thing is for sure - one of the diesel engine design requirements was to produce maximum torque and low rpms since the sole purpose for the engine was so farmers can use it in farm equipment and manufacture their own fuel...
alex
few cars
