# Why do diesel motors last longer than gasoline motors?



## MOTO13 (Mar 26, 2014)

I'm no mechanic, but the simple lubricity of the fuel has to be a big factor.


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## obermd (Mar 3, 2012)

Gasoline is very caustic to rubber and plastic; diesel isn't. Seals and other non-metal components in gas engines tend to wear out quicker as a result. As for longevity, we have a few members over 100,000 miles with their Diesels and CruzeEcoBlueTopaz has close to 300,000 miles on his 2012 ECO MT. When taken care of the Cruze is generally a very durable car.


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## spacedout (Dec 7, 2010)

If you compare equal or close to it sized gas and diesel engines the diesel will be way heavier. This extra weight I assume comes form needing to contain the higher compression, the block and head being made beefier.


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## boneheaddoctor (Dec 10, 2014)

Many reasons. Diesel burns in a slow controlled manner, gasoline abruptly explodes, diesels are built heavier due to the very high compression ratios, most diesels also tend to turn slower RPM's than most gas engines...there are others as well.


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## warloc (Dec 10, 2013)

I'm no expert either but I now own two diesels, the CTD and a Ford F-250 SD. The biggest difference between a gasser and diesel motor is the operating RPM. My diesels run at less than 2000 RPM on the freeway at 70MPH, most gassers run higher RPM's so I would expect a lot more miles out of the diesel motor. I had a Mazda that would turn 3500 RPM to do 70 MPH, my older corvette turns 3000 at 70. The motors are typically built much more stout for the higher compression and power generated with diesel also.


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## MOTO13 (Mar 26, 2014)

With slower revving and lower RPMS, do diesels generate less heat? This would lend itself to a longer lifespan.


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## ChevyGuy (Dec 13, 2014)

Along with the above reasons, I'd suggest that it's also the duty cycle. I'll bet a typical diesel probably runs far more miles per thermal cycle than a consumer auto. The problem with running cold is that parts don't fit together well because heat expands things at different rates. This causes more wear.


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## roadrunnerA12 (Jan 21, 2015)

Boneheaddoctor, I think you've got it backwards. Gasoline engines burn the fuel slowly, otherwise you get "knock" aka detonation, which can break chunks of pistons off, etc. Diesel engines, being compression ignition, "run in detonation". That is why they are so noisy - gas phase detonations are much louder than slow burning gasoline combustion. That's why diesel pistons are so thick on top - to resist detonation damage all day long. As you may know, automotive engineers worry so much about "knock" (detonations) in gasoline engines that they are all now equipped with knock sensors (high tech fast acting stethoscope, sort of) which quickly retard timing if knocking is sensed.


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## NickD (Dec 10, 2011)

Very true with a Cummins and Detroit, over 3 million miles before even an overall is required, diesel locomotives are ran for a continuous seven years, then ships.

But not with a 1981 Cadillac, time will tell with the Cruze.


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## boneheaddoctor (Dec 10, 2014)

roadrunnerA12 said:


> Boneheaddoctor, I think you've got it backwards. Gasoline engines burn the fuel slowly, otherwise you get "knock" aka detonation, which can break chunks of pistons off, etc. Diesel engines, being compression ignition, "run in detonation". That is why they are so noisy - gas phase detonations are much louder than slow burning gasoline combustion. That's why diesel pistons are so thick on top - to resist detonation damage all day long. As you may know, automotive engineers worry so much about "knock" (detonations) in gasoline engines that they are all now equipped with knock sensors (high tech fast acting stethoscope, sort of) which quickly retard timing if knocking is sensed.


Not really...diesel DOES burn slower.....thats a large reason why diesels run lower RPM's, when you get much above 6,000 rpms the fuel is still burning when the exhaust valves open. Both of My mercedes are goverened to 5,400 rpm, a slight adjustment to the IP will let you go further before it starts pulling back fuel, You aren't going to throw rods on that engine until something above 6,700 rpm, way past its peak power range anyway. I've ran mine over 5K rpm for hours on end on midwest highways. Don't try that on most other diesels. 

Knocking on a gas engine is more a result of the fuel igniting BEFORE its intended time for a number of reasons...but a higher octane gas does burn slightly slower than lower octane does. And like Gas, diesel does come in different grades...but you genrally have a lot harder time finding the better stuff in many areas, which has a higher CENTANE rating. You can tell the difference between a low centane and a high centane diesel....the Higher runs smoother, quieter and makes more power.


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## Cruze2.0TD (Feb 12, 2014)

I've often wondered with diesels if it has something to do with the type of driver's that buy them. It seems that the majority of people who buy diesels drive a lot. Driving 100k miles in 2 years with all highway driving everyday is a lot easier on a vehicle than driving 100k miles in 10 years with a short city commute everyday. Although, I do think diesel provides some lubrication that gas does not, the engines are built stronger, they run cooler, diesel burns slower, and they turn a lower RPM. So, my guess on why diesels last longer would be a combination of all the things I listed above.


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## rajon (Mar 11, 2015)

boneheaddoctor said:


> Not really...diesel DOES burn slower.....thats a large reason why diesels run lower RPM's, when you get much above 6,000 rpms the fuel is still burning when the exhaust valves open. Both of My mercedes are goverened to 5,400 rpm, a slight adjustment to the IP will let you go further before it starts pulling back fuel, You aren't going to throw rods on that engine until something above 6,700 rpm, way past its peak power range anyway. I've ran mine over 5K rpm for hours on end on midwest highways. Don't try that on most other diesels.
> 
> Knocking on a gas engine is more a result of the fuel igniting BEFORE its intended time for a number of reasons...but a higher octane gas does burn slightly slower than lower octane does. And like Gas, diesel does come in different grades...but you genrally have a lot harder time finding the better stuff in many areas, which has a higher CENTANE rating. You can tell the difference between a low centane and a high centane diesel....the Higher runs smoother, quieter and makes more power.


Well put. I built a ridiculously over boosted knock happy L67 once upon a time so I became an expert in knock and preventing it. The higher the octane rating, the higher the resistance to ignition. Octane doesn't really affect the speed of the burn but makes it harder to ignite so it can be run at higher pressure and temperature without detonating before the cylinder reaches TDC (top dead center). This is why knock, or predetonation, is so detrimental to the cylinders - the cylinder head is moving at tremendous speed to raise the compression in the cylinder. If it is not on the negative stroke the force of the detonation is absorbed by the cylinder head rather than being transferred to the crank shaft. 

Diesel burns slowly and ignites predictably under very high pressure hence our ridiculously high pressure injectors. If a little gas injector was put in a diesel cylinder the fuel would have enough pressure to actually enter the cylinder. 

Sorry. I geek out about this stuff and it is my first diesel automobile.


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## JRB'sOilburningCruze (Feb 25, 2015)

I always thought it was the lubricating quality of diesel fuel, as well as being built pretty stout to handle the high compression.

As well as gasoline tends to be an abrasive.


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## ChevyGuy (Dec 13, 2014)

My understanding is that diesels (at least classic diesels) normally ping. That's because the ignition of the fuel can't be timed like it can with a spark plug. That's why the engines are so big - so they can survive ping all day long. But I think with recent advances (direct injection?) they're better able to time to to reduce the noise and improve performance.


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## boneheaddoctor (Dec 10, 2014)

ChevyGuy said:


> My understanding is that diesels (at least classic diesels) normally ping. That's because the ignition of the fuel can't be timed like it can with a spark plug. That's why the engines are so big - so they can survive ping all day long. But I think with recent advances (direct injection?) they're better able to time to to reduce the noise and improve performance.


Diesels have timing just like any other engine. Because it does need injected at the correct point of the cycle...and a few degrees either way really does matter. Just like ignition timing in a gasser.

The noisy ones most people think about are the older IDI (indirect injection) engines...where the fuel is not actually injected OR ignited in the combustion chamber, but the prechamber. Our Cruze Diesels are of the newer direct injection type where the fuel actually IS injected into the combustion chamber. Injection on the newer engines isn't a single injection, but usually a series of various length injections.

ThisCruze is actually the FIFTH diesel vehicle I have owned....and I still have three others, the 1979, the 1983 and the 1987 vehicles in my signature, the other three are gasoline. I need to get rid of a few.


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## Aussie (Sep 16, 2012)

Knocking in diesel engines is no longer happening. The diesel rattle you hear is the injectors working. I have the Australian Cruze with a newer designed diesel to the one used in the US. The red line is at 4,500rpm and the engine almost never gets over 3,000rpm.

View attachment 138506


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## mr overkill (Dec 1, 2013)

coming from a mechanic 

1. Less cruzing rpms
2. less causic fuel
3. MUCH beefier parts
4. Less operating temps 
5. the fuel acts as lubricant


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## boneheaddoctor (Dec 10, 2014)

Just remembered something others have mentioned. Lubricity of the fuel. That USED to be true, but todays Ultra low sulfur diesel the Environazis imposed because of the excessive emissions controls...actually has very poor lubricity, the sulfur that used to be in it actually provided most of the lubricity. Older mechanical injection pumps tat REQUIED the lubricity by design, will eventually destroy themselves without additives without putting additives into the fuel on your own dime to compensate.


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## Aussie (Sep 16, 2012)

Diesel is still a lot more oily than ULP. I think it is the low Ctane used in US fuel that causes the VW problems, here in Australia the minimum standard is 50 Ctane and the VW fuel pump seems to last better.


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## jblackburn (Apr 14, 2012)

Lower revs and higher-strength components needed to make power at lower revs.

If you were to pile on boost to a gas engine @ 1500 RPM, it would bend the rods.

The extremely high compression ratios necessitate higher-strength materials for rest of the motor, too.

Remember when GM tried making a Diesel out of a Gas 350? They blew head gaskets and stuff like crazy because it wasn't built strong enough.


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## jalaner (Dec 28, 2013)

Environazis? The adoption of ULS diesel fuel was a prerequisite to make the entire selection of eco diesel vehicles available. Sulfur in diesel fuel is converted to toxic sulfur dioxide (SO2). Add a little water and corrosive sulfuric acid (H2SO4) is produced, damaging the complex and costly ecodiesel emissions systems. I drove a 1985 Mercedes 300D for many years (purchased new). Great highway car but the clouds of toxic smoke produced made me feel sorry for anyone who had to follow me. The fumes also seeped into the cabin in city traffic causing irritation. Just unsatisfactory for a luxury car and dangerous for people with preexisting lung problems. My CTD is twice the car for half the money. The major fuel economy advantage of diesels is produced because of less waste heat compared to gassers. This decreases wear to the engine and adjacent underhood components. The lubricity of the fuel (vs gas), required robust diesel engine construction and low rpm torque all add up to increased diesel longevity.


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## Invierno (Nov 23, 2012)

obermd said:


> As for longevity, we have a few members over 100,000 miles with their Diesels and CruzeEcoBlueTopaz has close to 300,000 miles on his 2012 ECO MT. When taken care of the Cruze is generally a very durable car.


The diesel Cruze hasn't been out too terribly long, and people already are hitting 100k?!?! My 2012 Cruze (gas) has 45k, and _*I*_ thought I drove it a lot! Who the heck has *300,000 miles on a 2012 *car of ANY make or model!??!?! 


I didn't even know the Cruze was available in 2012 either, I thought it was a 2013+ release?


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## jblackburn (Apr 14, 2012)

> I didn't even know the Cruze was available in 2012 either, I thought it was a 2013+ release?


2011, showed up here late 2010 as a 2011 model.



> Who the heck has *300,000 miles on a 2012 car of ANY make or model!??!?! *


http://www.cruzetalk.com/forum/27-fuel-economy/13400-monthly-avg-mpg-log-4.html#post1721329

That guy, he's a courier.


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## Gator (Jul 14, 2013)

70000 0n my 2014 diesel and still happy happy happy


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## KpaxFAQ (Sep 1, 2013)

boneheaddoctor said:


> Just remembered something others have mentioned. Lubricity of the fuel. That USED to be true, but todays Ultra low sulfur diesel the Environazis imposed because of the excessive emissions controls...actually has very poor lubricity, the sulfur that used to be in it actually provided most of the lubricity. Older mechanical injection pumps tat REQUIED the lubricity by design, will eventually destroy themselves without additives without putting additives into the fuel on your own dime to compensate.


This issue has been remedied in 99% of diesel you get at the pump. In fact samples from random pumps around the country have shown wear scars to be equal or lower to pre-ULSD. The refining industry has adjusted since the initial launch of ULSD. I feel like 3,000mi oil changes this myth will continue for at least another decade or two.


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## boneheaddoctor (Dec 10, 2014)

Aussie said:


> Diesel is still a lot more oily than ULP. I think it is the low Ctane used in US fuel that causes the VW problems, here in Australia the minimum standard is 50 Ctane and the VW fuel pump seems to last better.


50 Centane, you lucky stiff. We are lucky to get 40 Centane around here where I live.


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## money_man (Feb 25, 2014)

boneheaddoctor said:


> 50 Centane, you lucky stiff. We are lucky to get 40 Centane around here where I live.


Minimum in Canada is 40 cetane. Shell claims there v-power diesel is 50 cetane however I notice no mpg increase or power increase. So I don't fully understand the bonus of the higher cetane. Engine sounds the same as well


Sent from the sexy electrician


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## Aussie (Sep 16, 2012)

money_man said:


> Minimum in Canada is 40 cetane. Shell claims there v-power diesel is 50 cetane however I notice no mpg increase or power increase. So I don't fully understand the bonus of the higher cetane. Engine sounds the same as well
> 
> 
> Sent from the sexy electrician


I suppose it is like the octane rating in petrol, you can't really tell much difference, but the higher numbers are better for the engine even though it is difficult to notice any difference. As diesel engines don't ping when the fuel is of a lower quality you really wouldn't feel any difference.


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## boneheaddoctor (Dec 10, 2014)

Aussie said:


> I suppose it is like the octane rating in petrol, you can't really tell much difference, but the higher numbers are better for the engine even though it is difficult to notice any difference. As diesel engines don't ping when the fuel is of a lower quality you really wouldn't feel any difference.


You would notice the difference on the noisier IDI diesels....


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## jalaner (Dec 28, 2013)

I'm a lot more concerned about rancid or water contaminated biodiesel causing damage to my CTD than ultra low sulfur fuel. Its not even labeled as biodiesel if < 5%. I lost trust with all biofuels after spending a lot of $ replacing sensors caused by using E10 in my 2001 BMW 740i. The BMW owners manual has warnings about ethanol related problems, similar to the biodiesel warnings in the CTD manual. I now pay extra running E0 in the BMW but it runs better, gets better fuel mileage and requires less repairs. Biofuels are just a scam to increase Monsanto profits.


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## diesel (Jun 8, 2013)

Gator said:


> 70000 0n my 2014 diesel and still happy happy happy


You're on my tail! lol


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## boneheaddoctor (Dec 10, 2014)

jblackburn said:


> Remember when GM tried making a Diesel out of a Gas 350? They blew head gaskets and stuff like crazy because it wasn't built strong enough.


Actually that was an urban legend. Also, the real issue with the head gaskets was they had was poor quality head bolts. Marginal clamping ability at best...plus people used starting fluid when glow plugs really needed replacing...and pushed may of those over the line. 

They didn't make much power, but they did get incredible mileage even without overdrive transmissions on big heavy cars ....but the later ones where the head bolt issues were resolved , would last a very long time. I have a master machinist/mechanic friend in North Dakota that put an incredible number of miles on several of them...the engines still running strong when the cars disolved around them eventually.


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## KpaxFAQ (Sep 1, 2013)

In my experience the only benefit of higher cetane is easier and more smooth cold starting. It seems to me once the engine AND fuel are both at temperature it really isn't that important at that point for normal operating parameters. I'm sure if you're dynoing something, etc there are measurable differences but not to the casual operator. 

That's my personal experience I'm not educated enough in specifics to state it as a fact.


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## KarlZap (Jun 30, 2015)

Now I can see that diesel owners know what they are talking about. Good posts folks! Only one thing that was not mentioned, diesel fuel is approximately 40% more efficient that gasoline (so much less fuel has to be burned for the same effect). Everything else mentioned are real factors as to why a diesel motor lasts longer, fuel, beefier parts, lower RPM. Again, you diesel owners seem much more intelligent than average.


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## oilburner (Jun 13, 2013)

WVDave said:


> My 2014 Cruze Diesel just hit 23,000 miles and I couldn't be more pleased with it. We just took a 3,000 mile trip to Florida and back and it's highway cruising ability was on full display. On most cars I've owned my goal is to get 100,000 miles out of them before trading them in. With this Cruze Diesel I'm almost a quarter of the way there, but I have my sight set on 200,000 miles. I hope the better suspension, brakes and heavyduty transmission will contribute to the car's longevity, but I'm really counting on the historic expectation that a diesel engine will last much longer than a gasoline engine. Prior to retirement, I was a school transportation administrator (not a mechanic) and know that even with the heavy usage on a school bus the engines lasted longer than the buses, to the point that when we sold the buses, some buyers bid on the buses just to get the motors. What is it about the diesel motors? Since they operate at a higher compression than gasoline engines one might anticipate similar wear and tear on pistons and rings. They don't have spark plugs but have the same number of valves and although operating at a lower rpm, still have comparable combustion cycles. Is it possible the greater lubrication in the diesel fuel coats and protects the cylinder walls while gasoline removes the oil film? Is the engine block just built stronger?


everything you said an lower rpm. if they where to build a heavy duty gas engine it would be similar to a diesel.


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## oilburner (Jun 13, 2013)

generally speaking diesels are over stroked to produce torque . small bore long stroke lower RPMs.
gas are more over bore, short stroke higher RPMs.


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## diesel (Jun 8, 2013)

My engine has 134K miles on it now and still runs like it did brand new. Zero oil consumption and full power.


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## NickD (Dec 10, 2011)

Injector pumps have disappeared like the distributor has in gas engines.










Would be a hose for each injector, difficult to time and fire about a 1,500 psi pulse. Using electronic solenoid stuff now and engine monitoring with computers and all that for the precise dwell and timing.

Detonation is not a problem, because when that piston goes up, just compressing air, not an air fuel mixture like typical gas engines. For gas, the compression ratio has to be extremely low, no limits with a diesel, but typically around 20:1. But has nothing to do with the fuel, direct fuel injection is the key. Also with that high compression ratio, that air gets very hot, so a spark plug is not required.

Can also use direct injection with gas, even some new vehicles have this, fuel economy can be increased as much as 30%, but 10% is more common. Reason, not putting pure oxygen in the combustion chamber, but with 80% nitrogen where if the combustion chamber temperatures start to approach around 2,200*F NOx emissions will start to occur, not good for the air nor us humans. So the fuel ratio has to be much higher to get that additional cooling, reducing fuel economy. Could eliminate the nitrogen. Doesn't do anything anyway except use up space. 

Sure a diesel engine has to be designed more robust than a gas engine, compression ratios are much greater. But has more to do with the market target than anything else, namely consumer, industrial, or military. Consumer is considered throwaway with very limited life. Typically industry is the most reliable, military is lot like a drag strip for extra performance and thus requires a heck of a lot of additional maintenance. 

One key advantage of diesel or even jet fuels, at lower levels, in the refinery stage than super high octane fuels for gas. And a lot more of it is available. Use to see this at the pumps, diesel fuel was much cheaper than regular gas. But add this to the history books, not just as expensive as regular or even more so at the pumps. But has nothing to do with technology or econmics, strictly politics. 

Yes, a gas engine can be designed just as robust or even more robust than a diesel engine, contribute this to marketing. Diesels also have more emission problems than gasoline, but ironically, the EPA for years turned their heads on diesels, because they love to pick on the little guys. But more recently, starting to take a look at it.

Early automotive engine were all under square, meaning the stroke of the engine was much larger than the bore. But the cheapest way to get more HP was to increase the bore. With that very short combustion cycle translated to very poor fuel economy, but satisfied the need for speed that you can't do anyway.

Cruze 1.4L finally reverted back to an under square engine, and could even go a lot more. Does decrease rpm, and with that longer lever, producers more torque that you really need to climb a hill. Key advantage of a longer stroke is gathering more energy to power the vehicle with a much longer combustion period. But some are still interested in performance so they can squeal tires at traffic light only to slam on their brakes for the next one. Love to pass these idiots up by good timing.


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