Debunking Diesels

[jro909]

i've heard through the years alot of info about diesels and i've always wondered whats true and whats not...

 

1) diesels have to idle before driving and before shutdown

2) blowing soot is healthy and not harmful

3) diesels get the same mileage loaded or unloaded

4) Diesels last longer then gassers

 

 

if anybody has any other diesel related questions, lets hear them...

[cc1999]

1) diesels have to idle before driving and before shutdown / Not really

 

2) blowing soot is healthy and not harmful / I doubt it really makes any difference

 

3) diesels get the same mileage loaded or unloaded / False

 

4) Diesels last longer then gassers / Maybe back in the pre-emmisison days (2003-back) Who knows now with all the emmisions crap that has been put on the trucks to satify the tree huggers.

 

Thats my take on it. I have owned several, but I have now switched about everything we own back to gas, do to reliabilty and cost issues related to the new heavily emmision controled trucks that are all that is offered from the mfgs now. In theory part of the reason they use to outlast the gas motors was one Gas motors were maybe not as well made as they are now, but mainly to do with the Diesels several years ago ran much cooler temps than Gas motors. Now with all the new Emmision regulations on the trucks post 2003, the opperating temps are way up there on diesels as well . So who knows how long they will last, and also how well all the emmision BS controls will hold up. I know Ford has had major issues with EGR valves, turbos, heads, ect. So unless you really need the power from a Diesel, I would say the other benefits of years past are history.

[r1byker]

1) diesels have to idle before driving and before shutdown/Like any engine, they should be driven gently until they reach operating temperature. Most diesels now have a turbo and for that reason they need to idle for about five minutes to allow the turbo to cool if one has just gotten off the freeway. If one is putzing around town, no need.

 

2) blowing soot is healthy and not harmful/Well, it's harmful for health, or so says the CARB, which has just put into effect stricter standards for particulate matter. Were you asking about if it's harmful for the motor? If it's blowing smoke, I assume it's creating excess soot, which can build up in the combustion chambers, which is not good. In our work rigs, we're given specific instructions on how to drive it so as not to build up soot in the motor.

 

3) diesels get the same mileage loaded or unloaded/Not true; physics demands that it's going to get worse mileage. I get about 4 mpg better when I'm not towing.

 

4) Diesels last longer then gassers/I'll find out. This is my first oil burner; I would think it would last longer just because it's not working as hard to accomplish the same work. I drive a big rig, and I'm getting ready to turn over 700,000 miles on a 10 year-old truck. Of course, that motor is quite stout, putting out 1,250 ft. lbs. of torque. It's a different animal than what's in our pickups.

[MarkD]

r1byker hit it pretty well. Some extra info

 

1.) In general, the biggest concern for a newer diesel is the turbo. The engine needs to warm up before the turbo is used to generate much boost to ensure proper lubrication of turbo shaft, which spins at tens of thousands of rpm. Same thing when shutting down. "Coking" used to be a big problem when turbo bearings would be very hot, and the oil would stop flowing to them (when engine was turned off). Advances in turbos and lubricants have reduced this problem, but it still exists.

 

2.) Blowing Smoke/Rollin' Coal/Etc is just another way of saying that the engine is being run overly rich. This can be "good' and "bad". Good- overfueling can cool the exhaust temps slightly (above 1250 degrees is generally considered bad). Overfueling is kind of like overpaying your bills. The extra fuel you are wasting will guarantee you will have "enough" fuel for whatever air the turbo can pump through the engine. Bad-Wastes fuel, pollutes environment, upsets treehuggers, contaminates oil, can cause hot spots in combustion and damage piston.

 

3.) Diesel engines by nature are more efficient. I have heard that diesel fuel has more "energy" than gasoline. Diesels are generally designed to work under load. When they are not under load/towing/hauling/etc the turbo does not have to spool to produce power at a certain rpm level and therefore can use less fuel. This is how 8000 lb trucks can get 20+ mpg and still make 600+ ft.lbs of torque. They can't do both at the same time.

 

4.) Pros

a. Diesel engines run at lower rpm, even when making power.

b. Diesel engines have fewer parts (essentially no electrical system)

c. Structurally Diesels are MUCH stiffer, resulting in better control of rotating assembly movement

 

Cons

a. Emission control systems have overcomplicated the drivetrain of current diesel engines

b. More complex usually = more fragile

c. Sulfur helps lubricate the fuel system and combustion cycle

Regular Diesel > 500 ppm of sulfur

Low-Sulfur Diesel < 500 ppm of sulfur

Ultra-Low-Sulfur Diesel <15 ppm of sulfur

Any diesel made after 2007 (that has a diesel particulate filter (DPF) has to run ULSD.

[ken1mod]

Gentlemen,

 

While a diesel definitely burns more fuel loaded than empty, the spread is smaller than a gas burner. My friend the 18 wheeler driver says his rig gets almost the same mileage loaded or unloaded, 8 mpg.

 

Ken

[jro909]

i see alot of cummins, blowing soot...i'm talking like leaving a pile, i was just curious about the questions...kind of curious how junky were the older diesels that diden't run turbos? i think i've seen early 90s powerjokes without turbos and they sounded sickly..

[Shaners]

If a diesel is chipped or turned up it will definetly blow soot under harder acceleration.

[pm26]

I have older Mercedes Diesel cars (83 and 85) and also a diesel 2.5 ton army truck. The diesels on the Mercedes cars are the old 5 cylinder 3.0 liter diesels that have cast iron blocks and a cast iron cylinder head. Cast iron heads do not warp easily and this feature makes these old engines literally bulletproof, unless you overheat them or run them out of oil. Both of these malfunctions can kill a diesel quickly.

 

Diesels have high compression ratio, typically in the 18:1 to 22 :1 range. Compression pressures of a healthy engine are in the 300-400 psi range (as opposed to about 150 psi for a typical healthy gas engine).

 

The advantage of the old diesels is that they have no electronic controls and as long as you supply fuel, air and you have adequate engine compression, the engine will run. If I lose the alternator on either of my Mercedes diesels, I can drive the car all day without running down the battery as long as I do not use lights or other electrical accessories. The injection pump is mechanical, fuel ignition is by compression, and there is no electrical ignition system or injection system to deplete the battery. Multiport fuel injection systems on modern gas engines utilizing electric solenoid injectors, require about 10 amps of current to run. The fuel injection pressure on old diesel engines are in the 2,000 psi range. There are typically no emission controls or catalytic converters. They provided these old Benzes with an EGR valve, which is about it for emissions.

The 2.5 ton truck I have has no emission controls of any kind. Not even a crankcase ventilation valve

 

Modern diesel engines utilize a computerized engine controls and a number of sensors. The engine construction is lighter duty - typically using aluminum cylinder heads. Injection pressures on modern high output diesels are extremely high - in the 20,000 + psi range, or ten times higher than on old diesels. Computer controls make modern diesels run more efficiently, but also mean more mechanical complexity and lower overall reliability. And they are very costly to repair. For example, to replace all fuel injectors on a modern Duramax diesel, you are talking several thousand dollars. I can replace all fuel injectors on my Mercedes for about $ 300.

[ColoradoSkiCountry]

1) diesels have to idle before driving and before shutdown

Like any engine, you want to allow enough time for the engine to warm up before driving. However it is NOT required to let the Turbo "cool down" unlike turbos of old. The Turbos made now a days are designed to not need idle/low RPM driving to cool down.

 

2) blowing soot is healthy and not harmful.

The Diesel's now a days have emission control devices to prevent this. Modifying your engine to blow soot is stupid and pointless (my opinion) and your just asking for a ticket of some sort from Law Enforcement.

 

3) diesels get the same mileage loaded or unloaded

Depends upon the load. Generally you will see a reduction in fuel economy when you haul/tow any load, but it won't be as noticeable with the Diesel as it will be with a Gas motor.

 

4) Diesels last longer then gassers

One of the MANY reasons why Semi's are Diesel powered are because of the longevity and lower cost of maintenance. If you do alot of towing & hauling then sure as hell your Diesel is going to last longer then a Gas motor. If your do light towing/hauling with your gas motor, then it probably will last a long time.

[BlackSilver]

I don't know anything about "bunk" or "debunk".

 

I run diesels because none of the "big three" provides a gas pickup which will pull the crosscountry loads that I need pulled.

[Silverado4x4]

Diesels DO NOT have to idle down before shutting down in pick-up trucks. Semi trucks is differant.

 

Not going to answer the breathing question, who wants to breath black soot?

 

Diesels do not get the same milage unloaded and loaded. Remember the black cloud coming out the exhaust is nothing but unburnt fuel.

 

Gas motors can last just as long as a Diesel motors.

[wtbrowne]

The one thing that I know about diesels is that once you had had a modern turbo-diesel - you won't ever want to go back to gasoline!

[Silverado4x4]

The one thing that I know about diesels is that once you had had a modern turbo-diesel - you won't ever want to go back to gasoline!

 

Not really unless you have a use for a Diesel and not just to say you have one. I had a 04 Dmax that I did boat towing with but after I didnt do boat towing and wasnt planning on doing it anymore I sold the truck because I could see a reason to keep something that I had no use for and the maintance upkeep so I went back to a gas motor.

[Big black truck]

I just sold a 6.7 cummins and have gone over to gas. The diesels are great but even with chips, cai systems and exhausts....they still suck when towing heavier loads. My buddy has an 08 duramax and was getting 7.5 mpg pulling a skidsteer in a dump trailer. We unhooked and loaded it onto my 2001 8.1 and I got 9.5 mpg.

[FarmerDave]

It is highly recommended to idle before shutting down, the turbo can be well over 1000 degrees, if you shut it off hot the oil burns up in the turbo and can damage the bearings. Let it idle for 2 or 3 min after hard driving.

 

Blowing soot is not healthy, nor is it unhealthy for a diesel. Modern diesels should rarely produce black smoke. Common rails gradually step up fuel rates as boost increases to avoid the black smoke, older diesels do not. Punch the throttle on an older diesel and black smoke is to be expected until the turbo spools up and produces enough boost.

 

Diesels do not get the same mileage unloaded vs loaded, ever, even in transport trucks. For example, a transport truck pulling a trailer with a total weight of 120 000 lbs, you will be using probably close to 25 gal/hr of diesel. If you are driving empty and the total weight of the truck with trailer is 50 000 lbs for discussions sake, you should expect to use 15 gal/hr. Not 12.5 because wind resistance usually does not change assuming your still pulling a trailer.

 

Comparable sized diesels will always out last a gas engine with similar driving histories. Every single component in a diesel engine is built stronger than in a gasoline engine.