Please Educate Me on Diesel Engines

Diesel is in my future for a variety of reasons and applications. It turns out it's sooner rather than later as I need to buy a new vehicle sometime in the next two months, and have decided that it will be a 4 door 4WD truck with a diesel engine. Diesel, primarily because I need for economic reasons to buy an older truck, and I know that diesel engines can get 500,000 miles if properly taken care of. Diesel, because it's time to take that step.

Beyond the truck, I see a diesel generator in my future, and will likely have other diesel powered vehicles when I escape surburbia in about five years.

I've been reading up, but there is nothing better than the collective practical experience of a mess of monkeys, especially when it's from a surviving perspective. So, please educumate me on things diesel.

 

When I purchased my 2004 F-250 the salesman tried to sell me the diesel engine, should have got it and I kick myself for it often.

 

EEK! All of the new trucks require the use of diesel exhaust fluid and have a multitude of additional sensors that are prone to failure. When (not if) they do fail, they will reduce power, some to the point of not being driveable. If you can get away with a slightly older model that does not have the DEF system, I would recommend that route.
But that's just me...

 

Let's start with truck motors, since that's in my near future. I'm looking at practical issues - are there some engines that last longer and work better than others? Any that I should avoid? Also, any easier to maintain and any maintenance tricks? I've also heard about systems that provide better oil filtration to extend engine life. Same for add on electronics that improve mileage and power. Basically, what does a curious chimp need to know before he lays down the money.

 

I thought the older diesels have trouble running the newer low sulfur fuel.

 

I've heard of that. The truck will likely be somewhere between 1995 and 2005, so I should be safe there.

 

Ones between about 2004 and 2010 seem to be doing ok on the ultra-low sulfur fuels...the older ones do ok, but I am seeing several injector issues cropping up. Old age or the new fuel, I can't with certainty state...

 

@techsar if you were buying a diesel truck today what would you buy?

 

Well, there are two ways I might go. First would be an older GM/Chevy with a 6.5 turbo and the non-electronic controlled injection pump. Finding one in good shape would be tough.
Second would be a Dodge with the 5.9, prior to the common rail injection setup.
The GM rides better, but the Dodge has tons of torque...both are capable of 20+ mpg.
The Ford 7.3 ((94 1/2 and prior) are simple reliable engines, but are kinda slooow on acceleration.
There are options to get rid of the DEF systems on the new trucks, but voids the warranty and will cost a bunch to convert (like around $3k - $4k) and that just bugs me

 

by an older one and run the dyed stuff in it ,,....
the say that the engine the came in the late 90s ford are the best engines ever made {just what ive heard} i think its the 7.62 liter or something like that ...
also it all dependes on who owned it and how they treated it and how you are gonna treat it and what u plan on doing with it ....

 

Thank you and I am now slightly more educumated... Now that that is settled, whaddya know about diesel engines that can help us ignorant monkeys?

Edit: note thread title change. One more grain of knowledge has been added to my rocky beach.

 

Running the red dyed fuel can get you a hefty fine...but you have to get caught first. Remember that many places don't filter the ag fuel quite as well...

 

There are a couple key years to consider:
2007 was the year that OBD II diagnostics became mandatory on diesel vehicles between 8500 and 14,000 points gross vehicle weight, hence affecting pickup trucks. The first year the manufacturers were trying to get the wrinkles out. The diagnostics were less problematic come the 2009 models.

2010 the emissions levels dropped and most diesel engines started using diesel exhaust fluid (DEF) which is 32.5% urea fluid made with very pure water (don't use agricultural 28 urea! It will kill the catalyst). In addition to the lower emissions and increased OBD requirements from California Air Resources Board (CARB) the US EPA mandated what is called SCR Inducement regulations.

The selective catalytic reduction system (SCR) is the catalytic convertor system that uses the DEF and needs the ultra low sulfur fuel. Sulfur will poison the catalytic converter and kill it so it stops converting nitrous oxides into nitrogen and water with the aid of the urea. The engine itself mostly does not care if the fuel is low sulfer or not. Oil quality remains good a shade long with low sulfer fuel. The "inducements" are features in the controls to detect if the operator fails to put DEF into the vehicle or tries to defeat the purpose of the SCR by using fluids other than DEF or by tampering with the system. The tampering diagnostics are getting pretty sophisticated and getting more and more difficult to defeat. When the inducements kick in, the first step is a warning lamp, then the power is cut back and after a bit more time the vehicle speed is limited to just 5 mph until DEF is added or the tampering reversed.

The SCR system has a doser system that injects DEF into the exhaust just upstream of the SCR. The are three stages inside the catalyst with the first being the decomposition cat. Here the heat of the exhaust breaks down the urea into ammonia (NH3). In the second section the NH3 reacts with the nitrous oxides (the browish gas the makes smog) converting it to just nitrogen (N2). N2 makes up 80% of air. The third section in the catalyst converts any unused ammonia into water and N2 so the vehicle doesn't stink and jar everyone at the bus stop wide awake.

The controls for the SCR are also pretty complex using special nitrous oxide sensors measuring the exhaust. The controls will also affect the engine operation. The cat temperature needs to be above 190-200 degrees C in order for the various chemical reactions to occur. If the exhaust is cool at start up or cools off while idling at a traffic light, the controls will pull various levers to put more heat into the aftertreatment system. Some of those include lowering injection rail pressure, changing injection timing, injecting fuel into the exhaust so the diesel oxidizing catalyst (used to clean up unburned hydrocarbons) oxidizes that fuel creating heat, opening an EGR cooler bypass valve or closing down a turbo or exhaust throttle to make the engine work harder and hence adding heat to the exhaust.

Personally, I like the high pressure common rail fuel systems. They are very flexible and permit injecting fuel at anytime the engineer wants, even mutilple injections during the main power stroke allowing better emission control and higher power with lower peak cylinder pressures which can increase engine life. They can also permit fuel injection pressures upto 30,000 psi which atomizes the fuel very well facilitating cleaner burns and better efficiency.

AT

 

Cummins started using a high pressure common rail fuel system (HPCR) in I think it was 2003. A 2005 or 2006 model year Ram truck with a Cummins is a very good year. On the 6.7 engine in the Ram, Cummins uses a Bosch rail and injectors but their own pump and controls. Ford and GM use the full fuel system from Bosch including Bosch controls and diagnostics. I don't recall the specific years they started using HPCR but also early 2000's.

Prior to the going HPCR, Cummins used a Bosch VP44 electronically controlled fuel pump. It worked quite well but if it got starved for fuel, it could quickly crap out. That made an electric lift pump back at the tank and good filters very important because if the lift pump quit, the VP44 could toast. Cummins started using that pump in about 1997 (mid year I vaguely recall) and a nice mechanical pump up thru 1996.

Personally, if I were getting a Cummins diesel pickup truck, I'd get either a 1995-1996 mechanical pump engine or a 2005-2006 HPCR if you don't mind electronics (better power and better fuel economy).

Oh yeah, the HPCR engines are much quieter, especially at idle. Much of the classic rattle of a diesel at idle is the unloading and cylinder slop of the piston, wrist pin, connecting rod and crankshaft as the piston come up about top dead center on the compression stroke. By shooting just a few milligrams of fuel into the cylinder before the piston reaches top dead center (TDC) a bit of combustion can add just a bit of pressure to keep the piston train loaded up and that kills the rattlIng noise. It is very good stuff.