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Diesel FAQ's From the Mailing Lists
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Simple questions on this page:


Fuel Economy

Why are  Diesels so noisy?

Comments and Q's heard at fuel stops
Discussions on separate pages:

Oil Changes

Oil Pressure

Engine Operation:
Idling, RPM, Axle ratios
Engine Timing HP and Torque Cold Weather
Other FAQ Pages Turbocharger Diesel Fuel

General Questions and Terms

Q: What is a dowel pin?    Note: 24 Valve engines are not vulnerable to pin damage.

Q: What is a CPL number?

Q: What is a TSB?

Q: What is an ISB engine?

Q: Can a 24 Valve ISB head be installed on my 12 Valve engine?

Q: What is a TST kit?

Q: Is there a TST kit for the 24 Valve ISB?

Q: What is a turbocharger and how does it work?
      Includes intercooler, boost, wastegate, and silencer ring

Q: What is the TDR?

Q: What is the difference between direct injection, and indirect injection?
Note: The Ram Turbodiesel and the Ford Powerstroke both use direct injection.

Q: What Are Delivery Valves ?

Q: What is the difference between a "wet sleeve" engine and a "parent bore" engine?
Note: The Ram Turbodiesel and the Ford Powerstroke both use parent bore engines.

Q: What is the difference between the 1998 Encore and Eclipse engines?

Q: Is there a difference, other than the PTO port, between the NV241D and the NV241DHD transfer case?

Q: The 97+ rams use the power steering pump and a hydraulic (instead of a vacuum) brake booster. Where does the truck get vacuum for AC, Cruise Control, etc?

Q: Is it safe to take the truck to the car wash, and spray the engine down?

Q: Which engines have a catalytic converter?

Q: The shift light doesn't work on my truck. Are they only for gas engines???

Q: What causes the chirp sound from under the hood when I shut down the engine?

Q: How often should I drain the water separator, and how do I do this?

Q: What are all of those radiators behind the grill?

Q: Where is the Cummins ISB computer, or the  computer that tells the engine what to do.  Where is the Dodge computer that monitors the Cummins computer, and if there are any other computers, where are they?

Q: How much does a gallon of diesel fuel weigh?

Q: What should the fuel pressure after the filter on a 24 valve be?

Q: Doesn't Ford own Cummins?   If the Cummins engine is so fantastic, why doesn't Ford use the Cummins engine?

Back in the early 90's, Ford bought less than 15% of outstanding Cummins stock. Many companies buy into other products to add diversity, corner a market, or form an alliance. In 1997, Cummins repurchased all stock previously owned by Ford, and no Ford management is now on the Cummins board of directors. Since 1998 in the pickup market, Cummins B engines are exclusively contracted to Chrysler, an arrangement that both companies are eager to continue. Ford medium duty (class 6 and 7) and heavy duty (class 8) trucks are available with Cummins B engines. Hey, if it's good enough for a Ford 10 ton truck, I think the Cummins B is adequate for my Ram pickup! You can keep your Power Stroke. :-)

From the Cummins website: Ford does not own Cummins stock
No, at one point Ford owned less than 10% of Cummins stock, but now Ford doesn't own any Cummins stock.

Again, from a Cummins press release:
       (Jan. 3, 1997) - Cummins Engine Co. Inc. today announced that it will issue 3.75 million shares of its common stock to an employee benefits trust for use in meeting the company's future obligations under employee benefit and compensation plans. While the trust shares may be used to fund a number of these plans, the principal use will be in funding contributions to employee retirement savings programs the company revised on January 1, 1997.
    Formation of the trust and issuance of the shares to the trust will have no effect on the company's earnings per share calculation. Shares of common stock held by the trust will not be used in calculating the company's reported earnings per share until the shares are distributed from the trust and allocated to a benefit plan.
     The company also announced that it has repurchased 1.3 million shares of its common stock from Ford Motor Company and has authorized the repurchase of an additional 1.7 million shares in the open market. In accordance with the terms of the company's 1990 investment agreement with Ford, Kenneth R. Dabrowski, a Ford vice president who has recently served on the Cummins Board of Directors under the terms of the investment agreement has resigned, effective with the repurchase. Following the repurchase from Ford, the company has approximately 38.2 million shares outstanding.
      Cummins, headquartered in Columbus, Ind., is a leading worldwide designer and manufacturer of diesel engines and related products. These engines provide power for its key markets: automotive, power generation, industrial and filtration.

Fuel Economy

Q: What is the typical fuel economy of a Ram with the Cummins diesel?

Here are some 12V rules of thumb:   YMMV!        Due to EPA emissions regulations, ISB engines get 2 mpg less than the 12 valve engines.

Diesel Engine Noise

Q: Why is the diesel engine so much noisier than a gasoline engine?

Note: the P7100 fuel injector pump is quite noisy in operation, and a fair percentage of the noise produced under the hood of 94+ 12 valve engines is from the injector pump.   (source: TDR)

Subject:     RE: What makes all that noise anyway?
From:        "Paul H. Mason" <74160.642@CompuServe.COM>

> I was wondering, the non-uniform combustion, would that cause piston
> rattle/slap as others have described?
> Or, maybe worded better, is that noise the combustion itself, or metal
> hitting metal?

While it's true piston slap causes a light rattle modern piston engineering has produced cam-ground pistons. Design forms the piston skirts tightly to the piston walls when the engine is cold and as the engine/piston warms up the clearance stays the same. Of course any high performance engine using drop forged pistons will rattle slightly cold or hot as the skirt to piston wall clearance doesn't change much and is usually fit loose in the bore. The aluminum alloy pistons used in modern diesel engines usually have a fairly close skirt clearance with some industrial Cat and other engines being the exception.

Rather than "metal hitting metal" it's the flame hitting the metal. Check out at: University of Wisconsin-Madison
"".  If you have a web browser there's a bunch of good diesel combustion research at the ERC (Engine Research Center) University of Wisconsin-Madison like:

> SAE 950162 "Single-Surface Flame Quenching Distance Dependence on Wall
> Temperature, Quenching Geometry, and Turbulence," by DJ. Cleary and P.V.
> Farrell. <

Another reason we have to treat diesel CI (Compression Ignition) engine coolant differently than SI (spark ignited) engine coolant is the high flame pressures cause "pitting" or "cavitation erosion." Cylinder wall "vibration" characteristics are also being studied by the ERC.

--Paul         Reference:

Q: After driving for a while on the highway, my 2001 diesel engine sound changes noticeably when the throttle is moved slightly. Is this normal?

When you are traveling at a nearly constant highway speed, any change in the throttle causes the engine computer to adjust both the fuel rate and the injection timing. The timing change produces a noticeable change in the sound produced by the engine. Note: The change is more noticeable if larger injectors have been installed to increase engine power,

FAQ/Comments Frequently heard in parking lots and fuel stops:

Does the 5.9L have enough power in a 2500?

Mertens, Darren  ( 
"there is no such thing as enough power in a truck, you must seek more"

"How do you like that diesel truck?"

Bruce W. Wells   (
Usually, somewhere
in the ensuing conversation, I use my analogy of this truck to sex for the first time.

How do you explain sex to the uninitiated person? Despite your best efforts at using the English language, you cannot command enough adjectives to describe the activity. So it is with the Dodge/Cummins combination. Most people (yes, even pickup owners who drag trailers around regularly) have no concept of what this truck/engine is about.

And finally, I end the page with this DiRT posting from Joe Donnelly:

Subject:   Re: DiRT: diesel aroma and music
In a message dated 98-07-19 13:42:23 EDT, someone with a V10 wrote:
<< You might be a redneck if.....the sound of a diesel sounds like Mozart.  Ha Ha. >>

naaah,    Mozart has too many violins.
More like Bach fugues at idle, or under full power - Wagner.

Joe, no one could have said it better !!

Other FAQ Pages on the web:

Cummins FAQ



CCJ Reference Section

Diesel Engine Glossary




Last update November 1, 2002