Diesel Fuel - API classifications

[Jeff Bacon]

Hi All:While searching high and low for some oil this weekend, I started wondering about the API classifications. Yanmar mandates an API CD classification for my engine. However, most places I went to had either no diesel oil, multi grade oil (Yanmar suggests single grade), or lots of oil with other classifications besides CD.Does anyone know how critical the CD classification is, or if there is a Higher classification that includes the CD classification (like CD II ). Also, why is a single grade recommended over a multi grade ?Anyone know if there is a web site to learn more ?Thanks........ JeffManateeHuron, Ohio

 

[Steve Dion]

are you referring to motor oil?

Jeff:are you referring to the Motor Oil for the diesel engine? I am assuming that is the case. If you do some research you will find that using an API rated motor oil for Sx ratings (spark engines) can cause problems with the rings.If you just purchase either Shell Rotella or the Chevron Delo you will have a high quality brand. Yanmar is now recommending either 30 or 10-40 multigrade. The oil for a diesel engine is rated as CD, CF (compress engines) etc. The greater the last character the more current the formula is.

 

[Lee Hadjiosif]

Diesel Oil

Jeff,The CD oil is no longer made. The first letter "C" designates diesel and the second letter is assigned based on the year the blend was certified. The higher the second letter, the better the oil. The current designation is CF, and CG which are the only oils you should be using. Gasoline engines use "S" as the first letter. Also the correct viscosity is 10W40 or 15W40 regardless what the manual says. When the engine manuals were written, oil technology was different and Yanmar seems to reuse the old manuals instead of updating them. Sometimes you will see the CD on the oil can, but this is just for marketing purposes only. The shops know that the Yanmar manuals still call for the CD and will mark the oil that way knowing that boat owners will be looking for that even thow the CD designation is more than 15 years old. Technically speaking, if the oil meets the CG it should also meet the older CD so there is no mislabeling issue here. You can find the CF or CG oil in automotive stores usually sold for heavy duty diesel trucks. Penzoil "heavy duty" API CG 15W40 is the one I use. S/V Calaloo

 

[Wim van den Toorn]

more or less

I do not totally agree with the two previous answers. CD grade is still made; CE, CF etc. are better, but more expensive. "Full synthetic" oils are eve better, but should NEVER be mixed with organic oil. The advantage of using CD is that you may use the same oil for the Kanzaki transmission, normally found on Yanmar engines.Wim

 

[Paul Akers]

I asked Yanmar

Although you can still find CD at West Marine (it's the only place), I inquired at Mack Boring about the designation. They told me that any Cx designation, equal to or greater than CD is OK to use. That is, CD,CE, CF... is OK to use. I continue to use the recommended 30w oil, since it is still available. My engine is an '88, so I've decided to stay with the recommendations for that year.