The low point for draining the coolant from the 370 engine is shown by the yellow arrow.
Recent posts on the Boat Diesel website and the Yahoo group Mainship, have questioned the proper coolants and change intervals regarding Yanmar engines. I have research this a bit further, and found a technical bulletin issued by Yanmar to their distributors. The bulletin is very explicit about this question and conveys the sense of importance using pictures of the destructive results of using improper coolants. This is a MUST read for owners of Yanmar engines. Although the bulletin specifies 500 hours as the change interval, regardless of the makers recommendation, my manual for the 6LYA-STP states 2 years or 500 hours, which ever is sooner.
My dealer says Rotella ELC is the coolant supplied with my Yanmar, but the Yanmar tech bulletin only mentions the Texaco brand. The two coolants have identical PH and reserve Alkalinity as received, which is important in the mixture of metals they are to protect. Except for the suggested service intervals, (Texaco suggests a slightly longer service interval,) the Texaco and Shell branded products appear to be identical in performance, meeting the same industry specs, and OEM recommendations. The Havoline brand is not an equivilent, as explained below. The following tech sheets can be downloaded for your own review, so you can decide what coolant is best for your Yanmar engine.
I have also recently been made aware that Chevron DELO ELC Coolant is also of the same ilk as the Texaco and Shell ELC products. (Texaco is a Chevron Company.) I have added the Delo ELC spec sheets for those interested.
The Yanmar .pdf file can be downloaded here: MSB 02-051.
The Texaco ELC Coolant .pdf file can be downloaded here: Texaco ELC
Havoline ELC .pdf file can be downloaded here: Havoline ELC
The Rotella ELC Coolant .pdf file can be down loaded here: Shell Rotella ELC
Chevron DELO ELC Coolant .pdf file can be downloded here: Chevron DELO
More on ELC Coolant
After reading through the above tech sheets, it just left me with a bunch more unaswered questions. So back to the web for some technical information. Most of the following 2 paragraghs come from a tech sheet put out by PENRAY®, another maker of chemicals used in the transportation industry. The rest of the article, is just my take on the situation.
Equilon (owned by Texaco® and Shell®) markets a European coolant technology, OAT, (organic acid technology) referred to as "organic corrosion inhibitor system" in the Texaco® /Shell® publications, that consists of ethylene glycol inhibited with a combination of sebacic acid and 2-ethylhexanoic acid supplemented with tolyltriazole. It was originally called "Long Life", but a lawsuit brought by Warren Oil, who markets a fully formulated coolant under the brand name "Long Life®" forced the retraction of that term from the DEXCOOL, Texaco and Caterpillar® packaging. (I wondered where the Yanmar service bulletin got the "Texaco Long Life" from as it does not appear on the market today.) The combination of a mono and dibasic carboxylic acids permitted Texaco to obtain a patent on the specific combination. Other companies have obtained similar patents, by varying the mixture somewhat and by using similar, but not exactly the same, chemistry.
General Motors® has been using this coolant technology in their cars and light trucks since the start-of-production of the 1996 model year vehicles (except Saturn®, which began in 1997). GMC® medium trucks equipped with Caterpillar engines, have been getting a nitrite-added form of DEXCOOL (NOAT) to insure protection against wet sleeve liner cavitation-erosion.
Texaco does have a patent for this organic corrosion inhibitor system (carboxylate corrosion inhibitors) that is used in the Havoline branded "Dexcool" version (today's product number 227994) and the Texaco ELC version (227997) of the coolant. The main difference is the addition of nitrite and molybdate in the ELC formula (excellent protection against pitting, corrosion and erosion even on hard to protect metals like aluminum.) The ELC formula meets the Caterpillar EC-1, and Navistar B1 specs, and is recommended for use in Caterpillar, International, Cummins, Detroit Diesel, Mack, MTU, John Deere, JI Case, Ford, GM, Volvo, and other original equipment manufacturers (OEMs). The Dexcool version is a general motors spec for cars and light trucks. The Dexcool specification does meet ASTM D 4985 for heavy-duty diesel service but does not contain nitrite and molybdate to help prevent the type of damage shown in the Yanmar bulletin. The Yanmar Bulletin does have conflicting information in it's recommendation and would lead you to believe Havoline 7994 and Texaco 7997 is the same, but Havoline 7994 is Dexcool, Texaco 7997 is the ELC. The part numbers have been lengthened by the addition of a prefix 22, as with many other Texaco product numbers.
It shouldn't be this confusing to figure out what coolant to use in the boat. I still am not completely sure what to make of the Yanmar bulletin. In other translations of Yanmar manuals from Japanese to English, I have see questionable and conflicting information due to translation. The Yanmar bulletin calls the Texaco product 7997 "long life coolant antifreeze" when today, Texaco calls it "Extended Life Coolant System". This causes confusion when other brands and products have similar names but different applications. The Havoline® Extended Life Antifreeze/Coolant is simply "Dexcool" compatible, with out the nitrite and molybdate found in the Texaco, or Shell "ELC" formulas.
Summary
From what I have found on the web, Mack Boring and the Yanmar technical bulletin, both suggest that either the Havoline "Dexcool" formula (7994) or the Texaco ELC formula (7997) is acceptable for use in the 6LYA. I have also found that diesels are susceptible to wet liner cavitation. After seeing the pictures of the cavitated aluminum componets in the Yanmar bulletin, I favor the Texaco® and Shell® branded "ELC" formulas that have the added nitrite and molybdate for the increased protection against pitting, and erosion.