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Author Topic:   Mercury releases Optimax Diesel
Jeff posted 05-19-2015 11:02 AM ET (US)   Profile for Jeff   Send Email to Jeff  
Set for initial release as a Military use outboard, I am sure it will see civilian use soon.

"Developed for the U.S. Department of Defense (DoD), this exclusive spark ignited, direct fuel injected 2-stroke runs on ultra-low sulfur diesel fuel, which is readily available around the globe. Mercury Government Accounts Manager Tony Nahitchevansky explains the history behind the development of our latest military engine.

A Navy ship crash in 1995, which resulted in an explosive gasoline fire, spawned a DoD directive for all gasoline powered engines and gasoline fuel tanks be removed from Naval ships by 2010, The mandate called for engines to be developed to operate on fuels that meet the following criteria:

1) Improve ship safety by minimizing fire hazards,

2) More economical and more efficient, and

3) Readily available as a single battle space fuel.

The 3.0 Liter V-6 Diesel, which produces 175 propshaft horsepower, shares 95 percent of its components with the gasoline engine from which it derives. And, with only a handful of unique parts, there are minimal additional training requirements necessary for maintenance." - From Mercury's Page

Spuds posted 05-19-2015 11:19 AM ET (US)     Profile for Spuds    
My first impression is: leave it to Mercury to screw up a diesel motor by adding spark plugs.
Teak Oil posted 05-19-2015 12:13 PM ET (US)     Profile for Teak Oil  Send Email to Teak Oil     
Exactly. Ask GM about what happens when you take a gas motor and turn it into a diesel. You end up with a half assed motor that does nothing well
kwik_wurk posted 05-19-2015 01:12 PM ET (US)     Profile for kwik_wurk  Send Email to kwik_wurk     
Interesting. Adaptations usually don't do to well, but time will tell if this is a reliable solution. -- Max RPM is still 5000-6000, seems a little high at first glance for a diesel.

Slight drawback (aside from reliability) for military usage is the engine still needs 2-stroke oil (specified as Merc Premium Plus). -- But that's not a new issue since all the outboards today need unique oils of one sort or another.

martyn1075 posted 05-19-2015 01:36 PM ET (US)     Profile for martyn1075  Send Email to martyn1075     
That premium stuff is not cheap either. I like the concept but to be realistic and exciting it really needs to prove it can meet diesel like mpg numbers or else it would just be another way to make money on a marginally different platform when it comes to performance. Reliability and mpg the two largest specs that everybody cares about. Maintenance is in there as well and I wonder where this engine would rank in that department.
jcdawg83 posted 05-19-2015 02:38 PM ET (US)     Profile for jcdawg83    
Reading the link, this doesn't sound like a real "diesel" engine. This seems to be more of a traditional gasoline engine that has been modified to burn diesel fuel.

If the longevity and fuel efficiency are up to diesel standards, I can see this being a big deal. If this is simply a way to avoid using gasoline in Navy ships, this won't be much of a big deal.

jimh posted 05-19-2015 03:25 PM ET (US)     Profile for jimh  Send Email to jimh     
Evinrude has a version of the E-TEC that runs on multiple fuels. I think it can run on jet aircraft fuel, grade JP-1, which is often found on military vessels.
seahorse posted 05-19-2015 04:48 PM ET (US)     Profile for seahorse    
The multi-fuel E-TEC has been around for years now and they power special forces rigs and other craft. The are designed to run on JP fuels that almost all ships have onboard. They got rid of gasoline years ago.

Over the years Optimax tried various multi-fuel engine attempts but never had a reliable and consistent working product. This time looks better for them. It is not a diesel engine but can burn regular diesel fuel, but that is very dirty burning compared to JP 4, 5, and 8 fuels used by the US and NATO.

Peter posted 05-19-2015 07:28 PM ET (US)     Profile for Peter  Send Email to Peter     
This is not a compression ignition engine, a.k.a. a Diesel. It's a spark ignition engine that happens to burn Diesel fuel.
Jefecinco posted 05-19-2015 07:41 PM ET (US)     Profile for Jefecinco  Send Email to Jefecinco     
There have been many diesel engines equipped with spark plugs and magnetos. Many very large stationary diesels used in industrial and power plants use spark ignition. They are fired by natural gas but as we know if natural gas is compressed sufficiently it liquifies. To overcome this inherent problem a very small amount of diesel can be injected at about TDC of compression which then acts as a pilot fuel when it explodes or the large engine can be have it's fuel spark plug ignited.

Some diesels were started on gasoline using a compression release device, run until slightly warmed up, then switched to diesel by cracking the throttle and releasing the compression release lever.

There is very little very new in the engine design with which we are all familiar.


Don SSDD posted 05-19-2015 09:01 PM ET (US)     Profile for Don SSDD    
It will boil down to price, reliability, emissions, and fuel economy.

For military use, does it have to meet any "normal" emission standards? Looks like the weight should be similar to the same gas model.


Peter posted 05-20-2015 07:02 AM ET (US)     Profile for Peter  Send Email to Peter     
The military can do what it wants. It is not bound by the emissions regulations that are applied to its citizens. The weight should be similar given that it is NOTa Diesel motor running compression ratios in the 20 to 1 range requiring a heavier construction than a gas 6 to 10 to 1 compression ratio gas engine.
Jefecinco posted 05-20-2015 09:15 AM ET (US)     Profile for Jefecinco  Send Email to Jefecinco     
Generally the military very carefully complies with all EPA regulations. Engines used by the military are most often off-the-shelf designs used in civilian equipment. The military saves huge sums by using off-the-shelf equipment when the performance, size and reliability meet military requirements. Often all that is required to militarize an item is a paint job and an ID plate.

As amazing as it may seem the people who run the military are also concerned about the environment and the World in which their children may live.


seahorse posted 05-20-2015 09:43 AM ET (US)     Profile for seahorse    

Here are a couple more links to the new Opti diesel burning outboard

What is interesting is that there is a glow-plug for starting the engine plus it uses a multi-strike ignition system for combustion, just like the earlier FICHT and E-TEC engines did.

http:/ / info. mercnet. mercurymarine. com/ rs/ mercurymarine/ images/ M ercury%20Racing%20OptiMax%20Diesel%20Key%20Features%20FINAL%20050715. pd f?mkt_tok=3RkMMJWWfF9wsRoiv6XJZKXonjHpfsX%2F6OkrX7Hr08Yy0EZ5VunJEUWy34sH SdQ%2FcOedCQkZHblFnVgMSq2nXaYNrKIL

http:/ / info. mercnet. mercurymarine. com/ rs/ mercurymarine/ images/ M ercury%20Racing%20OptiMax%20Diesel%20Outboard%20Specifications_FINAL%200 5_14_15. pdf?mkt_tok=3RkMMJWWfF9wsRoiv6XJZKXonjHpfsX%2F6OkrX7Hr08Yy0EZ5V unJEUWy34sHSdQ%2FcOedCQkZHblFnVgMSq2nXaYNrKIL

bwguardian posted 05-20-2015 12:03 PM ET (US)     Profile for bwguardian  Send Email to bwguardian     
Does anyone remember the Maritime Engineering Vision 3.0L diesel engine from back in 2009?

jimh posted 05-22-2015 09:24 AM ET (US)     Profile for jimh  Send Email to jimh     
I don't see any obvious potential for the newly released Mercury outboard engine called herein the OptiMax Diesel to be attractive to recreational boats. From what can tell:

--the fuel cost for diesel is greater than for gasoline;

--the exhaust odor is more offensive with diesel than for gasoline; and

--the availability of diesel at convenient retailers, either on the highway or on the water, is more limited than for gasoline

Is there any difference in price between the engine called the OptiMax Diesel and the engine called the Pro XS? (Note that there are hardly any models of Mercury outboard engines using the Orbital Combustion System that are still called OptiMax engines. Most of these engines recently changed names and are called the Mercury Pro XS engine.)

As a recreational boater, what is an incentive to prefer to own a so-called Mercury OptiMax Diesel engine in preference to a Mercury Pro XS? I can't see any obvious ones.

Peter posted 05-22-2015 11:55 AM ET (US)     Profile for Peter  Send Email to Peter     
Not many recreational boaters are going to be able to get there hands on one of these. According to Mercury Racing

This engine does not meet EPA, C-ARB, or CE exhaust emissions requirements. A national security exemption or equivalent is required under 40 CFR 1068.225. This engine is not intended for installation on recreational craft in the European Union; it does not conform to the exhaust and noise emissions requirements of the Recreational Craft Directive 94/25/EC as amended by 2003/44/EC.

martyn1075 posted 05-22-2015 02:30 PM ET (US)     Profile for martyn1075  Send Email to martyn1075     
In addition to Jim's points,

-- the all important mpg.

If its next to nothing at all, there really is no point stop here.
If it can gain lets say another 2-3 mpg or more on top of a what a competitor gas model offers, well then maybe thats a different story, but from what we are gathering thats not the case as its just another engine that can run on a different fuel blend.

Don SSDD posted 05-22-2015 09:47 PM ET (US)     Profile for Don SSDD    
In Nova Scotia, diesel is about 6% cheaper now than regular 87 octane.

My diesel car does not smell at all and goes about 1100KM or more on 65 liters, similar gas car would go about 600KM on the same amount of fuel. It has more torque than a gas car.

Sounds like this diesel Merc has none of those advantages over a gas outboard, except you only have to carry diesel (and the military already have lots of that) and diesel is not explosive.

Interesting motor, but needs some improvements to work for the recreational boater.


jimh posted 05-22-2015 10:27 PM ET (US)     Profile for jimh  Send Email to jimh     
Here in Michigan diesel fuel is more expensive than regular-grade unleaded gasoline. Some recent prices were:


DIESEL FUEL: $2.70 per gallon.

The price for diesel was typically about $0.20 higher per gallon than for regular unleaded at many locations. In some places the difference was less, about $0.10.

For more data try

In the United States the distribution of diesel as a highway fuel for cars is not as wide as for gasoline.

Peter posted 05-23-2015 06:55 AM ET (US)     Profile for Peter  Send Email to Peter     
Last year diesel fuel was about 10 cents per gallon cheaper than the mid-grade gasoline at the gas dock.

It's unfortunate that Mercury calls this motor the "Optimax Diesel" when the motor does not operate as a diesel engine. It creates much confusion. There are comments in the Mercury Racing link for the motor and they demonstrate the confusion.

They should have called this motor the "Optimax D" similar to what they did for the Optimax JP -- -- but of course that would not have given them nearly the level of publicity they are getting using the misleading nomenclature.

The Optimax D looks like it is more or less the same as the Optimax JP with a different cylinder head to burn diesel fuel and maybe a few other changes here and there to tolerate diesel fuel. The Optimax D produces 175 HP at a fuel burn rate of about 15 GPH. In comparison, the Optimax 175 Pro XS produces 175 HP at a 16.5 GPH burn rate. The difference is attributable to the higher energy content in a gallon of diesel fuel. Interested parties should also keep in mind that a gallon of diesel fuel weighs 7.1 lbs versus 6.2 lbs for gasoline. So a full 50 gallon tank of diesel is going to add 50 lbs which will narrow the fuel efficiency difference. Also, to get that 175 HP at with a 1.5 GPH burn rate improvement, one has to add almost 100 lbs to the transom because the gas Optimax 175 is built on the 2.5L block rather the 3.0L block used for the Optimax D.

If the Optimax D was a true diesel or direct injected turbo diesel, then it's diesel fuel burn rate for 175 HP would be about 10 GPH or under and it's maximum WOT RPM would probably be about 4000 RPM not 6000 RPM.

Peter posted 05-25-2015 03:56 PM ET (US)     Profile for Peter  Send Email to Peter     
Update: diesel fuel is 30 cents per gallon cheaper than the mid grade gas on the fuel dock this year.
martyn1075 posted 05-25-2015 08:08 PM ET (US)     Profile for martyn1075  Send Email to martyn1075     
This is good sign but the whole thing doesn't sound as good as advertised the way I understood your post. It sounds a bit too good to be true but when you read the fine print its not as wow anymore.

Besides I still would want to see 2-3 mpg better at the prop before paying big money for a diesel that is if this motor was available for recreation boaters which it is not.

I suppose one might argue that since Diesel is cheaper then regular gas hey you might save a bit there so the time is now to get into a diesel outboard. I wouldn't buy an engine under those conditions as fuel is far too fragile with its pricing. The gouging at least where I live is very hard to stomach at times.

Peter posted 05-26-2015 09:55 AM ET (US)     Profile for Peter  Send Email to Peter     
Regardless of the economics, a recreational boater can't buy an Optimax D. I was just updating my observation about the price of diesel fuel on the dock when I was filling up yesterday. I was surprised to see a 30 cent differential this year in favor of diesel fuel. On the road around here, diesel is about 10 to 20 cents more expensive than mid-grade and a few cents less than the premium grade gasoline.
Mambo Minnow posted 05-26-2015 06:17 PM ET (US)     Profile for Mambo Minnow  Send Email to Mambo Minnow     
This is primarily intended for military applications. Navy ships operate on F-76, Diesel Fuel Marine (DFM) for main propulsion. Aviation fuel JP-5 is carried onboard for aircraft. Therefore out at sea, DFM is most readily available for small boat operations.
macfam posted 05-27-2015 08:36 PM ET (US)     Profile for macfam  Send Email to macfam
Diesel prices look pretty good on Cape Cod!!
jimh posted 05-28-2015 08:02 AM ET (US)     Profile for jimh  Send Email to jimh     
I believe that diesel fuel purchased at a fuel dock would not have the usual road taxes added, making the price of diesel at the dock lower than the price on the highway. I wonder if gasoline sold at marine fuel docks is also free of road taxes? I know the diesel fuel sold as off-road is usually dyed to a distinctive color so that it could be easily identified if found in the tanks of a truck. But gasoline at the fuel dock looks just like gasoline on the highway, that is, no difference in color.

If diesel can be less expensive at a marine fuel dock than on the highway, why can't gasoline?

Peter posted 05-28-2015 10:46 AM ET (US)     Profile for Peter  Send Email to Peter     
Currently the price of diesel on the dock is about the same as the price on the street. The price on the mid-grade on the dock is about 35 cents more than on the street. So road tax could be applied to one but not the other but I have not found anything in the state laws that says such. The way the state typically works is they charge a motor vehicle fuels tax and then it is up to you to claim a refund for non-road use of motor vehicle fuels.

Years ago when gas was well under $2 per gallon, I used to save all my receipts and then submit to the state for a refund. Of course, then the state would hit me up for sales tax but the difference still worked out enough in my favor to go through the exercise. When gas was in the $4 range, a very large portion of the refund was consumed by the application of sales tax such that it wasn't worth the effort.

macfam posted 05-28-2015 09:02 PM ET (US)     Profile for macfam  Send Email to macfam     
The marine diesel at the dock IS DYED. It is a distinctive red color.
Any spillage can be easily detected.
jimh posted 05-29-2015 05:00 PM ET (US)     Profile for jimh  Send Email to jimh     
If the diesel fuel is dyed, that is a good indication it is being sold without road taxes added to its price.

PETER--I don't quite understand why you'd have to pay sales tax a second time on the gasoline fuel you bought at a marine fuel retailer. Weren't you already paying sales tax as part of the price of the fuel?

Peter posted 05-30-2015 08:03 AM ET (US)     Profile for Peter  Send Email to Peter     
Did not pay sales/use tax twice. The road tax is in lieu of sales/use tax.

I always got refunds on my purchases from the gas dock. I had to submit receipts for the purchases so it is my understanding that the gas dock price included the road tax otherwise the state would not have refunded the road tax and made me pay the sales/use tax.

The 2014 refund rate was 25 cents for gas and 29 cents for diesel. Our sales/use tax rate is 6.35 percent. At the 2014 prices on the gas dock (and probably at the road pumps), paying the sales/use tax in lieu of the road tax would have resulted in paying more tax.

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