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Author Topic:   Mercury OptiMax: Gas/Oil Ratio
DeepSouthWhaler posted 03-18-2005 12:08 PM ET (US)   Profile for DeepSouthWhaler  
I have a 150-HP Mercury OptiMax and a 3-gallon remote tank under the rear deck of my Dauntless. The boat has a 60 gallon fuel tank. Will the 3 gallons of oil be sufficient to cover the 60 gallons of fuel? I don't know what the average mix rate is for the OptiMax. Do I have to worry about bringing extra oil?
where2 posted 03-18-2005 01:02 PM ET (US)     Profile for where2  Send Email to where2     
Being an Optimax, it should NOT use more oil than a conventional 2-stroke. A conventional 2-stroke mixed at 50:1 would need 50 gallons of fuel to mix with 1 gallon of oil. So, you will be fine...
prm1177 posted 03-18-2005 02:32 PM ET (US)     Profile for prm1177  Send Email to prm1177     
Depends on your running speed. The Opti will use more oil at slow/idle speeds that at cruising. I have a similar rig with an Opti 135 and an Outrage 17 (52 gallon tank). I generally get between 2-4 tanks on a 3 gallon oil fill.
bluewaterpirate posted 03-18-2005 02:36 PM ET (US)     Profile for bluewaterpirate  Send Email to bluewaterpirate     
I have a 225 Optimax the most gas I've ever used was 75 gallons oil 1 2/3 of a tank of oil. U'll have more than enough, however, I carry 2 gallons of spare just in case.
where2 posted 03-18-2005 07:35 PM ET (US)     Profile for where2  Send Email to where2     
Interesting, On OMC engines, the VRO system engine uses more oil at WOT than at idle.

According to Bill Grannis' wonderful exposition on the VRO system: "The older pumps idled between 150:1 (prior to 1990) and 100:1 (1990-1992), then richened up to 50:1 as the engine load increased."

At idle, an opti should be similar to an OMC and use less oil creating less smoke and being less likely to foul the plugs.

Whalerider posted 03-18-2005 07:53 PM ET (US)     Profile for Whalerider  Send Email to Whalerider     
EXACTLY right...where2


Swellmonster posted 03-18-2005 11:43 PM ET (US)     Profile for Swellmonster  Send Email to Swellmonster     
Just got done reading the manual.
225 efi will burn approx 160 gallons of fuel, 2 tanks, with the 3 gallons of oil reservoir. When the low oil alarm goes on, I have approx 30 min of oil at WOT.
jimh posted 03-19-2005 12:43 AM ET (US)     Profile for jimh  Send Email to jimh     
With 60-gallons of fuel and 3-gallons of oil, you'd exhaust both simultaneously with mix ratio of

60:3 or 20:1

The only two-stroke engines that run at 20:1 ratio are 1950 lawn mowers. A modern low-emission engine like the OptiMax probably runs at 50:1 at high RPM and probably closer to 100:1 at idle speeds.

If you left the dock with both tanks full, you will run out of gasoline before you run out of oil. However, I'd bring extra oil along. If you have to buy oil at a fuel dock or marina store, you pay full price. Off the water you can usually find oil on sale at a discount. Also, you may not be able to buy the brand and grade you prefer.

While one of the fundamental properties of oils rated TC-W3 is the ability to be mixed together, I would recommend not getting too many different brands and grades of oil running through an engine like an OptiMax. It has a recommended oil for best performance. You might not be able to get that grade at every fuel dock. If you have to use a lesser grade you may find the engine does not run as well or you may foul the spark plugs.

Clark Roberts posted 03-19-2005 08:15 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Interesting thread: Direct injected two strokes get oil delivered directly to the moving internal parts and not to these parts via mixing oil with the gas. In the case of the Optimax, the oil is delivered to a small,under cowling "ready" tank from the large 3 gallon remote tank via crankcase pressure. The oil is gravity fed from the ready tank to an electric oil pump (I don't think there is any mechanical pump but not sure). The volume of oil fed to the moving parts (crank, rods, wrist pins...)is determined by the electronic control module or engine controle module (ECM) based on throttle position, ambient air temp, barometric pressure, humidity, engine temp, rpm...etc..etc.. No oil is involved in the combustion process (except small amount wiped from cyl walls). Air is throttled through reeds at front of crankcase and also air is injected into combustion chamber in combination with the electronically injected fuel. I may not have this exactly right but direct fuel injected (DFI)engine oil consumption is dependent on lots of variables so best to determine useage on an indiviual basis. I ran a 135 Optimax for several years and it used very, very little oil, probably around 100:1 at cruise speeds... just can't remember exactly... hummmmm? Happy Whalin'... Clark... Spruce Creek Navy
handn posted 03-19-2005 09:08 AM ET (US)     Profile for handn  Send Email to handn     
My 225 Optimax got 100 nautical miles on a gallon of oil. The fuel tank on my Conquest 23 was 150 gallons. Running both oil and gas tanks bone dry, each would run out at about the same time.
To avoid running out, I would keep track of the miles and add a gallon every 100 nautical miles. It is easy to make a mess overfilling, so it is easiest to add a full gallon a time to the tank.
jimh posted 03-19-2005 11:35 AM ET (US)     Profile for jimh  Send Email to jimh     
Clark--Excellent point regarding modern DFI engines like the OptiMax, Ficht, HPDI, and E-TEC not mixing oil and gasoline.

Because only air is passing through the crankcase, instead of a gasoline/oil/air mixture, the lubricating oil injected into the crankcase is not washed away or diluted by the gasoline. The oil stays in place much better and provides lubrication with smaller amounts of oil being used than in conventional two strokes.

On the other hand, when you start an old two-stroke and clouds of smoke come out, you do get a nice feeling about the engine getting some oil. These smoke-less starts require a bit more faith in the technology.

DeepSouthWhaler posted 03-20-2005 12:56 PM ET (US)     Profile for DeepSouthWhaler    
Thanks for the info. I am using Mercury Premium Plus 2-stroke oil. I plan to keep the remote tank topped off before I leave the dock. I will also keep a spare gallon on board. Based on the information that this forum has provided, I should never have an issue with the capacity of the oil reservoir. Most trips are rather short.

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