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1996 90hp merc oil injection


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1996 merc 90hp oil injection.  
friends engine. Not mine. Haven’t seen it yet.  
If oil injection fails does it alarm or just go boom?  
Would you disconnect oil injection and mix in tank? 
he is trying to go fishing any help is appreciated.  

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There is a wire from the oil reservoir that goes to an alarm, that should warn you

 it who knows if it still works on a 27 year old motor 

when mine quit working and I replaced it with another used reservoir , I tested it by adding oil to the gas tank , marked the level of the oil in the reservoir and saw the level was going down each time I ran the motor. So I quit adding oil to the gas tank and ran with just the reservoir ran fine till I sold it 

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"Any known issues with these engines?"

3 cylinder 2-stoke Merc's have a history of the top cylinder not getting enough cooling, and therefore the head cracking around the sparkplug. I blew one up myself back in the early '90's. 

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I would suggest if this is an engine you want to be good and reliable, that this is the time to bite the bullet and spend some money to get it into the best possible operating condition.


You can replace the oiling system with new components so it will operate like new and be serviceable for many years or you could remove the oil injection system completely, and then mix your fuel with a high quality TCW-3 2 stroke oil.
Given the age of the engine one or the other will be necessary.
Before spending any money you should do a compression test to confirm that the engine is in good condition internally. As Crowman mentioned overheating is bad news, so it is most important to replace the water pump (I recommend every 2 years on these engines) check/test/replace the poppet valve and thermostat, cooling on these is critical and you don't want to destroy the engine due to overheating. Other items include possibly cleaning and rebuilding carburetors, replace fuel filter, install new spark plugs, replace the fuel lines with new ethanol compliant lines, change the lower unit oil and pressure test, check the condition of the plug wires and replace if needed, inspect all wiring for exposed terminals, chaffing etc. Make sure you have a good battery. It is very important to make sure that your RPM are in the proper range at WOT with a good quality prop in good condition. The boat should have a normal load in it for testing purposes. I believe you want the WOT RPM to be between 5000 and 5500 RPM. If you are not comfortable working on an engine like this then you should take it to good reputable mechanic. Hope this helps.
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A few years ago I was looking at buying a 19 foot Starcraft with a 150 Merc on it that the oil injection gear had stripped out. With a bit of research I found an electronic retro fit for the injection system. It consisted of a few sensors, control module, and electric pump. Everything else needed was scavenged from the original injection system. The deal fell through so I diidn't go any further with this retro fit system. But if you find that this engine's oiling system has failed it would be another fix? Sorry I don't remember what it was called but at the time it was an easy find while I was looking/googling fix options.


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