Advice on 1988 Merc 115hp 6 cyl

[Benn]

I'd like to hear opinions on the 1988 Merc in-line 6 engines. I know there are a ton of "tower of power" enthusiasts out there and I have done a lot of research and know these are highly valued engines, but I can find only vague references to some known problems.

I want to repower and I have seen several 1988 115 HP towers on sale on the local Craigslist. One guy has one that he claims is new and still in the crate.

I've owned Merc engines exclusively, but all 1990's or later. I currently have a 1995ish 75 HP ELPTO on a 1982 18' Privateer Retriever rated for 115 HP. I use this almost exclusively for fishing in saltwater. The boat is often moored for several days in saltwater. I flush it when I pull it out at the end of a trip, but it will be sitting with saltwater in it for a couple days at at time.

I'd appreciate any comments on any of these issues:

Corrosion resistance - I've heard the 1980's vintage were better, but are they as good at later designs?

Overheating - I've heard there are often issues with cooling in the upper cylinders (I always use synthetic blend oil).

Compatibility with 10% Alcohol fuel blends - basically all that is available in my region because of air pollution regulations - I have an oil/water separator.

Fussiness - I am not a mechanic and won't be doing any carburetor adjustments myself. Does 3 carbs mean more trips to the mechanic? Once a year tune ups are fine, but more than that...

Ignition systems - I know some 1990's Mercs had ignition/sator/control box issues. Is that the same for the 1980's in line 6's?

Oil Injection - I think the 1988's use the older oil injection system with an external tank and pump. They don't use these anymore. Were there systematic issues with them?

Thanks!

Benn

 

[BatDaddy1887]

Re: Advice on 1988 Merc 115hp 6 cyl

Hello Benn,

I too have a Mercury 115 1988 in-line 6 engine (see photos). I've owned it since 2005 and for 4 years it never gave me a lick of trouble...that is, until ethanol came to town. At the time, I didn't have a fuel/water separator and water got in the carbs I think 'cause I had to rebuild them along with replacing the rubber in the fuel pump. I have a water separator now and she still runs good....and, it starts right up, cold or warm.

I have never had any overheating problems (I also use synthetic oil). No corrosion problems...I change the impeller every 2 years, and change the lower unit oil every year during winterization.

I wish our wonderful government would make allowances for boaters to use regular 100% gasoline at marina pumps...

I haul the boat to salt water once or twice a year, I always rinse it down after the trip as well as flush the system for at least 15 minutes before heading home (upper Chesapeake Bay).

Carbs---there is no more maintenance on three than there is on one. When it's time to rebuild one, you rebuild them all. I took good care of my carbs by replacing the fuel filter every year, not running the gas tank dry, using Seafoam in almost every fill up, etc. Seafoam is the most amazing liquid made for outboards...I call it life-blood.

The engine ran for 20 years with no power issues, then last year I had to replace the stator and power packs...that's a long time, and I think we did something to effect that since we were trouble-shooting what later proved to be the carbs (it was a minute clog in one of the teeny tiny jets way inside. We had to use one of the fine metal threads from a length of twisted cable.

I never trusted the oil-injection system, although when I got the boat I used it for 6 months but it ALWAYS worried me so I took it off and just started mixing myself...only takes a few seconds longer anyway. The photos are old and show the injector still in place, I have since removed the entire apparatus and am much happier for it.

I have always been proud of my "tower of power" it never did let me down, even when we were pulling ski tubes...until ethanol came around...damned corn crap!

I hope this helps you with any decisions you make. Good luck and happy boating!

Jim

 

[arsenalpsu]

Re: Advice on 1988 Merc 115hp 6 cyl

The 80's towers are the end result of decades of refinement to these motors. They do need maintenance like any other motor, but taken care of properly they can last forever, especially compared to today's crap. Some people might say you're not getting a true 115hp but Merc started to prop rate their engines in the early 80's so an 88, 115hp is actually a 70's 150hp. Prop her to WOT at 5800, and if you're going to pull toys with a full boat get a second prop that's a few pitch lower, these motors hate to be lugged. Remove the oil blend and premix, replace impeller as soon as you get it and every two years. Also remove the idle stabilizer (little card looking box on the front of the motor) they have been known to cause issues at WOT and put a BB in each of the 3 tubes that go across the top of the carbs. This is a mid range gas saver that can cause lean running. Also set the secondary timing pickup to 20 at cranking speed (18 actual) If this really is new in the box add some oil to the cylinders before you turn it over to give it some lube. If you're not going to get to know your engine and do the work yourself, there are very few mechanics that know how to treat her right, find a 50+ one that knows these engines

For the salt issue, it's not good for any motor to sit in salt water, but if it's just for a few day's you'll be fine, just give her a good flush for 15 minutes when you get back.