1985 90hp mercury inline 6

[B-Dozer]

Just bought A longshaft 1985 90hp mercury with tilt/trim anyone had this motor and what kind of luck did you have with it?.

 

[jimmbo]

Re: 1985 90hp mercury inline 6

I had a 84 115hp merc for 14 yrs. Trim motor packed it in in first 8 weeks(first year for that design), Carb floats would occasionally stick and flood. Fried one switchbox. Had an issue with the waterjacket leaking water around sparkplug #2, replacing gasket was a temp fix. Eventually recieved a new cover(free, 4 yrs out of warranty), and never leaked again. Overall my favorite engine.

 

[B-Dozer]

Re: 1985 90hp mercury inline 6

Thanks Jimmbo makes me feel better about this motor. Seen it on craigslist cheap. Went to take a look and it was like brand new. Compression was good and came with controls and steering cable plus stainless steel prop. Guy wanted 500 I paid 450. I figured I could easily get my money back even if it was junk. Got the motor home and had her running in about 1/2 hour shifted good idles and sounds great. Wasnt pumping water so I took the lower unit off and I'm going to replace water pump. From the looks it needed it. As soon as I get that in the mail this week she will be ready for the water.

 

[pecheux]

Re: 1985 90hp mercury inline 6

Owned a 115 hp Tower of power for 6 years. Ran it 2 full days a week in boating season (I live in Canada) NEVER had any issue with that motor ... just ran great at all times. Changed plugs once in 6 years + adding oil in Tilt/trim pump a few times. that's it ..

Enjoy ...

PS: My OB mecanic (ex Merc dealer and personal friend) told me these were the work horses of OB's

 

[inthedirtagain]

Re: 1985 90hp mercury inline 6

I've got an 86 model on my 16ft Larson. Not too bad, but doesn't push me as fast as I want to go. Has great holeshot, though. Have occasional issues with carb adjustments and float height, but nothing major.

 

[B-Dozer]

Re: 1985 90hp mercury inline 6

Thanks for the info guys. hope I have as good of luck as you

 

[Texasmark]

Re: 1985 90hp mercury inline 6

I had an '88 115 on a 17' pad hull Ranger. It ran 6000 rpm at WOT and the wake looked just like Jimmbo's first picture. That sucker just sang like a meadow lark.

I too had a water jacket cover leak and other than that and a couple of sets of surface gap plugs, I didn't have to do anything for the 7 years I owned it and BIL still has it and is still running it.

Mark

 

[boatbonanza]

Re: 1985 90hp mercury inline 6

Have a 1983 90HP inline 6 and runs great, I love it. I did have some ignition trouble last year but repaced coils and the two switch boxes and no more problems. I had original coils and 3 that were cracked under the rubber boot (not visable until you remove them and the rubber). I replaced the switch boxes with CDI and their tech told me what to look for before just replacing the boxes and sure enough bad coils which is what caused the switch box failure. The coils are cheap, the switch boxes aren't. Check them, after 25+ years of abuse and high temps they can go bad and take out other good parts with them. Now it's all good!

 

[pecheux]

Re: 1985 90hp mercury inline 6

I've got an 86 model on my 16ft Larson. Not too bad, but doesn't push me as fast as I want to go. Has great holeshot, though. Have occasional issues with carb adjustments and float height, but nothing major.

My 115 Tower mounted on a 20 footer central console fiberglass Cadormat boat pushed me at 48 Mph. It overreved with the 19 inch pitch prop so I changed it for a 21 inch pitch that kept wot at 5800 rpm. (can you tell I miss that boat ...lol)

 

[Chris1956]

Re: 1985 90hp mercury inline 6

Hey, Inthedirtagain, if you have great holeshot and low top end, you might need to change the propeller to one with more pitch. Any idea what the WOT RPMS are? Those inline sixes had great mid-range power and top end power. They were challenged at hole shot due to low displacement.

 

[Texasmark]

Re: 1985 90hp mercury inline 6

Hey, Inthedirtagain, if you have great holeshot and low top end, you might need to change the propeller to one with more pitch. Any idea what the WOT RPMS are? Those inline sixes had great mid-range power and top end power. They were challenged at hole shot due to low displacement.

That's where the Laser SS prop came into play. Being ported, it relieved the challenge of the hole shot. It could pop me (250#) up on a slalom on a high dead rise transom padded boat, yet run 6000 rpm and 49 mph on the top end. Also, on the cubes, their V6 150's they upped the cubes from 2L to 2.5L to satisfy the hole shot problems on BBs.

Mark

 

[inthedirtagain]

Re: 1985 90hp mercury inline 6

cant tell any markings on the prop, so i have no idea what pitch it is. my seloc manual says the WOT rpm range is 45-5000rpm, and I'm right about 4800 under most conditions. Electronics are good (just replaced last year) and the compression is at 120 x 6cyl. If I can find markings, I would like to try other props out.

 

[Texasmark]

Re: 1985 90hp mercury inline 6

cant tell any markings on the prop, so i have no idea what pitch it is. my seloc manual says the WOT rpm range is 45-5000rpm, and I'm right about 4800 under most conditions. Electronics are good (just replaced last year) and the compression is at 120 x 6cyl. If I can find markings, I would like to try other props out.

On your compression numbers, my manual says that 120 is the dividing line between OK and suspect problems.

 

[Chris1956]

Re: 1985 90hp mercury inline 6

Mark, You are pretty picky. That motor is ~25+ years old and gauges are pretty inaccurate. As long as the cylinders are close in compression, it is fine....

 

[Jlawsen]

Re: 1985 90hp mercury inline 6

Mark, You are pretty picky. That motor is ~25+ years old and gauges are pretty inaccurate. As long as the cylinders are close in compression, it is fine....

135 is factory, 120 is on the bottom end of the life cycle but the wear is even on all six so a .015 bore would bring it back to life for another 25+ years. It's all in how you look at it. Good motor and good ignition system. I would have paid 500.00 for it if it was the original powerhead and I wouldn't have cared about the compression at that price.

 

[inthedirtagain]

Re: 1985 90hp mercury inline 6

Not to hijack this thread, but I actually thought about a possible replacement O/B. I'm rated for a max of 120hp, and would like to get somewhere near that. I don't like to rev it all the time just to pull tubes around the lake. This one is an '86.

 

[Texasmark]

Re: 1985 90hp mercury inline 6

Mark, You are pretty picky. That motor is ~25+ years old and gauges are pretty inaccurate. As long as the cylinders are close in compression, it is fine....

Sir that is a quotation from my Merc serv manual. If you want the page and paragraph I will look it up. Not my numbers sir!

Mark

 

[Chris1956]

Re: 1985 90hp mercury inline 6

Mark, Compression gauges like clocks, should to be accurate and reliable. Accurate means that they display the correct compression numbers. Reliable is that ther display the same compression numbers time and again for the same compression. Compression gauges can be real inaccurate, but are usually reliable. So if you get a close reading across all cylinders, you can be pretty sure the compression is about the same for all, however, you cannot depend on the accuracy of the gauge. In my opinion, if you see similar 100PSI+ readings on all cylinders, you are pretty sure the motor has not suffered any damage.