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Author Topic:   Unhappy with Four-stroke Mercury 90-HP
Sal DiMercurio posted 04-27-2003 06:55 PM ET (US)   Profile for Sal DiMercurio   Send Email to Sal DiMercurio  
I ran into an old friend I haven't seen in 30 years, asked him what he's been doing. Says he fishes 300 days a year. We started talking engines, and he said he has a horror story to tell me about his 2001 Mercury 90-HP four-stroke. Says it started right from the beguining to get water in the oil, kept bringing it back, the dealer would say it's fixed, then Mercury sent him a new powerhead, which also had the same problem, they sent him another (November 2002) and it's got the same problem. After a total of nine times being in the shop he told Mercury to give him his money back because he can't trust any of the 90's they sent him. Merc says no, so he is now involved with a lawyer who is suing Merc.

Merc called and said they would give him a 2003 90-HP, he said you just put a new 2003 powerhead on and it did the same as the others, plus after a leakdown test, two of the cylinders have grooves that are 0.035-inch deep and 20% less compression then the other cylinders. So it's going to court.

I'v heard the four-strokes are having this water-in-the-oil problem. Anyone here have that problem?

Dick posted 04-27-2003 07:35 PM ET (US)     Profile for Dick  Send Email to Dick     
I have had no trouble with my 50 4 stroke and have seen no service bulletins from Merc on this problem.
jimh posted 04-28-2003 09:26 AM ET (US)     Profile for jimh  Send Email to jimh     
I raised this same issue last month in my thread "Making Oil".


Say, isn' the 90-HP 4-stoke Mercury engine using a powerhead made by YAMAHA?

PMUCCIOLO posted 04-28-2003 01:16 PM ET (US)     Profile for PMUCCIOLO    

Apparently, the alleged problem (in cold environments) is not the powerhead, but the thermostat.

Am I correct in interpreting the capitalization of YAMAHA as a bash? Is Brunswick providing funding for you to put a pro-Mercury slant on things? It's a good thing there are fans of Yamaha engines here to balance things out a bit!


lhg posted 05-06-2003 02:37 PM ET (US)     Profile for lhg    
Paul - In reality you must know that Jim is not receiving funding from Mercury.

There are many photos on his website showing his twin Yamaha powered 20 Revenge.

Since Sal's headline is about problems with a Mercury 4-stroke 90, I think Jim is correct is pointing out that this is the same engine powerhead sold as a Yamaha 90, previously sold as a 100. Overall, everything I have heard about either manufacturer's engines on this block, 75-115, have been good. I have also been under the impression that this powerhead design is by Yamaha, but have not been able to actually confirm this. I believe both company's plants are producing the engines.

I do believe that your Yamaha 60 four-stroke is an all-Mercury produced powerhead.

kglinz posted 05-06-2003 03:01 PM ET (US)     Profile for kglinz  Send Email to kglinz     
This "making oil", through dilution by fuel, is something that can happen to all 4 stroke engines. This is the reason your car oil change interval is 3000 miles or 3 months. Cars used for many short trips, never fully warming up, tend to become diluted.
PMUCCIOLO posted 05-08-2003 01:53 AM ET (US)     Profile for PMUCCIOLO    

It seems that the intention of some of my statements is mistaken. I'm only having a bit of fun!

Considering what I see at work, there are very few things that bother me outside of that. If the members of this forum were sitting around, we'd be laughing our heads off at the jabs we toss at one another. It's unfortunte that the typed word cannot convey the inflections and intonations of our spoken word.

I neither know who made my powerhead nor do I care. All that I know is that the four-stroke 60 is smooth, quiet, and seems to have a lot more torque in the mid-range than the two-strokes I remember running on similar 15's we've had.


kgregg posted 05-08-2003 08:21 AM ET (US)     Profile for kgregg  Send Email to kgregg     
>It's unfortunte that the typed word
>cannot convey the inflections and
>intonations of our spoken word.

Hence the use of "smilies"... ;-) or [grin] or {wink} etc. They help convey inflections. You really must use them if you're "only having a bit of fun". Otherwise you will be taken at face value. My $0.02. Kevin

Salmon Tub posted 05-08-2003 12:05 PM ET (US)     Profile for Salmon Tub  Send Email to Salmon Tub     
It seems obvious that after recieving 2 powerheads that perhaps the powerhead is not at fault. Most engines get water/coolant into the block from faulty head gasket but I am not sure about how the Mercs are set up.
PMUCCIOLO posted 05-08-2003 07:39 PM ET (US)     Profile for PMUCCIOLO    

I appreciate your point. However, if written communications required such symbols to convey tone, literary works would be replete with them.

The examples you've presented cannot substitute for the complexities of spoken language. Expecting a common, consistent translation of symbols originating in the computer industry is unrealistic.

Ten to fifteen percent of the population reaches the stage of "formal operations," which carries with it the ability to perform abstract thought. (Imagination is another issue.) You are completely correct, when considering these dismal statistics, that things are taken at face value the majority of the time. That is most unfortunate.


jimh posted 05-08-2003 08:47 PM ET (US)     Profile for jimh  Send Email to jimh     
Use to search "Groups" instead of "Web" and you will find some discussion posted a few days ago regarding a 1997 Honda 4-stroke engine with this same problem.

Enter the search terms "making oil" and "honda" at the Groups search page.

This link may work:

PMUCCIOLO posted 05-08-2003 09:50 PM ET (US)     Profile for PMUCCIOLO    

Having reviewed the link you provided, I am perplexed. Is the problem the thermostats? the fuel additives? a diaphragm in a pump?

Anyone? I have limited mechanical knowlege and am not in a position to render an opinion.


dgp posted 05-09-2003 07:03 PM ET (US)     Profile for dgp  Send Email to dgp     
Anyone experiencing an engine "making oil" should immediately take an oil sample and take it to the nearest Caterpillar, Cummins or Detroit Diesel distributor to be sent off for an oil analysis to find out what's foreign in it. Costs only range from $20-30. The report will advise of fuel dilution, water or anything else that doesn't belong in lubricating oil.
PMUCCIOLO posted 05-09-2003 11:10 PM ET (US)     Profile for PMUCCIOLO    

Is an oil analysis capable of discriminating between unburned fuel (either gasoline or diesel) and oil?


dgp posted 05-10-2003 05:46 PM ET (US)     Profile for dgp  Send Email to dgp     
Yes. They also look for changes in viscosity.
PMUCCIOLO posted 05-10-2003 09:08 PM ET (US)     Profile for PMUCCIOLO    

Thank you. One more question: Is there a certain hour interval at which this type of analysis should be done. It would seem to me that it would be wise every "X" hours to send an oil sample for testing.


dgp posted 05-11-2003 09:21 AM ET (US)     Profile for dgp  Send Email to dgp     
The normal interval for oil analysis is every oil change. Idealy done on a new engine from the very first oil drain, you "trend" the engine and/or oil condition over time. With this information you can see declining engine condition such as wear metals or extend oil drain intervals based on oil condition. I don't recommmend the latter.
PMUCCIOLO posted 05-11-2003 11:17 PM ET (US)     Profile for PMUCCIOLO    
Thank you for the information.
Bigshot posted 05-13-2003 10:46 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
No water in mine or anyone else I know with a 4 stroke yet.

All engines get water in the oil, it is called condensation and hence the purpose of PCV(positive cranckcase ventilation) filters on all cars. Outbords do not have these but we are talking minimal amounts that will burn off when engine heats up to a certain temp. If your oil is getting have some issues to attend to.

Oil analysis is great but you can also buy a kit for about $50 that does multiple checks, same for fuel.

richyrose posted 12-17-2006 04:22 PM ET (US)     Profile for richyrose  Send Email to richyrose     
I have a 2003 90 HP Mercury 4 stroke that came with my Boston Whaler Montauk. I have every problem described in this and other posts regarding the carbs clogging up and water in my oil. I have rebuilt the carbs myself so many times I could do them in my sleep. There are some tiny holes you must poke through using balyhoo wire. My current problem is with milky oil. I am gettin a lot of water in my oil and I pulled off the plugs and the lower one hade a drop of waer on it. I'm thinking head gasket but the motor looks so new, it's hard to imagine the head gasket is shot. Any suggestions before I take the pane and pull hte heead?
The Judge posted 12-18-2006 01:58 PM ET (US)     Profile for The Judge  Send Email to The Judge     
I am other friends have been running suzukis since 1999 and NONE of us have ever had water in the oil. If I did I would be one upset camper and glad i have a 6 year warranty. After the 3rd powerhead or whatever, I would go the route of your friend if Suzuki said no dice. We have lemon laws in FL that protect us from these things.
WT posted 12-18-2006 02:16 PM ET (US)     Profile for WT  Send Email to WT     

Why don't you have your Mercury?boston Whaler dealer do the work under your warranty?


fourdfish posted 12-18-2006 02:55 PM ET (US)     Profile for fourdfish  Send Email to fourdfish     
I do not see a warranty on this issue here! Although!
One never knows what might happen if you make a lot of noise!
contender posted 12-18-2006 09:25 PM ET (US)     Profile for contender  Send Email to contender     
Another idea, is the same mechanic working and servicing the engine? could be he is missing something, does not makes sense that you have had more than 9 different power heads and its not working and doing the same thing (I dont like mercury but they can't be this bad). I also would look somewere else meaning the problem you are picking up water some how. (After 9 power heads I would have replaced the lower unit also)...good luck
george nagy posted 12-19-2006 12:41 PM ET (US)     Profile for george nagy  Send Email to george nagy     
I once had a yamaha 9.9 4 stroke and during a cleaning water had been squirted into the exhaust port next to the cooling indicator tube. When I checked the oil I noticed it had then mixed with water. Maybe there is something the operators of those engines are doing wrong too?
richyrose posted 12-20-2006 06:58 PM ET (US)     Profile for richyrose  Send Email to richyrose     
My motor is just out of warrenty, of course. Just to keep you all updated, I did a compression test and the lower cylinder, the one which had the water droplet on the spark plug, came in at 120-PSI. The other three were between 150 to 160-PSI. The main thing holding me back now is I can't find the gasket set anywhere. Anybody know where I can get a head gasket set to rebuild a 2002 Mercury-Yamaha 90HP 4 stroke Ser# OT551513 model:l90ELPT4ST?
Dick posted 12-20-2006 08:17 PM ET (US)     Profile for Dick  Send Email to Dick     

If that doesn't work for you e-mail me or post your serial number and I will check when I go back to work Friday.

slipjoint posted 12-30-2006 02:07 AM ET (US)     Profile for slipjoint  Send Email to slipjoint     

Hmmm - Mercury Part Sex Press - whats that all about:)

richyrose posted 02-26-2007 08:26 PM ET (US)     Profile for richyrose  Send Email to richyrose     
Latest on the milky oil in my 2002 90-HP Mercury four-stroke:

I pulled the head, which was pretty easy because the motor is only five years old, and no seized bolts snapping off. If the cam shafts were about 1/4-inch over they could have stayed on, but they do have to be removed first. Upon inspection, It turned out NOT to be the head gasket, but rather the head itself was corroded through. This allowed raw water to enter the second cylinder.The compression without combustion caused the raw water to blow by the rings into the oil.

So why would a five-year-old motor be so corroded around the cylinder? I do use the motor in brackish water. I do flush out after almost every outing. The cause was the head gasket (which appears to be made out of stainless steel). The head gasket is 2 layers of a thin non ferrous metal with a thin black rubbery coating. The dissimilar metals (aluminum and nickel) in contact with each other caused the aluminum to pre-maturely disintegrate. This was my theory. I googled it and found this article <> which confirmed my theory.

So what did I do? Using a Dremmel with a wire brush attachment I cleaned out all the troubled spots--there were several of them. I made a dam using masking tape around the affected areas. I poured JB weld into the molds. After curing, I used the Dremel with a router attachment to take down the epoxy to just slightly above flush with the head. Then used a fine flat file to make it perfectly smooth. I made a temporary gasket out of Fel-Pro Kerropak and Permatex copper spray-a-gasket. Put it back together and it ran fine with no water in the oil. I now am going to run it for a while then pull it apart again to inspect the epoxy fix. The question: do I buy another evil stainless head gasket? Thoughts are welcome.

deepwater posted 02-27-2007 04:55 AM ET (US)     Profile for deepwater  Send Email to deepwater     
You are the kinda person that likes to find solve fix a prob you have little fear and believe "It only has to work once and I can make it work again" If you get good results with JB weld BUT are not compleatly happy try the Marine Tex post some pics if you can
bigjohn1 posted 02-27-2007 05:00 PM ET (US)     Profile for bigjohn1  Send Email to bigjohn1     
I'm impressed with what you have accomplished on your engine. I am just thinking outloud here on root causes for a corroded head:

1. Bad alloy mixture when originally casting the head at the Yamaha factory? (I have not heard of this on any 90 or 115 Yamaha outboards.

2. Very hard water being used to flush the outboard after use. Remnants of this hard water remain in the weater jackets and eat away at the base metal of the head?

richyrose posted 02-27-2007 08:55 PM ET (US)     Profile for richyrose  Send Email to richyrose     
Take a look at the patent link I sent in the prior post. Here is an exerpt...

"In the case of stainless steel core gaskets not having a zinc coating, the aluminum cylinder head or engine block immediately acts as the anode and begins to dissolve as soon as the electrolyte is introduced."

The motor looks like brand new, I was really surprised at what I saw. The problem was only in the head, the block showed no signs of corrosoion. The aluminumm looks like very good quality, the machining is impeccable, the insides of the casting were even coated. It looks like they did a quality job in this motor design and manufacturing, the problem is the material they chose for the head gasgket. Does any one know if the new gaskets or the Yamaha equivelent gaskets are of this stainless material?

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