2004 Mercury 90 HP Shutdown

[LTBuddyF]

Greetings from Texas! We have a 2004 Mercury 90 with very low hours on a pontoon boat in a fresh water lake in Texas. We have only run one reservoir of oil through it to date. Here is the story, earlier this week my son went fishing in this boat. He tells me that the alarm was sounding when he first started it. He called to ask me what to do and I told him as long as there was oil in the reservoir and a water stream coming from the engine that it might just be a malfunction with the alarm. I myself had used the boat to fish in just a few weeks prior and was getting inadvertant alarms. I put a quart of oil in the reservoir at that time just to make sure there was oil in the system. After that I may have used only about 3 gals of fuel before docking her. For this reason, I told him that I was sure there was enough oil in the reservoir for at least 3 or 4 gals worth of fuel. My son said that after a while (several starts and short runs between fishing holes) he was crusing about about 3/4 throttle and the motor started to sputter and quit. Yes, I do believe that the alarm was sounding each time he ran it. After about 5 minutes he got it started and idled back to the the slip. Yesterday I opened the filler cap and found no oil touching the dipstick, I did not try starting the motor or pulling the motor cowling prior to putting oil in. I put in a quart and started the motor and ran it in the slip. Everything seemed to be fine until I took off on a run across the lake. About a half mile out the motor sputtered and shut down. I suspect that the temp guage is not functioning properly so I can not tell you what the temp was reading but water was coming out the port and it wasn't hot at all. After about 5 minutes I got is restarted and ran it back to the slip. I even ran it at a pretty good clip at the end but it started to sputter again so I back off and idled into the slip. One thing to note, this motor sat unused for the better part of two years (out of the water) due to my being overseas and the lenthy illness and subsequent death of my father-in-law. This was his boat. So, there you have it! Now my questions. Is this motor designed to shut down if the fuel oil mixture is too low to save the motor from damage? Are the symptoms consistant with the motor running without oil and/or water circulation or electrical related? Could the motor having sat up for so long have something to do with its behavior? Yes, I am planning on getting the temp gauge fixed next trip to the lake! Until then I am unable to determine the operating temp. Also, this motor has a hard time idling. It is especially troublesome when trying to dock in the narrow slip in rough waters (it dies regularly in this senerio) when you need to be able to go between forward and reverse which leads me to think the carbs need cleaning and adjustment. Thanks in advance for any responses. I have been a pretty good mechanic as far as cars and motorcycles but for some reason outboards have always intimidated me.

 

[tashasdaddy]

Re: 2004 Mercury 90 HP Shutdown

Welcome to iboats. if that motor at for 2 years, carb cleaning and impeller, are a must. when the oil tank runs dry you need to bleed the oil line to get air out. use rebuild kits on the carbs. the impeller is rubber and not using they dry out, and become brittle, it could still pump with broken vanes. here's good reading http://forums.iboats.com/showthread.php?t=158086

 

[LTBuddyF]

Re: 2004 Mercury 90 HP Shutdown

Thanks tashasdaddy! That was a great read and I plan on getting a quality service manual ASAP! I'm having an anxiety attack though about this oil issue. I will purge the oil line next trip to the lake but do you know if these Mercury motors are designed to protect themselves from damage if the oil runs out?

Cheers,
Buddy F.

PS: Go Gators

 

[Silvertip]

Re: 2004 Mercury 90 HP Shutdown

Even though the tell tale shows a good stream, that is not an indication the engine is cooling properly. All it proves is that the water pump is pumping. A stuck thermostat and poppet valve can cause overheating as can a malfunctioning oil injection system. I suspect the engine is overheating causing it to lose compression and die. Continuing to operate it that way will destroy it. Find out what's wrong! The next step would be to run a compression check. If compression is good you dodged a bullet. If not, you just experienced the effect of ignoring a warning horn. You must also verify not only that the oil is system is working, but working properly. With the engine tilted down, mark the oil level in the tank with a marker. Then add one quart of oil and mark that level. Place another mark midway between the two. Fill the fuel tank. Run the engine until the oil level has dropped to the middle mark. Refill the fuel tank. The tank should take about six gallons give or take a little if the oil system is operating properly.

 

[LTBuddyF]

Re: 2004 Mercury 90 HP Shutdown

Thank you Silvertip. I will follow your direction and keep my fingers crossed that I dodged a bullet!

Cheers

 

[Texasmark]

Re: 2004 Mercury 90 HP Shutdown

You didn't tell us what type of alarm you experienced.....intermittent beep (low oil) or solid horn (overtemp).

That engine has a thermostat and pressure relief (bypass). At low rpm's the stat is in control and at higher boat speeds and rpms the pressure relief provides increased, non temp regulated, flow. The stat is temp operated and the relief valve is pressure operated.

The telltale comes off the exhaust manifold and is not in the thermostat loop so it will/should be a lot cooler and at low speeds. It pees as soon as you start the engine and the water pump has had time to get water pressure up to your powerhead.

Your stat could be stuck closed and you can be overheating your engine which usually results in piston galling and internal damage. Like he guys said, all it tells you is that the water pump is delivering water to the powerhead.

Cleaning your carbs should help your idle. I have one of those engines which I bought used and cleaning the engine/carbs with Sea Foam greatly improved the low speed operation. Mine didn't sit for a long period as yours did but had considerable hours on it for only being 2 years old. However if you are in the overheat mode, the engine runs rough at idle because the pistons are jammed in the cylinders due to overheating.....lotta friction.

The idle speed for that engine is 675 rpm in F gear in the water, boat easing along.

I had a '75, 70 hp 3 cylinder Evinrude once that did what yours did....shut down after awhile at the higher rpm's. Let it sit for awhile and it would restart but ran rough. It had a stat (which I was unaware of with no bypass valve for higher speeds) which progressively got worse till it finally stuck closed and the engine seized one day at WOT requiring a complete powerhead overhaul and .030" overbore with new pistons.

Don't know if you ran your engine without oil or not when you said you found your oil tank dry. Then if you ran it hot AND without oil, I'd be ready to fork over some cash for a complete powerhead redo. Hopefully not.

Mark

 

[LTBuddyF]

Re: 2004 Mercury 90 HP Shutdown

Mark,

Thanks for the great info. I just talked to my son and he told me that from the get-go the alarm was going and it was continuous??? Even at initial start up before engine even warmed up??? This is perplexing to me! I would have thought that the alarm would have been intermittent. Regardless, I got no alarm at all when I was in the boat. I did put oil in prior to turning on the ignition and then she started fine and ran okay until the shutdown ? mile out from the slip. Again, no alarms for my little excursion?even when it sputtered and shut down. I believe the gauge on the console is disconnected but I?m assuming that this setup is such that the motor?s electronics dictate the alarm and not the gauge on the instrument panel!!! So, now I have yet another concern!!!! Everyone in this forum has given me great advice and I thank you so very much. I feel much more confidant now to at least attempt the diagnostic portion of the repair. If it doesn?t require the worst case scenario I may be able to pull this off. If I fall short, is there a reputable person to contact in the Houston, TX area for these repairs that you would recommend?

Cheers,
Buddy F.

 

[Texasmark]

Re: 2004 Mercury 90 HP Shutdown

I was reared down there and the last dealer I recall was C.B Delhomme who had a dealership down town. He was an OMC dealer then. The last time I was there was in 1960 and the reason is another story.

Good luck.

Mark