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Author Topic:   Troubleshooting 1989 Mercury 150
Tom W Clark posted 08-01-2005 03:57 PM ET (US)   Profile for Tom W Clark   Send Email to Tom W Clark  
I've got trouble with my Revenge 25 Walk Through; really the trouble is with one of the two Mercury 150 outboards.

This weekend my brother was using the boat. Yesterday he was preparing to head back to Seattle from our place on Bainbridge Island. He had his family on board, they had cast off and were idling away from the mooring when he heard some sort of waring horn sounding rapidly. He doubled back and called me.

I went down to the beach and clambered on board and we started the motors and idled around. The sound was gone by the time I got onboard and we discussed what sort of a sound it was. As we were idling along the sound reappeared. Clearly the (a) motor's warning horn was sounding rapid short beeps. I found it was the port motor sounding the alarm.

I knew this meant a low oil condition or oil pump failure, but the oil reservoirs were more than half full. I thought maybe it was a fuel restriction (memories of my Outrage 18 were coming back to me then) so I squeezed both primer bulbs. Both felt normal. While doing this the horn stopped.

I stopped an restarted the motors a few times but no further alarm was heard. I advised my brother to continue cautiously on the 20 minute crossing and that if the alarm sounded again he was to shut down the port motor and use the starboard motor for the rest of the trip. He had no fruther trouble.

So this morning I went in and discussed the situation with my mechanic, Dale at Ballard Outboard here in Seattle. He said that it could be the oil pump failing and that the problem could be intermittent. He described the plastic gears that Mercury used on the oil pump for these motors and how they can fail.

Bottom line: he strongly advised against using the boat until he can find and repair the trouble. It is the "high season" and he cannot look at it for at least two weeks.

The real problem: My brother was planning on departing for a vacation trip to the San Juan Islands tomorrow morning with the boat. Needless to say this is a BIG disappointment to his family.

Additionally my family is celebrating my Mom's life and scattering her ashes in the waters of Puget Sound this Saturday as she requested before her death a year ago. We were planning on using the boat for this.

So now we are stuck on the beach, so to speak. What I would like to know is: Are there ways to test whether or not the oil pump is the culprit? Dale said it could be any number of things that would cause the alarm to sound but that none of them are things the lay person could find. I'm not so sure.

Does anybody here have any experience troubleshooting this problem? Are there some simple things I could test? If it is not the oil pump I would just like to be able to rule that out and be able to use the boat with some level of confidence the motor will not run with a no-oil condition which would ruin it.

Premixing 140 gallons at 50:1 and running both motors on this mix does not appeal to me at all. One motor runs fine and even under normal conditions they smoke like hell.

Advice? I've got less than 24 hours to figure this out and save my brother's vacation.

bsmotril posted 08-01-2005 04:04 PM ET (US)     Profile for bsmotril  Send Email to bsmotril     
Pull the [oil mixing] pump and inspect the gears. Or disable the warning horn and run premix until you get it fixed. BillS
Buckda posted 08-01-2005 04:29 PM ET (US)     Profile for Buckda  Send Email to Buckda     
I had a similar intermittent horn sounding last year on my 1986 Black Max 150 HP. For me, it first appeared in waves. It turned out that the float on the resevoir on the motor was sticking down and then sending a warning signal that I was low on oil. I pulled the cap and thoroughly cleaned this mechanism (you'd think that 19 years of being immersed in oil would sufficiently lubricate this!) and have not had that problem since. I did, however, have to replace the overheat sensor as I later had a problem with this horn sounding.

At this point, ALL of my sensors have been replaced and I have a new horn to boot.

I'd check this float switch as you work your way through the problem.

I don't have my manual with me (it's in the boat) so I can't help you trouble-shoot from there. Hope it helps...


LHG posted 08-01-2005 04:32 PM ET (US)     Profile for LHG    
Tom, as you know, I have an identical engine on my 21 Outrage, except it is the 1988 version. Also had an oil horn problem on a Georgian Bay cruise last summer.

Is the engine still putting out its blue smoke? And is the engine mounted reservoir full, and staying full as you run the boat? Oil from the remote tank is first pumped into and through this engine tank. If so, it's getting oil and your problem is the warning module. This seems to be a common problem on these 2.0 liter 150's of the later 1980's. Buckda had same problem on his, and self repaired it with a new module. They can be gotten from Mercury parts overnight by any competent dealership. I think it's about a $200 black box, and easy to install. You might just want to buy one and put it on. Contact Buckda for help.

The talk about the plastic crankshaft gear is baloney. They are extremely reliable. You can also check the warning sensor in the on-board tank cap. My guess it's a module, just starting to go bad with erratic behavior.

I've put thousands of hours on Merc V-6's and never the hint of an actual oil injection failure, including the pair of 1989 200's I had.

Hope you find the problem and get it corrected. If you can confirm the engine is getting, and using, oil, I wouldn't let it ruin a vacation. He may be able to get it serviced on the water. You're going to find that blue start-up smoke is beautiful!

LHG posted 08-01-2005 04:34 PM ET (US)     Profile for LHG    
Forgot to say that in my situation, the problem WAS a defective alarm module.
Buckda posted 08-01-2005 04:36 PM ET (US)     Profile for Buckda  Send Email to Buckda     
Tom -

I may be mistaken, but I believe that this motor WILL NOT RUN without the oil. What I mean is, if that resevoir on the powerhead is full, unless one of the lines on the powerhead is kinked or otherwise restricted, the engine CAN'T run without oil since the fuel is mixed with oil as it enters the fuel pump. The design, as I understand it, is that even if the vacuum fails and you run the 3-gallon resevoir dry, that resevoir on the powerhead directly feeds the fuel pump. There is a sensor on that tank that senses when oil delivery stops (i.e. your main tank goes dry) and sounds the alarm, however the resevoir has enough oil to run for 30 minutes at WOT (50:1) before running out.

It's a pretty redneck solution, but might you consider running with the shroud off that motor to ensure and convince yourself that oil delivery is not a problem. At least you could do that for a half hour or so. If the level goes down while that horn is sounding, you know you have a problem pumping oil. If it doesn't, you have a problem with a sensor.

Make sense?

Buckda posted 08-01-2005 04:45 PM ET (US)     Profile for Buckda  Send Email to Buckda     
Larry posted while I was formulating that last response.

He's right - I think I paid 189 midwestern dollars from a certified dealer and he had to order the part. It was a very simple install - a few wires to each sensor (which were subsequently replaced by me as well) and you're good to go.

I agree with Larry - it's most likely a sensor, NOT a mechanical failure. I've grown to be pretty confident that although Mercury motors have a spotty reputation from some corners, they seem to be pretty tough customers when it comes down to it.

Tom W Clark posted 08-02-2005 01:52 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Whew! Long day. Thank you Larry and Dave for your input. To answer some questions:

Yes, the reserve oil reservoir was and is full.

Yes, the motor in question spews copious quantities of blue smoke as always, indicating the motor IS burning oil.

I'm not sure I follow all of Dave's and Larry's logic but at this point in time the deal is that my brother will depart tomorrow against the advice of my mechanic. We spent this evening pulling the boat out of the water and taking it to a gas station to fill up (126 gallons and 2.5 gallons of oil) and washing the boat.

Worst case scenario is the alarm returns midway through the trip and he has to shut that motor down. Actually the worst case is the motor seizes. We discussed it at length and he simply chose to take some perceived risk. We'll see.

Either way we will have some more data points when two weeks rolls around and I take the boat in to Dale.

My brother did spend some time this afternoon Googling this problem and perusing various forums. According to him talk of the "module" came up again and again so Dave and Larry have quite a bit of credibility in my mind...and I'm sure they wouldn't mind paying for a new powerhead should the need for one arise ;-)

Taylor posted 08-02-2005 05:35 PM ET (US)     Profile for Taylor  Send Email to Taylor     
The high season--of course, it must be a cosmic law that the failures will be just before the big trip. If the prime suspect turns out to be whatever sensor Larry and Dave are talking about, one thing to do would be to switch sensors from one engine to the other and see if the problem moves. But keeping in mind you have *two* engines - I think the decision to send Bruce on his way is not unreasonable or unsafe. If it turns out you need a spare boat on Saturday, you're welcome to Norka, she will be just sitting in the boat house the next two weeks while I'm sailing.
Einar posted 08-02-2005 10:32 PM ET (US)     Profile for Einar  Send Email to Einar     
If "Norka" is Taylor's Montauk I feel compelled to remind you that his Merc is well documented to get "high season fever" as well!
That said, I like the idea of swapping the sensors.

Are you sailing on a new to you Cheoy Lee? Or are you still wating for the fellow at the Yacht Club to let her go?


Tom W Clark posted 08-03-2005 11:28 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Thanks for the offer Taylor. I don't think there is time to get to Whidbey so Norka can have rest his weekend.

I agree that switching the modules will be the first test. Unfortunately I don't think my brother is equipped to handle that task.

I spoke with him by cell phone yesterday and he said they made it the first 50 miles with no alarm sound at all. At Deception Pass the alarm started up again. Eventually it went to a continuous rapid beeping . Starting an stopping the motor makes no difference. If the port motor is running, the alarm is sounding.

Oil reservoirs have oil and the rate of consumption between the port and starboard tanks seems to be equal. Blue smoke is still evident.

So we are hoping that the alarm is merely sounding falsely. If we are wrong we are probably destroying that motor. That's the risk we take.

In my research I find that the alarm module takes input from a motion sensor at the oil pump. It senses if the oil pump shaft is rotating. The oil pump shaft it driven by gears directly off the crankshaft. It also gets a signal from one of the cylinders so it know how fat the motor is turning. These two signal have to be in sync or the alarm module tells the horn to beep rapidly.

Royce was gracious enough down some mechanics on San Juan Island (his new home) and I may try to get one over there to check it out and swap those sensors and see if we can confirm that is where the real problem is.

Any other thoughts?

There was also one other (seemingly unrelated) problem yesterday according to my brother: While coming out of Deception Pass the Starboard motor seemed to loose power just a bit. The throttle needed to bee advanced more and more to keep both motors urning the same speed.

Bruce also noted that the temperature gauge for the starboard motor did not seem to be operating at all. After a few minutes the starboard motor sped back to its normal power level. At this same time the temperature gauge returned to life.

Does anybody have an explanation for this odd behavior?

On the Fourth of July after watching fireworks in Elliot Bay here in Seattle with a boat load of friends I experienced tis same slight power loss. The very next time I ran the boat the starboard motor was still running weakly for the first few minutes and then "kicked in" again and has run fine the the remainder of the month. I did not note what the temperature gauge was doing at those times.

LHG posted 08-08-2005 04:03 PM ET (US)     Profile for LHG    
Tom - After reading your responses, I am quite sure the first propblem IS the alarm module. Oil is definitely getting injected into the fuel or she would have long since seized.

Your second problem sounds like the beginning warning signs of an electronic component, possibly the stator, for which this vintage engine was famous. I would have the engine checked out by a good Mercury mechanic. Hopefully they will be able to find which of the components is going bad.

As for the temp gauge problem, I have no clue, unless it is related to power output from the stator also

Tom W Clark posted 08-12-2005 11:45 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     

Thank you for your latest response. I had missed it.

Here is the abbreviated epilog: Larry was right. It was simply a bad alarm module.

Larry may also be right about a bad stator or other electrical part. We'll know more by early next week when my mechanic finishes dealing with the numerous small problems that have been identified.

It's been a long week. I'm tired now but I will provide more details of this adventure later.

stant01 posted 10-13-2006 02:16 PM ET (US)     Profile for stant01  Send Email to stant01     
I have a 1995 Mercury 100hp (inline 4) on a 16 foot 7 inch Whaler. This engine uses a large on-board oil reservoir, and has a low-oil sensor, but not the pump motion sensor of the V-6's. On a trip a week ago, the beep-beep-beep sounded, so I added more oil to the reservoir. Still beeping.

When I got home I looked up the engine in a Clymer service manual. It said the diagnostic steps were to 1) unplug the wires from the low oil sensor (I did), and see if the beeping stopped. It did. SO I replaced the sensor.

However, this sensor is not a float - it is a small probe that inserts into a well in the bottom of the oil reservoir, and does not actually contact the oil. I have no idea how it works.

After replacing the sensor (less than $20), the beep-beep-beep continued; it began any time the key was turned on. So at the suggestion of the manual, I replaced the warning module (about $110). Still beep-beep-beep, but now the stakes are higher ($).

So I came here, seeking advice from those wiser in this than I. Does anyone know how this sensor works? There appears to be some sort of metal rod and float that inserts from the top of the oil reservoir. Could the sensor be detecting the distance to the "float"?

More practically, how can I fix this? Thanks for any help!

tbirdsey posted 10-13-2006 10:33 PM ET (US)     Profile for tbirdsey  Send Email to tbirdsey     
Had similar problems two years ago with my 1984 150. Acted like the oil pressure alarm - I went through the whole premix routine and the engine was smoking like crazy - obviously getting oil. Turned out to be a bad temperature sensor, somehow making the module send out low oil signal. Very easy to replace - just pops into the cylinder head and didn't cost much as I remember. Not sure if its the same for the 100, but worth looking into.
stant01 posted 10-14-2006 03:15 AM ET (US)     Profile for stant01  Send Email to stant01     
Thanks for the tip. I'll keep it in mind.
Flanders posted 10-27-2007 12:03 AM ET (US)     Profile for Flanders  Send Email to Flanders     
Any one know if the tan wire on the warning alarm module should have continuity to ground? I have constant alarm when the tan wire from the module is hooked up. The oil level switch is open and the heat sensor does not show ground (so it is open).
jimh posted 10-27-2007 10:03 AM ET (US)     Profile for jimh  Send Email to jimh     
In most older outboard motors which use a simple aural alarm to alert the operator, the alarm module supplies a voltage at its TAN conductor. Several alarm sensors are connected to this conductor in what is known as a WIRED-OR logic arrangement. If any of the sensors pull the TAN conductor to ground, the alarm is sounded. And correspondingly, if the TAN conductor at the alarm module is disconnected from all of the sensors, the alarm module should not sound an alarm.

Making a resistive measurement of the TAN conductor at the alarm module when it is disconnected from the sensors is not recommended. It is a voltage source, so resistance measurements will be difficult to make, and even if a source resistance for this voltage were found, interpretation of it would be difficult.

Flanders posted 10-30-2007 11:50 PM ET (US)     Profile for Flanders  Send Email to Flanders     
The motor is a 1989 100 hp Mercury. The tan wire goes to a terminal block under the same screw as the leads from the temp sensor and a tan and blue wire that is supposedly for a temp idiot light (according to the wiring harness directions). The horn sounds continuously when the motor is off or running. The temp sensor is open and the tan and blue wire is not in use per the instructions that came with my harness. I bought this motor as a running motor and never had it running on a boat I own. It starts and seems to run fine excepting the horn. I had to install a new wiring harness and all leads are terminated as directed. I just don't want to spend $178.00 on a module if that's not the problem. The horn stops sounding when I disconnect the tan lead. Neither the tan and blue or the black temp sensor wire has any effect when I disconnect them. The horn sounds until the tan wire is removed. Dose this point to the module in your opinion?


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