Yamaha 90TLR Drops RPM

Hello to all;

Need assistance on troubleshooting the following problem. I recently purchased my largest boat yet, a 2007 Key Largo 180 with a Yamaha 90TLR outboard engine. I bougth the used boat from a dealer and I'm guessing the boat sat on the lot for a while.

The first time I used the boat (ocean) it ran well for about 15 minutes and suddenly RPM's dropped from 5k (WOT) to around 1,800 RPM's. The motor never quit and since I was about a mile and a half away from shore I ran it like that until I was close enough and shut it down. Still in the water I checked around for loose hoses or wires. After about 5 minutes I restarted and the motor ran well for about 10 minutes and again the same thing happened. I tried the same procedure another couple of times with the same results. The motor never got hot and it had plenty of 2 cycle oil in the tank. No alarms went off. I even removed the cover and the motor felt ok to the touch and water was comming out strong and just barely warm.

Motor starts fine every time.

I suspected it was a dirty fuel filter/water separator and replaced it along with new spark plugs. I also pour in the fuel tank a fuel water treatment fluid. The following week I tested in the water and again had the same results.

At the Yamaha dealer I was told it could be one of three things: the thermostat, the oil sensor, or the water pump impeller.

This is what I have done so far:
- Replaced fuel filter/water separator and spark plugs. Added fuel treatment fluid.

- Tested thermostat and alarm went off loudly as it should.

- With all the wires still connected, removed the oil sensor from the tank and flipped it upside down a couple of times and the alarm went off as it should when is low on oil. On every try I noticed I had to turn the key off and on for the alarm to turn off. The oil, the tank, and the sensor screen looked clean.

- I did not check the impeller since I don't think is an overheating problem.

What could be the problem???? Please help

Re: Yamaha 90TLR Drops RPM

Sounds like you're getting a false high temperature signal putting motor into "safe" mode. You've checked the oiling system and the thermostat, but maybe check your thermal sending swith on cylinder head. Good Luck!

Re: Yamaha 90TLR Drops RPM

What do you mean by "Tested thermostat and alarm went off loudly as it should."
To test thermostat you have to pull and heat in a pot of water while measuring the temp of the water to see when it opens ,how far it opens, and when it closes. And compare that to the specs in the manual.
You can test the temp switch or sensor the same way.

If you do not know when the pump, thermostat,and PRV were serviced last I would replace them. They are normal service items called for by Yamaha.

Did you try restarting the motor right away to see if the alarm clears by just turning key off and the restarting? Or do you have to wait for awhile before the alarm will clear?
If it takes awhile to clear, it would give you a chance to unplug the pink wire from the high temp switch after it does it again and see if it is the temp that is causing the problem.
If it is not the temp switch then look at the oil system. You will need a manual and see what all will cause this to happen, There maybe something more than just the oil level that will cause the safe mode

Hopefully you made sure the strainer gasket #42 stayed in place when you pulled and reinstalled the oil level switch.I have read that it can restrict or plug off the oil flow if it gets away from where it is suppose to be.

Re: Yamaha 90TLR Drops RPM

Thanks for both of your quick responses.

I should first say I'm not an experienced boater. Let me see if I can properly answer your questions.

Based on your comments and questions I'm not sure I even tested the thermostat. Right above the top spark plug there is a small cover from which two wires come out. One is ground (black) and the other one is a pink wire that I traced to the buzzer. What I did is I grounded the pink wire and the buzzer went off. I assumed what is causing the drop in RPM's is some sort of electrical signal so I didn't bother pulling the thermostat out to see if it was mechanically working properly. In fact, where is the thermostat?

The boat came without the manual. I didn't know the thermostat and the thermal sending switch are two different components. Which one did I mess with?

I do not know when the pump, thermostat, and PRV where serviced. When you say pump I assume is fuel pump; right? Also, what's "PRV"? Are these expensive items?

I tried runnning the motor right after turn it off and the condition persist. I have to wait (motor off) about 5-8 minutes before it will run without problems. The motor always starts right away. I will try unpluging the pink wire on top of the spark plug, start and run the motor to see what happens.

If the temp switch checks ok, can I do the same procedure with the oil sensor pink wire?

I think I know what you are talking about; the strainer gasket is still at the tip of the strainer. I have not re-install it yet. I will make sure it goes back in correctly.

I like to learn as I do this, but if replacing the recommended items will fix the problem I would rather go this way. It's probably safer anyway, specially when all my boating will be done on open ocean.

Again, thanks for your comments, keep it comming!

Re: Yamaha 90TLR Drops RPM

The thing you checked with the pink wire is the temp switch, now maybe remove and check thermostat from behind that little cover on the cylinder head. That could be your problem, I hope so and good luck! You're going to need to buy a Yamaha manual to study and learn on your motor, and believe me, there's plenty to learn. Of course you don't really need to know everything, but enough to make your motor run well all the time.

Re: Yamaha 90TLR Drops RPM

as a new owner, you should change the water pump, thermostat and spark plugs; start you maint history from there.

you can get a copy of the owners manual from yamaha
http://www.yamaha-motor.com/outboard/service/viewmanuals/viewmanuals.aspx?ls=outboard

the 70hp manual is similar to the 90hp.

it sounds like a stuck/faulty thermostat to me.

Re: Yamaha 90TLR Drops RPM

From what I re- read in your 1st post, your motor RPM's dropped but the alarm never sounded. Is that correct? But it sounded when you tested it?
If it was temp or oil it should have sounded at the same time when it went into the safe mode. I am not sure what could cause that without the alarm.
do not pull the pink wire and run the motor as that will disable your protection system. What I said to do is disconnect it when you are having the problem just to see if that was causing the problem.

PRV is the Pressure Relief Valve. It relieves some of the water pressure at higher RPM's. It can stick or get trash in it not letting it close properly. That usually causes the motor to over heat at lower RPM. But it may affect it at higher RPM if the pump is weak.
You can replace all of these things we are talking about up front ,but I always like to find out what the problem was and replace the things that are not right just to know what fixed the problem.
You need to pick up a owners manual and a service manual for your motor at your local dealer or find them online, order a hard copy or download one off the web

Re: Yamaha 90TLR Drops RPM

That's correct; when the RPM's dropped the alarm never sounded. I fail to tell you earlier that at the dealer they told to start by checking the buzzer. I did. I disconnected the pink wire from the buzzer and supplied 12 volts directly. Initially the buzzer just made clicking noises and then it sort like cleaned itself and went off loud. The ground connection was a little dirty too. Since then the buzzer has been working fine, but I have not tested it in water to see if it will sound when the RPM's drop.

I got you on the pink wire; I will disconnect only after RPM's drop to see if motor will at least run without going into safe mode.

Sorry for the 90 questions, and I promise I will get the manuals, but where is the PRV located?

I'm like you. I get a better feeling of security knowing I was able to identify what was causing the problem. However, eventually I will change all the recommended items so I know what is my maintenance reference point.

I'm going to drop the boat in the water this weekend to see if I can isolate the problem. I will let all know monday how it went.

Thanks for everything, you guys are really bringing some light to all this cloud.

Re: Yamaha 90TLR Drops RPM

Hello Cousinabe;

I have checked in that same site for the manuals of my motor and the model number/serial number is not listed.

The model of my motor is: 90TLR

The serial number is: 6H1 L 1028411

Fabrication year: 2006 (can't remember the month)

Boat/motor where originally sold in Miami, FL in 2007.

Have any idea where I need to look for my manuals? Maybe at the Yamaha dealer?

Thanks

Re: Yamaha 90TLR Drops RPM

The older motors had one more letter after the 90TLR that represented the year, and a letter in front representing the series
like my motor C40TLRX which is a 1999 year modle. Look at this page toward the bottom and see what the modle numbers represent.
http://www.boats.net/parts/search/Yamaha/Outboard/parts.html

Re: Yamaha 90TLR Drops RPM

I echo the recommedation to change the water pump impeller, spark plugs and whatever else "reboots" the maintenance program that is a known schedule. I did just that when I purchased a used 175 Sea Chaser with 90TLRB (2003-ish era) Yamaha o/b. I never regretted rebooting. I boat with confidence.

Oh yeah, get a manual. Without one, I never would have found a 20-cent fuse inline with the starting circuit on my 40hp Force o/b. A mechanic would have likely charged me $42 an hour working in it.

Re: Yamaha 90TLR Drops RPM

If you are looking for repair manual, you can buy one off this site ( iboats), your local yamaha dealer, or any of many web sites.
Read this thread it may give you some ideas.
http://forums.iboats.com/showthread.php?t=361373&highlight=manual

The search tool on these web sites will find you all sorts of info if you look.

Re: Yamaha 90TLR Drops RPM

Hello To Everybody:

I was unable to test the boat in the ocean last weekend; the surf was high.

I did run the motor for about half and hour at about 3,500 rpm's and the problem never surfaced. I imagine since it was a no load test and the hose water was fairly cool the motor never got hot enough to go into safe mode.

For now I'm moving away from my posture of trying to identify the problem before replacing several components at once. Therefore, based on the general consensus I went yesterday to the Yamaha dealer and purchased the impeller, thermostat with new gasket, spark plugs, and tubes of lower unit oil/grease.

Next time I run the boat it should be a hazzle free experience.

I will post the results of this, hopefully, day's activity.