Whaler Central - Boston Whaler Boat Information and Photos

Posted by dmrose on 08/03/06 - 12:31 PM

I finally took my new to me 1985 Montauk out for it's maiden voyage last night. The boat has a 1985 90hp Yamer on the back and I believe it should cruise nicely at around 4500 RPM. For some reason at any RPM higher than about 3500 the overheat horn would come on and I would immediately shut it off. At one point the horn came on and the motor bogged down and ran rough.

After 15 minutes or so I would restart it and cruise along fine at 3500 RPM. The motor underwent an overhaul before I bought it and I checked for bags/seaweed in the intake and did not find anything. The water stream coming out of the back of the motor seemed slightly less strong than did the 8 hp kicker.

I'm thinking about replacing the water pump, does that seem logical? Thanks in advance.

Dylan

Posted by Joe Kriz on 08/03/06 - 3:02 PM

dmrose,

I have not owned a 90hp but I did own a 200hp Yamaha.

The 90 may be similar so I will mention this. If I am wrong, please, someone fill in the blanks.

First, there are two thermostats and two overheat sensors. One of each on each head.
We need to determine which overheat sensor is setting off the alarm. Or both?

On the 200hp, there is a water passage crossover to the other head.
This crossover was blocked and setting off the alarm on that head that wasn't getting enough water. (This happened just after I sold this boat to the new owner)
If you have this crossover, you might want to check it out and clean it if you can.

Also possible that one thermostat is not opening up all the way and not letting enough water through to cool the head at the upper RPM's....

After checking both thermostats and you still have problems, then you would want to take a look at the water pump impeller. It is however always a good idea to go ahead and replace any of the above, especially because you just bought this boat. Then you know you have two new thermostats and a new water pump impeller.

Posted by Joe Kriz on 08/03/06 - 3:26 PM

dmrose,

I believe every V4, V6, V8 outboard has a thermostat in each head. Also a temperature sensor in each head.

I'm just not sure if the V4 has the water crossover like the V6 engine has.

Edited by Joe Kriz on 08/03/06 - 3:27 PM

Posted by Joe Kriz on 08/04/06 - 9:02 AM

dmrose,

My fault then. I thought the 90hp Yamaha was a V4...
Then yes, you will probably only have the one thermostat and overheat sensor.
You will also NOT have the crossover water tube because you only have the one head.
Sorry for the confusion.
Those Yamaha's get a lot of power out of those 3 cylinders.

Posted by Jeff Cunningham on 08/04/06 - 2:27 PM

Dylan,

I'm the owner of the 1989 200HP motor Joe's referring to. I had the exact problem you're describing. The high temp alarm would go off anytime I tried to go above 3500 RPM's and the motor would drop into "safe" mode for about a minute then be fine.

I started by checking the high temp alarms (good), then the thermostats (good), impeller (good) then replaced the water passage crossover piston, spring and sleeve (which was stuck closed due to corrosion). Replacing these parts inside the crossover (about $10) helped but didn't solve it.

I finally pulled off the water jacket covers and found a bunch off corrosion which was preventing the cooling water to pull the heat off the heads. Cleaning these passage ways solved everything. I've put about 75 hours on the engine since and no problems...except filling the 77 gallon tank 6-7 times.

Jeff

Posted by dmrose on 08/04/06 - 4:12 PM

Before the engine went in for the overhaul and before I received the boat, the owner had told me that he was having the problem of the overheat horn going off and the shop that did the overhaul claimed it was a bad thermo.

I'm guessing a decent shop would check the water pump and thermo so potentially it IS a passage way problem. I just need a full day off to explore the problem and see what I can find. Thanks for the help!

Dylan