2002 90HP Overheating at low RPM

[nowakezone]

I have a 2002 90 HP 2 stroke and owned it since 2002. It always had an issue that when in gear at low rpm, like idle or under 1000 RPM, it will overheat. Many times when just idling under 1000 RPM it will overheat. I can only flush using a two-sided muff because a one-sided muff results in overheating after 3 minutes. Manual says 800 +/- 50 RPM is the spec. The overheat alarm does not occur in other situations. Since 2010 I have done the following: Replaced the impeller/housing kits 5 times, (gets a little better after replaced by the way – gets worse when it’s been on more than a year). I replaced the thermostat and popit valve three times. For another issue, I REPLACED THE ENTIRE POWERHEAD with a rebuilt version. I replaced the temperature sensor-and I tested the old one which was within specs. One of my former mechanics finally told me to just adjust the idle speed to 1000 rpm in order to idle without overheating and move on with my life. Four different mechanics have yet to solve this issue. What are we missing?

[dray0151]

Are you freshwater pr salt water? Did you notice any corrosion when replacing the therm or the popit? When idling what does the tale tell stream look like----weak or strong? When flushing on the muff you say if using a one sided muff the alarm goes off, have you investigated the system up to the pump for any blockage? If you have it on two sided muff you can idle at the correct RPM and no alarm?

I'm not sure you should increase your idle speed just to stop an alarm after all the apparent problem has not been fixed just put under the rug for a bit.

[99yam40]

was this overheating since new and also after power head was replaced?
You said impeller/housing kits.
I did not think Yamaha sold the housing and impeller in a Kit
were the ones you used OEM?

did you overheat and blow the power head?
or why did you have to replace it?

[nowakezone]

Dray, it is Saltwater use only. When I replaced the thermostat there was crud in the area which I flushed out as well. Its got a good stream both on flushing and while running. I have not checked the system from the pump - not sure if any of the mechanics have either. Might be the issue. I have not tried lowering the rpm with a two-sided but can try that.

99yam40, It was overheating before and after the powerhead work. Here is the kit I just ordered from boats.net 692-W0078-02-00 WATER PUMP RPR.KIT I only use OEM. The powerhead blew when I tired one of decarb efforts with seafoam and was running out the stuff. Turned out the carbs needed rebuilding but I ran it hard while misfiring - my bad.

[99yam40]

Those kits do not come with the plastic housing.
Maybe you need to replace the housing.
have you inspected the housing for any signs of melting?

Good chance if there was build up when changing stat and PRV there is more in other places.

you said you have owned this motor since new if I read you correctly, did it even not over heat at low RPM?

[pstephens46]

Well if this has been the case with booth powerheads it would seem like the problem would be between the block and pump. Assuming everything was assembled correctly. Does that motor have a flush attachment? Use two hoses when flushing. I would be curious as to how much water flows out of thermostat hole if you pulled it and ran it briefly. At idle, guessing not much. I would check that poppit again too.

[pstephens46]

So housing never replaced???

[nowakezone]

99yam40 I have always had a mechanic change the kits out, but I am planning on doing the next. I can order a new plastic housing for the job. I bought the boat in 2010 and there has never been a time when the overheating issue did not occur.
pstephens46 By two hoses you mean flush on the hose attachment and with the muffs? Never tried running it with the hose attachment off its base. Since I had serval mechanics work on it, I insist on the OEM kit. My guess is that since the housing is not in the case, it may be old. I can order a new housing and see if that fixes it.
<http://www.boats.net/parts/detail/ya...078-02-00.html> isn't that the housing in this kit?

[99yam40]

it only has the wear parts, gaskets,oring not the plastic housing

[nowakezone]

So I should order this part as well and replace?

[zenoahphobic]

Seems your mechanics ain't that good. How many "pumps" did they change without fixing the problem: 5!
You pretty much worked it out, new total pump and check the fit between it and the pipe (corrosion, damage and sealing).

[TownsendsFJR1300]

So I should order this part as well and replace?

If it truly overheated (say on the brand new test run for some reason), it could warp that plastic housing. As stated above, that WOULD limit water flow to the powerhead.

It's NEVER been changed so the issue may be following the plastic housing.


BTW, folks (including dealerships) do stupid things (one of my neighbor as well). They crank up the engine with NO water, just for a couple of minutes.
All you need is one new guy to crank it up before you bought (with no water to it)

Guess what you now need...

Also, there usually is a seal at the top of the "water tube" at the powerhead. If that's missing, you loose lots of water, especially at idle.

Cover the basic's...

[99yam40]

So I should order this part as well and replace?

I would open it up and have a look to see what it looks like to see if it needs a housing.
do you know if the housing was replaced ever when you took it in?
.
So you bought the rig used and it has had a problem all the time you have owned it.
you have no idea what was done to it before you bought it.
the plot thickens

also make sure the rubber grommetis in the plastic housing of the water pump sealing the water tube properly

along with the dampener and holder between the water pump and exhaust on the lower unit while you have the lower off.

was the people working on this a Yamaha shop with trained techs?

[TownsendsFJR1300]

I'd hope the impeller was not installed with the vanes in the wrong direction...

Dunno how well, if at all, it would work.


For the Op, if your somewhat mechanically inclined, pick up a manual. The water pumps aren't really hard to do...

And if you go by the book, you shouldn't have any issues..

[nowakezone]

Thank's everyone, I have a manual but live in a condo where its hard to work on anything. I have parts ordered (I'll go ahead and order a new housing too) and update this thread after they get installed.