2004-05 225HP Merc 4 Strokes (Yamaha OEM) low water pressure...

[239SuperSport]

I have a pair of 225 Merc 4 strokes on my 2005 29 super sport and regardless of the water pumps, impellers, thermostats, and filters being changed for new, the motors when idling tend to overheat (over a period of 10 minutes or so after running).  I only see this when trolling offshore and putting the boat in neutral to boat fish.   As soon as the they are back in gear and near 1000rpm, you can watch the temperature fall back to 150-165...  I have also noticed that these motors do not PEE while using the manufacturers flush ports on the cowling back at the doc (motors not running).  Has anyone run across a similar issue?

[231CALIFORNIA]

if the pee hole circuit  is clear, the thermostat working right and the water pump pumping, and the legs inlets in the water, are the rpms high enough to keep the pressure up?

do you have  water pressure guages?

any or you yamy or merc  4stroke guys run into anything like this?

sounds like bad impeller or thermostat but you have 2 that both do it and
you say youve checked them.
lets see if any of the guys have a similar condition that goes away when put in gear.
may just need tiny bit  rpm boost?
also no pieces of old impeller or stuff in cooling system?
with twins ?not likely tandem failures, di it just start?
check the impellers again?

[scblackbeard]

I am running a yammy 2007  4 stroke 200 hp.It has 50 hours on her.I just had her checked at there Yamaha dealer by computer.Had the impeller changed last year.The dealer said no problems as long as water is coming out.My does exactly as u describe, I give her gas and she starts cooling mine is at super low speed and at idle for about 4 mins.  She then starts the overheat alarm/When I got the motor it had 4 hours on her.
The dealer said it could be a bad sensor,  or thermostat. But no computer codes came up.
I don't run the boat much this past year maybe 10 hrs.But it is a aggravation.So I am wondering if I should replace the senor t-stats and impeller. Hate to waste money on stuff that's not needed . Got sea Tow for piece of mind but don't want to hurt the motor either. So I guess we got the same problem.

[239SuperSport]

It has been a problem i have been dealling with since i bought the boat 3 years ago.  It has been serviced religiously and everytime it is in, i have replaced the water pumps and impellers.   They also get no error codes on the computer.   For the motors to start cooling back down they need to be running about 900rpm, so setting the idle there is not an viable option...

[scblackbeard]

Finally I think I got my answer.I had the Yamaha dealer investigate this problem.
When you run your engine to flush the dealer said you needed ears that let run water in both intake inlets on your motor at the same time or it will cause damage  by overheating the water pump housing. Or low water pressure from your water source.Mind you no codes showed up. But he said on the big 4 stroke outboards they can over heat during flushing operations if you don't use the right ears and make sure you have good water pressure at the hose bib you are connecting to.

So the engine mechanic on my Yamaha 200 2007(70) hours only  4 stroke tore down the water pump.He found that the housing had gotten hot and heated up the metal which melted the plastic part of the housing .The melted plastic was constricting one of the water lines I believe the inlet to the pump by about 80%. He replaced the whole water-pump and sold me a pair of ears that allows water into both inlets on the motor. Now I also run a water house to the top side which cools the top end of the motor while it is flushing.I believe this will take care of the problem. If it does not i will re-post after I get her in the water.The mechanic also got a bulletin in warning of some gasoline randomly tested that had up to 25% ethanol in it.So Yamaha is now requiring a gasoline additive to combat the high ethanol levels mandantory by the engine owner or they will void the warranty.  There is a ongoing law suit by engine manufactures against the EPA regarding these high levels of ethanol in the gasoline.The ethanol is causing high carbon build up and costing a lot of boat owners CASH when the gasoline pump states no more than 10% ethanol added. Leave it to the government to screw the end user again by letting oil company's stretch there gasoline inventory. Wonder what it is doing to my truck?

[231CALIFORNIA]

test your fuel yourself, take a   tiny measured sample into a glass container(test tube etc) with a pre measured amount of water in it, mark water line first, shake. let settle , repeat, let sit for a while, see how much the  apparent water level increases. this is your alcohol portion, it will blend with the water and separate , the gasoline will float, the water will be in the bottom.
if you are good, green  and careful you can pour the gas off and add back to a fuel supply and toss only the water and the alcohol only ,tiny amount.
dont drink it.

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