Yamaha OX66 225 HP Overheating: Yamaha Techs?

[hotajax]

This is for the V-6 225 from year 1998 Running time 300 hours.

With engine in the water, and intakes below water level:

It is overheating. Not a faulty alarm, the block is hot.

Next thing, there is a GOOD STREAM OF WATER out of the tell tale ( or "pee hole" in the vernacular of where I fish )

I replaced the water pump, and it works well. It brings up water from the intake up to the top of the engine. The old impeller was actually in very good shape. Still very supple, and no chunks missing out of it, small amt of wear on the blades. The blades are almost full thickness as they were when they were new.

The water tube must be good, or else water would not be making it to the upper engine.

Engine rpms are low. And it stalled out a couple of times while sitting at the dock.

I'm thinking faulty poppet valve, and maybe faulty thermostats.

I had the overheating problem before I changed out the impeller, and that was what prompted the new impeller. But apparently the overheating is caused by something other than the water pump because that pump is working fine.

Would love to hear your opinions about where to look next. Thanks very much, gents.

 

[Parthery]

Been down this road....water pump was good...thermostats checked out OK when they were removed and tested in boiling water. Ended up being the poppits.

 

[hotajax]

Thanks, you always seem to have the right answer on what road to go down next. I appreciate it. Hot Ajax

 

[seasick]

Thanks, you always seem to have the right answer on what road to go down next. I appreciate it. Hot Ajax

If the poppets are stuck open, the motors will overheat at lower revs but not at higher ones.
If the water flow is limited, overheating may occur at any speed but will occur more often under load and at speed.

A infrared thermometer ( the cheap ones work fine for this) is a handy tool for overheating testing. Knowing what the cylinder bank temps are, if they are about the same temp and how fast they heat up all helps isolating cooling issues.

 

[Harpoon]

Poppet valve. Or, there is an off chance you have a great deal of scale build up in your cooling system.

 

[ttles714]

Where are the poppets located on this engine ??

 

[hotajax]

Location of Poppet Valve

Here's where it is on this engine. Stand astern of the engine. Look at the bank of cylinders on the right. You will see it below the bottom cylinder. Diamond-shaped cover with two 10 mm bolts holding it in. There's a 3/4' hose attached to it, coming in from the starboard side. I did the job before, you don't need to go through all that crap the guy on Bass Boat Central tells you to do. Just get another person to hold the cover against the spring while you get the bolts started. And don't do the bolts one at a time. Take a few turns on one bolt, then go back and do the other bolt, and keep going back and forth like that. Ideally, you want a 1/4" ratchet set for this, as well as a universal socket to do the bottom bolt on the cover. Best investment in tools you can make is to get universal sockets in 1/4 " drive for this engine. You'll need it when you do your low-pressure fuel pumps, too. BTW, strangely enough, there's only ONE poppet valve, but two thermostats. Go figure. And to make sure you get all the parts you need, call Andy at Shipyard Island Marina. Usually he knows what other parts to send you besides the ones you ask for. Gaskets and housing don't always come with the components you ask for.

 

[seasick]

Re: Location of Poppet Valve

Here's where it is on this engine. Stand astern of the engine. Look at the bank of cylinders on the right. You will see it below the bottom cylinder. Diamond-shaped cover with two 10 mm bolts holding it in. There's a 3/4' hose attached to it, coming in from the starboard side. I did the job before, you don't need to go through all that crap the guy on Bass Boat Central tells you to do. Just get another person to hold the cover against the spring while you get the bolts started. And don't do the bolts one at a time. Take a few turns on one bolt, then go back and do the other bolt, and keep going back and forth like that. Ideally, you want a 1/4" ratchet set for this, as well as a universal socket to do the bottom bolt on the cover. Best investment in tools you can make is to get universal sockets in 1/4 " drive for this engine. You'll need it when you do your low-pressure fuel pumps, too. BTW, strangely enough, there's only ONE poppet valve, but two thermostats. Go figure. And to make sure you get all the parts you need, call Andy at Shipyard Island Marina. Usually he knows what other parts to send you besides the ones you ask for. Gaskets and housing don't always come with the components you ask for.

Take notice of the order that the parts are in so that you will replace them in the same order.

 

[hotajax]

Poppet Valve Replaced, Shooting Lazer Beams

Thanks for confirming what I thought it might be. New stats, too. She's dying to get fish slime on her now.