OX66 Overheat Question

[Andrew93]

I have one motor overheating at low RPM. I usually do water pumps every other year, and they were done last year. Motor has the new style poppet valve also.

End of last season I hit a rock that stalled this same motor. Could that have damaged the pump? Boat is in the water, seems like a poppet valve to me but where they are the new style it makes me wonder.

Thanks

Andrew

 

[seasick]

Could be either a bad poppet or weak pump. How does the telltale stream compare at idle between the two motors? Do both motors take about the same time once started for the telltale to start spurting?


Also, when you start from cold, does the motor overheat if you let it idle and not rev it up? I doubt that hitting a rock would damage the pump. Check the water inlet grates for clogging.
Did the issue start after installing the new poppet or was that working fine and the overheating just started to act up? Some models of the poppet allow the spool to be inserted backwards
Generally a weak pump will cause over heating at speed and under load whereas a stuck open poppet will cause overheating at low revs

 

[Andrew93]

I am on the boat now. The tell tale is a little weaker in effected motor at idle. Maybe a second delay on startup.

The poppet valve in place is the half moon style, so it can only go in one way. The poppet valve has been in place a few seasons now. Anything over 12-1500rpms the motor runs at normal temp.

On my way out of the river today it started to get warm, gave it some gas, then was acting fine at idle, and now consistently running warm. The problem seems to be getting progressively worse over the last few weeks from running a tad warm to now getting hot

I visually checked the grates and they seem fine. I don’t have a ton of time today to mess with it, but debating on pulling it early Saturday morning and checking the poppet valve and pump. If it seems more poppet valve I can tackle that leaving it in the water.

 

[seasick]

I am thinking that the pump is bad. perhaps when you hit 'rock' you sucked in some sand or silt and chewed up the impeller.
Good luck on checking the poppet. Let us know what you find.

 

[wrxhoon]

I think pump as well or pump related.

 

[Andrew93]

Here is a photo of the water pump. Worn a little, but would this cause a weak stream? Doesn’t look that bad. The poppet check out fine

I am also going to look at the voltage regulator itself since the stream passes though that. I know those can clog at times. Motor had new thermostats also beginning of the year. When it was running warm it definitely seemed the starboard head was hit while the port seemed ok

 

[Andrew93]

I am thinking that the pump is bad. perhaps when you hit 'rock' you sucked in some sand or silt and chewed up the impeller.
Good luck on checking the poppet. Let us know what you find.

Where the pump does not look horrible and the poppet checks ok I took out the new thermostat and there was some crud around it. I am starting to think the cooling jackets are clogged but not sure. I hate to take the head off to find nothing, and the 4th right around the corner.

If it does seem to be the cooking jackets, if I can track down a new head gasket and whatnot the job doesn’t look too bad, unless there is more to it than i think

 

[Jdurb]

It's an easy job if you have the manual for torque specs. Also pay attention on which bolts to apply permatex thread dope to. Order your parts from boats.net and since your there do the tstats, poppet valve and impeller and your guaranteed no problems. Good luck

 

[DennisG01]

Impeller... don't forget to check the housing and wear plate. Any scratch that you even just barely get your fingernail caught in is too big.

 

[Andrew93]

So I replaced the water pump, inspected the new thermostats, and poppet valve. I put a cork in the water pickup tube while the lower unit was off and poured a gallon of white vinegar into the thermostat housing hole. Let it sit for awhile and drip out and then used a garden hose to flush it in the opening where the thermostat would sit. Reassembled and off to the boat ramp

Tell tale stream was much strong and this motor was actually running cooler than the other now. Hopefully this will get me through the season but thinking cleaning the water jackets may be in order in the off season if this lasts.

Thanks for the help and I’ll report back if symptoms reoccur. I have been using the Engine Watchdog for a temp sensor and I highly recommend it. It reveals a lot instead of just waiting for the alarm.

 

[seasick]

The new pump probably was the cure. You should be fine.
Flush after each outing and when you haul for the off season do a good flush with something like Saltaway

 

[wrxhoon]

I found that Yamaha water pumps are on the small size on the V6s but adequate when they are in perfect condition. They should last a couple hundred hours if you don't run in the sand or close to it so you stirred up. Merc pumps on big blocks are much more efficient , on my last 250 Merc I ran 600 hours and was still pumping the same as when it was new ( you have a pressure gauge on Mercs) , When I replaced it it was still like new .
Fire93Medic If I was you next time I would replace the water pump not just the impeller.

 

[Andrew93]

I found that Yamaha water pumps are on the small size on the V6s but adequate when they are in perfect condition. They should last a couple hundred hours if you don't run in the sand or close to it so you stirred up. Merc pumps on big blocks are much more efficient , on my last 250 Merc I ran 600 hours and was still pumping the same as when it was new ( you have a pressure gauge on Mercs) , When I replaced it it was still like new .
Fire93Medic If I was you next time I would replace the water pump not just the impeller.

When you say replace the water pump, are you referring to the housing? I usually replace the housing every year as well, but the kit come with a new cup that the impeller sits in also.

 

[seasick]

When you say replace the water pump, are you referring to the housing? I usually replace the housing every year as well, but the kit come with a new cup that the impeller sits in also.

The housing usually doesn't wear and doesn't need to routinely replaced. In some cases, an overheating impeller can damage the housing (cause it to melt and/or distort) but that would be obvious. Foreign objects in the cup could also cause damage but in that case the impeller would show that something was amiss.

 

[wrxhoon]

Seasick , you are correct but since he is having overheating problem , I don't know what the housing is like hence the recommendation.
Normally one changes the impeller as a precaution long before the engine overheats .