Low speed overheat

[greenhabah]

1995 225 txrt

I overheat while trolling at 6-700 rpm's.
Runs ok at 1200 rpm's and above. Not sure about in between.

Has not run right this season. (Did have a late start)
No problems last year.

Since last season:
New lower unit
New thermostats
2 new poppet valves (last one installed is the new rounded style)

The starboard side thermostat cover runs hot on the raised portion where the temp sensor is.
The port side runs about the same temp across the thermostat cover.

Pulled the starboard head cover and found an anode that broke free.
Yeah...."found" the problem.

Put it back together and it still overheats.

What next??????????????

I've seen other posts that were looking for a diagram of the water flow but I didn't see anyone find it. This would be helpful if anyone found this.

I assume the water splits on the way up to the 2 sides. Or does it cross over at some point?

Tell tale seems a little weak and slows down when I put it into gear.


I also have this over at the yamaha forum
http://www.yamahaoutboardparts.com/foru ... 13761.html

 

[no problem]

I would remove the water pump and re-install. sounds like you could be missing an o-ring or something.
i'm thinking maybe #11 or #13
http://www.boats.net/parts/search/Yamah ... parts.html

or #77 or #78 in this drawing
http://www.boats.net/parts/search/Yamah ... parts.html

Just a guess but it would explain low water pressure at low rpm's. Good luck!

 

[seasick]

A common cause for low speed overheating is a stuck open or weak poppet valve.

 

[greenhabah]

Poppet valve has been checked ..double checked and replaced.
All new spring, grommet, new style valve, cover and even new bolts.

 

[Grog]

It may be worn water pump housing. If they put in a new lower unit, they may have just replaced the impeller and not the whole.

Did anyone mess with your timing? If it's retarded, it will run hot.

 

[greenhabah]

The new lower unit came complete with a new water pump.

Timing has not been touched.
If it was timing would that only affect one side?

Same question applies to the earlier post of a missing o-ring...would just starboard side be affected?

 

[Grog]

Missed the stbd only part, no, it would effect both sides.

 

[Mike L]

You say you pulled the starboard head cover. By this do you mean the water jacket? I had a similar problem on a friends motor and the water jacket had clogged with salt. Just a thought.

 

[greenhabah]

Did pull the water jacket. No real salt build up. I do flush everytime.
Did find an anode that we assumed was causing the issue but it did not fix it.

 

[Mike L]

Does it have the hoses that run from the poppet area to the side of the water jacket? Maybe one of them collapsed or kinked?

 

[greenhabah]

It does have that hose from the poppet valve.
I did not notice anything wrong with it while working on the poppet valve but will check it out.

But my understanding of the pressure relief valve is that
at low rpm's there should not be any water flowing thru that hose.

 

[Mike L]

I agree. Just couldn't think of anything else. Sorry.

 

[Doc Stressor]

A basic question:

Did you measure the water pressure? What does it read at low speed? It should be around 4-5 psi at idle.

If it is low, I would suspect the water pump. It may be defective despite it being new. "New" lower units for older engines have typically been siting around for a long time. The impeller arms could have gotten brittle or permanently bent out of shape. Or it might have been installed improperly.

In any case, I would pull that lower unit and inspect the impeller and pump housing.

 

[greenhabah]

How do you measure the water pressure?

 

[catch22]

I would remove the water pump and re-install. sounds like you could be missing an o-ring or something.
i'm thinking maybe #11 or #13
http://www.boats.net/parts/search/Yamah ... parts.html

or #77 or #78 in this drawing
http://www.boats.net/parts/search/Yamah ... parts.html

Just a guess but it would explain low water pressure at low rpm's. Good luck!

First off, I agree with member "no problem"... check that grommet out, (part #77). If it's missing, pinched, or damaged, it will allow water to escape around the water tube, (part #12) and cause exactly what you describe.... low pressure and over heating at idle, or low rpm's. At high rpm's, there's enough pressure to make it up through the water tube and cool the block.

However... if it's only one side, (starboard, as you say)... then something could be restricted on that side. Can't help but wonder about that anode you mentioned... that, "broke free". How was it attached in the first place? Were there mounting screws of some sort? Any chance one of them might be lodged somewhere? Or a piece of the anode itself? Is it re-attached properly?... might be restricting or deflecting water and causing a hot spot?

You could try flushing the motor out without the thermostats, (thermostat covers installed). Remove the poppet valve also and block the port by either stuffing a piece of rag in it or make a blank for the cover, (like the gasket). Drop the lower unit and attach your garden hose directly to the water tube, (make an adapter out of 1/2" hose and a female garden hose fitting). With the water turned on full, kink the garden hose and release it... do that several times to blast water through the block. You might get lucky and dislodge something.

You could also try flushing the motor with salt away, (normal running... nothing removed from the motor). Use a plastic trash can full of the mixture and let it circulate for while, (till hot)... then flush the motor normally afterward.

By the way... that poppet valve, (pressure relief) opens whenever the thermostats are closed, (like during a cold start) or whenever there's excess water pressure. It's simply a bi-pass.