250 Sho overheat question

[dcathey]

I have a 250 sho and did a service this past week. Twice so far this weekend I have gotten an overheat warning and both were when trimmed out running 45-46 with jackplate on 2. When running 30-35 and idling all day it runs fine. Anyone ever had this ? After I shut down and turn back it pees fine so it’s not a blockage like my initial thought

[Headhunter]

Thermoststs

[jh141]

5 hours ago, Headhunter said:

Thermostats

I agree. I had A Strange temp problem on my SHO and found one thermostat was good and the other would stick half way open or not open at all. This is a good place to start and really easy to do. Remove the thermostats put them in a pot of water and heat the water. I used a cooking  thermometer to watch the water temp in the pot. They should open fully at or before 160 degrees I believe. Could be 140-180 degrees. May be off on the temp. If not Replace them. 

I also had a friend bring me his Hells Bay with a Mercury 60 hp ( black Yamaha). He had just had it serviced and it would heat alarm at 3/4 or above throttle. He would shut it off, wait a few then continue at 1/2 throttle and it would be fine. The service tech had dropped the impeller key into the water intake cavity of the lower unit and I guess not relived it had happened. When the motor was at 3/4 throttle of above it would draw the key up the water passage and jam the impeller. When he shut down and somehow the key would fall down again and the water pump would work. When I took it apart the damage to the bottom of the impeller was obvious but not the cause. When I turned the lower unit upside down the cause fell out and reviled itself. 

I have also seen impellers put in counter clockwise and cause instant damage to the impeller. Not likely since you have a water stream at the Pee indicator.....

 

[jh141]

Thermostats specs........start opening @ 136.0 - 144.0 degrees 

                                                                    @ 158.0 degrees  open to 4.3 mm or 0.17 in  or fully open

 

[SCFD rtrd.]

Where does the Poppet Valve come into play?

[FINCHASER]

The Pressure control valve (poppet) serves to relieve excess pressure from the system when running at higher RPMs.... if it isnt working too much pressure in the system is gonna blow out somewhere and cause a loss of flow 

[jh141]

4 hours ago, SCFD rtrd. said:

Where does the Poppet Valve come into play?

If Dcathey has a four stroke 250 SHO 4.2 L it does not have a pressure valve (poppet). The 4.2 liters have a low pressure high volume cooling system. It is not unusal for these to be below 3 psi at idle. The opposite of what you find on an HDPI vmax.

[dcathey]

So we ran all day as planned at around 4000 rpms... business as usual. I’m going to go ahead Tuesday or Wednesday and replace both thermostats , the motor is 10 years old and it is probably time anyways. I’ll post back after the swap out and let you know. Thanks for the help

[Headhunter]

I change my stats when I do the pump, every time.

[Moderator]

You're like me Chuck: We constantly do the next owners of our boats remarkable favors..

I have the stats cleaned and tested with new gaskets every year.  When my son is using the boat, or when I run 30 off, I don't want simple maintenance items to complicate my day.  If I stayed inshore in cellphone range, I might not be as particular.

MM

[Headhunter]

30 off is a long way to row my friend. Stats are cheap

[Wanaflatsfish]

9 hours ago, dcathey said:

’m going to go ahead Tuesday or Wednesday and replace both thermostats , the motor is 20 years old and it is probably time anyways. I’ll post back after the swap out and let you know. Thanks for the help

WOOOAHAHHHH...20YEARS and no thermostat change

you must be living right

I check and / or change mine every 100 hrs to be sure they are not full of crud....

easy peasy to do....3-4 bolts and a gasket....and/or a new thermostat ...$20 or so..

dc

 

[dcathey]

Type-O, 10 years and thermostats are probably 5 years old. Thought I’d clarify

[jh141]

Dcathey, Is your motor the two stroke or the four stroke.

6 hours ago, dcathey said:

Type-O, 10 years and thermostats are probably 5 years old. Thought I’d clarify

 

[dcathey]

17 hours ago, jh141 said:

Dcathey, Is your motor the two stroke or the four stroke.

 

250 SHO is a 4 stroke, I changed thermostats last night, gonna pull water pump just to be sure all orings are in place and didnt move when we change water pump last week. Thermostats were pretty rough looking

[jh141]

Got it. The 20 years threw me for a sec. Mine is also the 250 SHO four stroke 4.2 L. Did not want to waste your time, Just making sure, there is sometimes still some confusion between the HDPI vmax 2 stroke and the SHO 4 stroke. On mine I changed the thermostats and thermostat housings. Thermostats in most likely the cause, it was on mine. The manual says to rotate the shaft clockwise when installing the water pump housing over the impeller. Yamaha sure is proud of their thermostats. I paid $50.00 bucks apiece, but it solved my temp issue.

[Headhunter]

Good deal!

[dcathey]

Ok after thermostat swap and I pulled water pump again just to make sure the plastic housing cover was seated properly. Put the nose cone on and put it on hose, have to squeeze cone to get it to pump and if you don’t will overheat after several minutes. I think I have a warped cover and will swap that tomorrow. I’ve read when they’ve been hot( this one has signs that it has been) they can warp and *** air which makes sense when everything else is new. You guys got any other input on that theory?

[dcathey]

Old water pump pumped fine on hose and never gave an ounce of trouble , I think once old housing cover gets very hot then you get fresh parts under them they will not seat correctly 

[fishmanjj]

26 minutes ago, dcathey said:

Ok after thermostat swap and I pulled water pump again just to make sure the plastic housing cover was seated properly. Put the nose cone on and put it on hose, have to squeeze cone to get it to pump and if you don’t will overheat after several minutes. I think I have a warped cover and will swap that tomorrow. I’ve read when they’ve been hot( this one has signs that it has been) they can warp and *** air which makes sense when everything else is new. You guys got any other input on that theory?

If it has been ran “ dry” the impeller housing will warp and also be discolored and sometimes even brittle.  If it is slightly warped , that big O ring is a real SOB to keep in pace when you flip it over to seal it up.

[dcathey]

I put a dab of rtv silicone to hold it in place this time too. I’m changing housing tomorrow and eliminating that from possibilities

[dcathey]

At my wits end. Every part is new. It will not pump on hose very long. After trying various things I air tested by blowing air from pickup. No bubbles so I guess it’s not sucking air. I’ve tried the old impeller and wear plate again, same thing. Do these things just need to run a few hours sometimes to work the kinks out? Last weekend when it did this I ran fine other than WOT. 

[jh141]

Sorry to hear.......When I put mine on the flusher that goes on the lower unit when brand new or just for maintenance, to does take a minute or two to start pushing water out through the pee indicator, but just a minute or so.

I would start over on the water pump, same parts just take it all apart and check everything. I would start with the passage from the lower unit  pickup to the base of the pump. I use grease to hold gaskets and o rings, not rtv silicone. Make sure you turn the input shaft "clockwise" when placing the housing and stainless insert over the impeller. I also put a thin coating of grease all over the inside of the stainless insert. Make sure the impeller key way is in place. The next place is the transfer tube seal on the top of the housing. Another great place for a thin coat of grease. I have in the past trimmed the motor up with the lower unit removed and connected a hose to the transfer tube to run water thru all the passages in the powerhead. It makes no sense to me what you are going through. It just sounds like the impeller is not keyed to the input shaft correctly, like it is slipping. These Water Pumps are pretty stout because they are low pressure-high volume unlike in the past where two stroke water pumps were higher pressure and more susceptible to wear out. Even when my housing was damaged ( by my dealer running the motor on the flush port )  it still worked well and did not overheat when in the water at any speed. The only thing that has hindered my cooling system was bad thermostats. 

I know you have most likely done all these things. Wish I could help. If you need any info let me know, I have a Service Manual for these motors.

[dcathey]

JH141, thanks for the post. The first couple times we did grease everything. This time I thought it was getting air so we added a thin layer of rtv to perimeter of gasket and it’s not getting air. I’m going to run it today and see if it improves from last weekend in water

[dcathey]

JH141, thanks for the post. The first couple times we did grease everything. This time I thought it was getting air so we added a thin layer of rtv to perimeter of gasket and it’s not getting air. I’m going to run it today and see if it improves from last weekend in water