2004 257 Advance overheating (Yamaha 150's)

[patrick16]

The 2004 motors have just over 300 hours and the port motor is overheating. The mechanic replaced the water pump and t-stat and no change. He thinks it is a clog higher in the motor and thinks it is not worth trying to fix (given the age of the motor). Quoted new motors (2 x Yamaha 150's) at 31k.

The Boat is in otherwise good shape for it's age, but I was strongly considering an upgrade in the near future to something in the 30' range. We go 30 - 50 miles offshore regularly. I am not sure whether I should spend the $ on the new motors, sell it as is or something else.

I am very interested in getting the opinions of some of you more experienced captains.

Thanks for any help.

 

[seasick]

Are these motors 2 stroke or 4 stroke?
What are the conditions when the overheat occurs. Does it overheat only under load at cruising speeds or perhaps overheats at idle or low speed?

How does the telltale look when it overheats?
More info will help narrow down the possible causes.
Jumping to the conclusion that new motor are needed surprises me a bit. The issue could be something simple.
Do you have the old thermostats?

 

[patrick16]

Are these motors 2 stroke or 4 stroke? 4 stroke
What are the conditions when the overheat occurs. Does it overheat only under load at cruising speeds or perhaps overheats at idle or low speed? it overheats at high rpms under normal load

How does the telltale look when it overheats? normal
More info will help narrow down the possible causes.
Jumping to the conclusion that new motor are needed surprises me a bit. The issue could be something simple.
Do you have the old thermostats? mechanic should have them

He says the age of the motor makes it not economical to repair.

Thanks for any suggestions.

 

[Hookup1]

I have Yamaha F150's from 2006 with 2,300 hours on them. Regularly flush (everyday I use it). Telltale always working. A few thermostats and water pump rebuilds over the years. Motors run like new.

I'm not a mechanic but I'm surprised there isn't something more that can be done. Pull all the engine zincs and flush the motor. I don't know if there is a easy way to snake the block to check for blockages. Make sure good flow thru telltale - if not clean out from engine side. How "overheated" did you allow it to go? Thermonuclear overheating can damage a lot. I would test the motor and have a infrared thermometer handy to see which cylinder or cylinders are heating up.

 

[TMANN]

Find another mechanic. New motors.... good lord.

 

[seasick]

The data is helpful.
Can you tell us why the mechanic replaced the t-stat and water pump at no charge?
Did the mechanic mention if the t-stat housing was clear of crud?

I was hoping the motor overheated at low revs ( classic poppet valve issue)
There are still things to look at before declaring the patient dead.
I also think a check with an contactless thermometer is advisable to confirm that the motor is indeed over heating and its not a bad thermo sensor. The IR thermometer may help identify any hot spots.
A flow restriction is a possibility and a thorough engine flush with salt remover might be something to try. The worst case scenario is that there is an exhaust leak into the cooling channels. That could be a gasket or a crack or hole from corrosion.
At a minimum further investigation will require disassembly of cooling channel covers.
I would look deeper but that will entail labor. You might want to get a second opinion.
Oh, did the overheat just start mid season or did it start after perhaps winterization or routine maintenance ( Water pump e.g.)?