Heat alarm problem

[Donald Kilby]

Hi, I have a Z250turb 2003. The heat alarm goes off for no apparent reason. The engine weep hole is passing water and the engine does not feel hotter than the other one. When I stop the engine for about 10 min and restart it it seems to be ok. The only time it happens is when I am below 1000rpm. Would like some suggustions on how to track this problem down? Not being a two-stroke outboard person any suggestions would help.
The boat I have these engines on is a 2003 Wellcraft Scarab 32 ccf. This boat is heavy, about 9000lbs+. The motors will only turn about 4500rpm and 48mph on the gps. Would this be about right for this boat?
Thanks for any help I can get.
Don

 

[99yam40]

Re: Heat alarm problem

Check thermostats and PRVs.
Pressure relief valves can stick open and dump water at low RPM causing motor not to fill all the way up with water causing upper cylinders to overheat. Once the RPM comes up the water pump will furnish enough water to over come the stuck open PRV.

If the thermostats and water pumps have not been replaced latly I would do that PPM while at it.

I would think that the motors maybe over proped if they are only getting to 4500, but I am not sure on the proper WOT RPM for those on large boats

 

[rodbolt]

Re: Heat alarm problem

4500 at WOT indictes either an engine problem or its way over propped.
overpropped that much is begging to detonate a piston.
those engines liked to do it anyway.
it needs to be able to turn about 5300 to 5500 RPM with the load that day.
go by your local yamaha dealer,run the PID.
there were many many updates on the Z250TURB motors that should have been done.

 

[Donald Kilby]

Re: Heat alarm problem

Thanks for the info. The manual says the operation rpm is 4500 to 5500 depending on usage. Engines seem to be strong and the boat weighs about 10,000 lbs loaded.
The props are 23" pitch ss. I get about 48.9 mph at 4500, no throttle left.
dk

 

[99yam40]

Re: Heat alarm problem

Rodbolt is the man that know, so follow his advice

 

[Donald Kilby]

Re: Heat alarm problem

Hi Rodbolt,
I checked with Yamaha when I bought the boat. All of the updates had been done for those engines. The engines had 118 hrs on them when I bought the boat. I had a local Yamaha dealer winterize the boat, he said the engines were in great shape.
I hope so?
Thanks
dk

 

[rodbolt]

Re: Heat alarm problem

do as you wish.
4500 at WOT is going to detonate pistons.
support your local tech.
he needs bling on his car just like you.
are you sure its an overheat alarm? the horn tone is the same for ALL alarms on that engine.
the visual indicates on the tach tells you which one just triggered.
a clogged remote oil tank filter will drive the trained monkeys nuts.

 

[Donald Kilby]

Re: Heat alarm problem

Rodbolt,
The heat alarm on the R tach is blinking when the alarm goes off.
Both engines turn the same rpm at full throttle. 4500rpm. Boat is operated most of the time between 3000 and 3800 rpm about 38mph,top is about 48 mph at 4500rpm. Took the boat out yesterday for about 2 hrs did a lot of slow running, 800 to 1500 rpm. Alarm did not go off?
Thanks,
dk
P.S. I had not made any chages before I took it out.

 

[99yam40]

Re: Heat alarm problem

Even if you are not running it at WOT the motors is still being loaded too much by the props at the other RPMs also.

 

[rodbolt]

Re: Heat alarm problem

you either have a temp switch failing,a pressure control valve sticking or corrosion under the head passage blocking water to the area of the head the swich is inserted in.
keep running it overpropped.
this is gonna be good, takes roughly 16 hours to remove,undress, uncrate the new powerhead,dress it and reinstall.
the powerhead assy new from yamaha runs about 5100 dollars.
that engine DOES not have a knock sensor to detect detonation.
your first indicate thats detonation is occuring is when the engine loses power and the tech calls you about a 0 compression reading on a hole.
that is the first and ONLY symptom that 3.3Z motor will give.

 

[Donald Kilby]

Re: Heat alarm problem

Hi Rodbolt,
I get your drift. What prop would you recommend for this boat?
dk

 

[99yam40]

Re: Heat alarm problem

Check this site to see what they ran during testing on boats similar to yours

http://www.yamaha-motor.com/outboard/products/perfbull.aspx?ls=outboard

 

[Donald Kilby]

Re: Heat alarm problem

Thanks Ensign, will do.
dk

 

[rodbolt]

Re: Heat alarm problem

not the first hull ever left a dealership over propped or with the engines to high.
then I try to convince the owner its not a yamaha problem nor a hull manufacturer problem but the selling dealerproblem.
usual reply I get is: thats the prop the engines came with from the factory.
usual answer is no,the 3.3L motors out of the box from yamaha had only the prop attaching hardware.
but try to find the source of the overheats before getting wild about props.
if you reread the manual AND its a FACTORY Yamaha manual it says the operating range is 4500 to 5500 with a reccomendation for optimum performance and engine life to adjust(prop) the WOT engine RPM the the upper end of the reccomendation.
means that engine needs to be able to turn 5300 to 5500 with the load that day.
sold a 20 skiff a few years back,simple rig.
center console and a cooler seat and an F115.
came back with a hole in a piston.
also now had a t_top,seating for 14 people,curtains and an aft casting\observation deck.
you tell me what failed

 

[Donald Kilby]

Re: Heat alarm problem

Hi Rodbolt,
I bought the boat used with 118 hrs on the engines. It came with 23" ss props. I had no choice. Since I am new to the Yamaha 2-stroke, I am trying to do the right thing. If I have to change props, I will. Most of my experience is with big block chevy's and diesels. On my Fountain every 1" of pitch up or down was about +/-500 rpm. Do you think this would be about correct for these engines?
Thanks for your help.
dk

 

[rodbolt]

Re: Heat alarm problem

somewhere between 250 and 500 RPM.
its a heavy hull.

 

[Donald Kilby]

Re: Heat alarm problem

Hi Rodbolt, info for you. Since you seem to be the resident guru of z250's, let me relate a new experience.
The last two times I have had the boat out the heat alarm did not go off.
Today I tried a friends pair of 17p props. The motors went to 5500 but would not go further. I had abour 4" of throttle left but it would not rev any more. Do these engines have a rev limiter?
At 4400 with the 23p props the boat went 48mph on the GPS but the throttle was on the firewall. At 5500 the boat went 42mph with a lot of throttle left. I am trying to find the correct prop. I think 17s are two small. I was looking for the motors to over-rev with the 17s but they just would not go past 5500.
Hope you can help,
dk

 

[99yam40]

Re: Heat alarm problem

I am wondering if you may have motor or tach problems. I would think that the motors should push the 17 without a problem and over rev like you thought. What diameter props are the 17 and the 23?

This shows a @10,000lb boat with 21" props.http://www.yamaha-motor.com/assets/...n_otb_2StrokePerf_HPDI_250hp_02-252-JUP-B.pdf

 

[Donald Kilby]

Re: Heat alarm problem

Hi 99yam40, both sets are the same dia.
The engines run right up to 5500 but will not go anymore. With the 23p they ran up to 4400 and would not go anymore. With the 23p the throttle was all the way, with the 17p at 5500 I had about 3-4" left on the levers. No hesitation or missfiring. I checked the fuel pressure and they hold a steady 49lbs. This boat weighs 8700lbs dry without motors.
Thanks for your input,
dk

 

[99yam40]

Re: Heat alarm problem

Are they 14 7/8" props? the diameter make a difference also.
The ones in the bulletin were 14 7/8" X 21" and a gear ratio of 1.75:1
and that boat ran 53MPH at 5500. Same motor model # as yours

I would not think they should reach the 5500 before WOT and not increase anymore in RPM when the throttles are moved 3-4" more to WOT.
Did the 23s reach their top RPM before opening throttle all the way?
Do the linkages on the motors move anymore when the last 3-4" of throttle is moving?
I would not think the over rev limiter would keep it that close to the top RPM range of the motors design, but I am could be wrong about that.