Yami 150 Overheating Above 4200 RPM (S150TXRV - 1997)

[boatmon345]

Hello and thank you for reading.
Several occasions this weekend I took my boat out, and each time I went above 4200RPM an alarm would sound and revs would be limited. At first it startled me but then I realized it must be overheating. I pulled thermo switches and and checked them for proper operation. They close around 190F and open around 160F which I believe, but not sure, is proper operation.

So this tells me my motor is definitely getting hot. At overheat I took temperature measurements with a temp gun. I noticed the hottest parts of the motor was both sides of both top cylinders (behind the heads - the actual cylinders). Also, as a sidenote, my pressure relief valve is stuck shut so I don't believe that that could be the cause of the overheat, although I do recognize that I need to replace this device nonetheless.

I personally rebuilt this motor in 2006 and believe I installed new thermostats, but I suppose they could have corroded already. Also, I have never changed the impeller and I purchased the boat in 2004. I was told at time of purchase that the impeller had just been changed. Anyway, the pee stream is very strong. Additionally I also noticed that alot of water is blown out out of the exhaust holes. It seems to me that when I rebuilt the motor, not much water came out of the exhaust holes and year after year more and more water comes from these holes.

Motor is run in saltwater only, and flushed with hose attachment (not muffs) after each outing.

What could be the likely problem here? Thank you very much for your help.

 

[99yam40]

Re: Yami 150 Overheating Above 4200 RPM (S150TXRV)

Re: Yami 150 Overheating Above 4200 RPM (S150TXRV)

Replace water pump,stats and PRV. Check for corrosion build up in passages while you have those out.
Yamaha recommends replacing water pump every couple of years, I would do that if you can remove the bolts to do it.
That is another good reason to do it every couple of years so you can clean and lube the bolts.

PRV stuck open normally causes low RPM overheat

Old water pump may not put out enough water to cool motor if PRV is stuck open and dumping too much

 

[boatmon345]

Re: Yami 150 Overheating Above 4200 RPM (S150TXRV)

Re: Yami 150 Overheating Above 4200 RPM (S150TXRV)

I just removed the thermostat housings and thermostats. The passages were fairly plugged up:

Last time I cleaned out the passages and replaced TStats was 6 years ago when I rebuilt the motor.
I just ordered Sierra thermostats & gasket kits:
http://www.iboats.com/Thermostat-Kit-Sierra/dm/view_id.485816

Hopefully this resolves the overheat condition.

 

[boatmon345]

Re: Yami 150 Overheating Above 4200 RPM (S150TXRV)

Re: Yami 150 Overheating Above 4200 RPM (S150TXRV)

I just wanted to chime in and advise that I've received the new thermostats. I picked the lowest cost shipping option which was USPS, and it took only 5 days and arrived ahead of schedule. I also wanted to advise that stamped on each thermostat is 50C which I believe refers to the temperature. The reason I point this out is because nowhere on any documentation does it state the temperature. 50C = 122F. So at least if someone does a search in the forum they will be able to find this info.

EDIT
Well I figured out that my old thermostats were seized shut from corrosion.

I just installed the new thermostats, gaskets, and coated the mating surfaces with a sealing compound. The trickiest part was torquing the bolts to 5.6 ft lbs. I set my torque wrench for 6 ft lbs but it is so hard to detect that I was at 6 ft lbs that I believe I went a bit over on each bolt. Nonetheless, I am very optimistic that the overheat problem will be solved. I'll run her in the next few days and chime back in.

 

[99yam40]

Re: Yami 150 Overheating Above 4200 RPM (S150TXRV)

Re: Yami 150 Overheating Above 4200 RPM (S150TXRV)

service manuals give the temp it starts opening spec 50 and full open spec of 60C.
It pays to get a service manual in the long run

 

[boatmon345]

Re: Yami 150 Overheating Above 4200 RPM (S150TXRV)

Re: Yami 150 Overheating Above 4200 RPM (S150TXRV)

Well my point is that when buying replacement parts, esp. when it is not the exact Yamaha part, it would be nice for the specs (such as temp) to be spelled out so that you can compare them to what the manufacturer calls for. I do actually have a manual but that only gives you half the information when attempting to replace parts. To be sure, the supplier should indicate the specs too so that you know you are buying an apple to replace an apple. A recommendation I have for iboats.com is to indicate the temperature of their Sierra thermostat on their website. But it isn't just iboats; I found that other suppliers are lacking this information also. Just my $0.02 .

 

[99yam40]

Re: Yami 150 Overheating Above 4200 RPM (S150TXRV)

Re: Yami 150 Overheating Above 4200 RPM (S150TXRV)

my recommendation is to buy a Yamaha service manual for your motor and yamaha parts also

 

[boatmon345]

Re: Yami 150 Overheating Above 4200 RPM (S150TXRV)

Re: Yami 150 Overheating Above 4200 RPM (S150TXRV)

UPDATE

I just wanted to chime back in; I got a chance to test the repair this weekend: It did the trick. The new thermostats and cleaning of the related passages is allowing enough water to flow that my motor is no longer overheating at 4200+ RPM.

So I guess I get about 6 years out of thermostats under the conditions my Yami is being used. Good to know.

 

[99yam40]

Re: Yami 150 Overheating Above 4200 RPM (S150TXRV)

Re: Yami 150 Overheating Above 4200 RPM (S150TXRV)

looking at their condition after 6 years I would be replacing them before they get that bad.
At least pull and clean and test them every couple of years, do not wait until you are having problems

 

[yamatech43]

Re: Yami 150 Overheating Above 4200 RPM (S150TXRV)

Re: Yami 150 Overheating Above 4200 RPM (S150TXRV)

If anyone else reads this, please don't take boatmon's advice, check your tstats much more often than once every six years and don't
let your motor overheat to begin with....also, if your motor's passages ever look like THAT, pour some straight NeutraSalt in them and let it
sit for a few minutes, then rinse out...works like magic....hate to see someone abuse their motor and then say "see what I can do?"....

 

[boatmon345]

Re: Yami 150 Overheating Above 4200 RPM (S150TXRV - 1997)

Well here we are 11 months later and I am getting the overheat alarm again after briefly taking it to WOT. It is peeing strong. And I don't believe my pressure relief valve is the problem.

The thermostats that I purchased & installed back in July of last year were these:
Sierra 18-3608 which is the thermostat kit which includes:
-18-3540 thermostat
-18-0844 gasket

Before I go tearing off the thermostats and replacing them with the same model, has anybody had any short-life problems with these thermostats? And if so, can anyone recommend a better quality thermostat?

Thank you very much.
Also, thank you Yamatech43 and 99yam40; your advice is well-taken.

 

[craigwill]

Re: Yami 150 Overheating Above 4200 RPM (S150TXRV - 1997)

Also, I have never changed the impeller and I purchased the boat in 2004
Change every 2 years. Key way corroded in shaft for the impellar? Spend a little now and save alot later!
PREVENTATIVE MAINT. Thats all it takes
"Sierra 18-3608 which is the thermostat kit which includes:
-18-3540 thermostat
-18-0844 gasket"
Cheap means you get to do it twice!


Craig

 

[boatmon345]

Re: Yami 150 Overheating Above 4200 RPM (S150TXRV - 1997)

I just took apart the thermostat housings, and the passages were badly blocked with gook again, but after only 11 months.
After taking a toothbrush to the thermostats, they look almost new. Tested them for proper operation in a pot of hot water. I have renewed faith in these Sierra thermostats.

Cleaned it all up, coated the surfaces with Rustoleum Rusty Metal Primer (as I always have), and put it all back together. This time I used Permatex Ultra Blue gasket maker instead of pre-molded gaskets. Hope that wasn't a mistake. Will fire her up tomorrow after the gaskets have had a chance to cure.

I also have an ear-muff dual-side-fed type flush adapter on-order thinking that I am not flushing properly using just the Yamaha flush hose. The boat is on a lift, and I have never flushed the motor from below since I cannot reach it. I will finally engineer something to help me push the earmuffs onto the lower unit to flush it right.

 

[99yam40]

Re: Yami 150 Overheating Above 4200 RPM (S150TXRV - 1997)

I will finally engineer something to help me push the rabbit ears onto the lower unit to flush it right.

Something like a Kayak or little john boat works well.
Rig up 2 hoses and have both ears and flush going while running motor

 

[boatmon345]

Re: Yami 150 Overheating Above 4200 RPM (S150TXRV - 1997)

I just wanted to chime back in and advise that I took the boat to WOT several times after cleaning the thermostats & passages, and it is no longer overheating, so that did the trick.

I did try flushing with the earmuffs, but I had a strange overheat problem, and I have documented that in a separate thread: http://forums.iboats.com/yamaha-suz...rheat-97-2-stroke-yamaha-s150rxrv-613824.html

I will make a note to pull and clean the thermostat housings more frequently now, perhaps yearly, as a result of this experience.

Thank you all for the advice.