Head temp on Yamaha 250?

[Wellcraft238]

I have a 94 Yamaha 250. I just replaced the thermostats, water pump ass'y, flushed everything, and am alarming after running in the driveway for 5 minutes (was alarming before I changed everything out and the old impellor looked healthy). I checked temps and the heads by the spark plugs are 198 degrees and lessen as you check the lower head temps. the thermostat housing is reading 200-205. What temp do the thermostats open at and what temp should the heads read using a temp gun??

Also, Since the gage thinks I have no gas, does Yamaha set off an alarm for no fuel? The alarm is constant; no beeps.

[Wellcraft238]

Fixed the gas gage, so that's not it... Possible oil level sensor malfuntion? Float stuck? Does not alarm for 3-5 minutes after start up..

[ohsoslow]

Hey mate, gas gauge won't kick out a warning, my guess would be overheat, I can touch the top of my heads while running and they are hot, Almost too hot to touch, but not quite. I work in celcius, but I'd be guessing about 50C, so maybe 120-130f? I'd be picking if you're getting 200f, you've got a problem! Maybe water passages blocked?

Pull the thermostats out, and run it, see if it remains cool.. Won't do any harm, but will help eliminate them as a possible problem.

[Wellcraft238]

Thanks,

I pulled them and ran it and it still alarmed before replacing with brand new ones. The water stream is lukewarm (fine to the touch). I just cleared the oil level sensor to make sure it doesn't stick and will re-run. The temps of the heads are higher on the top cyl's than the lower. The lowers were about 119 F/mids 150 F/Tops 180-199 F and then the thermostat housings were 200 F measured using an infrared gun. Not sure if they should all be even....

[Wellcraft238]

Cleaning oil level sensor made no impact..time to pull the heads and peak in there..

[ohsoslow]

My engine gets hotter the higher up you go, but nowhere near 200f! More like, 130f top, 100 bottom. Sounds like theres something blocking your water flow through engine?!

(I think off memory the thermostats on mine are supposed to open at about 120f.. so 200f is way overtemp)

[rodbolt17]

have you checked/replaced the pressure control valve grommet?

[Wellcraft238]

I checked the grommet and all looked OK except for some junk on the ouside face of the relief valve/poppet..nothing obvious. Since the outside of the head gasket looks fairly corroded (whitish), I'll look inside to baseline what I have. Thanks for the input!

[boats.net]

Unless you have extremly good water pressure at your house then most V6 engine will overheat when run for 5 minutes on a garden hose flusher, might try putting boat in water and run it.

[Wellcraft238]

Sounds like you guys may be correct. I pulled one head and it looks fine with no blockage or crap in the passage ways. Pulled grommet again and it looks OK, ...I will re-assemble with one gasket set (not cheap!) and won't bother taking apart side #2 now... Will put in water and try out if my hose may be an issue. I never had problems with my Ocean pro 225 out there though, so I'm a bit confused.

Is there a torque requirement for head bolts?

[boats.net]

20 Ft Lbs on head bolts.

[Wellcraft238]

I bought a new poppet valve and grommet anyway for a piece of mind.. the new ones have a full radius on the seal side, unlike the originals with the stem insterted into the grommet.. hmmm

[Wellcraft238]

Bingo!

I should have listened to you Boats.net.... After snapping a head bolt, snapping an easy out, breaking thru the water jacket wall to get it out and epoxying a stud into the area so the head would go on, it overheated in the driveway after re-assembly, but was at 116 F when I put it in the water... ran it for approx 45 minutes and even banged 43 MPH on it... All is well and compression is still good... looks like all I had to do is stick it in the wfrom day 1... A good lessons learned for the next guy with a similar issue! THANKS!