Roady68

Did a wide open run in our Sig 300

14 posts in this topic

So we took the boat out last night for a cruise and some swimming.  On way back to the marina I decided to see what the upper end RPM performance was like.  I know the wife would have killed me if something broke, but we had been cruising around so far at 3200 to 3600 rpm and I wanted to see what top end would do.  So I threw caution into the wind and continued to nudge throttles towards WOT.  3600-3800 rpm, another nudge, 3800 to 4000, another nudge or two and we were sitting around 4400 rpm.  Continued for about 30 seconds before I got an alarm.  It was a continuous beep.  Temps were pushing up past the 170 line on the gauge maybe a bit more so I am assuming it was a high temp alarm.  Boat never lost power, but I pulled back down to about 4200 for about 15 seconds then eased down to 3600 for another few seconds and it went off.  According to the GPS and my phone app, we hit ground speed of 44 mph.  

Dropped back down to 3200 rpm, which seems to be where she likes to cruise, and all was fine.  Purred like a kitten all the way back. Temps sitting around 160, and oil pressure around 40.   Anyway, I thought the performance was pretty good for a 17 year old boat with half tank of fuel, a family of four and full water tank.  

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I agree... but: you shouldn't be getting overheat alarms at factory WOT power.

When's the last time impellers were changed?

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Sounds like the impellers weren't keeping up or you have corrosion buildup in the exhaust system.

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+1 on a possible impeller change needed.  

Can you see the fuel gauge dropping at WOT.  It moves down pretty fast.

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Impellers new.  Most likely possible corrosion in exhaust.  I was thinking of trying to get a hold of our FLIR camera from the shop and get some thermal images of the engines.  I may also borrow code reader from coworker to see what the code was.

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I did the same thing and my alarm was from the depth gauge.  going that fast messed with the readings and it threw the  shallow alarm.  Once I turned off the bottom reader, no alarm.

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While I'm no mechanic I still wonder, did both engines climb to 170? I was going to suggest a thermostat problem but on both at the same time didn't seem logical. 

My engine remains at or near the same temp regardless of throttle setting.

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I think I need to do another run and get better gauge readings.  Maybe next weekend.  So far both engines have responded the same.  They are usually with in a degree or two (within accuracy of gauge) and same oil pressure.  

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The rise in temp indicates an issue. If your manifolds/risers are original, it may be an indication that you are on borrowed time. Could also be a worn raw water pump housing not supplying sufficient flow at high RPM's. It is not normal for engine temps to spike on a WOT run.

i would also check what the recommended WOT range is for your engines. You are probably at the low end of the range.

I do periodic WOT runs, and know what is "normal" for my boat. Any deviation and I start looking for the cause. 

And the WOT run is kinda fun...

brick

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How does riser/manifold condition affect the thermostat housing (where the sensor is located) in a way that yields higher temp readings from the sensor/gauge?  I see this mentioned quite a bit across many forums but have yet to understand how this works?

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4 hours ago, Dennis A said:

How does riser/manifold condition affect the thermostat housing (where the sensor is located) in a way that yields higher temp readings from the sensor/gauge?  I see this mentioned quite a bit across many forums but have yet to understand how this works?

Restricted water flow due to clogged manifold.

brick

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14 hours ago, brick said:

Restricted water flow due to clogged manifold.

brick

So in general, the hot water going through the thermostat exits to the exhaust manifolds as well as back into the engine circulating pump.  If you restrict the flow through the manifolds/risers then more water will be forced back into the engine circulating pump leading to a rise in engine operating temp.  So, not only will the engine be operating at higher temps, so will the manifolds.  

 

coolfig6.jpg

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not saying people should drive at WOT all the time, but on a properly operating engine it should be far from harmful.  Actually driving WOT is a good thing lets you know what your boat is capable of and can also show you signs of a any symptoms the engine might be showing.

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23 minutes ago, soldier4402 said:

not saying people should drive at WOT all the time, but on a properly operating engine it should be far from harmful.  Actually driving WOT is a good thing lets you know what your boat is capable of and can also show you signs of a any symptoms the engine might be showing.

Yup

brick

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