Typical exhaust sensor temperature?

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chris-s

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We have a silicon marine exhaust temp monitor fitted with our raw water cooled VP2003, and this year we added the buzzer and set an alarm value of 50C. However, we are finding that at low rpm's circa 1500, this is exceeded and triggers the alarm. Annoying when needing to motor slower. Cruising RPM's arond 2000, the senor sits at around 40C. Is this just too low an alarm threshold?

I have no idea what it was last year, but since then we have also swapped to a featherstream prop, so may that could be over-propping us. The cooling system, pump, pipes, exhaust elbow etc are all in good shape, I've given them a lot of attention over the last couple of seasons.

Chris
 
I’ve got my alarm set to 50c but have yet to exceed 40 degrees. Freshwater cooled 3GM30. Sensor mounted on exhaust elbow.
 
Mid 30's is highest we have had (sea temp 12 ish). It generally settles out at 28, due to thermostat working, i think.

Can feel exhaust further aft with your hand, for a further check.
 
We have a Silicon Marine temperature probe and the reading generally about 28 deg rising to mid 30 high revs 38 deg. max. Alarm set at 60 deg. As suggested you may need to check the raw water flow
 
Thanks for the replies. The cam plate was the only bit that I didn’t replace when I rebuilt the pump in June. It was a part I looked for but couldn’t decide what was the right part to order, I’ll have another look. Whilst I fitted a new impeller at the time, it’s of course possible that something has happened to the vanes. I will take a look.
 
Hi, I have the same engine and cooling set up and concur with Aquanaught on exhaust temperatures as measured with a NASA probe in the flexible pipe just after the elbow. New impellor and SS elbow fitted last winter without change in readings. Have seen max of 40degC when run briefly at 2600rpm; normal cruising at 2250rpm and 34degC. Alarm set at 50degC.
 
My beta has a NASA temp sensor. It sits at 27⁰C when at 2000 revs. Does run hotter when ticking over. I always assumed the temperature would rise dramatically if there was an issue with flow
 
The temp reading will depend on precisely where the temp sensor is located. On ours, (Yanmar 3YM30) the exhaust temp sits at 40 - 45°C when motoring normally, 2000 - 2400 rpm. When we drop down to idle after motoring for a while it shoots up to around 75°C before gradually dropping down to below 40. The alarm set point is 85°C, and it went off quick enough when I started the engine having forgotten to open the seacock last year.
 
Update, I replaced the cam and the impeller and whilst I haven’t yet been able to motor off, I can visibly see better water flow out the exhaust.

The old cam was 2.3~ mm thick and the new one 2.6, I also saw that the two month old impeller was deformed more than expected. I know they get like that but haven’t seen this with such a new one. Replaced it anyhow.

Hopefully cooler times ahead, we’ll, engine wise!

IMG_0994.jpeg
 
When I installed my Silicon alarm the stbd exhaust was distinctly hotter than the port and exceeding 100oC. Silicon provided me a new sensor FOC, but I also re-positioned the sensor as I figured a jet of the exhaust gas might have been hitting direct on to the sensor. Now both read about the same. I have set the alarm up ~ 10oC higher than the highest temperature I have seen, ~ 55oC. This gives me plenty of warning that here is a problem before a serious overheat occurs.

The audible alarms are also linked to the water flow switches.

Having lost an engine on my last boat due to a fouled water inlet I now have a belt and braces approach to seawater system failure - flow switch and exhaust temperature monitoring, and I am surprised these are not standard fitment on larger engines, rather than the useless freshwater over temperature device that is there to tell you your engine is too hot after it has or is about to seize up !
 
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