Temp gauge creeping up - IR thermometer not concuring

spoilsofwar

Lieutenant Junior Grade
Joined
Jun 29, 2011
Messages
1,124
Engine: 4.3 GL-P

Issue: I dropped the boat in the water for the first time this year. When I was running it in the driveway on the hose, I noticed the temp gauge creeping up higher then I've ever seen it (200+ indicated). I thought it was maybe due to low water flow from the hose (new house, weird low pressure thing on the hose tap). Today, on the lake, the same thing happened, so running on the hose was not the culprit.

I brought along my IR thermometer today to help troubleshoot. Although the gauge takes a long time to get into overheat range (30+ minutes) it will eventually creep to around 210F. However, all my IR sampling was displaying only around 180F max. The thermostat housing was generally showing 170F, and pointing the IR gun directly at where the temp sensor sits in the intake manifold topped out around 180F. I am thinking either my temp sender or my gauge have gone south on me.

I am fairly sure this is not an actual overheat condition. My IR gun reads temps true, as I've measure it against some known temperature items and its been accurate. As for the engine itself, it has a brand new water pump impeller and brand new thermostat. The manifolds, risers and rest of the exhaust is cool to the touch when the engine is up to temp. Since the gauge reads hot on the hose and in the lake I know its not an air leak in the water intake stream from the drive. Water pump isnt leaking. The boat has never overheated or ran hot before, and besides this its running excellent.

I plan on replacing the sender (part #21) to see if that rectifies the issue. However, I am wondering what exactly part #22 does? This is the sensor in the thermostat housing. If I disconnect the wire from it when the engine is running, no alarm sends. It doesn't send to a gauge, so what is its purpose?
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Any ideas of what else could be responsible for this issue besides the sender or the gauge itself?
 

spoilsofwar

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Jun 29, 2011
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Well I just pulled the thermostat housing so I could proof the new tstat in some hot water on the stove... it works. However, I am pretty sure I made an amateur hour mistake when I first installed it - the rust ring on the tstat indicates I installed it upside down! I can't be sure because I didn't note which orientation it was before I pulled it out, but I'm 99% sure it was upside down. Seems that may have been my issue. Now to reassemble it and run it, and see....
 

GA_Boater

Honorary Moderator Emeritus
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May 24, 2011
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That would cause the issue because the pellet is in the cooler housing, not in the warmer block water. I think you found it.
 

spoilsofwar

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Jun 29, 2011
Messages
1,124
Yup, thermostat was upside down. Ran it for a few hours today on the lake and it's back to normal.

Silly mistake!
 

skydiveD30571

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Feb 13, 2012
Messages
1,042
And FYI, #22 is the temp sensor that will trigger a high temp alarm. Unplugging it will not activate the alarm, the wire needs grounded for that to happen.
 

greenbm

Seaman
Joined
Dec 6, 2013
Messages
54
what's the explanation for the difference between your IR thermometer and temperate guage?
 
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