Low engine temp....what would be first thing to look at....

[YeOldeStonecat]

So since we bought the boat over 3 years ago, engines have run quite steady, port engine nudging 170, starboard engine typically hovering 165. I cruise around 3,200 rpm....rarely take her to 4k and if I do, brief bursts only.

Had the yard replace water pump impellors this spring.

Have only done 3x short trips up the river so far, but on all, noticed the starboard engine temp gauge only makes it up to about 132 degrees. Engines sound fine, run fine otherwise.

Thermostat?
Faulty temp sensor?
If there was a "clog" I'd think I'd see high temps. ...but, just tossing this out there to those with more experience.

 

[ja308601]

I'd start with the thermostat. If you've never replaced it there's at least a decent chance it's stuck open.

 

[hughespat57]

Pickup a cheap IR thermometer at Harbor Freight or somewhere, very handy for engines/manifolds/exhaust.
If really too cool, likely stuck thermostat.

 

[R-and-R]

Pickup a cheap IR thermometer at Harbor Freight or somewhere, very handy for engines/manifolds/exhaust.
If really too cool, likely stuck thermostat.

Even with my VesselView monitors, I still frequently check temps at various points around the engine. I like making sure there are no hot spots that would indicate coolant blockages.

 

[hughespat57]

Even with my VesselView monitors, I still frequently check temps at various points around the engine. I like making sure there are no hot spots that would indicate coolant blockages.

Exactly, digital gauges read to greater precision (more digits) but that does not indicate better "accuracy".
The readout is no better then the sensor, and they are only 5% accuracy.
Even the IR is likely only 2-5% accuracy
The benefit is getting a baseline for your engine with your IR thermometer. Then watching for deviations from that.

I check my engines over every time I warm them up. Just had a very hot port manifold on port engine.
Checked all the hoses, no blockage (blew thru them), check the exhaust flapper, ok
Finally took apart the thermostat housing where all the hose come together. Had a clogged up elbow to the port manifold.
Cleaned that out and back to normal temps.

 

[YeOldeStonecat]

"Problems" with it running cool? Probably not as fuel efficient? Hoped on taking it on a 2x hour cruise to Pilots Point, Westbrook with a group on the weekend of the 4th.

Will pick up an IR...just for good measure. Although..gotta haul out the lounge seating 'n deck, so difficult to regularly get readings. But..still, once in a while to get some is good I'm sure.

 

[R-and-R]

"Problems" with it running cool? Probably not as fuel efficient? Hoped on taking it on a 2x hour cruise to Pilots Point, Westbrook with a group on the weekend of the 4th.

Will pick up an IR...just for good measure. Although..gotta haul out the lounge seating 'n deck, so difficult to regularly get readings. But..still, once in a while to get some is good I'm sure.

In the short-term, a cool engine shouldn't be a big problem. Efficiency and some excess engine wear would be long-term concerns.

 

[douglee25]

Confirm temps with an IR gun. Also have someone watch the helm while you rotate or move the temp sensor wire. I have seen the wire and or connector become faulty and give erroneous readings.

 

[Wanderer 290]

Year boat and engine type?
There is a temp sensor (feeds the computer if equipped) and temp sender (feeds the analog gauge if equipped) so cross check and verify.
If the indication is 30* low and the engine is really operating at normal temp then it may be operating over temp at an indicated normal temp….
So as previously mentioned verify actual temp with a ir temp gauge at the thermostat housing.
May be a gauge, sending unit or sensor depending on the specific application.

 

[ZZ13]

I had the same happen to a 3.0L I owned in a 175 Sport. Normally ran at 170. After a grounding on our sandy bottoms here it maxed out at 135. Turned out to be a single grain of sand wedging the tstat barely open. That’s all it took to affect the temperature.

 

[Stee6043]

I may be a simpleton, even though I do like cool new tools like an IR gun, but I'd suggest you get the engines up to operating temp (albeit low) and go down there and actually touch them. I had a t-stat stuck open 2 seasons ago and I could clearly feel the difference in temp when I put my hands on the exhaust risers. Made for cheap troubleshooting.