low engine temp and faulty temp sensor

[tpalu]

Hi All. I have a 2003 SANTE (778hrs) with low engine temperature and would appreciate any help. First time I took out the boat in May I noticed that the engine temperature couldn’t go above 120F. When the engine stopped it would heat up to 135F but as soon as I started again it dropped to 120F. I told my mechanic about the issue and suspected that it is faulty thermostat and asked him to changed it. He changed the thermostat, the impeller and the coolant sensor next to the thermostat. After his “intervention” now I have “coolant sensor see dealer” message and the engine still not heating up to the usual 175F.
I checked the engine temp with a laser thermometer and it is matching with the tachometer and engine temperature gauge so it is clearly not warm enough, still 120F
The mechanic checked with his diagnostic tool on the Faria box and it gives “high voltage” error for the coolant sensor.

What do you think the issue and the next step is?
How bad it is to run the engine with 120-130F temp?

[NautiqueJeff]

Normal temp on an Excalibur withOUT closed cooling would be about 163.

If it is a closed-cooled engine, it would be slightly higher.

It sounds like the thermostat is stuck open, or it was replaced with the wrong one.

Raw-water cooled should use this thermostat:
https://www.nautiqueparts.com/produc...-gasket-gm-tg/

Closed-cooled should use this thermostat:
https://www.nautiqueparts.com/produc...tes-rp026002f/

[MN Ryan]

When I bought my boat (w/ Excalibur 330), it was running in the 125 range. I replaced the thermostat with the one from Nautique Parts, and that fixed the issue (consistently runs 160 now).

I don't think you're going to cause immediate harm running below operating temp, but it's not something you want to do regularly.

Sent from my SM-G970U using Tapatalk

[tpalu]

Thanks for answers. We popped out the thermostat to test it as it was new. It opened up at 160F as it should so it works properly. Here are a few pictures.
It is similar to the previous one so I assume it is the right one.
Is there anything to pay attention when installing it? Those 3 holes need to be positioned in any specific way?

[tpalu]

So it turned out that the termostat that the dealer supplied was the wrong one with the 3 holes. I needed the one without the holes. The dealer finally sent one we popped it in and the temperature is fine.
However I am still left with the coolant sensor error. I am really angry because the sensors had absolutely no issue but the mechanic guy replaced them and now he doesn't know what to do....