Low Engine Temperature

[DocSki]

I have a 2007 Ski Nautique. Normally the digital temperature reads 158 to 160. Yesterday, after 45 minutes of pulling skiers, I turned on the dashboard heater. A little bit later I noticed the engine temp had dropped to 125. It ran fine, but I turned off the heater. The temp stayed at 125, climbed to 135 when I slowed (and rpm's went down), but then dropped to back 125 pulling skiers. The engine continued to run normally, and the manifolds felt normal temp. I run in salt water and installed a FlushPro flush-out valve between the water intake and the strainer. I noticed some bubbles being pulled into the FlushPro (clear plastic). I'm not sure what is going on. Any thoughts would be appreciated. Thank you.

[wakejunky]

Sounds like stuck thermostat to me

[James]

I had the exact same issue with my 2006 216 330 Excalibur two summers ago. A new thermostat solved the problem.

[DocSki]

Thank you both! Do you have any information or tips on how to replace the thermostat? I'm low to moderately skilled (I replaced the starter, installed the FlushPro, changed the oil in my boat, but willing to try something new). I found a .pdf posted on this Forum in 2011with instructions on changing the thermostat, but the link doesn't work anymore.

[wakejunky]

If you can do those other maintenance tasks then you can tackle a thermostat. It's sitting on the top of the engine towards the front, middle. The housing will have two big hoses running to each exhaust riser. Just undo hoses, loosen the bolts and it'll be against the engine block. You'll need a thermostat, block to housing gasket and potentially the upper gasket. The housing is two pieces. Put everything back together and test it before hitting the lake to make sure the thermostat works and there are no leaks. You can test the thermostat by putting it in boiling water to make sure the new one is working properly, or that the old one is not working properly

[NautiqueJeff]

Thank you both! Do you have any information or tips on how to replace the thermostat? I'm low to moderately skilled (I replaced the starter, installed the FlushPro, changed the oil in my boat, but willing to try something new). I found a .pdf posted on this Forum in 2011with instructions on changing the thermostat, but the link doesn't work anymore.

DocSki

Found the thread you were referring to with the .pdf file, and I fixed the link. It is actually just what you need, I think. I am attaching the file here as well.

CLICK HERE ---> Thermostat Replacement

[DocSki]

Thanks for fixing the link! Replacing the thermostat doesn't look too complicated...famous last words...

But, because even "simple" work on the engine raises my anxiety, I just want to verify with you experienced folks if it makes sense for a "stuck" thermostat to vary the temperature reading as I described above (that is, the temp holds at 125 when pulling a skier and rises to 135 with lower rpm's when slowing after a run)?

Thank you again!

[hal2814]

It’s consistent. Your water circulation is determined by how fast the water pump can get water to the engine. Water
pump speed is tied to engine speed via a belt. With a thermostat stuck open, there will be more water flow through your engine at higher rpms. But the only way I’ve
ever used to positively identify a broken thermostat is the water boil test mentioned above.

Engine work can be scary but the thermostat is easy to do and low risk. Even if you do something wrong you’re probably just looking at a small water leak.

[NautiqueJeff]

You may get lucky and find that it is just clogged, and whatever material is in there is not allowing the thermostat to close. You may be able to clear it out by dropping it into boiling water, letting it open all the way, and cleaning out the opening.

If you do need a new one, here's the part (assuming you have an Excalibur 5.7).

https://www.nautiqueparts.com/produc...-gasket-gm-tg/

Use discount code PND for 10% off.

[DVskier]

I have a 2004 SN196. Had the same problem and replacing the thermostat fixed it. Make sure that you have both gaskets for the therostat housing. Also make sure that the housing is smooth. Mine leaked initially after replaced the thermostat so I had to take it apart and smooth the faces with medium grit sandpaper. Works like a champ now, his 160-162 degrees all day long. Good luck!

[DocSki]

Success! Thank you everyone for helping me with this! The hardest part was cleaning the surfaces where the old gasket was. Ran it with fresh water through the FlushPro and the temperature came up to 151. No leaks. I'll take it out on Friday for some runs. The old thermostat looked pretty corroded. It opened (closed?) in boiling water, but I think its time had come. I'm very grateful for all the help.

[MTRBTR]

Do the Excalibur thermostats all fail open or do they sometimes fail closed? I really like the feature where they fail open. A lot of peace of mind that you don't overheat your engine. I used to have a 97 with the GT40 and I always had trouble with the thermostats failing closed and overheating.