Gt40 running at 180

[tmb]

The thermostat was bad so I replaced with a new one from Nautique parts. The boat is now running at 180 under load. The manifolds don’t feel extremely hot, the impeller looked good. What else could be the problem? Thanks

[NautiqueJeff]

Did you get part RP026002? Should be a 160-degree thermostat. Just making sure you got the right part.

180 isn't going to hurt anything, but it should be running 160-170 or so.

[tmb]

Yep, it was the correct t-stat.

[SilentSeven]

Carefully check the raw water feed line for air leaks. Hose clamps. Strainer. Strainer o-ring. All that.

Even a small leak can diminish the water flow volume.

Posted via phone. Sorry for the tpyos.

[tmb]

Carefully check the raw water feed line for air leaks. Hose clamps. Strainer. Strainer o-ring. All that.

Even a small leak can diminish the water flow volume.

Posted via phone. Sorry for the tpyos.

How would you check for air leaks. Soapy water?

[SilentSeven]

No, soap won't work. Water intake leaks are a vacuum leak, not a pressure leak. Theory is you are getting less water draw as air is getting sucked into the system. You can start simple by just making sure all the hose clamps are tight with a nut driver or similar. Check all connections from the thru hull to the raw water pump. Also, pull off your strainer bowl and clean the o-ring and re-attach.

My run warm issue was mostly at idle speed....engine temp would go up to 180+ and then drop as a I sped up. Found a loose hose clamp that wasn't fully tightened from winterizing. Tightening solved all problems.

[tmb]

So I checked every hose and replaced the o ring in the water strainer. Boat runs at a consistent 178 when at running speed but drops to 160 at idle. Any other suggestions?

[SilentSeven]

Did something change or is this the same as before? Hot temp looks the same; did the idle drop?

Posted via phone. Sorry for the tpyos.

[tmb]

I don’t recall it dropping down to 160 at idle but we just got the boat and had to change the original thermostat because it was shot. Completely rusted and wouldn’t close Or open all the way. The temp was running at 110-120.

[SilentSeven]

Do you know the boats history? Rusted out cooling system parts doesn't sound good. Was there much scale visible in the thermostat housing? Any saltwater history? How are your manifold riser gaskets - weeping or look ok?

Wondering if you might have an obstruction somewhere in the system.

Also, I recall it's easy to have the gt-40 raw water cooling pump reverse mounted....limiting flow. Can't remember exact details on this... something to search on.

Posted via phone. Sorry for the tpyos.

[tmb]

There were 2 prior owners, guy we bought it from had it for the past 10 years and said there were no mechanical issues he ever had. I can only go by his word. No saltwater use. The manifolds did have some rust where it looked like they had seeped from the gaskets but nothing has been leaking since I’ve had it. There was not much scale around thermostat housing. Here is a pic of thermostat.

[SilentSeven]

Hmmm. I'd research to see if the raw water pump might be mounted incorrectly.

[mpost]

Pretty sure if the RWP is installed wrong it will overheat quickly.
I have heard of problems with a hose on the intake side of the RWP collapsing under higher RPM. Old hose or wrong hose installed that cannot take the suction of the RWP at higher RPM.

[SilentSeven]

This old thread can be helpful with a few insights but sadly doesn't provide clear resolutions:

https://www.planetnautique.com/vb5/f...rheating-gt-40

All from this thread

Overheat at idle vs speed

https://www.planetnautique.com/vb5/f...930#post140930

How to check for correct pump installation

https://www.planetnautique.com/vb5/f...136#post141136

From different threads
GT 40 water flow diagram

https://www.planetnautique.com/vb5/f...270#post346270

Most common fix of overheating at speed is air leak.

[tmb]

Thanks. I think I'm going to remove the hoses and see if there is an obstruction anywhere, try the hand over the hose technique to test vacuum, and maybe change the impeller. Any good suggestions on how to get hoses off? These feel like they've never been removed and are on TIGHT!