1999 GT-40 thermostat replacement issue - broken housing?

[SMLNautique]

It’s called lower thermostat housing and unless skidim has them remade your out of luck. Back in 08 the company who cast the parts for Pleasurecraft went out of business and the molds were “lost”. You can find them used from time to time if someone is parting out an engine. You’ll have to attempt to patch it up for now while you look for another or have this one professionally repaired in the off season. There are places who specialize in repair of cast iron

Thanks, that's what I was afraid of. I've spent half the day searching for the exact part with no luck.

[SMLNautique]

I may be in luck after all. I contacted Skiddim and they verified that part https://www.skidim.com/prodinfo.asp?number=R025001 is correct, but that the picture orientation is showing the intake side port.

[gun-driver]

Gary Skidim showing them on their site so i assume they have them.

SML you may want to drop your thermostat in a pot of water and heat it on the stove to see if thats the culprit, if it opens your trouble is else where.

[SMLNautique]

Gary Skidim showing them on their site so i assume they have them.

SML you may want to drop your thermostat in a pot of water and heat it on the stove to see if thats the culprit, if it opens your trouble is else where.

I just tried this and the old thermostat did open as it's supposed to. Not sure what else to try in regards to the overheating. Maybe it's not overheating and its a bad sendor? Maybe a blockage somewhere else? Hmmm...

[gary s]

That's a good deal then if they have them- get one yesterday because I'll bet they don't have many. That part lasts quite a long time it is the upper that goes bad fast in salt/brackish water boats. They don't have the original uppers they have made them out of aluminum so if you were going to go through all the work to cast parts you would make the one that's needed most. Again- Grab one now

[gun-driver]

I just tried this and the old thermostat did open as it's supposed to. Not sure what else to try in regards to the overheating. Maybe it's not overheating and its a bad sendor? Maybe a blockage somewhere else? Hmmm...

Start with the checking easy stuff like I suggested the T-sat test and work your way to the hard stuff. Gary may chime in he has a wealth of knowledge with these boats.

You could ohm out the sensor and ground the wire to the gauge that will eliminate the easy stuff but looking at the rust in your housing I would think it may be the manifold risers not allowing the proper amount of water through the engine.

You can disconnect the hose to the water pump use a connector if need be and put it in a 5 gallon bucket of water and see if its moving water freely.

[gary s]

I wonder if the thermostat may have been stuck and pulling it out has freed it up? If you haven't ordered the housing yet get a 'stat while your at it. If you already have maybe soaking it in CLR might help. After you get it back together and if it's still overheating check all your hoses on the intake side of the raw water pump and the strainer and it's gasket as well. Pump seals can suck air as well. Exhausts can clog up but that's a big job that could involve broken bolts at the riser connection and at the manifold to head as well. As a last resort before pulling them I'd be tempted to put a temporary clear hose between the raw water pump and the upper thermostat housing to verify that the pumps seal is not drawing air or any of the hoses or cooler/strainer connections etc

[SMLNautique]

Thanks for the wealth of responses today fellas. I cleaned it up really well and then used JB Weld on it tonight. On Friday after its had time to fully harden I plan to gently clean the threads with a tap and then put it back together with a new thermostat. No reason to reinstall a 21 year old t-stat. I'll check all the hoses as well. We had a lot of flooding this spring and more debris in the water than usual so the strainer has had a lot of mulch like material in it and has been emptied every few trips. The strainer O-ring seems to seal it very tight although I did notice the elbows at the hoses move around a bit. Not sure if this is by design or not. Anyway, I'll report my findings.

Also, I purchased the new housing and the appropriate gaskets from Skidim and will replace the housing down the road.

[Jonny Quest]

You can verify temps with an infra red temperature gun. Handy to keep in the boat glove box. It can help find the trouble spots. I keep one in a zip lock bag in the glove box. It’s saved my a$$ several times.

JQ

[SMLNautique]

Quick update. I ended up ordering the lower housing from Skidim and had my mechanic install it with the appropriate gaskets. The temp gauge still showed hotter than normal temps even when the engine was cold, and the manifold were only warm to the touch. The mechanic changed the temperature sender and the gauge reads accurately now. I'll test drive the boat early next week when the rain subsides. Hopefully the sender was the issue all along.

[Jonny Quest]

I’ve been snake-bit With temp sending units...3 or 4 in the past 5 years. That’s why I carry the IR temp gun as I’ve come to doubt my temp gauge and sending unit.

JQ

[SMLNautique]

Ran the boat for several hours with a decent amount of ballast without overheating yesterday. Looks like the temp sender was the issue. Thanks again for all the help!