1999 GT-40 thermostat replacement issue - broken housing?

[SMLNautique]

I was replacing the 160 degree thermostat on my 1999 Nautique Super Sport and when reinstalling the second hex bolt the "housing" cracked. The bolt still threads into the housing, but is not very tight, and I fear the gasket will leak when I put her back in the water.

1. I have not been able to locate an exploded view of the 5.8L GT-40 motor to identify the part that is actually broken. I've been calling it a thermostat housing, but that may not be accurate.
2. Can this be repaired, preferably without removing the part from the boat? I don't want to cause further damage.

Any repair or replacement recommendations are welcome. Thanks.

[Fast351]

That looks like the boss on the intake manifold. I can't remember if they're steel or aluminum on this boat, but unless there is a replacement available, you're looking at removing the upper manifold, the lower manifold (the piece with the broken boss), and taking it to a fab shop to have them grind out the broken piece and weld in some new material, drill and tap.

I don't think there is anything you can do with it on the boat, sorry. Fortunately this is a fairly common repair, and any decent machine shop that deals with automotive work (look around for a racing shop they can probably point you in the right place to do this repair).

Chances are decent that you could find one of these in a junkyard too. Mid 90's EFI 351 truck motor should have the right manifold, but not sure if the PCM manifold has extra features. Personally I'd probably get yours repaired, since you have to tear the boat apart to get at it anyway.

[gun-driver]

https://www.skidim.com/prodinfo.asp?number=R025001

You will need a new gasket also

https://www.skidim.com/prodinfo.asp?number=RM0001

[Stevemo14]

You can always try the quick fix, JB Weld, Drill and Tap. I don't know if i would do it on my boat, but it can be done.

[SatherG230]

I would have JB Welded that up already. You can always tear your boat apart in the off season.

[SMLNautique]

https://www.skidim.com/prodinfo.asp?number=R025001

You will need a new gasket also

https://www.skidim.com/prodinfo.asp?number=RM0001

Thanks, but I don't believe this to be the right part. There is another hole next to the thermostat.

[SMLNautique]

I would have JB Welded that up already. You can always tear your boat apart in the off season.

That's the approach I am contemplating.

[gun-driver]

I would have JB Welded that up already. You can always tear your boat apart in the off season.

30 minute replacement 2 bolts and a gasket

[gun-driver]

Thanks, but I don't believe this to be the right part. There is another hole next to the thermostat.

That's the right part just a bad picture the side you see in the Skidim picture is where it bolts to the intake, the side in your picture (where the T-stat sits) is on the back you can kind of see it through the hole.

If you have any doubt call Vince at Skidim and talk with him.

[SMLNautique]

Ok thanks. I found part R025001 stamped into the housing.

[SMLNautique]

Here is another pic. Don't mind the rust remover liquid in the hole.

[Fast351]

Oh yeah, that's not the manifold. Lucky! Pic helped. I forgot that on marine apps they move where the thermostat sits (on a car engine the thermostat is on the vertical surface that your broken housing bolts to).

Skidim has this part:

https://www.skidim.com/prodinfo.asp?number=R025001

[gun-driver]

Make sure you get a new thermostat gasket also. https://www.skidim.com/prodinfo.asp?number=RM0003

Why did you change the thermostat ?

[SMLNautique]

Make sure you get a new thermostat gasket also. https://www.skidim.com/prodinfo.asp?number=RM0003

Why did you change the thermostat ?

The boat has been running hot for the past month or so intermittently. I checked the impeller and it looked fine, but I replaced it anyway. The strainer has been emptied a few times recently as well. On Monday the boat was running at 200 degrees consistently and the temp would not drop so I figured the thermostat was the next thing to try. My guess is this was the original thermostat because the bolts had the original black paint on them. I do have a new gasket as well.

[gary s]

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