Overheating GT-40

[mndanielsncsu]

I have a 93 Sport Nautique that I recently purchased. Today my wife and I tried to take it out for the first time since we've finally had nice weather and some free time, but to no avail. We got it in the lake, but before we even got to the main channel, the temp was running at about 200 degrees. We let it cool then headed back. I took it to a local dealer and found that the impellor was completely ravaged. Once that was replaced and we pulled all of the pieces (or so we think), I took it back out to test. It heated up slowly to 150-160 and stayed there for a while. The faster I would go, the hotter it got, so we headed back again. The temp got back to around 195, but as I slowed to the dock, it dropped back down to 180 or so. Any thoughts on the culprit? Thermostat?

This is my first boat, so pardon the lengthy description.

[wi54545]

RE: Overheating GT-40

You didn't get all the pieces. I'll bet you that you have some rubber clogging the inlet side of the pump.

[JUST-IN-TIME]

RE: Overheating GT-40

anytime you over heat
you better change the t-stat
you better back flush
you better cheack hoses and clamps
you better check exhaust hose

[my94sport]

RE: Overheating GT-40

Have you used the fresh water flushing system??? I had the same problem with my 94 sport. Ran perfect out of the dealership and I got it home and tried the flushing system to turn it on . Next time I used the boat it was heating up. There is a spring loaded valve in the back of the motor. That spring got stuck in the reverse position and does not let water out of the bottom of the boat and goes into the motor. That was the problem. Fresh water flushing system value (spring) got stuck and did not allow enough water to flow through. Hope this helps!!

[mndanielsncsu]

I haven't tried the fresh water flushing system yet. I was working on it with a guy from the local dealer who was actually a salesman who has owned Nautiques for 20 years. We unhooked the hoses, checked the water distribution pump, and replaced the impellor. He also hooked a water hose to the outlet hose for the strainer and ran water through the motor to check it. I'm not sure if all of that encompassed the fresh water flushing valve or not? Again, I'm new to boats and Nautiques, so I'm not very familiar with all the parts.

I have a new thermostat on order from the dealer, which should be in by the middle of the week. I'm planning on checking the inlet to the pump tomorrow as well, as suggested. All advice is welcomed...

[my94sport]

If he hooked up a hose to the back of the boat, it could be a possibility. Happen to me. If this is the problem there should be a "T" which connects 3 hoses in the back of the motor. The spring loaded valve is in there. The way this works is that water flows from the bottom of the boat through that "t" into the motor to cool. When you use the flush kit (or the hose connect on the transom) the water pushes that spring back (which has a cap at the end)so that the water does not go out of the bottom of the boat and goes to the motor. I saw the tech do it to mine, all he did was get a screwdriver and unstuck the spring and worked fine ever since.

[mndanielsncsu]

I've tried to find the "T" where the 3 hoses connect in the back of the motor, but I've been unable to find anything. Can you take a picture to point out where you're referring to. From the fresh water intake under the boat, the hose goes straight to the strainer. From the strainer to the pump with the impeller in it (not sure what it's technical name is).

Today I pulled all of the hoses for the cooling system and didn't find any more rubber from the shredded impeller. The thermostat looks pretty old, so I'm praying that it's the source of my problem. I checked the strainer also and it was completely clean.

[jward]

the raw water pump may need to be rebuilt. If it is sucking air it will loose its prime

[my94sport]

here's the pic...do you have one of these? if not it must be the t stat!

[my94sport]

another pic

[bgunterman]

" T "

I have a 99' pro air with a GT-40 5.8l and the " T " I believe is the thermostat housing and it's at the front of the motor. Trace the raw water pump hose out to the engine this hose is at the top of the raw water pump or "outlet" if you like that. This hose connects to a metal "T" that splits to each exhaust manifold. The thermostat is located there. My Raw water pump is removed right now but it should look the same. I also tore up my impeller and somebody stated to me that small pieces can get caught in places in the exhaust manifold and cause overheating. It didn't happen to me, thank god. Hope this helps, let me know.

[mndanielsncsu]

RE: " T "

Thanks for all of the pics! my94sport, I don't have a "T" like that on my engine. Mine runs from the strainer straight to the raw water pump. I've checked everywhere I can for pieces of rubber, but haven't found anything yet. I'm going to keep fishing while I wait on the T-stat to come in. I'll keep you posted.

[Laketexoma]

RE: " T "

Did you check the gasket on the raw water strainer?? I had min go out on my 00 SAN and it caused it to overheat while underway, and then shread the impeller. Just a thought.

[Fredk]

RE: " T "

If you have done everything else, try this stupid quick fix. Check the water strainer (seperater, whatever, I don't know it's offical name), looks like a plastic bottle that screws in to the hose towards the back left sideof the engine. Make sure it is tight, even a 1/16th of an inch turn may be all you need. It sucks in air at spped causing the overheating. Idle or low speed works fine. We used to have the same problem with our old '95 SN. Got to the point it was an automatic check whenever we went out.

[TRBenj]

RE: " T "

My guess is that you didnt get all of the impeller pieces out. Pull the 'stat housing, as thats the most likely place for them to be lodged. Also pull all the hoses coming directly off of it to check for rubber bits.

For everyone who is recommending to check for air leaks, keep this in mind:

overheat at idle = air leak. (The temp will come down with increased RPM.) Tighten hose clamps and strainer bowl.

overheat at speed = RWP problem or passage blocked. (The temp will go up with increased RPM). Check the impeller, check passages for blockage. If problem persists, RWP may need rebuild.