GT-40 Overheating! Help!

[JWAT]

I posted earlier about how I thought my impeller went bad on me. Well, I checked the impeller and it looks fine, so that's not the problem.

This is for a '97 Super Sport v-drive with the GT-40.

Here's what happened. . .Yesterday we had been riding for about 45 minutes or so when I noticed that the engine was starting to make a little louder noise. Then all the sudden it started loosing power, so we quickly put it in neutral and shut it off. When I opened the v-drive hatch I could here something popping a little bit (I think it was the oil boiling???). The temp had went up also. After letting it cool down, we started it back up and limped it to the ramp. The whole time going back the temp was around 200. I just figured the impeller had went bad, but when I looked at it today, everything looked fine to me. Does anyone have any other suggestions on what I could check? Could it be the thermostat? Thanks a lot for any help!!!

[slob02]

Did you take the impeller out. I have seen where the fins look good, but the incert inside the rubber was stripped. The shaft would spin, but the impeller wouldn't.
Also, did you check the fresh water filter. Make sure it is tight.

[JWAT]

I took the impeller out. When you say that the impeller would be stripped, do you mean that the metal part inside the rubber impeller would spin, but the actual rubber part of the impeller wouldn't?

Yeah, I checked the filter. That's the one with the metal screen in it, right? There was just a little debri in there, but nothing really major. I may check the impeller again to see if it is spinning around the shaft, but I'm pretty sure it's ok. Any other suggestions?

[slob02]

That is what I ment about the impeller. Make sure the filter is tight and not cracked. I am sure it is fine. I am out of suggestions except maybe the water intake on the bottom of the boat. No crap in it??? Keep us posted.

[JWAT]

Well, I went and checked the impeller again and everything was fine. Nothing was stripped at all. I'm not sure what else to do. The only other thing I can think of would be the thermostat. Has anyone ever had one of those get stuck or anything? Thanks for any other suggestions you can provide.

[skinautique]

JWAT,
If your boat is a 97, I would replace the impeller. It is a $30 or less investment. Sometimes, you will see an impeller that still has all of its blades on it but what happens is that the rubber gets so soft that it doesn't draw in enough water to cool the engine. I would replace that and then check every hose clamp to make sure they are snugged up and then make sure that the water strainer is on tight.
I would put money on it that the impeller is probably the culprit.

[slob02]

I have never had a problem with the thermostat. That really sucks! I know as soon as others read this post, they will have more ideas.

[JWAT]

Well, I have decided to go ahead and replace both the impeller and t-stat. Both parts were only $50, so I figured I might as well change both. My question now is, where exactly is the thermostat and is it very hard to change? I think it is on the port side on top of the engine with like 3 pipes coming off it??? Midwest CC said that changing the t-stat was pretty easy and I should be able to do it. Does anyone have any suggestions. Thanks again for all the help!

[Bamaboarder]

One other thing to look for is the O-ring in the strainer. If, by chance the O-ring is missing from the strainer cup, it could cause overheating problems. This may not be your problem, but it is worth a look see.

[skinautique]

Since you have taken the pump apart multiple times, are you putting it back on in the right direction? If not, you will not pump any water whatsoever.

[ccole]

I took my 1994 Sport Nautique in to be winterized running fine in Oct 04, then picked it up in March 05 from the dealer dewinterized and with a new impeller. Put it in the water and let it idle, but as I hit the trottle the over heat light came on. Took it back and in the shop with a water hose on it wouldn't overheat, but in a water test it would. What they found was a piece of impeller about the size of a dime broke off and was lodged in the thermostat and there was a loose fitting letting air in. The result was that with the hose enough water was forced in to cool the engine, but on its own, the pump didn't have enough pressure to pull water in. After the clamp was tight, the piece removed, and a second new impeller put in (the new one showed wear from the overheat) it now runs fine. Just something to think about.

[83sn2001]

That is where the t-stat is located. Make sure you get the old gasket material off of both pieces.Wouldn't hurt to put a little sealer around the housing before reassembly,just not too much. You don't want it getting on the t-stat. Good luck. It is fairly simple

[jonfo]

I had the pulley bearing on the sea water pump go on my 1995 GT-40 at around 800hrs. It caused intermittant temperature increases until i replaced the entire pump. The impeller was fine.

[M3Fan]

If you run it in the driveway attached to the hose, and you've got water coming out the exhaust, then the impeller is fine. If water is coming out the exhaust, yes, the next step would be the T stat. There are two hex screws that hold the upper housing to the lower. Undo the 3 hoses and unscrew the two hex screws. Replace the T stat, keeping the right side up, and replace the gasket with a light coat of sealant. Don't over-tighten the screws. If water is not coming out of the exhaust there is something wrong between the pickup on the bottom of the boat and the T stat housing. Strainer, trans cooler, hoses, RW pump.

[vortech347]

A piece of advice to all of you changing thermostats.

Test your new thermostat before installing it. All you have to do is put it in a pan of water on the stove. When the water heats up to the t-stats opening temp you will see it open up.

It's also a good way to test an existing t-stat if your not sure that's the problem.

Changing the thermostat on a Ford engine is a little harder than on the Chevy engines due to the distributor being in the front. Make sure you put the thermostat in the correct way as well or it will not open. It will have an arrow showing the water flow direction.