GT-40 idle overheat.... sometimes

[natetnc]

Hey guys, new to this forum, have searched through it a couple times but thought i would join up to see if someone could help me with my current issue. I before boats I was into sports cars and found forums were a very good source of info and ended up saving me a lot of repair $. ok onto the issue.

The issue is overheating at idle. The boat is a 1997 sport nautique powered by a GT-40. I have read through the many threads dealing with this issue and have checked over the suggested areas to the best of my knowlege. At first it would run hot at every idle, after tightening and checking for air leaks the problem changed a little. Now when I crank the engine it begins to overheat but when I start moving the temp drops to 160 in no time (5 sec) and stays there even at idle. So after the first run everything is great, confusing the heck out of me.

I don't know much about boats but my first guess was thinking it had to be the water strainer gasket. I thought it wasn't sealing until it got a little pressure on it. I checked it and it looked ok, the only thing I noticed was that it had twisted a little, would this be enough to cause the above problem?

Any help is appreciated,

-Nate

[NautiqueJeff]

RE: GT-40 idle overheat.... sometimes

I would go ahead and replace that gasket. New ones are very inexpensive, and can be ordered from the site below. Be sure to use the PN discount!

http://shopwhitelake.com/wafiga.html

Please also check out your impeller. If you haven't replaced it within the last year, order a new one and replace it. I bet that might be your problem.

http://shopwhitelake.com/shimkit.html

[natetnc]

how easy is the impeller replacement? do you know of a thread or somewhere you can link me to where it is explained?

[WakeSlayer]

Impeller is very easy to replace, especially on a direct drive. Should be three small bolts holding the plate on it,. Some guys remove the whole pump. I leave it on. Pull the impeller out and inspect. if it is missing vanes, you should track them down. Either in the thermostat housing, or exhaust manifolds. Re-install the rubber o ring and the appropriate gasket, and replace the cover. I would just get a new strainer gasket when you order the impeller. They are cheap. Occasionally, you need to go through the entire cooling system with a 5/16" nut driver and tighten all the hose clamps. They do loosen a little over time. If you do have to open your stat housing, carefully inspect that gasket too.

[Nbigger]

When you change the Impeller make sure you note the way it was before you take it out so you can put the new one in the same way. I take my whole pump off because it seemed easier to me.

[natetnc]

lots of help, ordering the parts. not sure when the impeller was last changed as i just bought the boat in april '09, after reading some of the threads indicating yearly replacement i was planning on looking into it, seems i will actually be doing it now though.

i am still interested in a link to help change the impeller if anyone knows of one off hand. it sounds easy enough but you never know when a little extra explanation might be needed.

thanks guys,

nate

[NCH2oSki]

When you replace your impellor if you decide to remove your raw water pump mark the top side outlet with something. It can easily be installed incorrectly and will not prime. I usually remove the bottom hose and keep the raw water pump connected to the top hose and then I dont have to worry if I have it mounted correctly.

The orientation of the fins of the impellor do not mater, they will correct themselves. I boated on Kerr, Harris, and Jordan and althoug they are clean lakes I still changed my impellor yearly. While you are at it, you might as well change your t-stat and gasket, also noting wich direction the point of the t-stat is facing.

[NautiqueJeff]

i am still interested in a link to help change the impeller if anyone knows of one off hand. it sounds easy enough but you never know when a little extra explanation might be needed.

Ask and you shall receive!

GT-40 Impeller Replacement Procedure (With Pictures)

[natetnc]

thanks for the link, great for a newbie like me

[Joesboatn]

If your going through all the trouble I would also replace the thermostat. I just had a similiar issue. Replaced my impeller and also replaced my thermo. Impeller was a little worn but not shredded. Between the two it fixed my problem. I think what was happening was the thermostat was sticking closed at idle but once i powered up there was enough pressure to open it. My temp was actually creeping a bit below 160 which it had never done while powering up which also led me to believe it was the thermostat at that point sticking open. If that doesnt take care of it and depending what your impeller looks like a lot of people say if your impeller is shreded the pieces a lot of times will end up in the transmission holes where water enters the tranny and will give you similiar symptoms.

[natetnc]

The thermostat was pretty cheap so I purchased that too just to eliminate any other inexpensive possibilities should it still overheat. I searched thermostat in the bar but didn't get any good hits on replacement. Is it difficult or easy? Another link with pics would be nice if there are any out there. Any tricks or things I should watch out for? I feel pretty good about the impeller install after the previous link. Lucky enough to live near a white lake marine, picking up the parts today to start this evening.

[NautiqueJeff]

You are lucky to live close to WLM. They are probably some of the most knowledgeable people in the world when it comes to Nautiques. Make sure they give you the PN discount.

[natetnc]

will ask them about the PN discount. i don't live near the original white lake marine but the affiliated shop (don't know if they carry the white lake marine name) located at belews lake.

[Chexi]

Be sure to put some lube (vaseline or mild dishsoap) in the impeller before you close it up. Starting it completely dry is hard on the fins.

I'll have to post some pics of the impeller from my other boat (Tige) that I just replaced my impeller on a few weeks ago. There were 0 fins left on it when I opened it up. Scary.

[natetnc]

where did you find them? is it a pain to search them out? hoping mine is not like that.