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GT 40 over heating at idle

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scottyb1838 View Drop Down
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    Posted: July-31-2017 at 8:27pm
My GT40 engine in over heating at idle. I've replaced the water pump,thermosat 160 degree, checked water strainer and hoses. Anybody have any idea why I'm running hot? It cools down when I'm running down the water. 97 Ski Nautique gt40 engine.
Scott Brasher
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Post Options Post Options   Thanks (0) Thanks(0)   Quote fgroce Quote  Post ReplyReply Direct Link To This Post Posted: July-31-2017 at 8:37pm
Hi and welcome to the forum. Have you replaced the impeller? Did you use the OEM brand.? The aftermarket one's may not hold up as well. Most people recommend changing them out every one to two years. Make sure you do not see any bubbles in the strainer, that will indicate a air leak. Make sure the gasket is not missing. Hope this helps.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote scottyb1838 Quote  Post ReplyReply Direct Link To This Post Posted: July-31-2017 at 9:09pm
The water pump can as a whole assembly with a impeller. Strainer seem to be fine also put Teflon tape around to make sure no leak.
Scott Brasher
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 63 Skier Quote  Post ReplyReply Direct Link To This Post Posted: July-31-2017 at 9:45pm
Not sure I understand your water pump comment in your last post.

Running it on the trailer is a good way to see how the water flow is at idle. I suggest you use a "Timmy Tee" setup, which is ideal for running on the trailer and mimics the pull of the raw water pump when the boat is in the water. You can watch the water flow out the exhaust, see if you have decent flow at idle or only when rpm are elevated a bit. Checking flow at idle would be a good start.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote swamp demon Quote  Post ReplyReply Direct Link To This Post Posted: July-31-2017 at 9:59pm
Is the o-ring in the strainer. How about the elbows that screw into the strainer, they may need sealed. Check inlet side of tranny cooler
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Post Options Post Options   Thanks (0) Thanks(0)   Quote fgroce Quote  Post ReplyReply Direct Link To This Post Posted: August-01-2017 at 11:23pm
Since you replaced the entire RWP you did not put it in upside down did you. It is real easy to do.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: August-02-2017 at 8:01am
Originally posted by fgroce fgroce wrote:

Since you replaced the entire RWP you did not put it in upside down did you. It is real easy to do.
In his first post in this thread, he mentions that it cools right off when run at higher speeds so I think he can rule out an upside down pump.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote fgroce Quote  Post ReplyReply Direct Link To This Post Posted: August-02-2017 at 8:30am
Missed that later on.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MourningWood Quote  Post ReplyReply Direct Link To This Post Posted: August-02-2017 at 3:15pm
Sounds like possible debris in the trans cooler or exhaust manifolds, a 'clog' that is overcome by the greater "at speed" cooling water amount.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRBenj Quote  Post ReplyReply Direct Link To This Post Posted: August-02-2017 at 3:19pm
Tee is not good for troubleshooting cooling system.

Blockages will usually manifest themselves as overheats at speed, same as a failing impeller. Idle overheat is almost certainly a small air leak between rwp and hull pick up. Sounds like you missed it the first time, look at all those hoses and connections again.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: August-02-2017 at 4:05pm
Originally posted by scottyb1838 scottyb1838 wrote:

My GT40 engine in over heating at idle. I've replaced the water pump,thermosat 160 degree, checked water strainer and hoses. Anybody have any idea why I'm running hot? It cools down when I'm running down the water. 97 Ski Nautique gt40 engine.


I'm kinda wondering what overheating at idle means?

Are you boiling water or is it just heating up some?

Numbers would be good to go by, like what it normally runs at, what it heats up to

Also what led to the problem initially and what made you decide to replace the old pump

In other words give a little more info
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Post Options Post Options   Thanks (0) Thanks(0)   Quote fgroce Quote  Post ReplyReply Direct Link To This Post Posted: August-02-2017 at 5:40pm
I wonder is it really overheating or maybe a voltage issue at idling giving a false overheat?
How about using an IR temp gun and checking the temperature.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote scottyb1838 Quote  Post ReplyReply Direct Link To This Post Posted: August-03-2017 at 4:44pm
When Idling I will get 185 +. Normally runs 160. When I pulled the RWP groves had worn into the back housing and wear plate. I thought they would've been enough water getting by to cause the overheat.
Scott Brasher
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Post Options Post Options   Thanks (0) Thanks(0)   Quote scottyb1838 Quote  Post ReplyReply Direct Link To This Post Posted: August-03-2017 at 4:46pm
Thank you. Should I pull off the hose and connection and re seal each?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRBenj Quote  Post ReplyReply Direct Link To This Post Posted: August-03-2017 at 5:06pm
Pull off each hose and inspect for cracks along the length of the hose, damage from previously overtightened clamps, proper mating depth, and inspect for damage to the hard parts. Trans cooler is especially vulnerable to damage from overtightening.

Strainer bowl needs to be TIGHT (so tight that you probably won't be able to remove it without a strap wrench) and obviously the o-ring needs to be in place and in good shape.

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