Nautique gt40 overheating

Postby noride » Fri Jun 15, 2018 3:59 pm

I have a nautique super sport with a gt40 pcm engine in it, when connected to the hose or when on the water it is heating up over 200f. I have changed the thermostat but this has not rectified the problem. If I remove the thermostat all together the temp sits around 160f where it should be. I have installed a new raw water pump impeller and removed all hoses and blown compressed air through the block via the drain plugs. The exhaust risers are fine( had them off and installed new gaskets)There is no debris around the transmission cooler or anywhere for that matter. Could it be the thermostat housing, or the engine circulation pump? Where to next?
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Re: Nautique gt40 overheating

Postby lewy71 » Sat Jun 16, 2018 8:43 am

Did you remove the raw water pump to replace impeller ? If so check correct orientation.

Did the original impeller have missing vanes when replaced ? You have checked most places they block but maybe a double check.

Last thing have you verified that you gauge is reading correctly ?
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Re: Nautique gt40 overheating

Postby Feetfirst » Sat Jun 16, 2018 8:48 am

Did you use an aftermarket impeller? I had the same issue not long ago and chased my tail for hours doing exactly what you did, switched to oem part and it was perfect.
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Re: Nautique gt40 overheating

Postby noride » Sat Jun 16, 2018 11:04 am

Sherwood impeller used, checked twice for blockages, the old impeller was intact. I think I might have to check the gauge is correct. Thanks for the advice. Also must add that the warning light does not come on.
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Re: Nautique gt40 overheating

Postby lewy71 » Mon Jun 18, 2018 9:04 am

The screw is on outside for counter rotating PCM (RH) engines pre 89 for normal rotating automotive (LH) engines with 1.23 trans this screw should be on the inside.
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Re: Nautique gt40 overheating

Postby mattygray » Tue Jun 26, 2018 11:31 pm

Is there a gearbox oil cooler between the pickup and the pump?

I had a similar problem and found weed on the intake side of the oil cooler.
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Re: Nautique gt40 overheating

Postby noride » Tue Jul 10, 2018 9:30 pm

Ok finally got an infra red laser thermometer and tested the temp, with the guage showing well over 200’f the temp at the sensor or the bottom of the thermostat housing never got over 152’f, next step sender and guage, any thoughts could it be the 20+ year old wiring?
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