zR409 Intermittent overheating

[Lakejackson]

I have a 2011 sport 200v with Linc 1 and ZR409 freshwater cooled engine. The boat is overheating occasionally when we sit in neutral with engine running. When it overheats, it will quickly cool down if I bring the RPM’s up. New impeller did not make a difference. Any suggestions appreciated. Thanks.


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[ESP]

Make sure pickup and screen are clean and clamps on the inlet are tight.

[SwiftnessNautique]

Since this is intermittent I'm reluctant to say that you possibly have a bad impeller. I would pull it to check and see if there is any dry fractures or missing paddles. If its at idol, it could mean that the water volume is dropping causing overheat due to the impeller going bad. When on the go you introducing more water volume quicker causing the temp to drop. Just a theory, but may want to pull and check, and have a new one to install.

[jpwhit]

This is the classic symptom of a vacuum leak somewhere on the suction side of the raw water pump. Any small leak lets air into the suction side and then due to the negative pressure the air expands into large bubbles and displaces too much of the cooling water. When RPMs increase, the raw water pump moves so much water that the engine is cooled adequately. Common places to check - hairline cracks in the plastic bowl of the raw water strainer, air leaking around strainer gasket, loose hose clamps on the transmission cooler or any other hose connection on the suction side, small crack in transmission cooler, crack in one of the plastic fittings, etc....

Another way to definitively confirm this is the problem, it to install a few inches of clear hard plastic pipe inline in the hose right before the intake of the raw water pump. If you see any bubble in the water flow, then you have an air leak on the suction side. MasterCraft makes this easier to diagnose because they use clear elbow fitting on the strainer which is the last thing before the raw water pump. I like that so much, that I've installed the same fitting on my Nautique's.

[Lakejackson]

Thanks for all the suggestions. I found leaves in the transmission cooler. It was about half blocked. Didn't get a chance to test it out, but I am sure that was the culprit. Not sure how the leaves made is past the water strainer. Guess I'll be checking this every year.


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[BT]

Check the screen for the thermostat. If you run in water with a lot of small debris it may have made it past the fresh water strainer.

[Lakejackson]

Boat is still overheating at idle and at WOT. I took apart the heat exchanger to clean it. I tried to order new gaskets for the end caps, but Nautique Parts is saying that you have to buy a kit that includes gasket, new metal end caps, and new bolts. Costs about $150. Anybody found just the gaskets?

[Lakejackson]

Bump.


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[Lakejackson]

The problem ended up being with the gaskets on the heat exchanger end caps. They deteriorated and pieces where stuck in the exchanger blocking the flow of raw water. Replaced the gaskets and works great now.


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[ally505]

did you find the gaskets only at a reasonable price?

[Lakejackson]

I don't remember exactly how much they were. I think it was less than $20 for the pair.


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