89 Ski Nautique 2001 over heating

[NickSN2001]

Greetings from Tasmania, Australia!
I have recently purchased a 1989 Ski Nautique 2001.

It has the PCM power plus engine.

I'm noticing the temp skyrocket when the boat is sitting idling. Overheating light has started to flicker on occasion. Temp starts coming back down as soon as we get underway again. When on the hose the engine sits nicely at about 140. when running the temp gauge will sit around 160-180.

I was told by the previous owner that the impeller was replaced just before I purchased the boat.

When running the boat on the hose, I noticed some water weeping from the raw water strainer, could this be turning into an air leak when the boat is on the water?

What would be considered normal operating temps for this engine?

Also looking for prop recommendations, we will use the boat mostly for wakeboarding and surfing so I expect to have the boat loaded up a bit once we get this overheating thing sorted out. Pretty sure we have the 1.23:1 drive.

Cheers

Nick

[NautiqueJeff]

That engine should run around 160 degrees. You likely have an air leak somewhere, but I would go ahead and replace the impeller again anyway, just so that you're SURE it is done. Check all of the hose connections for tightness, and make sure the water strainer has the O-ring in place. Those often go missing, and that will cause an air leak, which can lead to overheating.

This is the impeller you want. Don't buy an off-brand one. They fail very quickly.
https://nautiqueparts.com/impeller-s...ts-all-gt-40s/

This is the O-ring for your strainer:
https://nautiqueparts.com/water-strainer-gasket/

If you order from NautiqueParts, be sure to use our discount code (PND) for 10% off.

[Rednucleus]

If it continues after following Jeff's plan, consider replacing the motor's waterpump as well (different than the raw water pump).

[jpwhit]

Yes, you have the classic symptoms of an air leak on the suction side of the raw water pump. Since the suction side is at a negative pressure, even a small amount of air that enters turns into larger bubbles that displace enough water to limit cooling. When the engine runs faster, the raw water pump draws in so much water, that the engine cools down. The fact that it does cool down at higher RPM, tells me your impeller is most likely fine.

As others have mentioned, a missing o-ring on the cap of the filter is a common culprit. Also, the clear strainer covers tend to develop crack around the threaded area that can also allow an air leak. Another fairly common cause, is someone tightens the clamps too tight on the transmission cooler. It's also on the suction side of the raw water pump. If you tighten the clamps too much, it deforms the hose barbs on the cooler and then doesn't seal properly.

Since you see water leaking out of the strainer when connected to a hose, you're problem is almost certainly an air leak in the strainer.

[NautiqueTim]

Air leak or the impellor has small flat spots on the ends of each blade which causes it not to lift adequate water at idle. The cam in the pump could be worn too.

[NickSN2001]

Thanks for all the great info guys. I have pulled the pipes of the impeller pump and had a look at the impeller, it all looks good. Ordered a new raw water strainer so will try that and hopefully get a win.

[NickSN2001]

Well, took the boat out today and she was absolutely perfect. Sat around 140-160 all day no dramas. Was definitely the air leak in the raw water strainer. Replaced that and everything is peachy!
Thanks all for the good advice!

Now for my next question, what prop should I get. current prop is slightly damaged and out of balance. not to the point that it is un useable, but it is annoying.
boat will be used mostly for wakeboarding. Usually with 5-6 adults onboard or equivalent ballast. Maybe some surfing on occasion.
ACME 422?

[Rednucleus]

Should be able to get your prop repaired and continue using, or keep as a spare.

[Jonny Quest]

If you do mostly wakeboarding and surfing, I would look at the ACME 654 or 1868. The 422 is for full-speed operations (waterski speeds) and may be too much pitch. Wakeboarding is typically below 20 MPH and surfing is between 9 to 13 MPH.

I had the1868 on my 1994 Ski Nautique and hole-shot was amazing. I had to pay attention to the tachometer, as I could over-rev by 400 to 500 RPMs at wide-open-throttle.

JQ

[NickSN2001]

Thanks for that info Johnny, that’s all good to know. Current prop is an OJ 14 16 Cup. I’m not sure what that means but I will be getting it repaired.
im interested in what you mentioned with regard to over revving. What rpm would be considered over rev?

[jpwhit]

If you look up the specs for your motor, there will be recommended WOT rpm. That's the RPM where the motor makes the most power. If you go above that, it's not going to hurt anything unless you exceed the motor's max RPM, but you'll get the best top speed with a prop that run at the recommended RPM when wide open throttle (WOT). The props typically used on the 5.7L Nautiques in the order of lower RPMs to higher RPM at WOT are

Acme 422
Acme 654
Acme 1868

Since you talk about wakeboarding and surfing, if you're going to load the boat with ballast and/or lots of people, you may want to tend towards a higher RPM prop. Newest CNC props are really much improved over older props. I'd recommend getting a new prop for everyday use and either just keep the old one as is for backup. Or getting the old one repaired for use as backup. Some places will rebuild an old prop for free if you buy a new prop.

If you call Acme with the info on hand for the diameter, pitch, cup, the current actual WOT RPM, boat speed at WOT, they are very good at recommending a prop. Your OJ prop should have a model number stamped on the hub in addition to other info.