1980 Ski Nautique overheating

Postby Robm » Fri Nov 06, 2020 6:23 pm

Hi All,

First post in years. Have a 1980 Ski Nautique that hadn't been used for 9 months or so (kids, life getting in the way!), took it out and it got hot after about 6-8 minutes of runtime and actually stopped. I'm assuming the fuel was vapourising??

Anyway, got it home, and pulled the raw water impeller out and it was perished. So put a new one in and fired it up at home on the trailer. It ran fine, but when i revved it to 3500rpm or so for a minute or two, the temp got up to 190-200. Typically it would only previously get to this temp if you pulled a skiier flat out for a long period, then would drop back to 160-170 within a minute of backing off. On the trailer now, even when i got it back to idle (garden hose running through the inlet) it stayed around the 185 mark. So its running too hot, and i can imagine on the water under load it will get hot very quickly.

So: a few questions and open to any ideas on what to test/replace etc...

1. Could i have done something nasty to the engine when it got to 200 (only for a few minutes)
2. The raw water pump appears to be fine as water is being blown out the exhaust - however i did note the black manifold on one side that mounts to the exhaust ports is rusted a bit where it connects and water was dribbling out a little. That said, this has to be fresh water (not part of the closed cooling system), so while not ideal, can't see this being the overheating issue?
3. I had to top up the closed system water, and did this with fresh water (not coolant) - i put an estimated 3 or 4 litres of fresh water in. Would the lack of coolant have that significant overheating effect?
4. A few bits of the perished raw water impeller were in the pump housing - could some other bits have gone through the system and blocked it, or could it be a bit corroded and blocked? Is there any easy way to test for blockages or flush the closed cooling system?

Any other ideas gladly welcomed on what to test or inspect!

Thanks

Rob
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Re: 1980 Ski Nautique overheating

Postby Feetfirst » Fri Nov 06, 2020 8:17 pm

Hi rob, I know when I had issues last time the transmission cooler which is directly after the impeller was chocked full of weed and other rubbish. This could be limiting the amount of water getting through.
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Re: 1980 Ski Nautique overheating

Postby lewy71 » Tue Nov 10, 2020 8:42 am

If the impellor had missing vanes then they could be lodged in the hoses restricting flow. Disconnect at both ends and flush them with the hose. Sometimes they manage to get back down the inlet hose to the screen on transmission cooler.
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Re: 1980 Ski Nautique overheating

Postby Feetfirst » Tue Nov 10, 2020 1:10 pm

Another thing, you mentioned it got hot running it on the trailer with the hose at 3500 revs. I don’t think your hose could supply enough water at those revs to adequately cool it. It would be drawing far more than that at speed on the water, and the inlet pickup also rams the water in. Just a thought.
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Re: 1980 Ski Nautique overheating

Postby Robm » Tue Nov 10, 2020 6:11 pm

Feetfirst wrote:Another thing, you mentioned it got hot running it on the trailer with the hose at 3500 revs. I don’t think your hose could supply enough water at those revs to adequately cool it. It would be drawing far more than that at speed on the water, and the inlet pickup also rams the water in. Just a thought.


I'm hoping you are onto it. I pulled the heat exchanger off and cleaned it. It was pretty clean but there were a few rubber bits of the impeller that I got rid of in there.

Talked to a local mechanic and he agrees there is not enough water flow from the hose. So will take it on the river when I can and test. Haven't topped up with coolant, just fresh water in case I need to pull it apart again. Once good will put new coolant in there but can't see it significantly raising operating temp.
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