1980SN Getting Hot

[robm]

Hi All,

First post - i'm from Australia. 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

[James]

I am not an expert or a mechanic but I have a few thoughts... It is concerning the engine stopped on it's own as a result of the overheating. That usually means it got very hot. It would have been better to turn the engine off as soon as over heating is noticed but that is in the past. Assuming the coolant in your closed system was full before the impeller issue I suspect the overheating caused a blown head gasket and possibly a warped head. The need to add 3-4 litres of water to the closed system means the coolant was lost either into the oil and or out the exhaust. Pull the oil dipstick out and see if the oil level is high and if the oil looks like a milk shake. If so and you ran the engine under those conditions you unfortunately may have a more serious problem... ie. engine rebuild. If there is no water in the oil you may have gotten lucky and the coolant is going out the exhaust meaning you need a need head gasket and/or work on the heads. If the coolant level was low initially that would amplify the overheating when the impeller gave out. I would also check/flush the raw water side of the system to remove all the pieces the the old impeller and check all hoses (including the exhaust hoses for overheating damage). When all is done be sure all the hose clamps are tight as is the raw water strainer the prevent air suction issues. Maybe you got very lucky and just have bits if the impeller blocking the cooling passages. There are a number of experts on older Nautiques like yours on Correctcraftfan.com. I would recommend posting there as well. They will talk you through step by step to diagnose and repair your engine.

[SilentSeven]

Let me make sure I'm clear - your boat has a self contained cooling system and a raw water system? And the self contained cooing system was down 3 or 4 quarts of water? And the boat overheated and stopped? So a few thoughts.

First, the raw water pump (in this setup) is responsible for two things a) it pumps water into the exhaust manifolds for exhaust cooling. b) it pumps water to the engine close loop heat exchanger. When the impeller failed you lost exhaust cooling and engine cooling. You should visually check the rubber and fiberglass exhaust sections for heat damage. And the muffler as well.

The failure of the raw water impeller combined with the low water condition in the engine cooling system is concerning and you may have seriously overheated the engine. When there is no water in the system, the engine temp gauge may not reflect how hot the engine actually is as there is no water in contact with the temp sensor. The temp sensor measures water temp and it appears you had little to none. Like James suggests above to be aware of possible engine damage.

I'd do the following. a) inspect the oil as James suggests b) change the oil, it may be baked c) fill the closed water system and bleed it to make sure there are no air pockets d) put the boat in the water and see how it runs. Funny noises like clattering or knocking suggest lubrication failure damage and you'll need a mechanic to diagnose. Before the engine temp rises, pull off the water system cap and put the palm your hand over the fill hole; blip the engine a few times. If you feel positive pressure, you may have a head gasket failure. Repeat the test without your hand and look for bubbles in the cooling tank each time you blip the throttle. If you see bubbles, pretty much for sure a head gasket is toast. Let the boat idle and see if the temp is stabilizes. If OK, generally run up the RPM and see how it runs. If it runs OK, you make be good. If not OK, you'll want to do a compression test and see what that shows. If the boat overheats at idle, you'll need to figure out what part of the cooling system is not working...if might be a vacuum leak in the raw water hosing, problem with the raw water impeller, blockage or a bad heat exchanger or a bad engine cooling circulation pump.

Keep checking the water in the closed loop system...it shouldn't loose any. And keep looking for signs of moisture in the oil.

Hope this helps! Good luck....