1990 SP overheating badly, why might that be?

[NotAbrahamLincoln]

I posted earlier about my 1990 SP taking on water but did a lake test today anyway. After about 30 minutes, with breaks every 10 minutes to check and drain the hull, we noticed that the yellow paint on the head looked darker than it was before. When a bit of water dripped off my hand and fell onto the head it boiled. I assume if the engine was hot enough to discolor the paint it was a lot hotter than it should have been, but I don't know why the temperature sensor didn't turn the engine off.


What might have caused it to overheat so badly? It was running way too rich but I don't think that would cause overheating. Someone I know told me it could possibly be the wear ring. I know this machine has sucked up some sand before but the "pee hole" above the jet nozzle was spraying water so I know some water was making it through.

 

[Spider4real]

Cooling would have nothing to do with the wear ring. It sounds like you have no water getting to the engine. The bleeder stream is coming from the exhaust, but that does not mean it is getting to the engine. At least not enough to keep it cool. I would try running it on the hose to back flush the system to see if that helps clear the restriction. But sounds like it might be best to open up the engine and make sure the water channels are clear of sand an dirt.

The temp sensor does not turn the engine off. It is attached to a beeper that warms you the engine is hot. You might have a defective temp sensor or maybe the beeper is bad

 

[mikidymac]

IF the wear ring is bad it will cause cavitation which will not create enough pressure to feed water to the engine.

If the wear ring is ok then it sounds like you have a blockage and flushing on the hose might fix it but make sure you never have the hose turned on without the engine running.

 

[NotAbrahamLincoln]

IF the wear ring is bad it will cause cavitation which will not create enough pressure to feed water to the engine.

If the wear ring is ok then it sounds like you have a blockage and flushing on the hose might fix it but make sure you never have the hose turned on without the engine running.

Ok, I took the nozzle off the pump and was able to get a pic of the wear ring and of the impeller. It looks pretty bad to me, but I'd like to get a second set of eyes on this to confirm. Took the head cover off and saw a few grains of sand in it. Haven't been able to see deeper inside the engine itself

 

[Spider4real]

When you did the water test when you discovered the overheating issue, was the ski performing ok or was the engine reving up and the ski would not get up to speed? If it was cavitation it would be like being in a car a spining the wheels and not really moving very fast.

 

[NotAbrahamLincoln]

It was revving up, holding rpm, and taking a while to get up to speed, but I don't know if it was exactly "spinning the wheels". It didn't exactly feel "in gear" though. I haven't been on another PWC in a while, so I don't remember exactly how "in gear" it should be.

 

[Spider4real]

Hmmm, sounds like mikidymac was correct with his diagnosis and likely the wear ring was causing cavitation and insuffent water flow. The clearence on the impeller does look a little more than normal to me. But I will let the pros here confirm that.

 

[Spider4real]

This is what mine looks like

 

[mikidymac]

It looks like the rubber on the wear-ring has blown out which is very common as the get old. Bad cavitation and overheating are given.

 

[NotAbrahamLincoln]

Ok, new wear ring, impeller tool and neoprene o-ring are ordered and on the way. While I'm taking the impeller out anyways would it be a good idea to switch out the original impeller with something like a 14/21 pitch impeller from a later SPi, or should I generally leave that kind of thing alone?

 

[Spider4real]

I am no impeller expert, but I would probably stick to the stock impeller for now, get it going and see how it performs. You can always change the impeller down the road. With some hours on the stock impeller it may give you an idea of what direction to go with a replacement. If you still think it is necessary.

I can't really see much in the pictures, but you might just need to clean up the leading and trailing edges with a file if you see any nicks from a rock. It does not need to be perfect. Do not touch the outer edge.

 

[NotAbrahamLincoln]

Did another lake test today. This one was about 5 minutes long. With the new wear ring installed it rides much better but it still overheated. The head was over 212 after 5 minutes. It was definitely running lean but I don't think running lean alone could get the head over 212 degrees if water was flowing. The exhaust expansion chamber was about 100 degrees so I think there must be a blockage between the exhaust and the head. Does that sound about right?

 

[Spider4real]

Sounds like you have a blockage to me. I think that would be a good starting point. Did you try to flush it on the hose to see if that will clear it up?

But once you clear up that blockage you will need to tackle the lean condition ASAP before you have more serious issues.

 

[NotAbrahamLincoln]

We don't have the flush port, planning to build our own flush kit ASAP now that the cavitation problem is gone. I will be able to get the carb off tonight to do some work and fix that lean condition.