Need jet boat help(Mercruiser)?

[Robjack]

So I have a 2004 Polaris LE 2100 jet boat and cant figure out my issue, boat starts only when you give it gas, then runs for almost exactly 10 mins then stops and wont start back up till it cools down, thought It was a fuel issue but now im told it may be a thermostat because one hose was hot and the other cold, so I pull her out to change the hot side thermostat and I let it run on the hose to see witch side heats up and nothing! Runs perfect on the hose for 20+ minutes?!? Does this tell me theres something stuck in the intake under the boat or something else, lost and havnt had any use all summer- very discouraging

 

[Gym]

Sounds like it's shutting down on overheat. You could have a blockage or a stuck thermostat. Have you tried running with the thermostat out?

 

[Robjack]

Not yet, seems like it only overheats in the water but not on the hose now?

 

[tdonoughue]

Hmmm... Not a lot to go on there, but let's give it a try.

When you say it heats up and 'nothing', does that mean it keeps running?

On hose running perfectly and failing in the water after 10 min does sound like something blocking the intake path. Not sure where it is on your boat. Might try some weed whacker line up the intake (wherever it is) to see if you have a mud dauber nest or something blocking somewhere.

Are you in salt or fresh water? If you put your location in, that will help some, too (and we may have someone nearby for onsite help). If salt, do you flush regularly?

 

[tdonoughue]

(this is what happens when you type a reply, get distracted, then hit send later only to find 3 intervening posts)

 

[Robjack]

In fresh water in Boston, in the water one of the thermostat hoses heats up and the other stays cool then shuts down almost exactly 10 mins. Im going to double check and put her back in the water to confirm that its atill doing the same, shutting down in the water and running fine on the hose..

 

[Gym]

Before putting it back in I would look closely at the underneath of the boat where your water intakes are and make sure there are no obstructions or trash sucked up there.

 

[Robjack]

Going to do that today but if its clear then what?

 

[RedBarron55]

I don't know about your Sport Jet, but my old one gets it's cooling water from a hole in the jet impeller zone.
There could be a rock or trash clogging the inlet tap.
The jet mechanism comes off fairly easily and this can be inspected and probed with a wire or??
there is an O ring seal where the wear ring attaches to the main housing.
You have to disconnect the steering and fwd rev cables and remove 8 bolts and some screws.
It wouldn't hurt to finish the annual lube service at this time.
Google annual service for sport jet and you get:

https://www.outlaweagle.com/forum/files/sjannualservicev1.1_190.pdf

There is a
hole on the right top of the wear ring that feeds cooling water to the housing when the engine is running.

As an aside if the engine is not idling high enough there is not enough cooling water to keep the engine cool.
My engine has to idle about 1000 - 1100 to keep the engine from buzzing the over heat warning after a while.
Check your manual of your specific engine.
If you have run into sand or mud this might have blocked the passages.

 

[Robjack]

Yea im told it may be the fresh water pump but taking that out is above my skill level

 

[RedBarron55]

There is no separate fresh water cooling pump.
The cooling water is tapped off of the main jet pressure.
If the engine is running in the water the jet pump will pump at least some water.
It takes 1ooo to 1100 rpm to flow enough water to keep it cool at idle.

 

[Gym]

Yea im told it may be the fresh water pump but taking that out is above my skill level

@Robjack. Why not add your ciry/state to your profile. That will add you to our member map. Possibly there is a member close by that can help out.

 

[Bilmon]

There is a cluster of, I think 5, holes about 1/8 inch dia. each in the wear ring. That is your intake when in the water, on the hose the water enters differently so if there is a partial blockage in the wear ring that could be why it stays cool on the hose

 

[biffdotorg]

First off, the Polaris boats ran Mercury SportJets and they should have been either the 240 EFI or 250 Optimax. I have yet to see one with the 240, but supposedly they were made.

One thing with the 240, was the head temp sensors. There were something like three of them. They did cause this sort of issue, and folks would chase after cooling lines, inlets etc just to find that the head temp sensor was throwing the engine into limp mode, or not allowing the engine to start at all. And mostly when the temp was within spec. This is not to say you don't have blocked inlets, as that could be true as well.

If you have the 250 Opti, check a service manual to see if they an the similar head temp sensors. I do believe they do. It's not an expensive part, and should be available online. And you should be able to swap them yourself.

Good luck!

 

[Bilmon]

The 240 has 2 temp sensors, one on each head. I believe the 250 has a third one on the compressor . I know from experience failure on the 240 will cause the computer to default to a cold setting and run the engine rich but not overheat. Don't know how the 3rd sensor on the 250,which he most likely has, affects things.