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LPski

Over heating at speed

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LPski

We have a 1999 Malibu Response LX with monsoon engine. I am experiencing overheating at speed. The symptoms are: The boat runs fine until a couple passes through the slalom course at which time the engine temp climbs fast. Stop the boat to idle ande the temp goes back to 160 degrees. I have changed the raw water impeller, changed the thermostat, checked the transmission oil cooler for clog, even checked the exhaust manifold elbow for clog. I am thinking it might be the temp. sensor is bad as the engine does not really act like it is that hot when this occurs. I read one post on here that said the main water pump was broken. Wouldn't I have some noise or leaking if this was the case? Thanks for any help you can offer.

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Killer

check every hose connection, you'd be surprised what a little bit of air will do at high speed when the boat is on plane, the pickup doesn't grab as much water.

I will concur with the main water pump and/or impellar potentially causing this. Also check the serp. belt and its tension, as well as the intake grate at the hull for debris or damage.

I'd say run it on land bypassing certain aspects of the cooling system but you say it only happens at speed.

start with the small stuff first and see if you can nail it down. must figure out what is causing it before you throw money at it.

the main circ water pumps are notorious for burning out prematurely & are not expensive or hard to replace.

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eyepeeler

Could you give us a little more info please. How many hours on the boat? How many hours on the raw water pump? Any water leaking from the RWP? How hot is hot? Have you looked for clog at the raw water intake? :dontknow:

:plus1: on hose connections and belt tension.

Edited by eyepeeler

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Ndawg12

Be sure to pull the impeller and make sure it's still in good shape and that the metal collar and the rubber fins are all still secure. I've heard of them seperating, the impeller looks fine but as rpm's increase the metal collar spins with the shaft but the fins don't spin at the same rate, thus overheating at higher speed.

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LPski

Could you give us a little more info please. How many hours on the boat? How many hours on the raw water pump? Any water leaking from the RWP? How hot is hot? Have you looked for clog at the raw water intake? :dontknow:

:plus1: on hose connections and belt tension.

The boat has about 800 hours, the original raw water pump but have replaced the impeller many times. I have been dealing with ski boats for 38 years. The belt is tight, just replaced it. In fact, I forgot to mention, The first time out, the belt broke. I replaced it, then this problem. I am confident that loose hoses are not the problem. I have checked the water intake and it is clean. The main engine water pump has me scratching my head. Thanks

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Bill_AirJunky

The engines water pump isn't likely the problem. It will be leaking out the weep hole on the bottom if it's bad.

Check for clogs downstream from the impeller... where pieces of old impellers can clog things up.

And replace the thermostat.

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LPski

Be sure to pull the impeller and make sure it's still in good shape and that the metal collar and the rubber fins are all still secure. I've heard of them seperating, the impeller looks fine but as rpm's increase the metal collar spins with the shaft but the fins don't spin at the same rate, thus overheating at higher speed.

I just installed a new impeller and the old one looked fine. It pumps water well when I disconect the hose from trans. oil cooler. Thanks

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eyepeeler

LP go back to where your belt broke while you were running. What are the details?

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LPski

The engines water pump isn't likely the problem. It will be leaking out the weep hole on the bottom if it's bad.

Check for clogs downstream from the impeller... where pieces of old impellers can clog things up.

And replace the thermostat.

Thanks, bill, that is what I thought about the main water pump. In the past, I have had impellers come apart and get cloged at the transmission oil cooler. Also weeds. But we havent had an impeller come apart in over a year and the trans. oil cooler is clean. I have checked every thing posted above more than once. I am thinking water temp. sensor. Any thoughts?

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LPski

LP go back to where your belt broke while you were running. What are the details?

First slalom set of the year for me, My buddy is driving, third pass boat goes into limp mode, we stop the boat, go back to dock (private lake) find broken belt, Oh how easy-not, go to belt store buy new belt, replace.

Go back out, I pull him this time, he makes 4 passes with one stop. temp. is fluctuating some.

I ski 2 passes, stop, boat goes limp. we stop.

Since then, replaced thermostat- same problem, replace impeller- same problem, took apart exhaust manifold elbows because I was told by a marine mechanic that this is a common place for blockage. checked all hoses etc. every thing appears clear.

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Bill_AirJunky

Temp sensor? So your thinking that it's not really hot, but the sensor is saying it is?

Possibly. Never heard of that happening.

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eyepeeler

You may want to double check the new thermostat in hot water. I have heard of bad thermostats right out of the box.

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BuFootin

The boat has about 800 hours, the original raw water pump but have replaced the impeller many times. I have been dealing with ski boats for 38 years. The belt is tight, just replaced it. In fact, I forgot to mention, The first time out, the belt broke. I replaced it, then this problem. I am confident that loose hoses are not the problem. I have checked the water intake and it is clean. The main engine water pump has me scratching my head. Thanks

Experienced a frustrating problem with overheating myself. My issue was I never replace the impeller housing gasket (just used the old one from the prior year) when I removed the impeller during winterizing. Never could get a consistent good prime on the raw water pump which led to overheating. Spent $2.00 on a new gasket if you don't have one already.

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99response

Are you sure the boat is actually overheating? My rule of thumb is if you can comfortably touch the risers your temp is good.

-Chris

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LPski

Are you sure the boat is actually overheating? My rule of thumb is if you can comfortably touch the risers your temp is good.

-Chris

No, I'm not sure it is actually overheating, you can touch the exhaust manifolds when the temp guage rads over 200 and I even stuck my hand down by the exhaust and it was not scalding hot coming out. That is why I'm thinking it is something to do with the sensors or other electronically related issue. I did install a new gasket with the impeller. 2 bad thermostats may be the problem but seems unlikely. Thanks

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glenn

No, I'm not sure it is actually overheating, you can touch the exhaust manifolds when the temp guage rads over 200 and I even stuck my hand down by the exhaust and it was not scalding hot coming out. That is why I'm thinking it is something to do with the sensors or other electronically related issue. I did install a new gasket with the impeller. 2 bad thermostats may be the problem but seems unlikely. Thanks

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glenn

Did you ever figure out the problem. I have a similar problem with the same boat. Temp Gauge is all over the place. Got a new gauge, sensor, and thermostat coming but still not sure if it's not an electrical problem.

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