engine overheating

[kilowake66]

I have a 85 ski nautique 351/C. My boat started overheating one day. got to 200. we then ripped out the termistat and did not put a new one in. it still overheats. Then we bought a new water pump and impeller. I think I put it in ok and not upside down.I checked all hoses for air leaking all good. still overheating. any help

[skinautique]

RE: engine overheating

Check all of the hose connections, check your water strainer bowl to make sure that it is tight and NOT cracked. Make sure you get a thermostat back in there as well. Also, make sure that your water strainer bowl is clean. Also, when you replaced your impeller, did you get all of the missing pieces out from the old one? They will stopp the waterflow as well.

[kilowake66]

still over heating

checked all the hoses today. they are all tight. found out my flush kit valve was sucking air in and put a cap on it. it still over heated. even checked the exaust manafolds they are all good. There may be pieces of the impeller left but all my hosees are flowing smoothly. could it be the maian water pump that pumps the water through the engine?

[Jesse1]

RE: still over heating

Might want to check to see how much water is coming out the exhaust. Put a water hose in the water inlet and run the engine while it's out of the water. Check for a good flow of water out the exhaust. Could also be a bad temperature sending unit. Make sure you installed the rubber impeller correctly with the vanes in the right direction.

[kilowake66]

Thanks I am going to check that today. I think it could maybe be the circulating pump

[Jesse1]

How many hours on the engine? The worst case could be a blown head gasket!

[kilowake66]

I have 781 hrs. I ordered a new thermistat today. it will be here in 4 days I will try to see if that is it. If not i am going to check the head gaskets. Thanks

[M3Fan]

I think there would be visible problems if it was a head gasket, like water in the oil, etc. It's not what you'd call a "minor" thing to "check". It's taking the whole top of the engine off and everything with it. I have had brand new thermostats, right out of the box, not work correctly so don't discount that. The circulation pump is a very basic device. Usually their failing includes leakage of water. Another thing to check would be the keyway in the sherwood raw water pump that ensures that the impeller rotates with the shaft. The sending unit was another good suggestion.

[gunnin4six]

overheating

I had a similar problem, although not quite as bad as yours. I was getting minor overheating.
It turned out to be a clogged riser. The risers had filled up with corrosion/slag and very little water was getting through.
The symptoms that lead us to the source of the problem was when we got it out of the water and connected a hose, little to no water was coming out of the exhaust. Also, the riser was extremely hot. normally you can briefly touch the riser without burning your hand. The manifolds were clean, just the riser were clogged.

Good luck!

[mrese]

RE: overheating

Put your t stat in a pot of water on the stove with a thermometer. Check it to see at what temp it opens and closes. An easy trouble shoot to narrow down a problem. Saves time and money instead of just throwing parts at a problem trying to fix it.

[nms1991]

RE: overheating

Where does it overheat? at idle? At full throttle?

[j2nh]

With the engine off, pull the freeze plugs from each side of the block. Water should flow freely out of them. If not take a wire coat hanger and gently work out the junk that is preventing good water flow. Similar condition to what you describe happened on a neighbors Malibu. Once I poked in the hole, junk flowed out for around 20 seconds. Lots of little pieces from a long gone impeller. Worth a try.

[skinautique]

j2nh,
It is not that easy to get at the freeze plugs. I would say, wait and see what nms1991 comes up with. He is an amazing tech.

[kilowake66]

I think we figured it out

I went today and pulled out the entire cooling system. I found lime rust that happens in radiators all in my heat exchanger and hoses. Enough to restrict flow. I am going to soak the heat exchanger in CLR for a day and the hoses.

[Bobby]

my '82 did that EXACT same thing this last summer. I went through everything you went through, and I swore up and down that I had the impeller in correctly, but it turns out that I didn't. Make sure that the screw in the impeller housing is facing away from the engine block.