Overheating for no reason?

wcmaness

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Aug 2, 2008
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Ok - there must be a reason, but I haven't found it. A couple years ago I spun the hub on my 1985 XR2 Black Max 150, and she overheated. Melted a few wires. I changed the T-state, and the water hoses, and the impeller for the water pump. I even installed a new oil pump to be safe. Started right up & seemed to run fine with water muffs, but a little hot. The pee hole water was real hot. So, I took it to the lake for a test, and decided to make a run accross the lake. Within a minute, the temp guage redlined. The pee hole turned to steam, so I shut down and took it home. Why would this be happening? I don't know what else to change or check.
 

CharlieB

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Apr 10, 2007
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Re: Overheating for no reason?

A spun hub will not overheat an engine. By unloading an engine it cools down.

You had another problem occur. What did that old impeller look like when you changed it, had it lost any of its vanes?

Had it EVER been started out of the water, with no cooling water?

Is the pump housing square with the world, (not warped any).

Have you checked the poppet valve, stuck shut?

The list goes on, any number of things can cause serious overheating, you GOT TO check everything or you will burn it down, again.
 

wcmaness

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Re: Overheating for no reason?

A spun hub will not overheat an engine. By unloading an engine it cools down.

You had another problem occur. What did that old impeller look like when you changed it, had it lost any of its vanes?

Had it EVER been started out of the water, with no cooling water?

Is the pump housing square with the world, (not warped any).

Have you checked the poppet valve, stuck shut?

The list goes on, any number of things can cause serious overheating, you GOT TO check everything or you will burn it down, again.


The old impeller looked fine

I bought it second hand, so I expect it could have been started out of the water - but it ran fine for a couple years before this problem occurred

I didn't notice anything wrong with the water pump housing - but I'm no expert

Looked at the Poppet, and it seemed ok. I could pull it open & shut - but I don't really know what I'm looking for on that

I guess I am at the point of just taking it in. I am stuck.

I keep thinking maybe I put the water pump in wrong, or got a feed tube crooked or something - but wouldn't the pee hole show a problem then?
 

j_martin

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Sep 22, 2006
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7,474
Re: Overheating for no reason?

A water pressure gauge would help immensely in figuring this out.

It could be anything from plugged internal passages, to a bad head gasket.

I sawed a log in half with mine once. Didn't hurt the lower or prop much as the log was pretty rotten, but I picked toothpicks out of the cooling system for a month till it got it to run cool again.

hope it helps
John
 

outhere99

Seaman
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Jun 13, 2008
Messages
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Re: Overheating for no reason?

By "poppet valve" are you guys refering to a thermostat? Maybe the thermostat is stuck closed.

How about if a water jacket is full of sand or gunk (like J_martin had)? Can you easily remove a head (cover) and to look at the water jackets around the cylinders? At the same time you have a good look at the cylinder walls and pistons (on that side at least if it's a V-6).

BTW.... If you melted wires, etc. I'd do a compression check before anything. You might have more work involved.
 

j_martin

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Re: Overheating for no reason?

The poppet valve is a pressure release valve, usually set at about 12 lbs that lets water off the engine block at higher rpms. It is low on the starboard side of the engine, either 2 or 4 bolts, depending on which one it is.

The exhaust plate can come off and reveal some passages. The heads can come off and reveal a bad head gasket, which is a possibility. It also gives you a pretty good look at the water jacket around the cylinders. You can pick up on pinholes through the plating in the cylinders, also.

Plugged passages in the exhaust plate, another possibility, require pulling the power head. If you have overhead lifting ability, a lifting adapter that screws into the flywheel center hole, and the bolts aren't frozen, it's not all that hard to do.

The overheating is a seperate problem unrelated to the spun hub. It sounds like it might have gone on for awhile undetected and might have done some more serious damage. For sure I would suspect a warped head and blown water gasket. Overheats tend to be pretty hard on the exhaust divider plate, also.

Pull the plugs and look into the cylinders. If you have a plug and cylinder that looks like new, instead of a little dirty and oily, you have water getting into that cylinder.

hope it helps
John
 

wcmaness

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Aug 2, 2008
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Re: Overheating for no reason?

Thanks for all the diagnosing help. I have learned a lot about my motor. The poppet valve is good. The cylinders are good. I took the lower unit off again, and discovered the impeller had apparently gotten something lodged in it & meled part of the fins off. It moved water, but not well. Replaced it and all seems to be running dandy.
 

j_martin

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Sep 22, 2006
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7,474
Re: Overheating for no reason?

Hate to sound like a broken record, but a $25 water pressure gauge would have picked off that problem in about a heartbeat.

hope it helps
John
 

wcmaness

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Aug 2, 2008
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Re: Overheating for no reason?

Point well taken. Getting one now for future adventures.
 
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