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Old Merc. 350 mag heating up.

Old 07-26-2008, 09:52 AM
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Default Old Merc. 350 mag heating up.

350 Chevy block. Lower unit is off, impeller like new. What would cause motor to run hot? didn't overheat,, just running hot so I quit using it.
Thermostat? Any good and easy way to check water flow?
BTW it's running hot on higher RPM's

Thx
p
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Old 07-26-2008, 09:55 AM
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Track water flow thru upper housing, water hose thru transom , power steering cooler. Also check risers for obstructions.
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Old 07-26-2008, 11:20 AM
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Bad risers will do that.. Also, just because the impeller looks good doesn't mean the rest of the pump is. Check the base and upper housing carefully. Next step is to check the entire water system. Backflush everything, see if pieces of old impeller or whatever are stuck in it. Last, pull risers, inspect for blockage..
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Old 07-26-2008, 11:26 AM
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Impeller is replaced. Pump looks good. Checking stuff on motor and hoses next. But not today. Time for lunch with the Avanti.
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Old 07-26-2008, 01:36 PM
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Check the hose that comes off the transom plate inside of the transom.I know it is hard to get at and inspect but I had one that was restricting flow at higher RPMs.

Paradox where in Florida do you live?
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Old 07-26-2008, 01:46 PM
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Originally Posted by tommymonza View Post
Check the hose that comes off the transom plate inside of the transom.I know it is hard to get at and inspect but I had one that was restricting flow at higher RPMs.

Paradox where in Florida do you live?

I was thinking the same thing. There have been a number of guys that have had the hose kink/ collapse due to age.

BTW, if you back flust it and it flows well it could still be bad and collapse under suction.

Darrell.

Last edited by DMOORE; 07-26-2008 at 01:47 PM. Reason: ADD
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Old 07-26-2008, 08:55 PM
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On an alpha, it's not under suction, it's after the pump...
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Old 07-27-2008, 09:47 AM
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Originally Posted by tommymonza View Post
Check the hose that comes off the transom plate inside of the transom.I know it is hard to get at and inspect but I had one that was restricting flow at higher RPMs.

Paradox where in Florida do you live?
New Port Richey... just North of Tampa.
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Old 07-29-2008, 12:44 AM
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You say the pump "looks good" so I assume your getting water out the exhaust so the raw water pump is flowing. Overheating at higher rpms could mean a few things.
1. Passages blocked by pieces of impeller or chunks of rust.
2. Bad Thermostat
3. Disintegrated or disconnected impeller in the recirculation pump.
Also get a cheap mechanical temp guage and screw it in place of the electrical one. Just a thought... IS your temp guage working right?
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Old 07-29-2008, 08:29 AM
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THanks 29.. My mistake.. I should have said the "impeller lokos good" not just the "pump"

Impeller is removed and changed. THe old impeller did not had any peaces missing and was still fexible, not dry.
Will check thermostat and all the water ways. guage is good.
Possible circulating pump on the block.
More research is due.
Thx
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