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

Track water flow thru upper housing, water hose thru transom , power steering cooler. Also check risers for obstructions.

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..

Impeller is replaced. Pump looks good. Checking stuff on motor and hoses next. But not today. :) Time for lunch with the Avanti.

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.

On an alpha, it's not under suction, it's after the pump...

New Port Richey... just North of Tampa.

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?:p

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

you should also check the water hose that runs from the drive bell housing to the transom assembly. it can kink and restrict water flow. how olds are the manifolds and risers? they do not live long.

[QUOTE=mrv8outboard;2637917]you should also check the water hose that runs from the drive bell housing to the transom assembly. it can kink and restrict water flow. how olds are the manifolds and risers? they do not live long.[/QUOTE]

:) I think they about 10+ years. The boat was repowered late 90's.
THanks I'll check..

I'm having a simular problem with my older 350 too. Haven't had time to go thru everything yet, but so far, its not the raw water pump or the thermostat. Haven't had time to check hoses or drive intake area for issues. Have been wondering if maybe the risers are partially blocked. In your case, have you checked the ignition timing? If its too far off, that can cause overheating.

I'm curious as to what you find the problem to be.

Good luck

Skip

I will let you know what I find this weekend.. Serious trouble shooting are in the plans. :)

Paradox

Any luck with the trouble shooting?

Water ports in exh. manifold/risers are a good canidate for overheating.

Water is flowing free everywhere. Have to check the timing. and tune up isues next. Possible thermostat issue. or circulating pump... but the lines, risers etc. are good.