Re: [OMC-Boats] overheating

Jeff,

Assuming that the seawater impeller is good, here are some things to check:

1) Does the motor show signs of overheating like a boiling sound when you shut down? If not then it's probably the sender.

2) Check the thermostat. If it's not opening at temp, then you'd keep recirculating hot water and eventually overheat.

3) If not 1 or 2, you're probably getting either air or exhaust gas into the cooling system some how. I had a similar problem with mine and it turned out that the head gaskets were leaking. That allowed exhaust gases into the cooling system which ruined it's effectiveness and caused it to overheat. Before I owned the boat, the motor was replaced with a car block which of course had normal automotive gaskets. Fresh water doesn't have the anti corrosive properties of antifreeze so?the gaskets failed in a few years. My boat overheated but not in 30 seconds. It would take 5 or 10 min at WOT to get the idiot light to come on.

4) Since your boat seems to run OK at the dock and overheats quickly when you run it up, it sounds like you may have a leak at the seawater pump or pick up tube. When you are at the dock most of the outdrive is submerged so it would be drawing water through the leak. Once it's on plane, most of the drive is above water and the leak would draw air. It doesn't take much air to break prime. If this is the case, your impeller is probably getting wrecked in the process. The leak could be from the pick up tube seals, swivel housing seals or the pump housing itself. If the pump housing wasn't sealed properly, it will leak. This problem wouldn't show up while running on a hose either because the hose is forcing water into the block under pressure at a point above the impeller.

The Seloc manual for OMC Stringer Drives has a good section about diagnosing cooling problems. If you don't have one, I'd strongly suggest getting it.

Hope this helps.........Dave Rusilas

-----Original Message-----
From: JEFF DOOD <jdood@...>
To: Evinrude & Johnson Boats of the 1960's and 70's <omc-boats@...>
Sent: Mon, 11 Aug 2008 2:46 pm
Subject: [OMC-Boats] overheating

i am getting very close to being able to use my boat finally, won't
go into all the recent past history but it's been a journey. long
story short, i have a different engine in it now. another buick
v-6. runs, starts, sounds good, doesn't backfire and lose all power
at mid throttle, etc. only one problem. when on the hose, it's
operating at normal temps. when under load, the temp gauge is just
races right up to the overheat range. thought i might be the gauge,
no such luck. on 2nd test, same thing. idling at dock it temp
gauge barely moves. but after about 10 seconds at full throttle it
starts moving up and within about 30 it's almost pegged. putting on
a new sending unit next, seeing if that does anything. if it's got
blockage somewhere, then wouldn't it heat up while on the hose at
the mechanic's shop also? it's getting water through there. pretty
sure mechanic replaced impeller at last go around. and there
doesn't seem to be any obvious leaks or cracks anywhere in the
manifolds. any ideas?

jeff
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Received on Monday, 11 August 2008