Re: [OMC-Boats] overheating

From: Ethan Brodsky <brodskye@...>
Date: Mon, 11 Aug 2008 13:57:53 -0500 (CDT)

On Mon, 11 Aug 2008, JEFF DOOD wrote:
> 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?

My first thought would be to check the thermostat? Is it working. Is it
the right one? Engines in cars usually ship with thermostats that open
around 180-200F, while marine engines are usually supposed to run around
140-180F. If you've got an automotive thermostat in there, the gauge will
show it as overheating all the time, and it'll be running a lot hotter than
it should. If it's sticking shut, that would also cause overheating.

If that's not it, I'd ensure that all the cooling passages are open by
testing them one at a time. Look at a drawing of the coolant ciculation
patterns (in the service manual) and hook up a garden hose (engine off) to
each of the inlets and make water comes out the corresponding outlet.
Check both passages in each exhaust header and the engine block passages.
Also try opening the two drain cocks on each side of the engine and see if
you have water pouring out.


<a href=""> Ethan Brodsky </a>
Received on Monday, 11 August 2008

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