Re: [OMC-Boats] overheating

well.......frustratingly close to getting the problem solved. but
still not there. it's very weird. here's whats going on - my
mechanic has had it for a couple days. it was overheating on the
hose for him also (good thing, so not just happening underway). So
he checked for blockage etc - one part of one manifold was running
very hot, while the others were fine. swapped out that manifold.
Now engine is running at normal temps (albeit, on the hose), but
every gauge he hooks up to it says it's overheating. He swapped out
all the sending units to different ones from another engine (not new,
but different). Still, even trying different gauges, it says it's
overheating. He is confirming the actual engine temps with a special
heat sensor thing he uses - same as fire dept eqpt, say he trusts it
more than any gauge. Could be the engine IS actually overheating and
his eqpt is bad - but i don't think so - it sounds legit. maybe
other mechanics use this too when they can't trust any gauge.
nonetheless, assuming that's not the prob - then it would seem like
the sending units. but again, he swapped those out too.
possibility of 2-3 bad sending units in a row, but that seems like a
stretch. any idea?

if it were a crack, or blockage, or bad thermostat, or hoses, etc -
the engine would be running hot - which it supposedly isn't. yet
trying different gauges and sending units didn't make any
difference. Any other parts of the chain we're forgetting about here?

the weekend is coming and i'm so close to having this thing usable
again its driving me nuts!!!

jeff

On Aug 11, 2008, at 11:57 AM, Ethan Brodsky wrote:

> 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.
>
> Ethan
>
> --
> Ethan Brodsky
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Received on Thursday, 14 August 2008