Re: [OMC-Boats] overheating

From: Lee Shuster <lee.k.shuster@...>
Date: Thu, 14 Aug 2008 15:00:15 -0600

Sorry, for not following this saga more closely, but is in the same boat
that had the confusion over (even/odd-fire) distributors? How did that
get resolved?

Not that it should really matter, But what's the source of this current
Buick V6? 231 (odd or even fire?) or 225 (odd fore)? As someone else
pointed out, something as simple as the wrong manifold gaskets can lead
to problems.

Again, I go back to someone else's suggestion: Get a decent (hopefully)
color flow diagram of the entire cooling system. Then start breaking the
system down into it's individual parts. The original OMC manuals as well
as the third-party SELOC & Clymer's are must have for you and your
mechanic. A good understanding of the "theory of OMC cooling" is
essential and can hopefully reduce the "chasing one's tale" approach to
troubleshooting. This is part of what I meant in an earlier post about
checking something as simple as the proper connections for the four hose
mounting locations for each cylinder bank's manifold-to-thermostat hose
routing. Direction of flow matters, kinda like + or - in electricity.
Also what spec T-Stat are you running? Remember this is another area
cars and boats differ. OMC spec'd at 140 def F 'stat. Cars are typically

What is meant by " 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),......

Not sure if this mean manifold is fine to the touch? Or what method or
metric if instruments are suspect? How about some actual data points, in
degrees F?

I understand what you are saying about gauges/instrument sensors, but
remember that is only one point of reference.
You or your mechanic should be checking flow rates @... various points in
the entire cooling system. Has anyone pulled the ends off the manifolds
and checked for any restrictions or blockages? Swapping parts,
especially used ones, when they are KNOWN to be good could lead one to
draw the wrong or inconclusive results.

Don't get too frustrated, sounds like you are making progress. Still
some quality boating time this year yet to go.


-----Original Message-----
From: omc-boats-bounces@...
[mailto:omc-boats-bounces@...] On Behalf Of JEFF DOOD
Sent: Thursday, August 14, 2008 1:39 PM
To: Evinrude & Johnson Boats of the 1960's and 70's
Subject: 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!!!


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
> _______________________________________________
> OMC-Boats mailing list
> OMC-Boats@...

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Received on Thursday, 14 August 2008

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