Re: [OMC-Boats] Instrument Question

On Tue, 3 Mar 2009, jd wrote:
> but normal for an automotive engine? that makes me feel alittle bit
> more relaxed about it. i am no expert at all, but just thinking
> about the big picture here - whether it's an auto engine or an auto
> engine mfgr'd for use in a boat (Buick 155), they're both made from
> the same metal. So in theory, if that same metal can withstand 210
> in a car without something cracking, it seems it should be able to in
> a boat. right?

It'd be normal to see temperatures of 210 degF in a modern automotive
engine - the thermostats are typically set for 190-200 degF, so hotter
parts of the engine (especially those not near the cooling jacket) might be
a bit higher. The metal can certainly withstand it (and much higher
temperatures, though the external temperatures have very little relation
to the cylinder wall temperatures, which can be close to the limits of the
metallurgy) and all the other components in the engine are designed for
these temperatures. I don't know whether this is true on a 40-year-old
engine that was designed for a 140 degF thermostat. They could be using
different gasket materials and other components that can't withstand the
temperatures seen in modern engines. Or it could be fine - I don't know!

> maybe - those hot spots were right at the cylinder # stamps. but
> just the two in the front. #1 & #6( ?can't remember firing order).
> anyway, pointing the gun laser at the #1 stamp produced 200+ readings
> most of the time.

Find a picture of a head gasket and see if there is coolant jacket in those
areas! If it's an area without a water jacket between the cylinder wall
and outside of the engine, you'll see much higher temperatures.

> well, i have the intake manifold off, and had planned on taking the
> heads off too - but it looks like i would have to mess with the
> distributer and therefore timing after -which is a nightmare for me.
> i don't think i could get the timing back to where it is on my own,
> which means waiting on a mechanic and $$.

I don't know about marine engines, but when I replaced the distributor on
my Honda Accord, I just had to mark a line on both sides and then ensure it
was reinstalled at the same angle. It might be more complicated on the OMC
though. I do recall that it was very easy to check the timing with a
timing light (which you can often rent or borrow from shops like Autozone).
I can't remember if it's marked on the front pulley or the flywheel in the
back, but there's scribed numbers so you can check the timing.

> > I don't think the
> > geometry is such that you could get bubbles trapped in that location
> > (assuming the engine is level) - getting air bled out of the
> > cooling system can be a challenge on some smaller high-performance
> > engines.
> how might i get air bubbles trapped?

Bubbles naturally get trapped in high points in the engine. In a closed
system that's not meant to be drained frequently, it can be hard to get the
bubbles out - sometimes it takes several cycles of heating and cooling, or
opening bleeder valves in certain parts of the system. In some powersports
applications (e.g. snowmobiles), you often have to tilt the vehicle to get
the bubbles out. Since boats are meant to be drained frequently, their
cooling systems are generally designed to avoid getting trapped air. I'm
not quite sure how they do it though - it seems like there's no way for
bubbles to bleed from the manifolds... I doubt that is the problem for
you.

Ethan

-- 
<a href="http://www.engr.wisc.edu/~brodskye/"> Ethan Brodsky </a>