Re: [OMC-Boats] Instrument Question

On Mar 3, 2009, at 3:42 PM, Ethan Brodsky wrote:

> On Mon, 2 Mar 2009, jd wrote:
>> As far as the water sending unit, another interesting point you
>> raise. I am wondering if mine is even in the spot it's supposed to
>> be. That could be contributing to weirdness.
>
> I can't recall where the temp sensor is on my 225, but I would
> generally
> say that a water temp sensor should be in the engine's internal
> cooling
> loop (the portion that has water cycling through it even when the
> thermostat is closed). Typically this is near the thermostat, though
> anywhere in the cylinder water jacket should be reasonable,
>
>> The culmination
>> of all this mess of not knowing if my engine is actually overheating
>> or not came at the end of last season when i had to ditch the gauge
>> setup and go with pointing a heat sensing gun at various points all
>> over the engine. Not the easiest thing to do while underway!
>> Anyway, assuming it was accurate, that seemed to work well and
>> helped
>> me see exactly which parts of the engine were running hot. The
>> main
>> part that seemed to be hot was the front left and right cylinders
>> just
>> above the spark plug hole. On both sides in those areas I was
>> getting readings of around 200 - 215 after only running at 3/4 speed
>> for a couple minutes. The weird part is above the other sparkplug
>> holes and most other places, things seemed to stay about 170 or
>> less. And this was all running the engine with clear tubing
>> everywhere and being able to see the water move through. So
>> knowing the hoses weren't clogged, I thought maybe the manifold was
>> clogged towards the front, or maybe a port was blocked or
>> something. Nope. But I got it cleaned out anyway at a machine
>> shop - even though it didn't really need it. Also got the
>> disassembled water pump cleaned. So now the engine is still semi
>> torn down, but ready to reassemble with new gaskets. But I'm
>> really hesitant to put things back together yet, because I don't
>> think i've solved the problem (if there even is one). As crude as
>> it seems, pointing a heat sensing gun at the top front areas of the
>> engine and getting 210 temp readings doesn't seem good. What do
>> you think? Temp gun too crude of a method to be able to conclude
>> that?
>
> Infrared thermometers are actually fairly accurate - I believe the
> Raytek
> unit we used is specified for +-1.5% of the reading - assuming that
> you are
> using it on a non-reflective surface. We generally put a small spot
> of
> flat black spray-paint on whatever we're trying to measure - it
> reads way
> off when used on shiny metal. Anyway, you should be able to measure
> temperature within 5-10 degF that way with good repeatability. A
> technique
> that might be easier if you're working alone is to use wax
> indicators -
> it's basically a set of crayons that you use to mark the engine with
> - each
> one melts at a specific temperature. I think we've used a brand
> called
> "Tempil Sticks" before. You could also buy a cheap thermocouple
> reader.
>
> I don't know what to think of temperatures of 210. That'd be very
> normal
> for an automotive engine, but is seems rather high for an engine
> with a 140
> or 160 degF thermostat.

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?

> In areas where the water cooling jacket is between
> the cylinder and the outside surface, you should never see a
> temperature
> higher than the coolant temperature. Is it possible you are looking
> in a
> place where there is no cooling jacket?

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.

> Are you measuring temperature
> while running

while running at 1/2 to 3/4 speed

> or after shutdown - you typically will see an increase in
> temperature after shutdown, as coolant flow ceases and temperatures
> equilibrate.

also good to note. i think i remember noticing that at the dock.

> Could you determine if the cooling jacket was clogged up in
> that area? You'd likely need to pull the heads to see, but perhaps
> you
> already have things apart enough that that'd be easy.

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 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?
>
>
> Ethan
>
>
>
>
> --
> Ethan Brodsky
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Received on Tuesday, 3 March 2009