Re: [OMC-Boats] Instrument Question

well, i have a cracked inst. cluster faceplate. no chance of
replacing unless i get lucky and find a good one. gauges are kinda
trashed. so i was already to do a full replacement of it all here
in a few weeks. so re-calibrating sounds fun but isnt' gonna
happen. i'd rather have new and not have to mess with it.

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. 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?

On Mar 2, 2009, at 4:02 PM, Ethan Brodsky wrote:

> On Mon, 2 Mar 2009, jd wrote:
>> So just to clarify, as long as it's a matching set (oil sender/
>> gauge water sender/gauge) than a person could go with any brand,
>> not
>> just Faria, right?
>
> Barring any bizarre exceptions I can't think of, that's generally
> true.
> The sender has a resistance that varies with temperature or
> pressure, and
> the gauge has a needle that moves in response to changes in
> resistance.
>
> Most old-school temperature and oil pressure gauges use single-wire
> senders
> and are grounded through the engine. So the gauge is wired with
> +12V going
> through a resistor on the gauge and through the variable resistor on
> the
> sender to the engine block ground. The gauge senses the current
> through
> this path and moves the needle accordingly. On modern systems, the
> sender
> is typically wired through the engine computer, and the gauges are
> driven
> over a serial bus from the computer.
>
> For temperature gauges, make sure that they stick into the coolant
> stream -
> installing them on an extension or a tee can lead to very delayed
> readings.
>
> As for jdood's uncalibrated gauge, why don't you calibrate it
> yourself?
> Take the sender out of the engine and use a small jumper wire to
> ground the
> body of the sender to the engine block (make sure it's a good ground
> - get
> something with an alligator clip or ring terminal, and ground it to
> a bolt
> or a spot where you've scraped off the paint and corrosion).
>
> Then dip it in a cup of boiling water and see what the gauge reads.
> You
> know that is 100 C. Put a meat thermometer in the water as it cools
> off,
> and record the gauge reading vs. the thermometer reading. Then
> relabel the
> gauge with a sharpie (or take the glass off and print a new face -
> sometimes we get fancy!). All you really need are two marks showing
> the
> range of normal operation. Newer boats were designed to run at
> 160-180
> degF, but I think the older OMC engines use 140-160 degF thermostats
> (efficiency and emissions weren't such a concern back then).
>
> Ethan
>
> --
> Ethan Brodsky
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Received on Monday, 2 March 2009