I've got a spare sending unit and gauge for water temperature. Being
the anal gauge watcher that I am I would like to mount the sending
unit on my 90hp Merc so I can get a better indication of engine
operating temperature before the alarm goes off. Any suggestions? I
was thinking of just putting it right on the water jacket on the power
head. I assume somewhere next to a spark plug would be a good place
too. It doesnt' need to dead accurate. I just want to get an
indication if things are working differently than normal such as if
something got plugged up with sand or something ugly like that. The
last time I was at the coast the telltale water tube clogged with sand
or seaweed so the whole time I was worried that I was about to
overheat when everything was ok the whole time except for that tube.



tks
Don
WA5NGP

"Don WA5NGP" wrote in message
om...
I've got a spare sending unit and gauge for water temperature. Being
the anal gauge watcher that I am I would like to mount the sending
unit on my 90hp Merc so I can get a better indication of engine
operating temperature before the alarm goes off. Any suggestions? I
was thinking of just putting it right on the water jacket on the power
head. I assume somewhere next to a spark plug would be a good place
too. It doesnt' need to dead accurate. I just want to get an
indication if things are working differently than normal such as if
something got plugged up with sand or something ugly like that. The
last time I was at the coast the telltale water tube clogged with sand
or seaweed so the whole time I was worried that I was about to
overheat when everything was ok the whole time except for that tube.

I know what you mean. First weekend with my "new" used boat and motor, the
tell tale quit working. I had no idea what to do except what I was taught
as a lad - don't run it if the water isn't streaming out. Now that I know
the alarm does indeed work I'm not as concerned, but have also learned the
"feel" of the head and leg at normal operating temp and can check that if
need be. I've also learned how to quickly clean out the tell tale when
needed. I also have a water pressure gauge so don't have to keep looking
back to fret over the tell tale. I've been toying with replacing the
pressure with a temp gauge, but...

As for your temp. sender. I think your ideas are good. You might check the
web page of the gauge/sender manufacturer. For instance, if it's a Teleflex
set up, I'm pretty sure their web site will have an installation manual for
the sender that will tell you where to put it on your particular engine.
Some of the other manufacturers of "universal" gauges have similar resources
on line.

Cam

I have a temp guage and I just hooked up a pressure guage since I have an
overheating problem that is pressure related (Mercury is working on it but
that's another L O N G $800 story)
In retrospect I think the pressure guage might be more important than the temp.

I only wish I had the pressure readings when it was working right.

There is usually a water jacket port where you can connect either water
pressure or temp. It should be up near the thermostat.

On my old 2 stroke 75 I had it simply touching the head, mounted on a bracket
on a threaded boss between #1 and #2. I had a blob of heat sink compound under
the sensor and it worked pretty well.

Ok, thanks for the advice. I'll try to find someplace that will hold
it in place with some heatsink goop. The actual measurement value is
not so important as is a relative reading that its either like it
normally is or something that is different. I've already used it
like this to check the tranny fluid temperature on my suburban. I
think I found out that the radiator usually warms up the tranny fluid.

I don't have a pressure gauge. Does the pressure gauge sending unit
simply connect to the telltale spout on the water jacket and elininate
the telltale?

tks
Don WA5NGP

"Don WA5NGP" wrote

snip:

I don't have a pressure gauge. Does the pressure gauge sending unit
simply connect to the telltale spout on the water jacket and elininate
the telltale?

I bought a teleflex pressure gauge. It came with a variety of fittings for
a variety of apps. On mine (older, large Jonnyrude v6) it T's with the tell
tale. A very simple installation. Now that I know it works, and have
gotten in the habit of glancing down at the gauge instead of turning and
looking back at the tell tale, I could change the fitting and connection to
just replace the tell tale since it's not really needed anymore. The only
problem I had was that the tubing included (a small, hollow flexible
plastic/rubber tube runs from the motor to the gauge) was not long enough.
I found some similar tubing at a local industrial supply house (very cheap),
but I imagine that it uses tubing similar to a pitot-type speedo. (which I
don't have, so I'm not sure).

Cam

I would hesitate to block the telltale but that is where the "T" can go to
sense water pressure.

"Don WA5NGP" wrote in message
om...
Ok, thanks for the advice. I'll try to find someplace that will hold
it in place with some heatsink goop. The actual measurement value is
not so important as is a relative reading that its either like it
normally is or something that is different. I've already used it
like this to check the tranny fluid temperature on my suburban. I
think I found out that the radiator usually warms up the tranny fluid.

I don't have a pressure gauge. Does the pressure gauge sending unit
simply connect to the telltale spout on the water jacket and elininate
the telltale?

tks
Don WA5NGP

You want it up high on the motor. First place for water to be vacant.

"Calif Bill" wrote in message link.net...
"Don WA5NGP" wrote in message
om...
Ok, thanks for the advice. I'll try to find someplace that will hold
it in place with some heatsink goop. The actual measurement value is
not so important as is a relative reading that its either like it
normally is or something that is different. I've already used it
like this to check the tranny fluid temperature on my suburban. I
think I found out that the radiator usually warms up the tranny fluid.

I don't have a pressure gauge. Does the pressure gauge sending unit
simply connect to the telltale spout on the water jacket and elininate
the telltale?

tks
Don WA5NGP

You want it up high on the motor. First place for water to be vacant.

If the impellor quits pumping water, how will water be "vacant"? It
will simply overheat the water that is there. In order for the water
to leave, it there would have to be an opening to the intake, or else
when the water tried to run out, there would be a vacuum. If the
thermostat sticks closed, there is no opening to the intake.

"basskisser" wrote in message
om...
"Calif Bill" wrote in message
link.net...
"Don WA5NGP" wrote in message
om...
Ok, thanks for the advice. I'll try to find someplace that will hold
it in place with some heatsink goop. The actual measurement value is
not so important as is a relative reading that its either like it
normally is or something that is different. I've already used it
like this to check the tranny fluid temperature on my suburban. I
think I found out that the radiator usually warms up the tranny fluid.

I don't have a pressure gauge. Does the pressure gauge sending unit
simply connect to the telltale spout on the water jacket and elininate
the telltale?

tks
Don WA5NGP

You want it up high on the motor. First place for water to be vacant.

If the impellor quits pumping water, how will water be "vacant"? It
will simply overheat the water that is there. In order for the water
to leave, it there would have to be an opening to the intake, or else
when the water tried to run out, there would be a vacuum. If the
thermostat sticks closed, there is no opening to the intake.


Some of the engines will get an air bubble up high in the engine (Merc
Optimax) from long idling down the channel when first starting out. There
builds up a bubble on the upper cylinder waterjacket. Upper cylinder
overheats. So put it up high. If partial failure of the impeller and low
flow, H2O may not reach the upper cylinder.
Bill

"Calif Bill" wrote in message
news:1Lekc.17663 Some of the engines will get an air bubble up high in the
engine (Merc
Optimax) from long idling down the channel when first starting out. There
builds up a bubble on the upper cylinder waterjacket. Upper cylinder
overheats. So put it up high. If partial failure of the impeller and low
flow, H2O may not reach the upper cylinder.


I have seen this approach backfire.

The sending unit wants to measure the temperature of the water. If there is
no water, then it will either measure the temperature of the air/water vapor
or of the fitting that it is bolted into. The sending unit is usually
brass, which conducts heat pretty well. Maybe not on an outboard, but most
inboards what you screw it into is cast iron, which does not conduct heat
very well. The water to brass heat conduction is very good, much better
than air to brass, so when there is water the sending unit will make a
reasonable measurement of its temperature. If there is no water there, then
the sending unit will measure something between the block temperature, the
inside air temperature and the outside air temperature. That's kind of hard
to predict what the result will be.

Rod