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Author Topic:   Wiring a Temperature Gauge
BobL posted 10-30-2005 09:12 PM ET (US)   Profile for BobL   Send Email to BobL  
How difficult is it to wire a temperature gauge? I have a 1987 Yamaha 50 hp on my classic 15 and the only gauge it has is a tachometer. This engine and boat are new to me and I’d like to know whether it is running in the normal temperature range or not. Also I would like a recommendation of a good brand of temperature gauges.
Thanks, BobL
LHG posted 11-01-2005 12:15 PM ET (US)     Profile for LHG    
A cylinder head temperature gauge is not a difficult installation, and C-H range temp gauges from Teleflex are available that include the mandatory temp sender, which has to be installed on the engine. Since Teleflex uses the same sender for the I/O water temp gauges, they can be used too if numeric temp degree readings are desired. They cost about $45. The wire from the temp sender has to be bundled to the engine's ignition cable. I am not familiar with Yamaha factory equipment, but at 50 HP I would not imagine the engine came with a temp sender. If by chance it does, and temp sender lead wire is already in the ignition harness, as Mercury did on pre-Smartcraft V-6's, then the gauge installation is even easier
jimh posted 11-01-2005 08:23 PM ET (US)     Profile for jimh  Send Email to jimh     
The temperature gauge is matched with a sender unit. Most outboard motors have pre-drilled and pre-threaded holes (bosses) where you can install a temperature sender. The wiring is very simple. It usually is just a single conductor from the engine sender unit to the gauge. The gauge will need other wires for gauge illumination, battery positive, and battery negative.

You can chose from many vendors. You may wish to purchase a gauge which matches the other gauges in your current instrument panel for aesthetic reasons.

Larry posted 11-02-2005 09:34 AM ET (US)     Profile for Larry  Send Email to Larry     
What do the bosses look like and where would they be found on OMC v-4s? Sould one be put on each cyl head?
Does anyone know why outboards mostly don't have temp gauges while inboards mostly do?
(I know I ask a lot of questons for "someone from New Jersey")
LHG posted 11-02-2005 05:29 PM ET (US)     Profile for LHG    
Hey, with a name like "Larry", what can we expect!!!

Seriously, though, the Teleflex outboard temp gauges which I am familiar with come with complete instructions on mounting the sender on various brands and sizes of outboard, and an assortment of clips, etc to accomplish this. Some, as JimH mentions, can simply be screwed in.

Outboard temp is CYLINDER HEAD TEMP, vs inboards which is water temp, I believe. On outboards, the sender is not in the water flow passages. Depending on how your enigne is factory rigged, one would need either just the guage, or the complete Temp gauge kit, which includes sender.

Mercury, for one, has included temp gauges, and factory engine sender, with all of their 2-stroke V-6 models for years, and this being in addition to the overheat alarm horn. On smaller outboards, temp has not been used as often. Not sure what the other brands have used.

I have heard that OMC utilizes a temp sender on each V-6 cylinder bank, but mercury and Yamaha do not do this. Generally, the temp sender is located on the highest cylinder head, the first one to heat up should flow be impeded

BobL posted 11-02-2005 07:25 PM ET (US)     Profile for BobL  Send Email to BobL     
Thanks guys, I will see if I can locate the spot on my Yamaha that the sender would screw into.
jimh posted 11-02-2005 08:47 PM ET (US)     Profile for jimh  Send Email to jimh     
Here is a close-up view of a temperature sender installed into a boss (or pre-drilled and tapped hole) on the cylinder head of an E-TEC 225-HP V6 outboard:

Photo: Temperature Sender on V6 Block

swist posted 11-03-2005 08:12 AM ET (US)     Profile for swist  Send Email to swist     
Does anyone know if the 2004 (carbed) Merc 90 4-strokes have provision for mounting a temp semder similar to that shown in the photo?
kingfish posted 11-03-2005 08:30 AM ET (US)     Profile for kingfish  Send Email to kingfish     
Teleflex has an alternative bracket that will bolt under the head of a typical head bolt or other bolt in the vicinity where you want to measure temperature, that when there is no boss or removable spare blind plug, will hold the temperature sensor hard against the raw metal of the head. You have to clean the paint off that particular spot so the metal of the sender can come in direct contact with the metal of the head.


Larry posted 11-03-2005 10:09 AM ET (US)     Profile for Larry  Send Email to Larry     
To put the sensor under the cyl head bolt do you also have to loosen all the head bolts and then retork?
kingfish posted 11-03-2005 10:18 AM ET (US)     Profile for kingfish  Send Email to kingfish     
No (at least I don't think you do)- it's just a "z" shaped bracket that goes under the head of one bolt.
Larry posted 11-04-2005 09:53 AM ET (US)     Profile for Larry  Send Email to Larry     
Will add one next spring for sure.
(LGH, I'm told my other choice was "MOE")
LHG posted 11-04-2005 12:54 PM ET (US)     Profile for LHG    
That Evinrude temp sender looks EXACTLY like the Teleflex temp gauge sender furnished in the kit, so I would think any OMC instation would be simple. It looks NOTHING like the Mercury V-6 factory temp sender, which lays flat against the cylinder head.

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