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Author Topic:   Temperature Gauge Question
Jersey Jim posted 05-30-2001 08:01 AM ET (US)   Profile for Jersey Jim   Send Email to Jersey Jim  
My 2001 Montauk has a Mercury 90 with Merc tach, temp gauge, and volt meter. The tach and volt meter work, but the temperature gauge has never moved from the "cold" position. I have never owned an outboard with a temp gauge and I was wondering if this is normal or if I could test the gauge myself before I pull the boat and drive 3 hours to the dealer.
Thanks for your help.
jimh posted 05-30-2001 08:23 AM ET (US)     Profile for jimh  Send Email to jimh     
It does not sound normal. The temperature gauge should show some reading, especially after prolonged use, like more than an hour.
The only way it would stay on the lower peg: maybe you're operating in near-freezing water!

Before I'd haul it back to the dealer, I take a look for something simple, such as a wire that has come loose, either at the gauge end or under the cowling at the sender end.

dgp posted 05-30-2001 08:52 AM ET (US)     Profile for dgp  Send Email to dgp     
Read this thread.
Tom W Clark posted 05-30-2001 10:33 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
I would suspect the gauge is not working. There are only three wires (apart from the instrument light, if it has one) that make it work. Power, + and -, and the tan wire from the sender. It should be easy enough to test the power leads with a multimeter and you could also test continuity of the sender wire. Also check the sender itself to see if it is positioned correctly on the powerhead.
triblet posted 05-30-2001 11:17 AM ET (US)     Profile for triblet  Send Email to triblet     
I suspect the minus lead at the guage is
only for the lights. The typical wiring
would be +12 to the guage, through the guage,
to the tan wire, to the sensor, and thence
to ground on the head or block.


bigz posted 05-30-2001 12:01 PM ET (US)     Profile for bigz    
dgp, your situation as mentioned in the previous thread is not uncommon, that is the gauge may be calibrated to high for the specific application or motor.

The question here for Jersey Jim what temperature does your gauge start to read if you have temp. figures on the gauge face. If it is a "dumb" gauge with just a cold/normal/hot range again it may be to high for this engine's range. Certainly doesn't mean the gauge is faulty though that or the sending unit could be.

Make sure you have power to the gauge and that the ground is good is the first step. If ok proceed to test the gauge.

Place a jumper wire on the sending unit terminal and the other end on the negative terminal, the gauge should spring up to the highest reading.

If the above happens then the gauge is fine however it is possible either the sending unit isn't functioning or there might be a break in the sending line. To test the sending unit, remove the wire from the sender and with the ignition switch ON, ground the wire to the engine block,the needle should jump to highest reading if it does your connection is good and the sending unit is the problem. Let me restate a WARNING. Regardless, as mentioned above, you must first determine the calibration of this particular gauge for an outboard application the usual range is 50 to 200 F and the "hot" warning range is usually between 175 to 200 F. I have seen outboards with dealer installed temp gauges 120 to 240 F and unless you have a major break down in the cooling system you'll never see the gauge move! This can also be the situation with a "dumb" gauge the range is to high for the application. (this information on temp. range might be found written on a tag on the rear of the gauge)

Your over heat warning buzzer or horn I guess has never gone off! So I suspect the engine temperature is operating well with in range.

Dan posted 05-30-2001 12:52 PM ET (US)     Profile for Dan  Send Email to Dan     
My 115 temp guage does the same thing -- had it checked and it's okay.
lhg posted 05-30-2001 04:16 PM ET (US)     Profile for lhg    
The temp gauge is getting to be a standard item for outboards, and I believe BW/Mercury wouldn't install one if they didn't work.

Short of really cold water, which does keep the gauge reading very low temp, my guess is a defective sensor at the engine. Same thing happened to me with a brand new Merc 200EFI.

bigz posted 05-30-2001 04:48 PM ET (US)     Profile for bigz    
Larry is "probably" correct that is "if they didn't work wouldn't install" and I'm sure they do work, duh! They just put in temp gauges that start to register to high, in my mind, which is fine ain't going to hurt anything your just going to look at COLD until your engine hits say 120 F. Most of your Teleflex gauges read to high. The older gauges started as mentioned at 50 F/60 F and progressed, at least with these you could see the gauge working.

That said Jersey Jim yes you can test it easily as outlined in my post above before you drag the boat over to the dealer which is no fun to find out like Dan did it is fine!

Good luck,

GMINET posted 11-17-2002 01:52 PM ET (US)     Profile for GMINET  Send Email to GMINET     
This forum helped me solve my problem, how about making sure that that sending unit has a good ground, if you use teflon tape you may be insulating the sender
captbone posted 11-18-2002 03:43 PM ET (US)     Profile for captbone  Send Email to captbone     
I do not like temp gauges, i feel that unless you check them every 20 seconds that it is a waste, I would switch out the temp guages for a water pressure gauge. By the time you have a full block, it only take a few seconds at 4000 rpm to overheat. with the water pressure gauge you can see if you slowly pick up weed. It would be less than a 2 hour job and 100.00 for the gauge.
John Bocskay posted 11-18-2002 04:34 PM ET (US)     Profile for John Bocskay  Send Email to John Bocskay     
Just put a water temp gauge on my 22B/W 250 Merc $32.00 at the Marine Connection, in Ft Pierce Fl, and I think they ship.
oysterman posted 11-18-2002 04:59 PM ET (US)     Profile for oysterman  Send Email to oysterman     
I have same boat, same motor and had same problem. The Whaler mechanic told me that the temp. guage reacts at 170 degrees. The Motor has a temp. around 120 to 130 degrees. You may get the temp. up if you really work the motor for awhile. Otherwise there was no problem. The temp. guage is just for show most of the time I guess.
lhg posted 11-18-2002 07:03 PM ET (US)     Profile for lhg    
I'm not familiar with the 90's, but I can tell you on the 200's the temp gauge ALWAYS registers, even in cold water. When idling along in 80 degree water, the gauges show almost full HOT. They ALWAYS register during idle speeds, and generally show about 1/4 at running speeds. I would check for a defective sender, a simple item to replace.
phatwhaler posted 11-18-2002 07:12 PM ET (US)     Profile for phatwhaler  Send Email to phatwhaler     
"I believe BW/Mercury wouldn't install one if they didn't work."

I don't know about you guys but my trim/tilt guage is completely worthless. It works like all the others I have seen. Which means It tells you that your engine is up or down, but that's about it.

It's about to be replaced with a remote for my stereo.

phatwhaler out.

bsmotril posted 11-20-2002 08:05 PM ET (US)     Profile for bsmotril  Send Email to bsmotril     
On Older Mercs (pre-98), I never had a trim gauge sending unit last more than 2-3 years max. They are relatively cheap and very easy to replace. 99 percent of the time, that sending unit is the source of the trim gauge problems. It is located where it will get wet, and older ones are not sealed that well. My 98 Mercs are still going fine on the original sending units.
lhg posted 11-20-2002 08:28 PM ET (US)     Profile for lhg    
We're changing the gauge subject here, but Mercury trim sending units are, indeed, a waste of time, usually. I have given up on them, and my Mercury mechanics say not to bother with them either. But that does not interpret to mean the temp gauges do not work. Mine have worked perfectly for 13 years now, and I think they're very important to have. With Mercury, they are also backed up with an audible horn signal, on a separate sender. So that tells you how important cylinder head temp is.
dgp posted 11-20-2002 09:09 PM ET (US)     Profile for dgp  Send Email to dgp     
Larry, the first Mercury supplied water temperature gage that came with my 50 four stroke was a 120-240 degree range gage. The dial scale was marked C to H. With the engine at operating temperature the gage pointer barely moved off the C mark.
My dealer supplied me with a different gage with a 60-200 degree range. The scale is marked C-H with 5 increments:
#1..60 degrees
Now, at normal operating temperature it's reading about 110-120 degrees.
The temperature sender will read about 600 ohms with cold engine at ambient temperature.
The guy at Teleflex said " most O/Bs operate on the cool side. My own Evinrude 88 SPL runs about 135. If you can hold your hand on the cyl. head its running cool."
I believe this is the same problem that Jersey Jim is experiencing.
Dick posted 11-20-2002 09:46 PM ET (US)     Profile for Dick  Send Email to Dick     
When I rigged my Montauk it had the factory installed temp gauge but the Merc 50 4 stroke did not have the sender installed. That was a dealer install option.

Check your engine and see if the sender is installed and the wire attached. If not it is a cheap and easy installation. Took me all of 10 minutes to install it and drink a beer.

If everything is there take it back to your dealer for warranty repair.

lhg posted 11-20-2002 10:31 PM ET (US)     Profile for lhg    
Be sure we are not confusing 4-stroke WATER temp gauge (like a car has, and with degree gradations on it) and the 2-stroke cylinder head temp gauge. The head temp gauges only read C-H, but as I have said, at least with V-6 200's, mine always register at least 1/4 after a few minutes of idling, even in 35 degree water. Merc's 2-strokes come with the sender factory installed.

It could be that in a 4 stroke, the WATER temp barely rises, because there is continuous cold water intake. Not like a closed automotive system.

My guess is that the Montauk's were rigged with the 2 stroke temp gauge on the production line, assuming a 90 2-stroke would go on the boat. They would not function on the 4-strokes unless the sender is on the head, not in the water flow.

There evidently is a difference in head temp and water temp on a given engine. Water temp would always be cooler, as the fresh water supply continually cools off the block.

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