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Temp gauge not working

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bronc

New member
Have a 2003 M/C 5.0l,Searay 300 sundancer, Temp gauge not responding, replaced thermostat, switched temp sensor from other engine to not working still nothing. The gauge is in a cluster with one gauge working /reading, oil, volts,trim position. When I turn the engine seitch on the gauge moves ever so slightly. Checked in the back of gauge , everthing seems tight and no rust. Any suggestions would be great.
 
Ground the engine temp sensor w/ignition on...if all is good the gauge should peg to max temp. If it doesn't then go to the back of the gauge and again ground the same wire on gauge that is on the sender. If it doesn't peg to the max temp the gauge is faulty. If the gauge pegs then the problem is between the gauge and the sender. Clean the wire to the gauge connection w/light sandpaper. Pull the engine barrell plug off and look at the pins for corrosion.
 
Thank you. I tries everything, the temp gauge does peg when grounded. Should I know replace the wire?





guyjg said:
Ground the engine temp sensor w/ignition on...if all is good the gauge should peg to max temp. If it doesn't then go to the back of the gauge and again ground the same wire on gauge that is on the sender. If it doesn't peg to the max temp the gauge is faulty. If the gauge pegs then the problem is between the gauge and the sender. Clean the wire to the gauge connection w/light sandpaper. Pull the engine barrell plug off and look at the pins for corrosion.
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With power on (key in run position) if you briefly touch the sender post on the guage to the ground post the guage should peg!

If it does not replace the guage..................
 
Yes the gauge does ped, I have swiched sending units from the one engine that works to the other, I have cleaned both sending units and sanded the corrision off. The gauge did peg but when startedthe eng still no temp gauge working, thanks
 
Then there is a connection between engine and guage that is bad.


Start and run both engines for a while that would typically warm it up to at least 120-140 degrees.

if you have a digital volt meter then select OHMs and disconnect the sending wire at the sending unit on each motor, connect one lead to the post and the other to the body of the sending unit Not an engine ground. Take a reading. the sending unit is ~ 60 - 240 ohms so you would expect to see ~ 130 ohms (guestimate)

If you get approx the same reading from both now go to engine ground and see if it is the same again. If not the threaded hole is not making a good ground at the sending unit.

If it is the same (approx) then go to the guage for each and diconnect the sending wire from each guage, attache one lead of the meter to the sending wire and the other to ground. The ohms reading should be the same or very close as the readings from the motors for each motors guage. If the one in question is not the same then it is a wiring issue, Most likely either a bad connection at the main wire harness plug or a damages or pinched wire somewhere......

is the same guage used for both motors? do I understand this correctly? What exactly does the switch, switch?

One other question? where is the sending unit located? Is it threaded into the block or the thermostat housing.

If it is threaded into the thermostat housing the base gasket has brass star washers that make continuity from the block to the housing. If that area is no longer clean the ground may be hindered. Try grounding the sending unit body to battery ground with a jumper and see if the guage works.......if it does then it is the base gasket.
 
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bronc said:
Yes the gauge does ped, I have swiched sending units from the one engine that works to the other, I have cleaned both sending units and sanded the corrision off. The gauge did peg but when startedthe eng still no temp gauge working, thanks
Click to expand...


Swapping the wires on senders won't tell you the answer. One is a "sender" for the gauge and the other is a "switch" for the alarm and is an open / closed switch, not a variable sender. If you ground the wire at the sender and the gauge pegs, then either the sender is kaput or the ground on the housing is bad.

Get a good ground on the housing with a jumper wire from it to a good battery ground and see if that makes it work. Did you have that housing off? If so, was the gasket with the 2 rivets on it used between the thermostat housing and the manifold when replacing with NO silicone. Silicone can insulate the ground path to the manifold even when the riveted gasket is used..

Let us know what you find.
 
04fxdwgi said:
Swapping the wires on senders won't tell you the answer. One is a "sender" for the gauge and the other is a "switch" for the alarm and is an open / closed switch, not a variable sender. If you ground the wire at the sender and the gauge pegs, then either the sender is kaput or the ground on the housing is bad.

Get a good ground on the housing with a jumper wire from it to a good battery ground and see if that makes it work. Did you have that housing off? If so, was the gasket with the 2 rivets on it used between the thermostat housing and the manifold when replacing with NO silicone. Silicone can insulate the ground path to the manifold even when the riveted gasket is used..

Let us know what you find.
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He has dual motors, not refering to the sending unit and over temp switch I dont believe..........I think he is refering to one sender on one motor vs the other and I think he has a switch to change motor 1 to motor 2 for gauge cluster..........I think.

He is not 100% clear
 
Yes I took the good sender/sensor that is working and reading properly off the port eng and switched it to the stb eng. Still doesn't work. I replaced the theromstat with the rivet gaset and no silcone just gasket. Each eng has there own sending unit, 5.ol m/c B3. Sending unit is located it the thermostat housing and it's a screw it type. Seperate gauges for each motor.
 
Sounds like a ground issue at the gaskets......try tightening the thermo housing bolts or run a ground jumper from the sender base to battery ground and recheck, Pull the sender out, connect the sending wire to the cenetr post, connect jumper from threads to battery ground and hit it with a hair dryer or bic lighter and see what happens... (of course the heat goes to the base of the sendoer not the top...........)
 
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kimcrwbr1 said:
I`m thinking the thermostat housing is not grounded to the engine maybe try putting new lock washers on the bolts for the thermostat housing. To check if the sender is grounded short the guage wire to the base of the sending unit it should peg the guage hot?
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I don't think a lockwasher will to it, since there is a gasket above and one below the housing, insiulating it pretty well. I drilled and tapped my housing (not in the water jacket area, if you were wondering) and ran a ground wire directly from the housing to good ground. Eliminates need for the riveted gasket, also.
 
Your roght Its a ground issue. I ran a jump wire from the port engine to the wite on the stb engine and the gauge went right to 160 or so. All the grounds on the engine look ok and are tight. Maybe a new ground wire will work. Thanks
 
Sorry to bother you guys reviving an old thread, but I have been following a couple of these threads trying to solve my temp gauge problem. I have a 98’ Chaparral 2130 SS with a Mercruiser 5.7L carbureted Thunderbolt. When I bought it, the temp gauge didn’t work. I tried grounding the sending wire and got nothing. I tried grounding the threads on the sending unit and still got nothing. I removed the temp gauge and tried to put power to it using a 9V battery and got nothing. The light in the gauge wouldn’t even light up. I went to O’REILLY auto parts and bought an Iequus temp gauge that most closely resembles the original guage. It has three prongs on the back. One says “S”, another says “+” and another has some kind of symbol resembling a sensing unit. When I hook the tan wire to the “S” and the purple wire to either of the other 2 prongs, it pegs all the way hot. If I ground the sensor wire at the motor, the needle goes down. It’s completely backwards. I’m at a loss because I’m not very electrically inclined and I am not sure what to do from here. Any help would be greatly appreciated. Thank you so much for your time and help.
 
S= Sender
+ = Battery voltage supplied when key is on and wire color shiuld be purple
The symbol most likely is sever horizontal lines on top of each other. That = Ground

I am not sure, using a 9 volt battery will work a gauge. They may require 11+ VDC bur a few amps more than a little 9 volt battery may supply..

If you take original gauge, attach two 2-3 ft wires to ground connection and battery/power connection on gauge, then connect to your boat battery.

Once connected, very quickly while looking at gauge, jump across the two wires on back of gauge and see if needle pegs. This is a very quick and momentary test to prove gauge functions only
 
a 9 volt battery won't power most gauges....

For the gauge to function, it needs a good 12VDC power source and a good connection to a functional sending unit providing the correct resistance values. the connections are as kghost explained.

I'll expand in kghost's quick test for clarity....once you have the gauge powered up, the gauge should show a minimum reading (ie cold). Now take conductor (bare wire) and, while watching the gauge, momentarily short the S terminal to the ground ( - ) terminal.; the gauge should peg to full scale...if these two tests work as indicated, the gauge is ok and the problem is in the wiring to the gauge or sending unit...or the sending unit itself.
 
kghost said:
S= Sender
+ = Battery voltage supplied when key is on and wire color shiuld be purple
The symbol most likely is sever horizontal lines on top of each other. That = Ground

I am not sure, using a 9 volt battery will work a gauge. They may require 11+ VDC bur a few amps more than a little 9 volt battery may supply..

If you take original gauge, attach two 2-3 ft wires to ground connection and battery/power connection on gauge, then connect to your boat battery.

Once connected, very quickly while looking at gauge, jump across the two wires on back of gauge and see if needle pegs. This is a very quick and momentary test to prove gauge functions only
Click to expand...
@kghost and @makomark Thank you a bunch for taking the time to help me. The original gauge has an “I” and an “L” instead of “+” and the symbol. I am not sure how to do that test on it like you’re asking. When I took it off, the purple wire was hooked to the “I”, and there were 2 grounds connected to the center stud and a blue wire connected to the “L”. I am assuming the L is the light and the I is the hot? Thanks again.
 
L = guage light and is nirmally blue in color.
I stands for Ignition and that should be purple in color
Black is 99.9% of the time, Ground and any purple or black and blue connections may have more than one wire as they "daisy chain" ignition power and ground and light power to multiple gauges.

The S is where the tan wire from sender connects.

I was mistaken and Mark corrected me. Use his description for testing gauge function.
With power and ground to gauge, you momentarily jump from sender terminal to ground and gauge should peg all the way in the hot direction. This can be done at back of gauge or if everything is connected normally you can jump from ground to center terminal at sending unit at engine
 
kghost said:
L = guage light and is nirmally blue in color.
I stands for Ignition and that should be purple in color
Black is 99.9% of the time, Ground and any purple or black and blue connections may have more than one wire as they "daisy chain" ignition power and ground and light power to multiple gauges.

The S is where the tan wire from sender connects.

I was mistaken and Mark corrected me. Use his description for testing gauge function.
With power and ground to gauge, you momentarily jump from sender terminal to ground and gauge should peg all the way in the hot direction. This can be done at back of gauge or if everything is connected normally you can jump from ground to center terminal at sending unit at engine
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Ok. Thanks again. I’ll give it a shot and let you know how it turns out. I feel like I may be getting in over my head on this electrical stuff, but I’m definitely going to try.
 
PharmD said:
Ok. Thanks again. I’ll give it a shot and let you know how it turns out. I feel like I may be getting in over my head on this electrical stuff, but I’m definitely going to try.
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Well, I didn’t have any luck. I did what you said and didn’t get any response. I can’t really even tell if it has power to it or not. I did check the continuity of the sending wire and it checks out.
 
Power only goes to the guage, not sending unit.

if you checked continuity then you must have a meter?????????

Turn the key to the on/run postion. All gauges should have power including temp gauge. Measure it at the purple wire. If no voktage there check purple wire at ignition switch. If yes at switch, then follow purple wire to find where the connection is lost.

With the key on, you should read battery voltage between purple wire and ground wire at back of gauge, If not change location of black meter lead to a different possible good ground. If that works then the black ground wire at gauge may be your issue...
 
kghost said:
Power only goes to the guage, not sending unit.

if you checked continuity then you must have a meter?????????

Turn the key to the on/run postion. All gauges should have power including temp gauge. Measure it at the purple wire. If no voktage there check purple wire at ignition switch. If yes at switch, then follow purple wire to find where the connection is lost.

With the key on, you should read battery voltage between purple wire and ground wire at back of gauge, If not change location of black meter lead to a different possible good ground. If that works then the black ground wire at gauge may be your issue...
Click to expand...
Yes. I have a meter. I will try that. My trim gauge was working fine before I started troubleshooting this temp gauge, now it’s not working. I’m probably going to end up taking to the service center because that mass bundle of wires under the dash is quite intimidating. I’m pretty sure I can do what you’re talking about without taking that gauge out again.
 
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