Mercruiser 4.3 Temp gauge not working

[Rob406]

Hey everyone, need a little help diagnosing a temp gauge that isn't working. Just bought the boat, the gauge was stuck pegged all the way, always, key on or off. I pulled the ground wire from the back of the gauge and cycled the key and it swept back to zero. When I put the ground wire back on it maxed out again. I removed the wire from the sender and using a jumper from battery ground i can get the gauge to bounce from zero to max. Does this mean I have a bad sender?

 

[achris]

Or a shorted wire somewhere. ..

 

[Rob406]

Any insight on how to diagnose this would be appreciated, the wiring looks intact from what i can see. What would be my next step? Also right by the sender wire stud I have a tan with blue stripe wire with an eyelet that is tied back connected to nothing. I read this is for my audible alarm but not sure where that is located or what this wire should be connected to. Wiring is not my specialty but as always trying to learn. Any specific help would be appreciated, thanks .

 

[Scott Danforth]

easy, pull the wires from the back of the gauge and look at gauge, did it move?... is gauge still pegged, since you state the gauge is pegged all the time. most likely gauge is shot, as a key-off would normally kill all your gauges. in this case, since the gauge doesnt move, that would indicate a high probability its a bad gauge.

however you also state that removing the ground make it go to zero. that would indicate a few things..... your gauge is hot all the time and it shouldnt be. you need to trace that, the purple wire should only have power when the key is on.

since removing the ground causes the gauge to go to zero, you need to also ohm out the pink wire (gauge sensor lead) to see if its grounded anywhere.

 

[GA_Boater]

Disconnect the wire on the temp sender on the motor. If the gauge drops to zero, it's the sender. If it stays pegged, it's the wire up to the gauge.

 

[harringtondav]

Maybe. Put the boat on mufffs. Attach an ohm meter between the sender terminal and a good ground. Start the engine. The resistance should change as the engine warms up. From your test it sounds like your gage max's. at 12V, and drops from lower voltage (higher resistance at the sender). So the sender should decrease resistance as the engine warms. If this doesn't happen change the sender.

 

[Rob406]

Ok so the gauge was pegged always, When I removed the ground wire to the gauge it went to zero. When I put it back on it would pin again. Then i removed the wire to the sender and can't remember what happened from there, but right now the gauge is on zero, the wire is on the sender, and when I turn the key on there is a couple second delay then the needle bounces up like a 100th of an inch . Was it just a dirty connection?

 

[alldodge]

Disconnect the wire on the temp sender on the motor. If the gauge drops to zero, it's the sender. If it stays pegged, it's the wire up to the gauge.

This is your test

Removing the ground wire from the gauge just removes power from it, and without power the needle goes to zero or OFF.

Then i removed the wire to the sender and can't remember what happened from there, but right now the gauge is on zero, the wire is on the sender, and when I turn the key on there is a couple second delay then the needle bounces up like a 100th of an inch . Was it just a dirty connection?

I think you either have a bad sender, or your have some insulation scraped or burnt off the sender wire. When the wire was removed to test. the wire was no longer grounded. When reinstalled, the grounding didn't make contact again. So if wire is good, replace the sender

 

[Rob406]

Thanks for the advice. So after putting the retaining clip back on the back side of the gauge and tightening down the nut (one missing) now the needle comes up in about 50 degree increments, stopped in the middle for awhile, and after cycling the key a few times did this until it stopped all the way pegged again.... By the way the one nut that is still there, the stud on the back side of the gauge spins around inside the gauge. Was definitely messed with at some point and probably over tightened. Wondering if it is making contact with something inside the gauge? A sender is cheap and apparently so is a gauge. Thinking about just buying both since it will take a week to get either one, summer is dwindling down. My next question is can i use any gauge (like a faria or a sierra replacement gauge) is there anything specific I need? looking around they are readily available for 20-30 dollars but don't have specific details or pictures of the back side. Mine is 100-250 range but some are 120-240, does it matter? Is there anything specific i need to look for for wiring connections or are they all the same? About the only information anyone provides is they are 2" diameter. Does the new sender have to match the range of the gauge or just go with a standard replacement mercruiser 4.3 sender? Not sure if there are different temperature ranges. Would like to get something in the mail asap. IF this does not work i will chase wiring. All exposed visible wiring I can see is in good condition. Everything on the sender side I brightened up to shiny metal and on the gauge side all the spade connectors are clean and free of corrosion. All visible wiring is intact and free of any type of visible damage. Thanks for all the help guys.

 

[alldodge]

The north american marine standard is 240 to 33 ohms (cold to hot). If you replace the gauge and sender, then it makes no difference

 

[Rob406]

Thanks for the fast response I think in that case I will go with the Sierra because it resembles the existing one more closely however the temperature range is 120-240 instead of 100-250

 

[Rob406]

what is the difference between sender code d and sender code j?

 

[alldodge]

what is the difference between sender code d and sender code j?

In the words of Ricky Recardo (dating my self) esplane Lucy
Where are you seeing d and j ??

 

[Rob406]

So on the Sierra line of gauges, 120-240 range, there are two models which appear identical, but one is listed for I/O and one for outboard, then in the description the I/O model says sender code D and the outboard says sender code J

I think my Sierra replacement temp sender is code D although it does not say that anywhere in the description. Found on another site someone asking a similar question .... detective work .... Just not sure if I could get a definite answer

 

[alldodge]

With that expanation, you would need the I/O