Temp sending unit issues

[DblSee]

First time caller, long time listener...
Hello,
My Port engine will not display engine/water temp. The shop installed a new temp sending unit last year and the gauge still won't display temp. I just now replaced the gauge, still nothing. So I removed the temp sender and it is scorched and bubbled up, so I installed a new one. Now when I start the engine, the gauge pegs out at max regardless of engine temp (I have a hand held laser temp gauge) Do I have a ground issue? Whats my next move?
89 Amberjack twin 5.7 V-8
Any help would be appriciated,
Thanks

 

[Bt Doctur]

did you use a marine sender or auto ? Either the wires to the gauge got changed and are pinched. remove the wire from the sender , turn key on, gauge should read all the way to the left, no temp.
If no reading, now ground wire from sender, gauge should go full right, max temp

 

[DblSee]

Thanks for your response. Yes it is a marine sender, and I did test the gauge like you said, it checks out. Interesting idea about the the pinched wires...
The engine was rebuilt two years ago and the temp gauge has not worked since. You might be on to something. Now what?

 

[Bt Doctur]

If the gauge and the wiring passed the test I`m guessing with the wire off the sender the gauge reads to the left and when you ground the wire the gauge reads to the right?

 

[Bt Doctur]

What color wire in on the sender Tan ot Tan Blue

 

[DblSee]

tan wire

 

[DblSee]

correct on both counts. When I ground the sender wire the gauge pegs to max

 

[Bt Doctur]

if the gauge and wiring passed the test, the sender is bad

 

[DblSee]

I understand the thinking that the sender is bad, I just installed a new one yesterday. The old one was pretty scorched...

 

[Bt Doctur]

I ordered a package of 10 from the supplier, and 8 didnt work. The gauge reads resistance , nothing else.Testing the gauge and wiring as above proves the wiring and gauge are wired and working.Go to a radio shack or electronics store .Get 2 resistors 30 ohms (250 Deg) and 99 (100 ohms) 175 Deg
Install the 90 ohm between the wire at the sender and a good ground. key on gauge should read approx 175 Deg at the gauge If yes, replace sender
I hate giving away all my secrets

 

[Fishermark]

Did you use teflon tape on the sender? That will cause it not to work.

 

[Bt Doctur]

Fish, gets a constant full scale to the right
http://www.tadiesels.com/assets/docs...ance_Value.pdf

 

[Fishermark]

Yeah - I missed that part. That indicates it is grounding out. The tape would keep it from grounding out.

 

[DblSee]

I did not use the tape, are saying I need to?
Thanks

 

[Bt Doctur]

No, no teflon tape on senders, they need a ground

 

[04searay]

having similar issue with my 04 searay. temp gauge stopped working. replaced thermostat. tested wiring and gauge and thought it was sending unit issue. grounding tan sending wire pins gauge to right. replaced sending unit, still no luck. Resistance on sending unit is 800+ ohms at room temp. Resistance decreases as temp increases, so appears sending unit is fine. Can't seem to get a reading when running separate wire from gauge (S term) to sending unit post, only to sending unit hex portion. Any ideas or suggestions would be appreciated.