Temperature sender/gauge

[blacklab75]

I have a 96 merc 3.0 and when I first start the motor the temp. gauge bounces wildly often from one side of the gauge to the other and often hovering around high temp side. As I get underway (5-10) the the gauge needle calms (somewhat) and bounces less wildly showing a more correct temperature. With the ignition off the gauge shows the correct temp with no bouncing.

Do I have a bad sender, gauge, or short somewhere?

Thx for looking at my post.

 

[Bondo]

Re: Temperature sender/gauge

Ayuh,... Sounds like a Bad connection,... Look at the gauge,+ the sender,..
Sender is in the T-Stat housing...

 

[Don S]

Re: Temperature sender/gauge

I would start checking connections. Especially the main engine harness 10 pin connector. Corrosion, loose, or an overtightened clamp on the connector will cause your problem.
Could also be the gauge, or sender.
There are tests for the sender, have a look in the adults only stick for the service manual link.

 

[blacklab75]

Re: Temperature sender/gauge

Ok, I tested the gauge because that the simpliest thing for me to check. According to the Merc service manual you disconnect the sender wire, turn the ign key, and the gauge should stay dead...it does.

Next, with sender wire diconnected you should run a jump wire from the sender post on the gauge to the neg post on the gauge, turn the ign, and the gauge should peg out...it does.

Here's where I get confused. Initially the gauge checked out so I'm thinking I need to replace the sender. So, I reconnect the sender wire to the gauge and the needle stays pegged out when I turn the ign. I disconnected the sender and run the gauge test again and it's still pegged out. I decide to hook up the hose and run the engine and the needle stays pegged from a cold start. So now it's looking like I do need gauge and not the sender. Does all of this sound correct or am I missing something?