Electrical: Temp gauge pegging

[BShaw]

(289 v/8) I installed a new temp sender when the new motor went in a while back. For a long time my gauge was performing as it should. However, now I am getting sporadic readings. Some times it reads properly (steady 180 +/- when fully warmed up) but sometimes it'll just climb up to 240 (max) and sit there but it isn't running hot) No amount of wire jiggling, tapping, key wriggling or swearing will get the gauge back to normal. When I turn the key off the gauge goes to zero.

As I am technologically brain dead today, I ask... Is it most likely a ground (open)? A short? Something else? Thanks.

[bezhawk]

The sending unit is a variable resistance to ground. The hotter it gets the less resistance. So I would bet you have the sending unit wire grounding out somewhere.

[jbroomer]

The sending unit is a variable resistance to ground. The hotter it gets the less resistance. So I would bet you have the sending unit wire grounding out somewhere.

Agreed, must an intermittent ground somewhere in the harness. To rule out a wonky sender check the resistance when the gauge is reading correctly and then when it's pegged. If the resistance is close you can rule out the sender.

[R_David]

Agree with the above posts. I had exactly the same problems, random temp readings and it pegging out hot even when it wasn't. You have a ground problem, in my Hawk it turned out to be the ground to the gauge box had broken, so I wired the ground directly to the back of the temp gauge in the dash and it fixed my problem. 10 minute fix for a problem I lived with for 10 months.

[BShaw]

Thanks for the comments. It has to be a grounding problem. I picked up a cheap aftermarket temp gauge and wired it independently. As it was used with the S-W sender the reading was way off at least it allowed me to monitor the temp and be able to drive it to the Memorial Day car show with some confidence. As I hadn't driven more than a few miles on the new motor I was concerned about such things. No need for concern. Ran great and I cruised like a king at 70 mph to many thumbs up along the freeway. The five speed OD kept the rpms well below 2000 at 70. My speedo is off by a bunch so I will heed to replace the gear. Experienced a little steering vibration at around 75 but will be getting a steering component check and alignment soon.

Anyway, back to the grounding...I am going to take some steps to ensure that the gauge and entire dash is getting a solid ground.

[jclary]

... Experienced a little steering vibration at around 75 but will be getting a steering component check and alignment soon.

OH MY! That was no ordinary event...the ecstasy of a Studebaker "Speed Organism!"

A common occurrence after dormancy or long periods of "Speed Abstinence."

Easy to miss-diagnose due to unfamiliarity with the experience.

[bonehead007]

Good Afternoon. Been a while since I've been on this site. Decided to work on my Packard Hawk which has been sitting in the garage for the past two years due to not having time to fix it and this very problem.

Worked on it today. Replaced the thermostat, started it up. Within 5 mins was pegging temperature gauge. Was going to try a different gauge then noticed this on the site.

Check the back of your gauge. I had a white/black cloth wire going to the ignition switch on the bottom lug. On the top lug I had a black wire which I thought was the ground but believe went to the sender unit on back of the engine. After 5 mins , decided to check the nuts on the gauge. Guess what..

The top one was loose and required a couple of turns to tighten. Put the wire back on , started the Hawk and let it run 30 mins. Stayed at 140ish most of the time.

Never would have looked at that without the help from this site. Thanks for the help. Good luck .