Temp gauge help

Midwest Amphicar

Worlds Largest Amphicar Destination
Temp gauge was reading almost hot. But actually was at 175. I replaced with new sender and now reads very hot. Any advice on changing resistance? Thanks, Dave
 

mike_israel

Amphicar Forum Admin
Staff member
Saw this on another forum. Maybe it will help ...

Look for maybe a 500 Ohm "potentiometer"/rheostat.

Here is a 250 Ohm model, which would work:
http://www.allelectronics.com/cgi-bin/i ... HAFT_.html

Radio Snack may have some also.

Connect the center terminal and one of the outer terminals
where the sender would normally go. Turn pot shaft till
the gauge reads Min or Max and then use an Ohmmeter
to read the Ohms the pot is set at,.​
 

Midwest Amphicar

Worlds Largest Amphicar Destination
Nope not on the car formerly known as Pontiac Moon. The problem with the gauge/ sending unit is I need to have less resistance. Which means I need to run a parallel resistance to ground to lower over all. But I think it would back feed the positive ground. So than I would need to add a diode. So....... I told owner be happy don't worry. A digital thermometer is nice to check actual conditions. Later Dave
 

strandweiss62

Active Member
Dave,
Can you measure the resistance of the sending unit in cold, normal and hot condition? Cold, it should be about 60 Ohms, hot much higher. The resistance of the gauge is about 35 Ohms. In some cases you can adjust the end positions of the gauge with a screwdriver through the two holes on the back locked with tape, but don't play with that. If you run a parallel resistance to ground, the gauge may not indicate correct if engine is really hot.
PeterTemp Gauge.jpg
 

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azpaul50

Member
Where's John F.? He usually has the answers to these problems. Both my cars had temp problems and I spent months trying to sort it out (2 gages, 3 sensors). I finally gave up on my remaining Amphi after lazer confirming what temp meant what and having a correction chart in my head. It was especially important since I use the Amphi to haul my trailer and scooter. The problem is indeed usually in the grounding meaning that any adjustment will have to be redone as the car ages made even worse with prospects of water intrusion. don't forget that cars that had a polarity change also changed the gage's relationship to ground. Most modern temp TCs are alumel/chromel (2-wire pair) and independent of surrounding grounds. This one isn't like that so it is only as good as the car's grounding itself. During my investigations I discovered that those coming from a certain vendor are only checked for continuity from probe to ground. There is no test jig. I got better results using a new sensor from Moss Motors but it still didn't fix the problem entirely. By the way... is everyone selling their Amphis? Seems like there's a ton of them on eBay.! Hey, ChasG... where do the Isetta guys meet on the web? I got one and can't find anyone to talk with! I got my own German car club going on... and it's all your fault! - azpaul50 **hero-worshiper of the truly kewl**
 

strandweiss62

Active Member
As azpaul remarked most problems result in increasing transition resistance due to corrosion. Negative ground conversion has no effect to temperature gauge. There are many electrical connections on the way:

Ground to sending unit
*Sending unit to plug
Plug to cable (red/white)
Cable (rear wire harness)to plug
*Plug to main rail connector in engine compartment left
*Main rail connector to plug
Plug to cable (red/white, main wire harness)
Cable to tab
*Tab to gauge
*Gauge to tab
Tab to cable (black, instrument panel)

Positions marked with * you can disconnect and clean with a glass fibre brush, may be that helps.
Peter
 
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