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Old 01-07-2016, 20:19   #1
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Water temp gauge reads 140 when off

I am fixin to test start my rebuilt engine tomorrow and, while running through the systems this evening, I noticed something unexpected.

Water temp and oil pressure gauges show values when no power is applied.

When the batter switch is turned off, the water temp shows about 140 degrees and oil pressure shows 20 psi.

When I turn battery switch to on, water temp gauge pegs out on the zero stop. It hits pretty hard with an audible click when it smacks against the stop. The oil pressure gauge gently goes to zero.

It makes sense that the gauges show zero when ignition system is energized, but is it normal for gauges to have readings when no power is applied?

It's been so long (7 months) since I've run the engine and I never paid attention to the position of the needles when system was off.

The engine is not on and the negative wires from gauges go to the negative bus, which is connected with negative post on battery.

Positive wire goes from positive bus to the first gauge and they are connected in series.


2/0 cable connect negative post on battery with unpainted exhaust flange stud.
2/0 cable runs from pos batt post to on/off switch, then to the starter stud.


Sense wires are the red wires on the lower left (to left of positive stud/wire) on each gauge
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Old 01-07-2016, 20:28   #2
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Re: Water temp gauge reads 140 when off

The needles probably just going to a natural resting place where gravity pull evens out. When I start a rebuilt engine for the 1st time, I use mechanical gauges.
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Old 01-07-2016, 20:31   #3
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Re: Water temp gauge reads 140 when off

If you turn the power off at 140deg, the meter movement should stay at 140deg. There is nothing to make it go to 0 until you turn power back on and the actual water temp is off scale.
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Old 01-07-2016, 21:27   #4
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Re: Water temp gauge reads 140 when off

I think I understand what you wrote. Since the water temp is abut 80 degrees (the ambient temp in the shed this afternoon), when I apply power, the sensor detects the 80 degrees and, since that is off the lower end of the scale, the needle heads down to 80 degrees; therefore, this behavior is normal, not indicative of faulty gauge/sensor.

If that is correct, why does the needle go up to about 140 when I disconnect power.

Remember, the engine has not been run for 7 months and has been completely torn down and rebuild over the last several months.

Lepke, I wish I had known about your mechanical gauge advice. Maybe i'll grab some from auto store tomorrow.

Thanks
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Old 02-07-2016, 11:26   #5
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Re: Water temp gauge reads 140 when off

Quote:
Originally Posted by Lepke View Post
The needles probably just going to a natural resting place where gravity pull evens out. When I start a rebuilt engine for the 1st time, I use mechanical gauges.
When the key is in the off position, the needle can go just about anywhere. The important thing is when the key is on. When starting a rebuilt engine I always check the water coming out at the exhaust before it get hot! No water,,, shut it down before it gets hot. A infa red thermometer is great for first start ups.
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Old 02-07-2016, 11:57   #6
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Re: Water temp gauge reads 140 when off

Quote:
Originally Posted by scherzoja View Post
I am fixin to test start my rebuilt engine tomorrow and, while running through the systems this evening, I noticed something unexpected.

Water temp and oil pressure gauges show values when no power is applied.

When the batter switch is turned off, the water temp shows about 140 degrees and oil pressure shows 20 psi.

When I turn battery switch to on, water temp gauge pegs out on the zero stop. It hits pretty hard with an audible click when it smacks against the stop. The oil pressure gauge gently goes to zero.

It makes sense that the gauges show zero when ignition system is energized, but is it normal for gauges to have readings when no power is applied?

It's been so long (7 months) since I've run the engine and I never paid attention to the position of the needles when system was off.

The engine is not on and the negative wires from gauges go to the negative bus, which is connected with negative post on battery.

Positive wire goes from positive bus to the first gauge and they are connected in series.


2/0 cable connect negative post on battery with unpainted exhaust flange stud.
2/0 cable runs from pos batt post to on/off switch, then to the starter stud.


Sense wires are the red wires on the lower left (to left of positive stud/wire) on each gauge
Pic # 4----shows 2 wires on same temp sensor-why?
Pic # 4---also shows a second temp sensor with no wire on it?

Possibly-you have a high temp alarm sensor that would operate a buzzer or light on over temp,PLUS a sensor that feeds your gauge??

You have good old fashioned reliable Stewart Warner gauges & personally,I've never seen SW gauges do what you describe,if wired correctly. I have seen other brands do it though

Cheers/ Len
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Old 02-07-2016, 12:06   #7
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Re: Water temp gauge reads 140 when off

I test temp gauge in ice water, 32 and boiling water 212 at sea level..
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Old 02-07-2016, 17:49   #8
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Re: Water temp gauge reads 140 when off

Yeah, the pictures.. . . I mislabeled one of them. Picture #3 shows two labels to and from fuel pump. THat is wrong. I copy/pasted those and forgot to change words. Those go to the pos ad neg busses.

Deblen,
Those are two wires on the same connection,but only one actually goes anywhere, to the Sense stud on the water temp gauge. The othe wire (the one with blue sleeve ) is a remnant I left there so I would nto forget what goes there. The cut wire only goes aobut 1/2".


The other sensor is for a buzzer. I have a buzzer that sounds with low oil pressure and high water temp.

I started the engine to day and it started right quick. RAn it aobut 30 seconds with no compression, then cranked for about another 20 seconds while fuel filled the last inches of the high pressure pipes and bled out the air. The thing fired right up and went up to about 180 degrees (it has a 180 degree thermostat). I checked the temp gauge against and IR thermometer and the two were close. Oil pressure gauge went up to and stayed around 60 psi and oil pressure buzzer shut off within seconds of engine starting.

It starts quick (within a second) and runs a lot smoother with this rebuild.

Thanks for ya'lls help.
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Old 02-07-2016, 17:59   #9
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Re: Water temp gauge reads 140 when off

Quote:
Originally Posted by scherzoja View Post
Yeah, the pictures.. . . I mislabeled one of them. Picture #3 shows two labels to and from fuel pump. THat is wrong. I copy/pasted those and forgot to change words. Those go to the pos ad neg busses.

Deblen,
Those are two wires on the same connection,but only one actually goes anywhere, to the Sense stud on the water temp gauge. The othe wire (the one with blue sleeve ) is a remnant I left there so I would nto forget what goes there. The cut wire only goes aobut 1/2".


The other sensor is for a buzzer. I have a buzzer that sounds with low oil pressure and high water temp.

I started the engine to day and it started right quick. RAn it aobut 30 seconds with no compression, then cranked for about another 20 seconds while fuel filled the last inches of the high pressure pipes and bled out the air. The thing fired right up and went up to about 180 degrees (it has a 180 degree thermostat). I checked the temp gauge against and IR thermometer and the two were close. Oil pressure gauge went up to and stayed around 60 psi and oil pressure buzzer shut off within seconds of engine starting.

It starts quick (within a second) and runs a log smoother with this rebuild.

Thanks for ya'lls help.
Good to hear!!
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Old 03-07-2016, 20:16   #10
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Re: Water temp gauge reads 140 when off

AC lies and DC dies, or is DC lies and AC dies. One of those is gouge for airplane gauges which I never can remember.
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