Temp guage working...sort of.
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Senior User
Joined: Feb 2009
Posts: 283
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From: San Diego
Temp guage working...sort of.
I didn't think my temp gauge worked because it always sat at cold, until now. Sense the outside temp has dropped, I have noticed my temp gauge needle moving, BUT in the wrong direction. It goes from hot to cold. Starting off with the needle pegged at hot then when the engine warms up I can watch the needle travel the full spectrum of the gauge and end up pegged at cold. The I6 runs great with no over heating issues. Can some one tell me what's going on with this gauge? Is it the sending unit?
Post Fiend
Joined: May 2008
Posts: 7,641
Likes: 21
From: Poway, Ca.
Temperature gauges in the trucks were "parked" in the "H"/ hot position when the power was off and the oil pressure was "parked" in the "0" position when power was off. The reason was that if there was a power failure to the gauges they would revert to their worst case positions and alert the driver of a problem - saving the engine if there was in fact a problem.
First, is your truck still 6 volt positive ground? Or is it 12 volt now? It sounds like the gauge is getting 12 volts of opposite polarity. Is the stock sending unit in it?
Or, did you put in a new sending unit that may be designed for 12 volts and use the same gauge???????? But you have to use the stock sender. If it's the stock gauge and you didn't use a voltage reducer on it, but tried to use a 12 volt sender, it will do this - it's reading double so instead of being at half hot it goes up all the way.
Give me a little more info and we can figure out how to fix it. Don't use it as is or you will smoke check (fry) the gauge.
First, is your truck still 6 volt positive ground? Or is it 12 volt now? It sounds like the gauge is getting 12 volts of opposite polarity. Is the stock sending unit in it?
Or, did you put in a new sending unit that may be designed for 12 volts and use the same gauge???????? But you have to use the stock sender. If it's the stock gauge and you didn't use a voltage reducer on it, but tried to use a 12 volt sender, it will do this - it's reading double so instead of being at half hot it goes up all the way.
Give me a little more info and we can figure out how to fix it. Don't use it as is or you will smoke check (fry) the gauge.
Thread Starter
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Senior User
Joined: Feb 2009
Posts: 283
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From: San Diego
HI Julie, That's a cool piece of info about the gauges. Makes sense too.
My truck was converted over to 12v by the PO. He did say his mechanic tried to get all the gauges working but for some reason couldn't fix the Temp gauge. I've had the truck almost a year now, it runs great with no heating issues so I never bothered trying to fix it. I have had the gauge pod out, to replace a couple indicator bulbs, and ended up giving it a good cleaning. That was almost 6 months ago. Visually all the gauges seem to be original, all had the same patina. So that leads me to believe the gauge itself has not been replaced. So it has a 12V system with the original gauge. Most be the sensor right?
My truck was converted over to 12v by the PO. He did say his mechanic tried to get all the gauges working but for some reason couldn't fix the Temp gauge. I've had the truck almost a year now, it runs great with no heating issues so I never bothered trying to fix it. I have had the gauge pod out, to replace a couple indicator bulbs, and ended up giving it a good cleaning. That was almost 6 months ago. Visually all the gauges seem to be original, all had the same patina. So that leads me to believe the gauge itself has not been replaced. So it has a 12V system with the original gauge. Most be the sensor right?
Fleet Owner
Joined: Jul 2004
Posts: 27,303
Likes: 1,062
From: NM
What engine are you running? If not a stock engine, did he use the sender that was on the donor engine? It won't work 99% of the time. If it's a stock engine, particularly a flathead V8, there are two "senders", one is really a switch. You can get by with only the one that has the actual sensor in it, but I've seen where people connect up only the switch, which makes the gauge read dead cold all the time. See below
Post Fiend
Joined: May 2008
Posts: 7,641
Likes: 21
From: Poway, Ca.
Good stuff Ross!
Well if the gauge moves at all it's still good. So there's a plus.
Knowing what I know now, either the sending unit doesn't match, it hasn't had the voltage reducer installed OR they are trying to use a single voltage reducer for all three gauges and the polarity on the temp gauge is reversed. But it sounds like the sender is not compatible.
I solve this problem in my trucks by switching to mechanical oil and temp gauges using new gauge internals and installing them in the original stock cases with the original faces glued on. See my gallery on that - it's easy and I really trust the mechanical gauges much more. Plus you can see your engine temp with the ignition off - it reads all the time
I guess what you need to ascertain is, was the sending unit changed on the engine. If it was you need to get an original one to reinstall, and then use a single voltage reducer on the back of the temp gauge. That should do it.
Well if the gauge moves at all it's still good. So there's a plus.
Knowing what I know now, either the sending unit doesn't match, it hasn't had the voltage reducer installed OR they are trying to use a single voltage reducer for all three gauges and the polarity on the temp gauge is reversed. But it sounds like the sender is not compatible.
I solve this problem in my trucks by switching to mechanical oil and temp gauges using new gauge internals and installing them in the original stock cases with the original faces glued on. See my gallery on that - it's easy and I really trust the mechanical gauges much more. Plus you can see your engine temp with the ignition off - it reads all the time
I guess what you need to ascertain is, was the sending unit changed on the engine. If it was you need to get an original one to reinstall, and then use a single voltage reducer on the back of the temp gauge. That should do it.
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