Gauge issues

[m0par0rn0car]

I have a '69 Plymouth fury with the 318 and it gets up to operating temperature without a problem and the heat blows hot but the temperature gauge only reads a quarter of the way up. Is this a gauge problem or a sending unit problem?

 

[Ross Wooldridge]

Depending on the efficiency of your cooling system, coupled with the correct thermostat to your driving style, environment and season, the needle showing the the lower end of the warm section of the gauge is nothing to be concerned about. My Monaco tended to sit between 1/4 and 1/2 way when all was well.

I would be more concerned if your engine never gets warm, or the gauge needle is always just below the danger zone.

Are you able to ascertain what the actual operating temp is? An engine that sits comfortably at 180° is a good thing!

I saw in another thread you were having issues with a 69 Fury with little or no heat (temperature of the air), and non-functioning HVAC controls. Is this the same car? If so, you say in this post it's blowing hot air, so did you get those particular issues worked out?

 

[traintech55]

Sounds like a sending unit problem. Are your other gauges working correctly? They all get there power supply from the same place.

 

[m0par0rn0car]

Depending on the efficiency of your cooling system, coupled with the correct thermostat to your driving style, environment and season, the needle showing the the lower end of the warm section of the gauge is nothing to be concerned about. My Monaco tended to sit between 1/4 and 1/2 way when all was well.

I would be more concerned if your engine never gets warm, or the gauge needle is always just below the danger zone.

Are you able to ascertain what the actual operating temp is? An engine that sits comfortably at 180° is a good thing!

I saw in another thread you were having issues with a 69 Fury with little or no heat (temperature of the air), and non-functioning HVAC controls. Is this the same car? If so, you say in this post it's blowing hot air, so did you get those particular issues worked out?

the heat issue is a different thing, I havent tried yet to get that to work but I can feel the heater core is warm and the radiator hoses are hot. I just installed a new thermostat, the gauge just reads low. the picture is as high as it'll go

 

[m0par0rn0car]

Sounds like a sending unit problem. Are your other gauges working correctly? They all get there power supply from the same place.

the alternator gauge works right but the fuel gauge stops halfway too

 

[traintech55]

the alternator gauge works right but the fuel gauge stops halfway too

The Temp., and Fuel gauge gets their power from the voltage limiter on the back of the cluster. Bet it is going bad. Find one of the new constant power transistor ones.

 

[Big_John]

the alternator gauge works right but the fuel gauge stops halfway too

Ahh... That little tidbit of info helps point to a possible problem with the voltage limiter for the gauges. It's a 5 volt voltage regulator that resides on the back of the dash. Unlike fine wine, they don't get better with age and can be an issue.

Best thing is to replace it with a modern electronic version.

 

[Ross Wooldridge]

Interesting. That temp gauge is definitely reading colder than I expected see... but you say things are nice and warm in the engine bay... so...

Two things to check. You say your rad hoses are both hot (which is good), how about the heater hoses going to the firewall from the front of the engine? They both should be hot too, or at least not a really noticeable difference between the two. If there is, you've got a blockage. That explains a less than satisfactory amount of heat from the heater, but doesn't explain the low reading on the gauge. @Big_John and @traintech55 posts above essentially beat me to it... read on.

If the other gauges are also not functioning properly (except the Amp gauge), this tells me it's the voltage limiter for the gauges. While I could be wrong, the Amp gauge does not get the same kind of power the other gauges do. Those gauges operate on 5V, which is supplied from a little voltage limiter capacitor thingy typically mounted on the rear of the gauge cluster. They can and do fail, and there is an article on how to make a new one using readily available parts from an electronics supply store. Search for that and I would go there first in terms of seeing if that restores your gauge performance.

As well, check on the heater/defrost door linkage operation as described in the other thread you've got going.

 

[m0par0rn0car]

Interesting. That temp gauge is definitely reading colder than I expected see... but you say things are nice and warm in the engine bay... so...

Two things to check. You say your rad hoses are both hot (which is good), how about the heater hoses going to the firewall from the front of the engine? They both should be hot too, or at least not a really noticeable difference between the two. If there is, you've got a blockage. That explains a less than satisfactory amount of heat from the heater, but doesn't explain the low reading on the gauge. @Big_John and @traintech55 posts above essentially beat me to it... read on.

If the other gauges are also not functioning properly (except the Amp gauge), this tells me it's the voltage limiter for the gauges. While I could be wrong, the Amp gauge does not get the same kind of power the other gauges do. Those gauges operate on 5V, which is supplied from a little voltage limiter capacitor thingy typically mounted on the rear of the gauge cluster. They can and do fail, and there is an article on how to make a new one using readily available parts from an electronics supply store. Search for that and I would go there first in terms of seeing if that restores your gauge performance.

As well, check on the heater/defrost door linkage operation as described in the other thread you've got going.

the heater core hoses are both hot but I'll pull the dash tonight and check the voltage limiter

 

[traintech55]

the heater core hoses are both hot but I'll pull the dash tonight and check the voltage limiter

The factory voltage limiter is hard to check in the car. It uses a set of points the open and close rapidly. This keeps it at the 5 volts. When you check with your meter don't be surprised if you get a lot of bounce on your meter.

 

[cbarge]

the heat issue is a different thing, I havent tried yet to get that to work but I can feel the heater core is warm and the radiator hoses are hot. I just installed a new thermostat, the gauge just reads low. the picture is as high as it'll go

View attachment 354442

You are in Plymouth Michigan? When it is freezing outside (temp 30 degrees F or 1C
--I checked),
in your pic the temp gauge reads normal and just inside the "operating" temp zone.
If your engine does not have a clutch fan,it is pulling cold air contantly--OK for summer but not an advantage in cold weather.
Use a digital radar temp gun and when the temp gauge stops point the gun at the thermostat housing when the stat opens. record the temperature.
Just for shits and giggles,put a piece of cardboard in front of your rad,and see if the temp goes up. record temperature from radar gun again.
No change at the gauge yet the radar gun shows a higher temp, then as recommended replace the 5 volt limiter with an electronic one.
I use the electronic one in every build I had done--no questions all my cars have them.
As a process of elimination check the resistance of the coolant temp sending unit with a multimeter. Hot and cold

 

[m0par0rn0car]

You are in Plymouth Michigan? When it is freezing outside (temp 30 degrees F or 1C
--I checked),
in your pic the temp gauge reads normal and just inside the "operating" temp zone.
If your engine does not have a clutch fan,it is pulling cold air contantly--OK for summer but not an advantage in cold weather.
Use a digital radar temp gun and when the temp gauge stops point the gun at the thermostat housing when the stat opens. record the temperature.
Just for shits and giggles,put a piece of cardboard in front of your rad,and see if the temp goes up. record temperature from radar gun again.
No change at the gauge yet the radar gun shows a higher temp, then as recommended replace the 5 volt limiter with an electronic one.
I use the electronic one in every build I had done--no questions all my cars have them.
As a process of elimination check the resistance of the coolant temp sending unit with a multimeter. Hot and cold

I'll try the cardboard thing since you're right, I don't havr a fan clutch but how do I check the resistance?

 

[cbarge]

I'll try the cardboard thing since you're right, I don't havr a fan clutch but how do I check the resistance?

I don't have the FSM handy (I am at work) but if you have a factory Shop Manual it will give you the properties of the coolant temp sensor resistance in Ohm's and how to check it with a multimeter..
Even better,use an aftermarket temp gauge and hook it up to your temp sensor,compare readings to the radar gun and it.

 

[CBODY67]

Using the infra-red heat gun can quickly tell you what's happening. Check the thermostat housing and then the heater hoses where they attach to the heater core under the hood.

The car should spec something like a 195 degree F thermostat. The "C side of the "normal range line" on the dash gauge should be 100 degree F. The center should be 200-210 degrees F, and the "H" end of the line should be about 260 degrees F, I believe. End result is that the needle should be in the middle or slightly below the middle in normal operation.

Seems like somebody in here sells the solid state voltage limiters? Similar to the factory 1980s transistorized units?

Enjoy!
CBODY67

 

[Demonic]

MOPAR Products

Real Time Engineering's website. They make nice limiters w/ short circuit protection.

 

[Gerald Morris]

MOPAR Products

Real Time Engineering's website. They make nice limiters w/ short circuit protection.

Good looking products! Much neater than using a USB power supply to get the steady 5 V DC. I'll get one of these when I replace my instrument panel....