Temperature gauge question

[Tom Millward]

Hello fellow Carrier owners and knowledgeable persons,

I had my Carrier out on Salisbury Plain a few weeks ago, driving the many graded range roads and a bit of cross country.. I’m starting to use it more and so I need to fix my faulty temperature gauge. When switched off it reads maximum temperature. When switched on it moves to the mid range temperature and once the engine is running very quickly moves back to maximum again. Hence I don’t have a true reading of the engine temperature.

Can these gauges be repaired? Does anyone know if a modern replace that can be fitted as a stop gap? Or even better does anyone have a spare they’re willing to part with?

My Carrier is running on 12v, I’ve replaced the voltage converter thinking that might be the cause, but it made no difference. Could the senders be at fault? (I hope not as they’re about £75 each here in the UK!).

I have a road run coming up and I’d like to be able to monitor the engine temperature. It seems roasting hot after a decent stretch of road running, but without a working temperature gauge it’s impossible to tell!

Cheers,

Tom

[Tony Smith]

This thread http://www.mapleleafup.net/forums/sh...ad.php?t=28237 explains the operation of the Ford temp sender and gauge in the standard 6v system, and notes the different system in 12v setups. Perhaps your 12v conversion has used different components and resulted in a dysfunctional circuit?

The gauge operates by voltage heating a bi-metal conductor which deflects the needle. This should not be polarity dependant in a Positive or Negative earth change.

[Tom Millward]

Thanks Tony, I’ll have a good read of those posts and try and figure out where my circuit is going wrong.

[Phil Waterman]

Hi

Have not played with it yet but would switching polarity, this is based on the Amp meter if the polarity reverse the needle moves the wrong direction.

Cheers Phil

[Bruce Parker (RIP)]

Tom, if it's a Canadian UC then your gauge is doing exactly what it's supposed to do. Ignition off, with no current going to it, it reads all the way to the right (ie. max). Switch the ignition switch on and the needle, now with current, goes all the way to the left (ie. cold, assuming the engine is cold). As the engine runs it shows the temperature of the engine. I expect if your gauge is reading hot after a good run hill and dale it's because the engine really is hot.

[Tom Millward]

Hi Bruce, my gauge is doing as you say when the ignition is off, but when I switch it on with a cold engine it only goes halfway down the gauge, and reads normal operating temperature (engine is cold). Hence when it starts to warm up (not fully warm) the gauge goes to the right and reads off the scale.

[Tom Millward]

Originally Posted by Phil Waterman

Hi

Have not played with it yet but would switching polarity, this is based on the Amp meter if the polarity reverse the needle moves the wrong direction.

Cheers Phil

Hi Phil, I’ve not tried switching polarity yet, I’ll try that as well.

[Tony Smith]

Polarity makes no difference.

The gauge works by current flowing though a wire winding around a bi-metal strip. As the winding heats the strip, it bends, deflecting the needle on the gauge. The current flow, and the frequency of the circuit opening is dependant on the temperature of the sender on the Cyl Head.

For the gauge to correctly indicate, it needs the correct voltage and amperage flowing through the wire to cause the strip to heat at a certain rate, but polarity doesn't change the heating of the bi-metal strip.

The gauge operates with MORE current showing a COLDER indication, and LESS current showing a HOTTER indication. A full 6v across the gauge should move the needle fully to cold.

Tom, I'd be putting a Multimeter on the back of the gauge with the Ignition on + engine cold, and then again as the engine is running at operating temp (and showing off the scale).

To me, it seems like you are putting less than 6v through the gauge. This could be caused by the 12v reducer not giving you a full 6v at the gauge, or defective wiring with too high a resistance, or a poor ground (either at the Instruments, or engine to hull).

There is also the chance that the gauge or sender are defective, but as they seem to be showing some of the right functions, I would say they are working OK if given the correct diet of electrons.

[Lynn Eades]

Tom, on 6 volts it would work correctly. You need to buy a step down resistor from the likes of Gotham parts, Macs autos or Dennis Carpenter or lots of other vintage parts suppliers, to cut your supply (only to that gauge) to 6 volt The gauge is a 6 volt unit and will not function correctly on 12 volt.

[Tom Millward]

Hello Gents,

I have a voltage step down resistor, and recently changed it to see if that was the issue, but it made no difference. I will check the voltage at the gauge next and try to rule out the senders or gauge. Thanks for the advice.

Tom

[Grant Bowker]

Please understand that I'm not familiar enough with Ford and or Carrier electrics to be considered a "reliable expert". I have the impression that Ford 6V systems actually ran at 4.8 V in part. If I'm right on this and if the converter in use is designed to give 4.8V and if the statement that the gauge system is performing as if it is getting too little voltage are all correct - could this all fit together to make sense?

[Tony Smith]

Originally Posted by Grant Bowker

I have the impression that Ford 6V systems actually ran at 4.8 V in part.

Ford Ignition Systems do run at a reduced voltage through a resistor to give approx 4.8v to prolong the life of the points in the distributor, but the rest of the electrical system (Generator, battery, lights gauges, horn, etc) are not part of the reduced circuit, but use the full 6v (which is itself a nominal figure, as the Gen and the battery, when the engine is running and the Gen is charging, actually put out between 7.0v and 7.3v).

[Bruce Parker (RIP)]

Originally Posted by Tony Smith

Ford Ignition Systems do run at a reduced voltage through a resistor to give approx 4.8v to prolong the life of the points in the distributor, but the rest of the electrical system (Generator, battery, lights gauges, horn, etc) are not part of the reduced circuit, but use the full 6v (which is itself a nominal figure, as the Gen and the battery, when the engine is running and the Gen is charging, actually put out between 7.0v and 7.3v).

Agreed. The resister stepping down the voltage is to the ignition coil only.

[Lynn Eades]

To add to Bruce's input. The voltage going to the coil is the full 6 volts (battery voltage) This is to aid in supplying good voltage to the coil at start up. As the resistor heats up, so does the voltage (to the coil) drop to the 4.8? (4.5?) volts. The ignition resistor has a tin cover with holes in it (the cover is to stop you burning yourself + other things. Make sure your gauge resistor connects in from before that.
The problem with diagnosis via internet is that those attempting to help usually don't get the full details, and so the chances of getting it right are a bit like trying to win lotto.
Having read a bit about faults in Jeep fuel gauges, the gauge body has to have a good earth in the dash panel. In turn, a part of the gauge circuit needs a good earth inside the gauge body. These are common faults in old Jeeps. There are many things to consider.
Tom, the resistor you are using, Is it matched to the gauge? What I mean by that is that the gauge needs to receive a 6 volt input while the load (the gauge) is live (operating)
Does your carrier have 1 sender or 2? (one in each head?) In your left bank you should have one with a single terminal, and in the right bank you should have a sender with 2 terminals.(wired in series) The single terminal one does a gradual signal while the 2 terminal one is just a "hot on" "cold off" switch. I dont think Ford made a separate single terminal one for a 12 volt gauge (matched pair) but your original gauge is 6 volt so you have to use it that way (with correct resistor)
The system (less the resistor) is covered in the info that Tony directed you to. If you cant sort it out your self, then point the info to your 50+ y.o. auto sparky.
The Ford v8 is like 2 separate engines and the water only meets in the radiator. If you took the two wires off the R.H. sender and connected them together and insulated the join, then you could pull the sender out of the R.H. head and fit a separate bowden tube (capilliary) type gauge to that bank. It would then give you an idea of what's happening.
Lastly, you want the engine to run as hot as possible, but at the same time, to never have it boil. Good luck!

[Tony Smith]

Originally Posted by Lynn Eades

Tom, the resistor you are using, Is it matched to the gauge? What I mean by that is that the gauge needs to receive a 6 volt input while the load (the gauge) is live (operating).
Does your carrier have 1 sender or 2? (one in each head?) In your left bank you should have one with a single terminal, and in the right bank you should have a sender with 2 terminals.(wired in series) The single terminal one does a gradual signal while the 2 terminal one is just a "hot on" "cold off" switch.

Other way around, Lynn. Cold=Closed, Hot=Open. BOTH senders are on/off, not a graduated resistance, the temperature each one sees determines the duration the contacts are closed, and therefore the time that the current heats the winding in the gauge.

I don't think Ford made a separate single terminal one for a 12 volt gauge (matched pair) but your original gauge is 6 volt so you have to use it that way (with correct resistor)

'Smatter of fact, Ford did! When they converted to 12v vehicles in the mid 50's, they continued using the same style gauges and senders by King Seely, but with different resistances to apply with 12v. (Temp, Oil and Fuel). All are visually identical to the 6v, but marked 12v. The 6v senders use screw terminals, while the 12v ones have 1/4" blade terminals. They can be handy if converting to 12v neg grd, as the systems are not polarity dependant, but there is a trap for the unwary as mixing them up will screw with the accuracy. I DO NOT recommend using the 12v senders if you're not fully on top of what you're changing.

Anyhows, the 12v Temp sender with single terminal is B6C-10884.

[Lynn Eades]

Thanks Tony. I had a gut feeling there were 12 volt ones, but my quick search never found them. The mixing of components was what I was concerned about and that's why I touched on it.
My personal experience with the senders is that they are very reliable and the biggest reason an old one is no good is because someone has damaged the terminal end.
When it comes to "on-off" my point was that the 2 post one is either open or closed, showing either cold or hot (for the right bank) and nothing in between. With the left hand single terminal unit, Yes it has points, but the ratio of open verses closed gives a specific temperature reading at the gauge which varies with L.H. cyl. head water temp. This then gives the operator a real time indication of the (L.H.) engine temperature across the range of the gauge. Basically the left bank indication is a reasonable indication of the whole engine until the 2 post sender is activated, which sends the needle to hot.
Addendum:
Five minutes after this the operator sees the steam coming from under the bonnet (hood) and looks at the gauge. Then, depending on how much water has gone, the temp gauge could be reading normal, because the sender bulbs are in the air (inside the heads)
Later in the workshop whilst looking at the scored bores he declares " I always watch my gauges, religiously!" (mechanic thinks to himself "yeah right!")

[Tom Millward]

Thought I’d share a picture of our group training on Salisbury Plain. Thanks to all the fellow Carrier owners who have helped get my Carrier to the point where I can use it like this.

I have a new found respect for Carrier veterans, it was a hard weekend driving it for two days! It was an epic battle trying to keep it on the road. On the heavily cambered gravel tracks around Salisbury Plain the Carrier has a tendency to fight you quite a bit, especially if the camber suddenly changes or you hit a bump and the track tension changes!