Sending Unit again

[marfulle]

I bought a new tank for my 48 plymouth. It has the 6 cylinder motor with 12 volts to it. The original sending unit is bad and need to get a new one. I have called a couple of shops up and they need to know what the ohms (2 or 4)of the original gauge is to match it up. Can someone shead some light on this issue. Does the now 12 volt system effect the outcome? The only other option I have is to buy an after market gauge and mount it.

Eric

[Norm's Coupe]

The sending unit doesn't care if the car is 6 volts or 12 volts. You can get a new sending unit from Atwater Kent. Contact information is in the reference or links section of the main P15-D24 site. Just tell them you want one for a 48 Plymouth. You see them on ebay sometimes too.

[marfulle]

Norm,

I called that guy you referred me to and he said that 6 and 12 volts do make a difference. The sending units that they put into the tanks have heat to them to run the float. The heat is low, but if you run a 12 volt system through the sending unit that is designed for 6 volts it can make for an interesting day (Boom). You need to split a 12 volt system in order to run the correct sending unit.

[Norm's Coupe]

Norm,

I called that guy you referred me to and he said that 6 and 12 volts do make a difference. The sending units that they put into the tanks have heat to them to run the float. The heat is low, but if you run a 12 volt system through the sending unit that is designed for 6 volts it can make for an interesting day (Boom). You need to split a 12 volt system in order to run the correct sending unit.

In that case I guess Don Coatney and many more people in the hobby should not be here today, or least their cars shouldn't.

[marfulle]

Norm, I understand that he probably went a little overboard and I am just repeating what he said to me. I am going to get the sending unit and split the volts right before the unit inself. That should do the trick. Thank you for the referral.

[Norm's Coupe]

That's ok. The only reason I said what I did was because there are lots of guys who have switched without splitting it. At least several on the board that I know of from conversations on the forum, plus a few local old Ford people I know. If what the guy at Atwater said was 100% someone would have had a problem by now. Think Don said he's put over 10,000 miles on his car that way.

The sender does produce a small amount of heat. However, so do the senders in newer cars and of which some of them are submerged in gas to help keep them cool. Had a Dodge dealer tell me once in the 90's to make sure I didn't let the gas tank get too low. If I did the sender would overheat and burnout. Not meaning the tank would explode though, just that the sender would burn it self out because it would overheat.

[Young Ed]

Norm I think its the fuel pumps that overheat and burnout in the modern cars. Let me tell you not a fun job to change one of those!

[Norm's Coupe]

Norm I think its the fuel pumps that overheat and burnout in the modern cars. Let me tell you not a fun job to change one of those!

Ed, I stand corrected. You are right. Had one burn out on me on my 90 Caravan when I owned it. And like you said, that's not easy to change. I didn't change mine myself, had it done. However, you have to drain the tank and drop it to change that pump.

Marfulle,

Did the guy at Atwater say you had to split the wires at the sender, or under the dash? Most people have to add resistors under the dash for the gages to work right after converting to 12 volts from 6 volts. So.......since the gage is then only getting 6 volts and both wires for the sender are attached to that, the sender will only get 6 volts. That may be why people who have switched over have never had a problem with exploding gas tanks.

[Plymouthy Adams]

in the case of the two wire sending unit..the guage has the 5 volt regualtor contacts built into it and will and does open at 5 volts be it powered by 12 volts or 6 volts..it is the speed of the contacts opening that is affected by the higher voltage..

[Norm's Coupe]

in the case of the two wire sending unit..the guage has the 5 volt regualtor contacts built into it and will and does open at 5 volts be it powered by 12 volts or 6 volts..it is the speed of the contacts opening that is affected by the higher voltage..

So Tim, in short you are saying that the gage needle will simply rise to the occasion faster. In which case you need do nothing with resistors, etc., right.

[Plymouthy Adams]

many people are running their's that way...using a CVR with this unit would be trick at best due to the fact that the CVR is doing the exact same thing the guage points are doing..only difference really is that the 12 CVR bi-metal strip is more slower and more in line to original 6 volt operation..remember, when the cars went to 12 volts..the guages did not...IF you wish to power yur unit from 12 and supply a constant 6.8-7.2 volts more in line to OEM battery..then building a voltage regulator would be you best best..the one I have pictured is very small in size..totally adjustable and constant up to 12 amp out, surging to 15 amp...I pulled this off the internet somewhere and built my own...

[47heaven]

in the case of the two wire sending unit..the guage has the 5 volt regualtor contacts built into it and will and does open at 5 volts be it powered by 12 volts or 6 volts..it is the speed of the contacts opening that is affected by the higher voltage..

Well then how come when I tried to connect the guage to a 12v battery it started to smoke?. Back before I had sent the gauge and sending unit to you to have fixed, I remember telling you about that and you asked me how long I had let it smoke for, which wasn't long. You said, before I sent it to you, that I may have fried it. Can't remember if I had or not.

[Plymouthy Adams]

Here is what I built years ago for my Sunbeam Tiger as the Smiths CVR is like a impossibility to find. This is solid state...will allow those converted to 12 volt system to drop your voltage to that of a 6 volt battery..the choice of the 6.2 or 6.8 zener sis your choice..remember this will feed the voltage input of the guage itself..do not connect to post 1 or 2 The voltage regulator of the guage STILL MUST be operational even for this...This has been in my Sunbeam for years..works very well for myself...

pardon the quick paint drawing...am not an artist...

[oldmopar]

Here is what I built years ago for my Sunbeam Tiger as the Smiths CVR is like a impossibility to find. This is solid state...will allow those converted to 12 volt system to drop your voltage to that of a 6 volt battery..the choice of the 6.2 or 6.8 zener sis your choice..remember this will feed the voltage input of the guage itself..do not connect to post 1 or 2 The voltage regulator of the guage STILL MUST be operational even for this...This has been in my Sunbeam for years..works very well for myself...

pardon the quick paint drawing...am not an artist...

Tim, a question do you know what the resistor would be to drop it to 5 volts. Some of the 60's-70's mopers although they had 12v used 5v for the gas gauge.

Ed

[Plymouthy Adams]

actually the voltage should be higher than 5 volts for this unit..that is why you can use the 6.2 or 6.8 zener diode...this will simulate the actual battery and charging system of your car and allow the 5 volt regulator built into the dual wire guage to do its job...so if in reality if you wish to have 5 volt out, use a 5 volt zener..the resistor is dropping current and the 2 watts should be enough to handle the load...will get a tad warm but not hot...

I never had to repair a 60-70 Mopar guage in my life but as a mechanic for Ford a couple years we fought the CVR on a daily bases..they were a tad flakey..and being a bi-metal heater type I am thinking they also would cut out (contact open) about 5.8 to 7.2 volts..therefore the slight difference in tank/temp reading car to car..the same CVR powered both circuit, temp and fuel...