Temp gauge

464Saloon
464Saloon Senior Contributor
edited November -1 in HUDSON
I think my temp gauge is reading low but I am not sure. It read what I thought was low when I first got the car then shortly after quit. I grounded it and it when to full hot so I assumed it was the sender. I purchased a new sender from Bill A and it started working again but never read much over the cold mark. I finally got around to putting a temp gauge in the radiator and let the car run for about 45 minutes. The thermostat kicked in at 160 and the car slowly climbed to 185 then held steady. The guage read just over cold as usual. Is this normal or is it reading low? If it is low, how do you correct it? Its a 54 Hornet.

Thanks,

Comments

  • mars55
    mars55 Senior Contributor
    Is your gas gage reading OK? If not, your Constant Voltage Regulator is inoperative. If your gas gage is reading OK, you have bad connection, bad cylinder block sender unit or a bad gage. Make sure that all the temperature gage connections are clean and tight and the gage mounting screws are tight. If you have a voltmeter, one of the temperature gage connections should read 5 volts to ground and the other connection should read less then 5 volts to ground.



    To check the cylinder block sender unit do the following:

    a. Submerge the unit in water up to the hexagon shoulder in a pan.

    b. Connect a ohmmeter between the terminal and the case of the unit.

    c. Heat the water to 160 degrees F.

    d. The ohmmeter should read between 25.8 to 30.8 ohms.



    If the above checks out you have a bad gage.
  • 464Saloon
    464Saloon Senior Contributor
    Thanks. The fuel gauge is right on or damn close. Connections a wiring should be OK as I just converted it to 12V and had the Instrument cluster out. Fixed cleaned and tightened everything I could find under there. The sending unit is new. Gauge works the same as before the 12V conv. I could test the sending unit, just because it is new doesn't mean it is good. Easier to pull it out and test it than the gauge. Maybe I will get lucky and it is the sending unit.
  • mars55
    mars55 Senior Contributor
    Well, if it was me I would check the 5 volts at the gage also just for grins. Easier then replacing the gage and finding out that the Constant Voltage Regulator is bad.
  • 464Saloon
    464Saloon Senior Contributor
    Well from the tests nothing is good. Sender reads 50 ohms at 75 degree water temp (tap temp) and 10 ohms at 160. I did this with an analog and a digital meter, both were the same. As for the gauge test more confusion. I have a solid 12v going into the regulator but the voltage jumps up and down anywhere from 0 to spikes over 6v. Same with the other side of the gauge. Fuel gauge gives the same readings, jumping all over the place but it reads practically spot on what is in the tank. I would think the voltage spikes would be a problem, but if the fuel gauge is working ok then I would have to assume the same applies for the temp gauge. Apparently the sender flunk the test assuming the numbers Mars 55 gave me are correct. Thought or comments?

    Thanks,
  • [Deleted User]
    [Deleted User]
    I had a similar problem some time ago in my Hornet. Really didn't do much about it and then one day it started reading where it was supposed to be. Ken U is right about the possibility of a bad thermostat spring. Mine was an NOS unit that after so many years finally "popped" open and began doing its' job reading normally, no staying closed up.
  • 464Saloon
    464Saloon Senior Contributor
    That is of course possible, but I am suspect to the sender flunking the ohms test, even though it is a new from Bill A.
  • mars55
    mars55 Senior Contributor
    464Saloon wrote:
    Well from the tests nothing is good. Sender reads 50 ohms at 75 degree water temp (tap temp) and 10 ohms at 160. I did this with an analog and a digital meter, both were the same. As for the gauge test more confusion. I have a solid 12v going into the regulator but the voltage jumps up and down anywhere from 0 to spikes over 6v. Same with the other side of the gauge. Fuel gauge gives the same readings, jumping all over the place but it reads practically spot on what is in the tank. I would think the voltage spikes would be a problem, but if the fuel gauge is working ok then I would have to assume the same applies for the temp gauge. Apparently the sender flunk the test assuming the numbers Mars 55 gave me are correct. Thought or comments?



    Thanks,



    The value I gave came from the "Hudson Body Service Manual 1948-1954".

    I think Ken U-Tex is right about the gauge being bad. This is because temp sender is reading low per the Body Manual and this should cause the guage to read high because grounding the guage causes it read full scale so lower the resistance the higher the guage reads. Try reading the 5 volts with the analog meter (This is to try an average the pulses) and see that you get.
  • 464Saloon
    464Saloon Senior Contributor
    I found that in my books too. Are you talking leaving the volymeter hooked up and reading the gauge? Be pretty tough as it is all I can do to get in there and just touch the terminals. Actually am using a paperclip to extend up to the gauge. Don't know about the earlier cars, but a 54 I/P is not the easiest thing to work with. If the gauge does turn out to be bad, I will have to pull the I/P to get it out. Just no room to pull it out the back. Can the gauge be repaired or tested somewhere?
  • mars55
    mars55 Senior Contributor
    464Saloon wrote:
    I found that in my books too. Are you talking leaving the volymeter hooked up and reading the gauge? Be pretty tough as it is all I can do to get in there and just touch the terminals. Actually am using a paperclip to extend up to the gauge. Don't know about the earlier cars, but a 54 I/P is not the easiest thing to work with. If the gauge does turn out to be bad, I will have to pull the I/P to get it out. Just no room to pull it out the back. Can the gauge be repaired or tested somewhere?



    No, what I mean is read the output of the Constant Voltage Regulator. I am curious if the Constant Voltage Regulator is really putting out 5 volts despite the fact that gas gauge is working. I know how hard it is to work on things involving the dash. You have my sympathy.

    Yes, there are people who test and repair gauges. Try Bob's Speedometer Service.



    http://www.bobsspeedometer.com/bobs/
  • 464Saloon
    464Saloon Senior Contributor
    I have a steady 12 going into the regulator and on the out side it bounces between just above 0 to about 6. It's bouncing up and down which is the same as I get on the gauge. I seem to get the same or similar readings on all the gauge posts, both fuel and temp which is why I am leaning toward the sending unit. Do you know if there is a part# for a sending unit? My parts buddy can't seem to get anywhere on it. I assume it is somewhat universal. I know it is different than in my flathead Ford as it is a larger diameter. Not being that knowledgeable on gauges and senders, I am not sure how many different resistances they are made in or thread diameters.
  • mars55
    mars55 Senior Contributor
    464Saloon wrote:
    I have a steady 12 going into the regulator and on the out side it bounces between just above 0 to about 6. It's bouncing up and down which is the same as I get on the gauge. I seem to get the same or similar readings on all the gauge posts, both fuel and temp which is why I am leaning toward the sending unit. Do you know if there is a part# for a sending unit? My parts buddy can't seem to get anywhere on it. I assume it is somewhat universal. I know it is different than in my flathead Ford as it is a larger diameter. Not being that knowledgeable on gauges and senders, I am not sure how many different resistances they are made in or thread diameters.



    You might try contacting Bob's Speedometer Service about a temp sender. They work gauges all the time. So they should famillar with temp senders.
  • 464Saloon
    464Saloon Senior Contributor
    mars55 wrote:
    You might try contacting Bob's Speedometer Service about a temp sender. They work gauges all the time. So they should famillar with temp senders.

    I just got back in town and Bill A was kind enough to send me another sender. Not sure where he gets them and they might be NOS which maybe why the first one wasn't reading to spec. I am going to check this one out today and see what it reads. Maybe if I am lucky, that will be all it is.
  • 464Saloon
    464Saloon Senior Contributor
    The saga continues, I tested thew new sending unit that Bill A sent me and at least according to the ohmeter it is worse. The first unit tested at .12 at 160 and .47 at 75. The new unit is .6 at 160 and .26 at 75. Only difference I can see in the senders is the first one has a little longer probe on it. The rest of it including the threads is exactly the same. I am going to go ahead and throw it in and see what happens. Need to see if my new fuel pump works anyway. I can't believe with all the experts on this site that I am breaking any kind of new ground here. Surely with all the cars and how long they have been around this problem has come up before. I am really starting to think it is the sending units but apparently I am the only one with this problem :confused:
  • Unknown
    Unknown
    Even when bench testing sending units, make sure the temperature is consistent or you'll get different readings.
  • 464Saloon
    464Saloon Senior Contributor
    I checked that too. I am an engineer by profession so that was also one of the things I observed as I ran the temp up and down. Here is the weird part. I went ahead and threw it back in the car and I would have thought that the reading would be lower since this last unit really is out of the range the book calls for but it actually read higher. I still think it is on the low side but I put a temp gauge in the radiator and monitored it. At 160 the gauge reads about the 1/4 mark. At 200 it reads at the middle mark which is actually to the right. Not a real informative gauge. I was able to do this because I have an electric fan. I unplugged it and let the motor get a little hotter so I could see what the gauge did. I plugged the fan back in and it settled down around 175 and that was between about a 1/4 and that next mark up. At least I know now by where the needle is pointing what my temp is.
  • mars55
    mars55 Senior Contributor
    464Saloon wrote:
    I checked that too. I am an engineer by profession so that was also one of the things I observed as I ran the temp up and down. Here is the weird part. I went ahead and threw it back in the car and I would have thought that the reading would be lower since this last unit really is out of the range the book calls for but it actually read higher. I still think it is on the low side but I put a temp gauge in the radiator and monitored it. At 160 the gauge reads about the 1/4 mark. At 200 it reads at the middle mark which is actually to the right. Not a real informative gauge. I was able to do this because I have an electric fan. I unplugged it and let the motor get a little hotter so I could see what the gauge did. I plugged the fan back in and it settled down around 175 and that was between about a 1/4 and that next mark up. At least I know now by where the needle is pointing what my temp is.



    The gauge is working as I would expect it to. The gauge needs the temp sender's resistence to be very low i.e. full scale reading with short to ground and barely moving with 10 ohms. So 1/4 scale with 6 ohms would follow. This means that gauge is worn because takes so much more current or power to operate.
  • 464Saloon
    464Saloon Senior Contributor
    It is worrysome though that there is this much variance in the sending units. Neither supposedly brand new units met the specs in the service manual. Well I am going to live with it now because everything on this car is basically old or worn out and I am worn out working on it for a while. It's time for it to behave itself for a while and just haul my butt around for a while.:cool:
  • mars55
    mars55 Senior Contributor
    Well, if it any consolation, I have found a temp sender for you. Try a NAPA

    TS6464.
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