Packard Forum Index » Post-War (1946-54)

Hello, can anyone tell me what the correct ohm readings would be for a coolant temperature sending unit on my 1948, 327? I want to make sure that it is the sending unit that is my problem before I buy a new one. I tried searching the site to no avail.

48-50 models use a different gauge system than other years so fuel, oil, and temp senders do not have a specific resistance value. While other years use a changing resistance, the 48-50 models use a pulsing contact which is either on or off and connects straight to ground. The frequency and duration of the pulse depends on how the temp, pressure, or fuel level biases the bimetal strip in the sender to change the length of time the heater needs to change the temperature of the bimetal and make it work the contact. Some Ford products also used this same gauge system.

Here is a bit from an old Motor's Manual explaining the 48-50 system operation and also an oscilloscope photo of a gauge with fuel sender showing the pulsing action. Ford products mostly used two senders but Packard used a single temp sender so needs the single terminal sender. If you need a new sender, BDeB has said 40-55 Ford senders will work electrically and Dennis Carpenter Ford Parts has made repros. I don't know if anyone has tried the Ford sender in their Packard so do not know if the size thread Ford used for their head port is the same. If you do need a new sender and decide to try the Ford version please let us know if it fits.

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  48-50 K-S temp ga.jpg (570.16 KB)


  22-23 bimetal sender action.jpg (167.91 KB)

That is good to know, thanks. I will go ahead and order one of those sending units. I did just a quick measurement of the treads on mine and they show .64" the part sold by Dennis-Carpenter says it is a 3/8 NPT threading so I think it should work.
I will let y'all know my findings once the part is installed.

The reason I believe it is the sending unit is because the gauge reads as if the car is overheating once it gets warmed up, however a thermometer says otherwise. If this is an obvious sign that I need the gauge fixed please let me know.

UPDATE
I have received the new sending unit from Dennis-Carpenter. The threads matched up perfectly and it physically fits, only now instead of the reading going from cold to all the way hot. it starts at cold and goes past that to even colder as the engine warms up. Is there some wire that I need to change around to get this unit to function as the original once did?
Could this possibly be caused by a short? I would'nt think so, however my wiring is very old and crumbly.

Would you mind emailing Carpenter and seeing what the ohm range of that sender is?

The 48-50 need either the original bimetallic design, or one that reads 20 ohms cold and 100+ ohms hot. Idk if these really even exist.

Since yours reads cold when cold, but colder when hot, maybe it's a different ohm range. And also backwards.

I'm working on something in another thread that is an electrical signal adapter to convert between an otherwise-incompatible sender and gauge.
https://packardinfo.com/xoops/html/modules/newbb/viewtopic.php?topic_id=28197

I donot know anything about the temp sensor but I had issues with the fuel guage-I sent it to wolf to repair-it took them 2x to fix it but they were successful. It works I am told on the bimetal system. Good luck

Quote:
Email sent, awaiting reply.

If they followed the original specs there would not be a resistance range but you would probably get a reading thru the heater itself. I am wondering if they might have done something in their repro sender similar to what HPH is contemplating with his external circuit.

It is possible the Ford gauge works the same way electrically but is constructed so it mechanically works in the opposite direction. I have no idea whether Fords park at the low or high end but if they park high then instead of the bimetal heating and bending to raise the needle as is done with the K-S gauges Packard used, the Ford gauge would bend and lower the needle. I suppose it is also feasible the Ford gauge is the same but mounted upside down as compared to Packard. The gauge would work the same but needle position at rest and C - H lettering would need to be different.

Again, we have run into the issue that even though they might work electrically, without someone previously trying the Ford senders and reporting back it is unknown if they are a direct replacement. If other wiring issues are ruled out and the gauge is still backwards it seems like perhaps we have an initial NO as to compatibility and it's back to square 1 on finding a replacement or a workaround.

Let's recall that the SC and Howard's images of the sender manuals make it clear that while all 3 senders are constructed with the same TYPE of mechanism and also the same "ohm ranges", the water temperature sender and gauge are backwards, that the open circuit position on the water temp gauge reads high.

I suspect that, per DP's testing, a 20–120 ohm sender would be about right. However, it would have to read 20 ohms COLD and 120 ohms HOT which is the opposite of how pretty much every sender works, since most gauges read down the scale with an open circuit.

I really wonder whether your could disassemble and physically reverse the construction of the temp gauge to make it "normal". Unfortunately I neither have a gauge of that era myself nor even know anyone with a 48-50 car in the Pittsburgh area so I can't personally test this.

OOPS!
I have made a silly mistake.
Today while I was working on my car I noticed that my gauge does in fact go from cold to hot as it warms up.
still have a small problem as it still went up past the middle mark-albeit much slower than with the old sending unit. I used my thermometer and it showed that the engine was infact warmer than it should have been. I believe that the new sending unit from Dennis Carpenter is working as a viable replacement. I just want to verify by taking a temperature reading when my needle is in the middle and comparing it to someone else who has a known good system.

Can someone tell me what temperature their engine stays at after it warms up at idle and where your needle sits at that temperature (I have a 1948 327)
once I verify that this new sending unit works as a replacement I will feel confident adding it to the Parts Cross-Reference.