Re: 1956 Packard 400 Fuel guage & sending unit
Posted by HH56 On 2023/8/7 16:13:51
As I recall sender position doesn't really matter much but if there is clearance and no locating notch on the tank then if mounted so the float goes toward the side of the tank that tends to minimize the gauge changing if the float wants to move up and down as gas sloshes when doing ordinary stop and go driving. The 51-6 gauges are bimetal heater type so do not move very fast. Unlike the earlier magnetic gauges, later gauge changing is probably a non issue.
Unless you have an opening cut in the trunk floor to easily remove the sender it is a bit late and hard to check for proper sender operation. If you do drop the tank and remove the sender, using an ohmmeter connected between the terminal and the sender mounting flange you should read approximately 70-75 ohms at the empty end and 10 ohms at the full end.
The instrument voltage regulator works the temp, oil, and fuel gauges. If none of the other gauges are having problems it should be OK. To test the fuel gauge will require the use of a known good sender. From 1951 on all the gauges use senders with the same electrical specs and work the same way so that testing procedure is detailed on page 55 in the 1951 service counselor Vol 24 #12 Just grounding the sender wire will do a rudimentary test in that as soon as the wire from the sender touches ground the gauge will start to rise to the full end. Do not leave the wire grounded any longer than it takes to verify the gauge needle reaches full.
One other consideration is that a pinhole in the fuel pickup line inside the tank can mimic an empty tank. If the tank was actually empty and took about 20 gallons to fill then the sender or gauge is an issue but if it only took around 10 gallons there is a possibility of a pinhole and the pump started sucking air.
The two places pinholes have been known to occur are noted in this photo Ross provided showing the tank inside.
Attach file:
51-6 inside pinhole locations copy.jpg (131.28 KB)
Unless you have an opening cut in the trunk floor to easily remove the sender it is a bit late and hard to check for proper sender operation. If you do drop the tank and remove the sender, using an ohmmeter connected between the terminal and the sender mounting flange you should read approximately 70-75 ohms at the empty end and 10 ohms at the full end.
The instrument voltage regulator works the temp, oil, and fuel gauges. If none of the other gauges are having problems it should be OK. To test the fuel gauge will require the use of a known good sender. From 1951 on all the gauges use senders with the same electrical specs and work the same way so that testing procedure is detailed on page 55 in the 1951 service counselor Vol 24 #12 Just grounding the sender wire will do a rudimentary test in that as soon as the wire from the sender touches ground the gauge will start to rise to the full end. Do not leave the wire grounded any longer than it takes to verify the gauge needle reaches full.
One other consideration is that a pinhole in the fuel pickup line inside the tank can mimic an empty tank. If the tank was actually empty and took about 20 gallons to fill then the sender or gauge is an issue but if it only took around 10 gallons there is a possibility of a pinhole and the pump started sucking air.
The two places pinholes have been known to occur are noted in this photo Ross provided showing the tank inside.
Attach file:
51-6 inside pinhole locations copy.jpg (131.28 KB)
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