Hi all,
I have Rallye gauges in our '69 Bee. The temp reading is accurate (new sender and T-stat installed), fuel gauge is not (new sender from Van's) but at least it registers and I'm getting used to where the level is at certain points. My question is on the OP sender. I used a Standard Ignition gauge sending unit (bell type) and it says 90 PSI on the sender. My oil pressure says sub 20 PSI at warm idle - it looks to be about 10 PSI, maybe a bit less at times - and I have read that I may need an 80 PSI sender. I have not had a chance to buy a test gauge yet but I guess my question is do I have an incorrect sending unit? If so, any recommendations for the correct one? I read that Autometer 2241 is the correct (or one of them) 80 PSI sender for the Rallye oil pressure gauge.
Thanks,
Mikey
The oil gauge sender is a variable resistor that changes resistance between ~72 ohms and ~79 ohms depending on the applied pressure. The original pressure range for Chrysler sending units is 0-80 psi, but the latter 1970s shifted to a 0-100 psi unit, which superseded earlier units. The lower 0-80 psi range remained the same. Some gauges, such as the 1969 Superbee read points in numbers, others just indicated low and high. The 1972 - 1980 trucks read 0-100.
A 0-90 psi unit should read close enough on a factory 1969 gauge, assuming the lower 0-80 scaling remains the same, and otherwise built correctly. Unfortunately, with modern units, this, or just the unit general performance, can be questionable, so it might not read correctly.
Getting an older NOS original or US made aftermarket unit will yield a more accurate, and reliable reading, assuming the unit is okay. The original Chrysler units read more accurately and steadily than even the older NOS aftermarket units. If you can find an original Chrysler unit, it will be stamped "INTROL", which was Chrysler's Huntsville Electronics Division.
This style unit used on the 1969 application was used in the 1964 through 1987 eight cylinder applications (some latter 1980s differed as the post type was phased in). Earlier 1960s units and late 1980s units are similar but have a post terminal instead of a spade terminal.
The following images shows an original Introl unit and the unit compared to Borg Warner units.
The original unit is a little smaller than aftermarket units, most of which are based on the same design and housing.
The following list of original and aftermarket part numbers can help in looking for an alternate unit, particularly older company units. Note that some numbers got shifted by companies across applications and as companies changed. Some of the listed numbers are current, some are obsolete.
Chrysler, 2427237, 2495222, 3488609
AMC 5751951
AC Delco C1802
Advan-tech 1N4
Airtex 1S6699
Big A 320-24
Borg Warner S330
CarQuest SAC4571 or PS59
Delco Remy 1972319 or C1802
Echlin OP-6603 (NAPA)
E-Tron PS-17
Filko OP-58X
General Switches 2466
GM 01972319
G/P OPS 31 (Guaranteed Parts, which merged with Sorensen)
Kem PS91
Mopar CH-2473
Niehoff AL-133R
P&D OPS 206
Sorensen OPS 31
Standard PS-59, PS59T
Wells PS32
WVE 1S6699
The mentioned Filko company made excellent parts and finding their NOS stuff is worthwhile. Unfortunately, they were sold to Standard Motor Products who absorbed them, and ruined it. Standard closed the last US Filko plant in 2000 and shifted it to Mexico.
As Dadsbee showed, an oil sending unit can be tested with air pressure. The output can be rigged to factory, or equivalent, gauge to read in psi, or by reading the resistance.
For measuring the resistance values of the sending unit at 0 psi (low), 40 psi (mid), and 80 psi (high), use the following numbers:
Chrysler Specification:
0 = 72 Ω
40 = 22 Ω
80 = 9 Ω
Miller Special Tool C-3826 Specification (used by Chrysler for field testing):
0 = 75 Ω +/-5% -> 71.2 - 78.8 Ω
40 = 22 Ω +/-5% -> 20.9 - 23.1 Ω
80 = 10 Ω +/-5% -> 9.5 - 10.5 Ω
Note that the numbers may vary a little more depending on the setup, but close to matching the range point is usually good enough for this.
The following image shows a quick setup for an oil pressure sending unit test. This Introl unit is reading 23.6 ohms at 40 psi, which after negating test lead and connection resistance pits it within specification.
Additional Note About Measuring Low Resistance Values
When measuring low resistances, such as the lower end of the fuel sending unit winding or the high reading of an oil sending unit, and especially for low resistance ballast resistors, account for the resistance of the test leads connected to the measuring device. This can be done by shorting the leads together, noting the resistance, and subtracting it from the measurement readings, or use the meter's relative setting (if equipped) similarly with the lead shorting, or use a meter that measures conductance and convert accordingly, or use a four-wire ohms measurement setup with the appropriate device.
Note if the test leads' resistance is higher than about 1/2 ohm, better leads should be used, to reduce error and provide simpler accounting for test leads added resistance.
