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Another Controversey????


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There have been a flurry of oil pressure questions arising recently, both on this forum and off line, and I am a little snowed, it has been my experience that if you are running a 50 or 80 lb dash gage, and the appropriate sending unit, it will read reasonably close to a mechanical oil gage used as a check and control, however it now appears that there is more to this story that I am not aware of, due to the sudden appearance of almost double the oil pressure in a friends Zephyr when he attached a mechanical gage, anyone encountered this before?? It would really be good to know, thanks in advance for guidance-

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Maybe I can clear this subject up.<BR>1) If you have a 50 lb gage installed in your car, & you have a 50 lb oil sending unit, the direct pressure gage will read approx. the same as the car gage.<BR>2) If you have a 80 lb gage installed in your car, & you have a 80 lb sending unit, the direct pressure gage will read approx. the same as the car gage.<BR>3)If you have a 50 lb gage installed in your car, & you have a 80 lb sending unit, the direct pressure gage will read higher than the car gage. <BR>Now I hope someone will agree with me. If not<BR>Please tell us all what's going on. (This infomation in to spice up this Controversey)<P> rolleyes.gif" border="0

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HEY GUY'S Here's what I found during my recent V-12 engine tests, first off I agree on the differences between the mechanical and electrical sending unit's, generally electrical sending unit's LIKE INSTRUMENTATION used in the industry for varied pressure testing is more accurate then the mechanical gages, and depends mostly on the calibration to an accurately known standard. Generally if you have a good gage [MADE IN THE USA} it will be close to [plus or minus a few percent] However there are conciderations one must concider like oil viscosity. AS for the V-12's those sending units were designed for a specific oil that was used back in the early day's. I found after using the 10W30, and the straight 30 weight there was a 10 lb differential with my high volume pump.<P>I personally recommend the electrical sending unit and replace the old one used to a new or later design for 6 volts. The kicker here is that if you change your system over to 12 volts using the old 6 volt sender your readings will not be accurate, and so you must change the sender to a 12 volt calibration standard. <P>Bill Uhouse

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Good to hear from you Bill, was hoping you would get into this, there are some variables here that in real life are very confusing. Ford used two sending units for the factory equipped dash oil pressure guages, one for the 50 lb gauges, 48-9278, and another for the 80 lb dash gauges, 41A-9278, my research indicates that all the oil pumps, including the Lincoln, were all the same, 59A-6600, fits everything, Ford Mercury and Lincoln, '32-'48. The Ford gauge had a 6 volt hot lead on the proper side of the gauge that comes on with the ignition, all pretty straight-forward, but the problem that has arisen recently is that after plumbing in a mechanical, non electrical, gauge, on the same engine at the same time, there is a vast difference in the readings, and because it is so critical in the V-12 as a guide to engine condition, I thought it worthwhile to persue this and see if some conclusions can be reached, by actual experience, rather than obtuse theory. On the test engine I am using, there was no marking on the electrical sending unit, indicating it was probally the original 50 lb unit to go with the 50 lb instrument in the '39 dash, yet the reading is almost doubled on the newly installed mechanical gauge??? A long-winded way to ask the question for sure, but it is curious, we are now attempting to get a known good 50 lb sending unit to replace the original, and see if that effects a change, beyond that, I am stumped, help

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Thank you Rolf for seeing me through my oil pressure problem...Your suggestion that I find another sending unit and see if it makes a difference answered the problem..Now I have more oil pressure than I need! Was very worried for at least a month now and now I feel fine....

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OK ROLF, I have one other point to make regarding the original gages for your Z if you use them, make sure you remove the back cover exposing the terminal screws, and check the insulating material to make sure that the terminal screws do not contact the sides of the gage, as they are required to be centered on the back of the gage. On my testing I noted that the gage was a little irratic at times do to vibration, and after removing the back I noted that the insulation was the cause at the terminal posts creating an occasional short to ground. I used small nylon washers on all the posts to prevent them from contacting the sides of the gage so I modified all my gages with the nylon washers.<P>BILL

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Now what do I do?...My oil pressure idles at around 20 and when I get going at around 35 to 40 mph it hits 50...It used to hit 20 at high speed and then I replaced the sending unit and now I am running like this...Two things...1:I shouldn't complain because high is superior to low, or 2: the new gauge reads higher than it really is, or 3: sell the car?...Thanks, Marvin ps...I used to get an idle reading of zero to 5 on the old sender....the new gquge is for a 50# pump or so the old parts guy told me.....

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Hey marvin sounds close to what it should be<BR>with your new sender.with my 80 lb pump and 10 weight oil I get 15 pounds at idle and<BR>around 45 lb's at 2,000 rpm after I calibrated the pressure relief spring in the valve chamber, this was done so I wouldn't peg my gage.<P>BILL

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thanks for the fast reply Bill....I feel better now...I suppose my old unit was misreading then...only other thing is how silent should a V-12 be and Rolf mentioned that if I drive it down when he gets back from vacation he will give a listen...Respectfully...Marvin

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