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post #1 of (permalink) Old 02-28-2000, 05:44 PM
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Phony Oil Pressure Gauge

OK, so I was slow on this one. I knew Ford trucks of the late 80's had a oil pressure switch, instead of a true sender, to work the gauge. This is a phony setup, if the oil pressure is high enough to close the switch, the "gauge" reads mid-range. Just found (duh!) that my '94 has the same setup, and it checks out with the book.
So here's my question - Is there a true oil pressure sender that I can buy, that will make the gauge work like a real gauge? Or was the gauge designed only to work with the phony sender (switch)?
Has anybody tried to straighten this out?
TIA

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post #2 of (permalink) Old 02-28-2000, 07:55 PM
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Re: Phony Oil Pressure Gauge

Gauge only works with switch, I know it sucks bad. My 89 Bronco (same setup) the gauge started to fluxuate while driving, I panicked, thought my engine was going south.
I ended up 't' ing off the original sending unit and installing a manual gauge in the dash. After that I found out that my engine was fine, no flux in pressure even though the dash gauge "danced" around.
Even the 2001 SuperCrew and all 2000's are setup the same way


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post #3 of (permalink) Old 02-28-2000, 10:02 PM
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Re: Phony Oil Pressure Gauge

Yep, that damn phony setup will have you close to a heart attack. My sending unit desided to start acting as if I had really low oil pressure. So, I desided to put in a new Melling Performance High Pressure Oil Pump for my 5.0 Bronco. And when I started up the engine I had good oil pressure, until I drove it for a few miles, then NO OIL PRESSURE. Oh [censored]!
When under the vehicle to make sure the wire was still on the pressure sending unit, and then checked the gauge again and the pressure was fine. So, it was the damn sending unit that was flawed.
Now, I am going to do like Rockcrawler and put in a manual oil guage in the dash. Was going to put in an electric one, but found out the sending unit won't clear the Oil Filter. Boy, what a headache.

So, the bottom line is put in a manual oil pressure guage and be on the safe side.

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post #4 of (permalink) Old 02-29-2000, 02:38 AM
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Re: Oil pressure readings

I also insalled a mechanical (not electrical) auto meter oil pressure guage in my 87 Bronco (351). I was wondering what it should read at idle when the engine is warm. When I first start my truck, it will be around 60 PSI at idle. Warm engine at idle is around 17-20 PSI. Driving with the engine warm at 65 MPH (at 2900 RPM's) its at 30 PSI. After an hour of highway driving, it drops as low as 13 PSI (in drive but not moving).
I heard once that as long as you have 10 PSI per 1000 RPM's your OK, is this true??
Thanks for your time.
Tom

post #5 of (permalink) Old 02-29-2000, 07:51 PM
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Re: Oil pressure readings

BroncoMan..... Thats what mine reads at idle, 15-20 after warmed up. never had any problems. normal, 30psi at 65mph good.

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post #6 of (permalink) Old 03-02-2000, 08:11 AM
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Re: Oil pressure readings

rockcrawler: I was hoping there was a sender that could work the original gauge in the dash. I guess I wasn't looking at it very often since it took this long to realize it is a phony. Still think it should be a real one. Dodge puts real ones in. And Ford used to.
Thanks to all for responding.

post #7 of (permalink) Old 06-10-2000, 10:02 AM
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Re: Oil pressure readings

I was able to put in a different sender to make the factory gauge work, here's what I did. I realized the original switch was either go or no go on the pressure, with the engine off, it was open, and with pressure applied it was about 30 ohms. The resistance doesn't change, from 5 PSI and up. I got a sender from Autozone for a 87 mustang I (I think that was the application), anyway you can tell it's different, just by the size of it. The one you want is about 2 1/2" in diameter and about 3" tall. Obviously it wouldn't fit in the original location, so I relocated it on to the fender well. The hole in the block is 1/8 NPT, so I plumbed it in stainless by using the following: 1/8 MNPT to 1/4" Swagelock, 1/4 stainless tubing from the block to the sender ( I added some coils to the tubing so it would flex and not break- kind of like the brake lines off the master cylinder), 1/4 Swage to 1/8 FNPT, and sender. The sender mounted to the fender well with a screw and a hose clamp. I used a piece of rubber between the sender and the hose clamp for a cushion, so as not to damage the sender. Now for the electronics part:

I wasn't sure how the dash gage would respond to a varying input resistance, so I plotted it out using some different resistors I had laying around (you could use a decade box- but I didn't have one). My gage wasn't quite linear, but it was close enough. Resistance is from sender wire to ground. Around 63 ohms the gage was low redline, 40- low normal, 20- mid scale, and and 10- high normal. Then I measured the sender that I had purchased by hooking up to a hand pump and Teed in a mechanical pressure gage. The pressure input was slowly increased as I measured the resistanse of the sender, and plotted that curve out. I wanted 5 PSI to be redline, 10 PSI low normal, and 30 PSI midrange. After a little math, I added a 20 ohm resistor in series with the sender wire, and hooked it up to the sender. Using the hand pump again, I slowly added pressure, and verified the dash gage responded, it did, so I hooked it up to the motor, and have been using this setup for 3 years without problems.

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post #8 of (permalink) Old 06-10-2000, 06:13 PM
 
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Re: Oil pressure readings

WOW!!![img]/wwwthreads_images/icons/shocked.gif[/img]

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post #9 of (permalink) Old 06-10-2000, 07:13 PM
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Re: Oil pressure readings

I know it seems like alot of work, but it only took about 6 hours. [img]/wwwthreads_images/icons/smile.gif[/img] I wanted it right for my own piece of mind.

Maverick [img]/wwwthreads_images/icons/smile.gif[/img]
post #10 of (permalink) Old 06-11-2000, 07:32 AM
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Re: Oil pressure readings

I agree that there is no room for most aftermarket sending units on the stock small blocks. I personally like knowing what my pressure is instead of it just being OK in the middle all the time. I had a manual gauge and have broken the hose once, repaired it and decided that electronic was for me. I bought an Intellitronix gauge (digital-green too) and sender (looks like a small oil filter) from Summit Racing. The whole package cost about $80, but, now I know exactly what my pressure is all the time. When the sender would not fit I called Summit who gave me the 800 number of Intellitronix (also in Ohio). I called them, talked to a tech, and he called me back the next morning with the fix. He said that adding a 45 degree pipe fitting as an adapter would be fine. This re-angled the whole assembly for just the right fit, the pressure is accurate and comparable to manual style, and only cost about a 1.50 for a stainless fitting-use some teflon tape for a good seal. Just another option. Laters.

NUFF SAID
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