Mechanical or electric oil pressure gauge? - Ford Mustang Forum
View Poll Results: Most accurate oil pressure gauge?
Mechanical Oil pressure gauge 10 71.43%
Electric Oil pressure gauge + sending unit 4 28.57%
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post #1 of 36 (permalink) Old 03-24-2012 Thread Starter
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Mechanical or electric oil pressure gauge?

What is your opinion? Which do you find/hear/know to be more accurate?

Reason: my new 408 has an undetermined oil pressure.

My two electric gauges say that the pressure is ~8 PSI at warm idle (800 rpm), and ~35 PSI max at 2k rpm ish. Gauges are-new Autometer electric with matched sensor, and old Equus electric with matching sensor...both read within ~2 PSI of eachother.

My new Equus mechanical oil pressure gauge says that the ~8 PSI mark on the electric gauges is actually 19-20 PSI, and that the ~35 PSI mark on the electric gauges is actually 40 PSI. (I tested this after I removed the motor again, while using a drill to prime/drive the oil pump...actual max pressure is unknown using mechanical gauge)

These pressures are measured using a Melling M83, standard volume pump.I'm probably going to put an HV pump in it as my clearances are on the loose end of OK with new bearings. I'm also going to use my new mechanical oil pressure tester I bought to check things. And lastly I'm going to check the accuracy of the mechanical ones as best as I can via metered air pressure.

Just wondered what your opinions are.


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post #2 of 36 (permalink) Old 03-24-2012
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I am old school and tend to trust mechanical guages more, but if you have two electric gauges reading whithin 2psi, I would tend to side with the electric gauges. There are situations where electric gauges will vary, mainly at high temps, so I always install my mechanical gauge and take those numbers as my baseline.

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post #3 of 36 (permalink) Old 03-24-2012 Thread Starter
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I do wonder if it an issue of detail. The electric gauges have marks every 12.5 PSI while the mechanical gauge has marks every 2 PSI. it's hard to say.

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post #4 of 36 (permalink) Old 03-24-2012
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Mechanical. It's gives you an accurate reading quicker than electrical.

I know everything, just not all at once.
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post #5 of 36 (permalink) Old 03-24-2012
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this does not sound good! even with it being loose and a standard pump, it should have more pressure than that. sorry.....
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post #6 of 36 (permalink) Old 03-24-2012 Thread Starter
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5 gauges later I have 3 that say it was 20 at idle and 40ish at 2k (2 mechanical, one is diag tool, and one electric). And 2 say its low. I think the two that say its low are wrong.

I checked the mechanical gauges with metered air pressure and they are quite accurate, and the one electric gauge agrees with them. I think it's ok.

I did go ahead and put a hv pump in. Should be ok. Have an arp shaft. Its going to be harder on my cam gears...but i'll live.

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post #7 of 36 (permalink) Old 03-24-2012
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you put a HV pump in since yesterday? are these reading with your NEW hv pump?
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post #8 of 36 (permalink) Old 03-24-2012 Thread Starter
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It hasn't run with the hv pump yet. Those readings were with the new std volume pump. 20 @ idle, 40 @2k...warm and no load. Ok numbers...but we'll see what the HV pump does.

The motor is back in and preparing to run tonight.

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post #9 of 36 (permalink) Old 03-25-2012 Thread Starter
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Final results point to the motor not being any good.

Hot at 160*, where I keep it, it will idle at 13 psi with a known working/accurate mechanical gauge. Max pressure is 35.

Cold it started out at 45 psi. Within 10 minutes it was down to 17 psi at idle. After a 3/4 mile drive it was down to 13 at idle, and 35 psi under a load @ ~3,000 rpm...so I parked it.

The pressures are measured while using a new Melling M83HV, high volume, oil pump. The oil is Rotella 15w40.

Don't know what happened when the machine shop put it together...but they missed something. Now I don't have anymore time to work on it. Heck, I've put in over 50-60 hours in the car this week over spring break...just working on the motor. Now it looks like this is the final result. The dang machine shop has goofed this deal up from the start when the motor was dropped off. I let their reputation sway me into thinking they would do a good job. I should have just put it together myself.


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Sounds like the machine shop is going to get an irate visit and are going to have to eat the cost of a motor.

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I prefer mechanical gauges. They are more of a pain to install, but they are cheaper - Sometimes much cheaper.

But yes, those readings are pretty darn low

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post #12 of 36 (permalink) Old 03-26-2012 Thread Starter
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Yeah, I'm pretty bummed myself. The pressure just kept dropping and dropping, so I don't trust it a bit. I'm taking the car off the insurance policy for a while now...I don't have time to work on it much now that spring break is over. Not sure what will happen with the motor.

I'll probably leave it in long enough for me to move the car around and out of my way.


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Mine has a cheap Mech one installed on it from the PO, I hate them because the oil like has to run to the gauge & if it springs a leak it can be so messy..

Prosport offers good quality & reasonable priced gauges. I highly recommend them. I used them on my DSM cars without any issues at all. It is what I will be converting over to myself in the near future.
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post #14 of 36 (permalink) Old 03-26-2012 Thread Starter
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I prefer electric gauges as well...as long as they are accurate. I just revert to mechanical gauges to be absolutely sure.


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I see to problems here>>>> 15w40>>>>>160*

When the green light drops...
The Bullsh!t stops. :shiny:
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