For sure use a pressure gauge on it first to see if you have a real issue with pressure or if its just false gauge reading. Its a good idea to check both cold and operating temp pressure as well.
Ok, got my mechanical gauge on the car and did some testing / driving.
Cold, idle / 1200rpm, pressure was about 67#
Warm, idle / 600rpm, pressure was about 45-50#
Warm, 2500-3000rpm, pressure was about 68-72#
Seems like the mechanical gauge pretty closely matches what my dash gauge was indicating for my original sending unit after I changed the oil & filter. (That cheap replacement sending unit moved, but was reading very high all the time, which tells me it’s trash).
So, is 75# or so at high RPM something I need to worry about? That seems to put my dash gauge up close to - and maybe just inside - the high box (where it never used to go).
My 351C mech gauge measured real close to your numbers:
Cold idle /1200 rpm 75# (just above lower end of high box on dash gauge)
Warm idle / 600 rpm 55# (just slightly above middle on dash gauge)
Warm 2000-2500 rpm 70# (right at the lower end of high box on dash gauge)
If the 1970 specs Ford provided to the Automobile Manf Association are correct, your engine should run 45-65# and mine 50-70#. Yours may be slightly above spec for the 428, and it is strange that it suddenly changed. But I would be pretty happy with those numbers otherwise. Agree your new sending unit is bad.
Mike, how many quarts of oil do you put into your engine?
Has anyone found a decent oil pressure sender?
Has anyone compared the values when a sender is “cool” (<70F) to when it is hot (>170F)?
Yes, Mansfield Mustang sells NOS original ones. They work right.
Funny you should mention that. I’ve been planning on ordering one up, but I wanted to get through the mechanical gauge test first.
The sender will have an 80 or most likely 90 stamped into it. That means it should output 10 ohms at that pressure. This is what it takes to make the gauge read high. The gauge is non linear meaning to read in the middle you aren’t at 45 ohms you are about 23 or so. The sender is a transducer it simply produces a specific resistance for a given pressure.
Hook up both mechanical and factory oil pressure senders and then measure the resistance to see if the sender is accurate.
It sounds like your gauge might be a little off but you need one component working properly to troubleshoot the circuit.
The bad part is that the only time I have ever seen sudden increase in oil pressure was when a main bearing rotated blocking an oil passage. I would keep an eye on it. Get your gauge working right or mount the mechanical gauge so you can monitor this.
Got my oil pressure sensor from Autozone, and to my surprise it actually is a 90 psi unit that measured just above 20 ohms at 45 psi. Now the temp sensor they sold me was another story. It was way off, so had to go with NOS on that.
Oh, and if you don’t already have one, get one of Bill’s handy gauge testers to confirm your gauge is reading right.
Ok, got a Ford sending unit coming from Mansfield. Also put in my order for Bill’s Gauge Tester.
I’ll pick up a “T” connector so I can connect both the gauge and meter and get some comparison readings.
My original sending unit is stamped 90, and also 15 and 35.
The bad part is that the only time I have ever seen sudden increase in oil pressure was when a main bearing rotated blocking an oil passage. I would keep an eye on it. Get your gauge working right or mount the mechanical gauge so you can monitor this.
Ok, what am I keeping an eye out for? I imagine I’d be looking for the bearing to fail completely and oil pressure to drop significantly?
Got my meter tester from Bill last night and did a check of the oil pressure meter. Seems pretty ok to me!
Max is just under the max line, min is just above the min line, and mid is right in the middle.
Looking back to your first picture it looks like you were possibly hitting 80 or above
It sure does. Yet the mechanical gauge never went above 72# which would be the very lower edge of the high box. Seems smart to run both gauges for awhile as you are planning. I’ve sure been watching my oil pressure guage a lot closer now.
What’s the link for Bob’s gauge tester
I don’t know which Bob you mean but Bill has this one for sale:
https://desertclassicparts.com/product-category/gauge-testers/
Related to this topic I just noticed 1970 Service Bulletin #15. Notice on the 351C, Ford wasn’t concerned until oil pressure on a mechanical gauge went above 85 pounds, and revised the oil pressure spec on that engine upward to 35-85 psi.
And I love the fix - just go to Radio Shack and get a 5 ohm resistor and solder it in line with the gauge feed. Apparently the sensor and gauge weren’t considered to be all that closely calibrated.
Well, I think I FINALLY have it resolved. Faulty oil pressure sending unit.
I was FINALLY able to get a good one ~ Ford / Motorcraft unit. Reading matches right up with what the mechanical gauge shows, and also matches what my old unit would read too.
So, original unit had an “upper range” failure.
First parts store unit pegged to the high end immediately.
NOS Ford Sending unit never moved off the low peg.
New Ford Sending unit reads correctly.
Third time’s the charm, eh?
Congratulations! Glad it wasn’t anything wrong with the big block!