Hello guys
I recently went on a 2 hour cruise (1 way) 4 hours total. And the car was running perfectly. Cruising at 70 mph most of the way. Then I noticed the oil pressure was at around 40 where normally at that speed it would be around 70+. Got me concerned so now I’m looking at the oil pressure every 2 seconds. The wage is asking me if everything is ok. I’m like yes dear everything is perfect. But inside I was worried. So I pulled over shortly after to make an excuse to full up. I checked the oil and it was full and golden brown. Like new.
When we left the gas station and continued on the highway doing 70 mph I kept looking at the oil pressure. Then it was reading 60+ then later 40 then back up to 60+.
So when we got back home after the 4 hour trip I checked to see if the wire going to the oil pressure sensor had a good connection which it did.
My question to you all is. Have any of you experienced something like this and if so what did you do about it. Oh buy the way I should tell you the motor has just over 10,000 miles on a total rebuild. And the next day I started it up and the oil pressure looked normal
If a 390 car , id say you need restrictors in the cyl head/rocker feed hole. For street engine , reduce the 5/16 hole to .090/.120 dia. Race motor down to .045
351c 2v converted to 4v. Hoping it’s not something plugging up the oil pump. Like Silicone. Can see it though as I rebuilt the motor and used very little as I heard of silicone getting into the motor and wrecking it
Hoping a instrument glitch
Oil can stack up in the valve covers. Might try adding a quart and go for a drive. The Boss 351 engine had a dipstick calibrated to show full at 6 quart system capacity, but used the same pan as the Q-code which had a system capacity of 5 quarts.
Put a mechanical oil pressure guage on it to see what is really going on. It could just be the sensor.
That’s my thinking also. Guess I’ll have to buy one
I resisted for a long time, but they aren’t that expensive and it’s well worth knowing what pressure you’ve really got. My gauge was flaky too. Engine was fine, sensor wasn’t.
Go to know
I wonder if you can swop the original with the aftermarket one
The factory gauge is very highly damped meaning it responds slowly to pressure changes. This is intentional so people don’t panic over changes in pressure. Whether you like that or not is debatable.
What is important is knowing the minimum pressure when the engine is idling. Then seeing how well it maintains pressure doing constant highway speeds. You need 10 psi at idle and about 10 psi per thousand rpm on the highway
I think it is very educational to see how a mechanical gauge and the factory gauge correspond to each other.
That’s really good information. I bought an oil pressure gauge that also has it in digital. It is supposed to be spot on with a higher end mechanical gauge.
I get that the factory gauge is slow to repond. But when your doing 70 mph and it says 40psi then a few minutes later it’s at 60+ and you never took you foot off the gas pedal. It would be nice to know why
I used the Autozone oil pressure sensor for my 351C and it matches the mechanical gauge perfectly after 11 yrs.
I agree. Just keep in mind that it may take up to 30 seconds for the gauge to settle. Still I wonder what is going on. I wonder if the sender is failing.
CANCEL YOUR AMAZON ORDER AND GET A NEW OIL SENDER!!!
I have an almost mint 390 OIL PUMP that I took out of our 69 many moons ago for a similar reason…oil pressure was dropping to zero at idle on a freshly built engine!
I hadn’t invented the internet at that time, and had little local support so was on my own!
Put in new pump…SAME DAMNED RESULTS!!! Man was I pissed at myself…but then this was my first experience with such behavior!!!
New sender spiffied it right back up in the few minutes it took to replace the sender.
Steve
I just got it and tried to install. But I noticed the sending unit that came with the gauge. The threads are smaller than the original sending unit.
The have an old sending unit I could try or try and find an adapter for the new one. Do they make those?
The mechanical gauges (mine is a Sun) come with adapters that fit most engine ports. I was wondering if your gauge came with those - apparently not. At this point, I would probably just send that one back and try a new sender unit like Fastmerc suggests.
I went to a local truck shop and it’s just a 1/8 to 1/4 fitting. The guy just gave it to me. I’ll in stall it this weekend and see how the oil pressure really is. And maybe I will be buying a new original oil pressure sensor. Although the one that is on the car is as old as the rebuild. 11,000 miles. We’ll see, I’ll let you guys know what I find
So
I installed the oil pressure sensor and when I started up the car. Cold it reads 80-82 when it’s warmed up it reading 70-73. Is that normal? Seems high. But never had a mechanical oil gauge on the car before
Seems OK but you must have either a high volume or high pressure pump on that engine. Stock (normal volume oil pump) is maybe 50 cold, 35 hot. But I would be happy with what you have.
Spec for the 70 351C was 35-60 psi at 2000 RPM. Mine runs 75 psi at cold start idle and 55 psi at warm idle with both my original and my new high volume oil pump. Agree your numbers are a bit high. But as long as they are stable, engine looks good and sensor must be bad!