I do 100% of my auto work/repairs (engine and transmission overhauls, axle ratio changes, etc...), but here's one that I can't explain:

My 1969 F100 has 267,000 miles on it and a 1979 302 transplanted into it. The wrecked 1979 donor car had a transplanted engine (unknown miles)but ran great so I put that engine into this truck (changed it over to truck oil pan, timing cover, etc). Three years ago on a interstate trip, I noticed that the oil pressure would rise 10-12 psi on deceleration at 50 mph, and return when either the engine speed slows down, or I step on the gas again. The engine has been doing this for 100,000 miles without any long-term drops in oil pressure (bearing wear). I use a S-W mechanical oil pressure gauge, and I am confident that it is accurate. The truck has a 4spd with 2.75 gears, so sudden engine speed changes with throttle position changes are negligible. Since oil pressure is higher with high vacuum, I removed the PCV valve, and that had absolutely no effect. I suspected a suction leak on the oil pump, so I replaced it with a new Melling H-V oil pump - that raised the oil pressure (obviously) but did not change the symptoms. The engine oil pressure hot is 20psi idling and 40psi running @ 2000 rpm. I use 30W oil year-round (same thermostat) and use a block heater for cold winter starts. I have asked several knowlegeable engine people, but no one has an explanation. I don't want to tear this engine apart just to find the cause, since it is my daily-driver. I have also seen this on a friend's high mileage 1979 302, but have not had to repair that engine yet. Anyone out there got any ideas?

Art

artjz@twindisc.com

1969 F100 2WD 302/4spd
1969 F250 4WD 440/727
1979 F250 4WD 400/C6/Trac-loc Dana60 F&R
1934 Ford sedan 392hemi/clutchflite
and also tons of 67-79 Ford truck parts

 

Art if this has been hapening for 100,000 miles, and is still running OK, what difference does it make. Hell if it has gone that far it could go another. Find something else to worry about.


John

66 F100s
In the still cool hours of the night, you can hear chevys rusting away.

 

ok picture this when you let up off the pedal at 50 your oil in the pan goes forward away from the pick up pump the pump starts to suck air oil pressure drops. you step on the gas your oil goes back to the oil pump pick up tube oil pressure rises. you have to much clearence between the pick up tube and bottom of the pan. just add another quart of oil and the oil pressure should stablize. you might try just adding 1/2 then go up from there.

 

there i go again thinking of a chevy. never the less oil pressure will climb up when you slow down because its rushing to the oil pump. then when you slow down or drive slow it will stablize back to sucking air try putting more iol in it should take care of it......... i miss read thought it was loosing oil oil presure that would happen if it was a chevy. but a ford has the oil pump up frnt my bad.

 

 

86Ford guy:
I already ruled out oil pump starvation, as when I apply the brakes without lifting on the gas, the oil pressure is rock-steady. Over-filling the engine by 1qt. doesn't change anything either. Thanks for your input anyways.

jowilker:
I know it isn't broke and I plan on running it until it either blows up or quits running. It's just something I noticed and haven't been able to answer. Don't worry, I have lots of hobbies, like my 1969 F250 4x4 and my GM KILLR (that's what the tags say) drag car. I just figured I'd run into someone with the answer.

Art

1969 F100 2WD 302/4spd
1969 F250 4WD 440/727
1979 F250 4WD 400/C6/Trac-loc Dana60 F&R
1934 Ford sedan 392hemi/clutchflite
and also tons of 67-79 Ford truck parts