I've got a '78 Bronco with a 351M that has sat for about 13 yrs. and I decided a few months ago it needed reviving. After a new intake, carb, rebuilt tranny and transfer case, and many more mod.'s and updates I now have my baby back to the land of the living! I am experiencing one issue though and I feel it's related to the length of time the motor sat without being run. When I crank it I have excellent oil pressure and it keeps good psi for about 10 min.'s of driving then it slowly drops to about 20 psi, but stays quiet! I usually don't let it run much longer than this to see if it goes any lower cause I don't want to mess anything up. My guess is the top end of the motor has some old gummy oil clogging some of the returns and my oil is being trapped it the top end and not getting back to the pan fast enough. FYI...I did pull the pan when I had the tranny out and cleaned the screen so I don't think the problem is there. I've thought about trying some of those off the shelf engine flush products, but I've never used them before and don't want to mess up those old valve seals and things like that if I don't have to. Any suggestions and/or ideas from some of you guys with more experience than I?!?
Loosing Oil Pressure
- Thread starter 78 Bronco
- Start date
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swampthing
New member
could be as you said with the gunk build up..but it could also possibly be oil pump...or cam bearings..they will cause a loss of oil pressure
ricks73eb
Member
umm ive had more than my share of 351/400 man and 20 psi aint that bad...its not really good but with sitting around that long i wouldnt ask much more of it...
p.s my 78 f250 ran "when warmed" up 10-15 psi.. and that was with 20w50
p.s my 78 f250 ran "when warmed" up 10-15 psi.. and that was with 20w50
89Bronco58
New member
could be the sending unit also, my 79 f150 with a 400m did the same thing until i changed the oil pressure sending unit, you could try that
I've got a new manual gauge in it and I'm sure it's not the sending unit as the electrical gauge mimics the manual. I believe I failed to mention this 20-25psi is when I'm running about 45mph! That change anyone's thoughts?
89Bronco58
New member
the mph doesnt matter so much as the rpm of the mootor does, in my truck with my 456 gears at about 20 mph im screaming in first gear, but when im doing 50 in OD the rpm's are lower so the oil pressure is as well, 25 psi isnt bad for a cruising pressure, its most likely in neww of an oil pump and new screen mainly because its just old and worn out, are you able to replace it?
