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OT: truck oil pressure

L

Lou from Wi.

Well-known Member
Our 72 Ford F100 4X4 with a 75 cab has had a new experience. Since the muffler blew out, from the condenser separating from the wire and the fork terminal, the explosion caused the oil pressure to jump from 25 lbs to 50 lbs at idle. Checked it against a new gauge,still the same pressure reading 50 lbs cold. This engine all we did many years ago was to put new main bearings in it to help and ran STP oil treatment with each oil change (yearly). The oil is the same straight 30 weight,and was changed in the fall before plowing season,so it's not new oil. We have it plugged in with the block heater, and it starts like summer time. When we redid it we added a power steering pump to it which it never had from the factory.But back to the question, after the backfire why did the oil pressure increase? I never seen it happen before,any suggestions. It is used to plow around our tractor shed,so it is tractor related.lol. Picture is of the truck, before and after, it has a 390 V-8 with points system.
LOU
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Two things come to mind: the old gauge might have been wrong, and got a hydrostatic lesson, and it could have changed the pressure regulator causing it to be able to close tighter. Jim
 
I was thinking along the same lines as Janicholson, that maybe crud buildup had partially blocked the hole in the sending unit, and the backfire jarred it loose.
BTW, Lou, can you read the date of manufacture on that truck? Not that it matters, but it looks more like a 73 or later.
 
OK, OK, so I messed up! I had overlooked the fact that you said it had a 75 cab. That answers my question. (Sorry about that!)
 
Many years ago. I bought a car from my neighbor. The oil pump kept building pressure, and blowing oil filters apart. As I remember it had something to do with the oil pressure bypass valve sticking. This was around 40 or so years ago. Don't remember what I did exactly, but I fixed the problem. Stan
 
So fill in the blank. Is it an electrical sending unit or mechanical?? If electrical then good chance it got hit and is not working as it should. To me an electrical type is as bad as an idiot light
 
Have your outside air temperatures dropped a lot recently? Start up oil pressure can vary a lot with air temperature. A 30+ degree temperature drop could cause your heavy 30 weight motor oil to thicken enough to double your start up oil pressure or even push open the bypass pressure valve. I wouldn't be too concerned about start up oil pressure, but would still monitor the oil pressure after the engine reaches full operating temperature. 5W-30 motor oil would make starting easier in below zero F temperatures.
 
old, Read below "Its a mechanical gauge and checked with a new gauge (mechanical)." I don't trust electric gauges, for water, oil, pressure or temps, always mechanical, even then its a crapshoot as to capillary tubing pastes. Had a few that blew out the paste that was inside the capillary tubing.
LOU
 
I can't imagine how the backfire would change the oil pressure.

Possibly while in the distributor the point setting changed (those distributors had a bad design on the point plate, plastic pivot for the vacuum advance would wear/break causing the point adjustment and timing to vary) and caused the idle speed to go up.

Is the running pressure high too? If so, the pressure relief plunger may be sticking. Keep a close watch on it, if it sticks closed the pressure will go up, blow the oil filter or twist the pump drive shaft off.
 
Thanks for all the replys, very good suggestions from everyone. We were just talking (son &I) about maybe the copper oil line that runs to the gauge. Maybe it had a little air pocket in it and with the backfire, it pulled the air pocket out of the line (like a brake line with air) and it is now getting full pressure without the cushion of air in the line. We can't say for sure,so any more ideas on to why is helpful.
LOU
 
Steve,
The pressure stays at 50# both cold and warm, at idle and even when pushing snow(engine warm). We don't drive on the highway with it, just around our place so going over 15mph we can't say for oil pressure. But with this happening right after the backfire is odd to say the least.We didn't adjust the points,just loosened the nut for the wire terminal on the points for the condensor,so to change the timing or points gap would be almost impossible. Thanks for the helpful reply.
LOU
 
Nope, tubing is at the back of the engine,next to the firewall and runs thru the firewall with a rubber grommet to protect from chaffing, up to the gauge. All copper tubing is not kinked or crimped. Odd for sure.
LOU
 
It is possible that it could have spun a cam or main bearing . If it spun the cam bearing it may not show up as a problem wright away . Now the main on the other hand should raise it's ugly head real fast. If i had a dollar for every FE Block Ford i have worked on over the years i could take a nice LONG vacation away from the cold and snow.
 
It might be that when that happened something in the relief valve got out of place so the relief is not letting off like it should. I remember years ago I had a car that used tons of oil as in a quart every 100 miles and I tried one of those snake oils to slow oil loss and it locked up the relief valve so the engine started to blow oil filter gaskets which ened up costing me a few hundred to fix
 
I'd suspect your old gauge was not reading right to begin with. The bourdon tube/gearing in the gauge probably had a burr or something that did not let it move to correct position. The back fire shock probably shook it loose so now it matches your comparison gauge. Some of these China built gauges are pure junk, you didn't state what make you had although they are all made in China now.
 
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