351M Oil Pressure

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Dec 18, 2002 | 01:17 PM

78RangerXLT

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351M Oil Pressure

Hey guys, I have a 1978 f150 with a 351M that i just recently installed in there to replace the old one. The oil pressure is confusing me though...I put a new sending unit on it when i replaced the engine and notice that when it is colder or the engine is colder the oil pressure runs on the very high side of normal and after warming up it runs right in the middle...After cruisin on the interstate for about 15 minutes @75mph when i stop the idle is a bit rougher and the oil pressure rides on the low side of the normal line at an idle, but i have no power loss and otherwise runs great. Should I be concerned? for the record i use Motorcraft 10w-40 weight oil with a Morotcraft filter.

Dec 18, 2002 | 01:27 PM

79_250RangerLariat

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351M Oil Pressure

How many miles are on your "new" engine? The best way to see what your oil pressure is doing is put a gauge on it. The 351M and 400's are prone to early main and rod bearing wear causing low oil pressure. As far as your rough idle when was your last tune up? Something may be "breaking down" after it gets hot.

79 250 Ranger Lariat 4wd 400 C6 3.55's 33x12.50 16.5's
78 Bronco Custom 4wd 400 C-6 3.50's 31 10.5 15's
66 Mustang Coupe Sports sprint 200 c-4 cruise o matic 3.00's
99 Grand Prix GT 230 ft/lbs torque out of a non turbo'd 6 cyl hehe

Dec 18, 2002 | 10:28 PM

78RangerXLT

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351M Oil Pressure

there is 15,000 miles on my new engine and my last tune up was last week.

Dec 18, 2002 | 11:53 PM

Mr Brownsnake

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351M Oil Pressure

I dont really no much about the rough idle. but I have a manual oil pressure gage on my 77 f-250 with a 351- m and runs at about 50 pds when cold. after it warms up it drops to about 25 to 30 pds when driving. at an idle it even drops to ten with no lifter noise or nothing so i would not worry about it. i herd it is common for these to drop pressure.

Dec 31, 2002 | 08:25 PM

maynard2

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From: Milverton Canada

351M Oil Pressure

I just rebuilt my 351m and the oil pressure cold rides at about 75psi then as the engine warms up to 200-210f the pressure slowly drops to 20-25psi and at idle in gear it sits at about 4-5psi. We replaced the oil pump, checked all plugs all bearing clearances, everthing, and it's still the same. All the clearances where within the limits. There is also a new cam and bearings too. The motor purr's like a kitten and does'nt make any noises so I guess just keep drive'n till she finally blows. The oil pressure problems I've been hearing about now that i've been looking seem really common for these engines. Somebody somewhere out there must have figured it out, if so please drop me a line day or night and i'll sleep alot better. Good luck with your 351m hopefully she gives you lots of miles. Later.
Chris

Jan 2, 2003 | 08:42 PM

Polkat

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351M Oil Pressure

Jun 7, 2004 | 11:50 PM

stuck-in-AK

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My truck with a 390, and my budies bronco has a 351. My oil preesure has been doing ever since i've had my 390 rebuilt so about 4 years When I was in arizona I just ran a thicker oil bUT since i,m in alaska and it gets about 30 below I put some lucas oil in So I really wont worry I changed the oil pump sending unit and I put about 60000 miles on it