I have a 1984 F150. Originally the truck had a 302 and a C6 transmission according to the door sticker. After I bought the truck the engine ate a ring and I found that the tranmission had been replaced with an AOD transmission. I had the engine replaced with a rebuilt 351. I began noticing the in-dash oil pressure gauge kept staying on the low side so I installed a manual gauge. This leads me to two questions:

1. I have read that your oil pressure should be 10psi for every 1000 RPMs. I have also read that alot of people on this site have their oil pressure around 30-40 psi when driving on the highway. My truck at 55mph is only running around 1800 RPM and my oil pressure is around 17 - 19psi. Is this okay? When the truck first cranks up cold it stays around 40psi until warmed up which I understand is normal. I use 5w 30 oil. Even at lower RPMs it is dead on around 10psi / 1000 RPMs. I don't hear any loud noises coming from the engine at any RPM.

2. Since the the truck was originally installed with a C6 transmission I do not have the option on the shifter for OD. Right now I only have P N R D 2 1. To get into overdrive I have found that I have to get the truck up to about 57Mph and around 2500RPMs and then just barely let off of the gas and the transmission will drop into overdrive. It doesn't make any grinding noises, just a slight jerking motion when going into gear. To get out of overdrive I have to slow down to around 37 Mph and the truck again sort of jerks into a lower gear, but again without any grinding noise. Any concerns there? My main concern is I can't tow anything over 50 Mph or else my RPMs go through the roof since it is right on the verge of trying to go into OD. Any way of turning off OD without having it on the dash gear selector?

 

Sounds from your description, you have 10# per 1000 rpm.

I would never use 5w30 oil in an engine that old.
It was never meant to use 5w30, even when new.
Summer heat will make things even worse with thin oil like that.
I would use at least 10w30 in winter and 10w40 in summer.
That will raise your oil pressure slightly in itself.
But it will also protect your engine too.
Check your truck manuals and such...
It was NEVER meant to use such thin oil.
Dave

Edit:
DUH!
I read your questions after just skimming over your first paragraph.
Sorry.
If you got an AOD, the transmission function is controlled by a cable.
From what I hear, if the cable is misadjusted it can cause all sorts of trouble like you mention.
Also can kill the tranny.
So I would get a manual to find out how the TV cable is adjusted.

I stand behind my oil weight comments.

Also, I need to mention that Ford always posts in their trucks (often on the visor) that they should never tow in overdrive.
Don't exactly know how you do that with an AOD and no button...
Maybe the tranny has a way to sense it and keeps out of OD.

 

how is a 5w-30 any different from 10w-30 other than the winter weight of 5. it still has the summer protection of 30 weight. maybe the guy lives in a cold climate. i would stick to the 5w-30 if thats what has always been run in the engine. i seriously dont believe in changing weights of my engine oil by the seasons, just run the same oil weight year round.

 

the AOD is P R N OD D 1
the c6 is P R N D 2 1

ur D is OD
ur 2 is D
ur 1 is 1

 

I do live in the deep south so the thicker oil may help. Thanks. Back to my main question though, Am I okay at 17psi when running 55mph as long as my RPMs are around 1700 to 1900? Is it true that no matter how low your oil pressure gets as long as it is 10psi per 1000 rpms you are okay?

 

Sounds about right to me, or at least not bad. I don't have much to compare it to though, seeing as my truck is a 95 and the oil gauge is basically useless.

I would definitely go to a thicker oil though. It's been a while since I've looked, but I'm pretty sure my manual says to only use 5W30 when below 65F. Living in FL where it rarely gets cold, I usually run 20W50 or 15W40.

 

I don't care that they supposedly have the same hot rating, there is a difference.
Also, if you noticed, I said 10/30 in winter only, 10/40 in summer.
I use 20/50 or 15/40 since I am in the south.

I don't know about your situation, but it is a very good idea to change weights with the weather.
5/30 is too thin for hot weather use in a truck engine and oil like 20/50 can be too thick to flow on startup in winter.
Personally, I would never run 5/30 in anything.
The only reason car companies recommend it on new vehicles is to help make EPA rules. It has nothing to do with protecting your engine.
(I used to be in the oil business...)

Edit 1:
Oh yeah, I need to point out that the first number is cold flow and second is hot flow.
It is NOT a season rating.
No matter what the temp is outside, the first number is what the oil is supposed to flow when you first start the engine, then the second number is what is supposed to flow when the engine is at operating temp... No matter summer or winter.
Now, thin oil is thin oil, and 5/30 will be thinner than 10/30 even when hot, regardless of the same operating temp rating.


Edit 2
If an engine is running low oil pressures over time, you need to run a thicker oil.
A thinner oil will run a thin cushion between metal parts that are wearing and becoming futher and further apart. What is then happening is the oil is running out of the bearing surfaces quicker, almost like a leak, and the last parts in the system to get oil will get less and less as the engine wears. A thicker oil will take up these clearances some and stay in the circuit longer, as seen by more pressure reaching the gauge.
IMO though, if 5/30 can't run decent pressure, then going to 10/30 is not going to help.
That engine probably needs 10/40 winter and 20/50 summer.

 

I will take your advice and try some 20W50 for the next few months. It won't start getting cold (around 50) here (South AL) until probably January.