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Oil Pressure

g8rb8t

Bronco Guru
Joined
Feb 23, 2008
Messages
1,476
My oil pressure on my stock 302 fluctuates in a pretty wide range. From what I've read through searching, as long as I'm above 10 psi per thousand RPM.

Here's my symptoms:

Engine is cold - 40 psi
Engine warm and driving - ~25-30 psi

Engine Hot and stuck in traffic (stopped in drive) - drops below 10 PSI and approaches zero. I shift into Neutral and I'm able to get it up to 10 psi. Start driving again and it returns to ~25 psi.

I've seen that some guys use a mechanical oil pressure gauge. Any links to what you've used?
 

bronko69er

EB Addict
Joined
Oct 16, 2006
Messages
4,599
Loc.
Renton, WA
Mine behaves the exact same way. 50k on a rebuild from a reputable race shop (my guess it that they left more clearance in the bearings). Running 20w-50. Cheep mechanical gauge. Just pulled the main caps about 10k ago when replacing the a rear main seal and they look great with little wear. I know it doesn't promote peace of mind but its been working fine.

How many miles on your engine?
What weight are you running?
 
OP
OP
g8rb8t

g8rb8t

Bronco Guru
Joined
Feb 23, 2008
Messages
1,476
~82,000 miles on the engine

I get the oil changed around the corner, but my guess is 10w-30. Maybe I should switch to 10w-40?
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
47,345
Check your gauge for accuracy first of all. Are the other gauges reading correctly too, as far as you know? Or could the fuel and temp gauges be reading a bit low too? If they're all a bit low, it could be either your IVR or a bad wire/connection not allowing enough current to get to the gauges.

If it is that low, that's a bit too low. Getting below 10 even at idle is not a good thing. The old idiot lights tended to come on between 4 and 6 psi, if I remember, so that's getting into the light-on territory.
Ford calls for 40 to 70 psi range, so you might have to check into a few things if it turns out you're getting near zero pressure at some point.
In that case, thicker oil at the very least.

The 40 psi is really not that bad. Even the 25 to 30 when warm and driving is lower than normal for a Bronco, but isn't so far as to really worry that much either.
It's that 10 and below that is not anywhere near normal.
Some things to think about are:
Old worn out pump. Very unusual, but not completely unheard of either.
Old worn out main, rod and especially cam bearings. Also a bit strange at only 82k, but again, not unheard of. Especially if a PO wasn't very good about changing oil regularly and/or abusive to the engine.
A galley plug leak that is not bad, but gets worse as temperature rises. I think most galley plugs will show a leak on the outside though, so not sure that's an option here. Can't remember if there are plugs in the front under the cover, but if so, one of those leaking would not show up on the outside. The rear would likely drip down and look like a rear main leak.

Not really trying to be all doom-and-gloom on you, but as low pressure goes, yours is a bit lower than advisable in the long-run.
First things first though. Check and compare your gauge to make sure you're getting a correct reading. My gut feeling though, is that even if the gauge is off, that drop at idle when it gets warm is telling you something. Mine would start up at 70 when cold and idle at 40 all day long no matter what temp. I used 20w/50 oil in mine, but that was back in the day and I prefer thinner oils now. However, maybe yours needs a little help and that thicker oil is called for again.

Good luck. Let us know what you find.

Paul
 

DirtDonk

Contributor
Bronco Guru
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Nov 3, 2003
Messages
47,345
Forgot to mention. Even though mine was rock steady at those pressures, don't worry if you hook up a mechanical gauge and get readings like a tachometer! The oil pressure is likely going up and down all the time, but due to the stock gauge's method of powering (a pulsing voltage) probably reads falsely steady when everything is working correctly.
It's the range of fluctuation that you'll want to make note of.

Paul
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
47,345
Looks like that specific one needs a separate install kit. You should be able to find one with all the goodies already included. Most will have multiple fittings so would be considered at least partially "universal"
The kit should come with a pipe-fitting that will simply screw into the hole currently used by the stock electrical sending unit. It's a small tube screwed into the side of the engine block just above and behind the fuel pump.
.
One other thing you could do that I forgot to mention, is to simply replace your stock sending unit with a new one and see what happens.
And make sure to add a ground wire/strap from the engine to the body so a good signal gets where it needs to go. A braided strap between the intake manifold bolt and the firewall is a convenient spot.

If it still reads low, then you can add the mechanical gauge permanently.

Paul
 

Explorer

Bronco Guru
Joined
Mar 2, 2008
Messages
4,390
Loc.
Raphine, Virginia
The SunPro gauges will work just fine and cheap. While they come with everything you need, I would advise getting the copper tube kit. I just hate the cheap plastic tubing that comes with ithem.
 

markperry

Bronco Guru
Joined
May 8, 2009
Messages
4,175
X3 on the copper! My Mustang's plastic line touched the header and pumped 4 quarts of oil on my driveway:cry:
 

Viperwolf1

Contributor
electron whisperer
Joined
Aug 23, 2007
Messages
24,316
You need to make sure the copper doesn't rub on anything or it will wear a hole in it. You can slip some vac tubing or wire loom over it to protect it.
 

73azbronco

Contributor
Bronco Guru
Joined
Nov 11, 2007
Messages
7,796
try some 20w-50 oil, that will most likely raise idle pressure, just change it back when it gets cold.
 

Broncobowsher

Total hack
Joined
Jun 4, 2002
Messages
34,834
The last mechanical gauge I ran I used AN braided line and a bulkhead fitting through the firewall. No worries about that!

Neat part was the AN4 was large enough that the viscoscity of the oil no longer acted as a buffer to the gauge. You could see the needle move the slightest amount very clearly. Bearings were set a little loose during the build so when the right cylinders fired you could see the oil pressure vary. Steady speed but change the load, the crank would drop a little deeper into the oil film and you could see the oil pressure change oh so slightly. With the plastic line (only ran for a short time as I didn't have all the AN stuff ready) the gauge was slow and lathergitic. It would show oil pressure but it would take a second or so for it to change to the new value. That fat AN4 was lightening quick to respond. Same gauge, just a different line feeding it.
 

fordtrucks4ever

Bronco Guru
Joined
Oct 8, 2006
Messages
1,280
Loc.
DFW
If you are close to oil change time, go to a straight 40wt, like Vavoline Racing oil. If the pressure stays way above 10psi when hot, you know the cam bearings are worn.
 

Michael Homan

Sr. Member
Joined
Feb 17, 2008
Messages
487
Loc.
Dayton,Ohio
I agree with the copper line for a pressure guage. Plastic is not good for pressure.

I had an engine that did the same thing as the above mentioned . I ended up using 20-50 oil to help with the pressure. Seems that the PO didn't install rings correctly, had some of the gaps lines up .(found after tear down for rebuild)

Good luck and keep us posted
 
OP
OP
g8rb8t

g8rb8t

Bronco Guru
Joined
Feb 23, 2008
Messages
1,476
Thanks so much for the input guys! One of the reasons I love this site...

I'll try out some of the suggestions once the work schedule lets up some and let you know what I find (could be a while because things are crazy now...)

Thanks again!
 
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