Crabby oil pressure problem

[schwinger]

Never experienced this before but im having a wacky *** oil pressure problem on a newly rebuilt magnum 318 that I put in my 72 dart. oil pressure when cold is at 65 psi when revved up which I believe is normal, like to see it higher but yea, and idle at 20 and when warmed up idle pressure is close to 15 at 700 rpms. Now when I drive it (city driving) pretty much staying under 3000 rpms pressure goes low when I accelerate for a brief moment from 5 to 10 psi then goes up but when I decelerate it increases 5 to 10 psi then goes down while decelerating. What would cause that. On the hwy at cruising speeds pressure stays a steady 55 psi but notice a slight increase in pressure when I decelerate for a brief moment. Engine is .020 over, standard crank that was in great shape and still within specs, reground late 80s cam that has the long snout, rebuilt magnum heads, Dakota 5 speed on back, bearing clearences were within specs. engine kit that I rebuilt the engine was factory kit but oil pump tho was a kmj which was the first time I ever heard of them which I took apart, had some shitty casting flash under the gears which I cleared up but clearances were good. Running 15w 40 Rotella

 

[teringer]

sounds like your a quart low in stop and go traffic.

 

[schwinger]

my oil level is on the full mark which I thought that was the problem to.

 

[nm9stheham]

So the pressure goes up momentarily when you decel, and drops a bit for a moment or 2 when you accel? The one theme here is that pressure is varying the opposite of flow when you transition RPM's.

Just thinking out loud: What do you have for an oil filter and any filter adapter or oil cooler? When you back off the RPM's, the pump pressure and flow will decrease, but if the filter is crappy, then the pressure drop across the filter will drop with the flow. The pressure sensor is after the filter so if you had an abnormal variation in pressure vs flow in the filter, or its adapter/coolers/etc., you might see the type of odd behavior described.

The other thing that comes to mind is the rod bearing and rod side clearances being way out of whack.

BTW, was the square drive plug in the block under the oil filter adapter if that is what you are using?

Are the head & block Magnum?

 

[schwinger]

I'm running STP S8A which I always run and never had problems with. No oil filter adapter or cooler and the plug was under the filter which I double checked as well as all plugs before I closed everything up. And yes head and block is magnum. Engine is carbed, has la timing cover.

 

[Dubob]

What gauge are you measuring by? Have you plumbed in a known good mechanical? Also filter design can change over time or you can get one that's defective. The only other thought I have is what was the crank shaft thrust clearance?

 

[diymirage]

could be there is a rod bearing going out
when your on it, the rods are pushing down and there are tight clearances
when you let of, the rods begin to float, the clearances open up and oil pressure drops

 

[jdehart]

I've seen cam bearings do that.cam floating around.

 

[schwinger]

I have a sun pro mechanical gauged hooked up and worked good even with the previous engine. thrust bearing clearance was at .006. I guess I can try another filter design. Possibly the magnums take different filter. Not sure about that but I already did the 500 mile break in with the same type STP oil filter and still had the same problem.

could be there is a rod bearing going out
when your on it, the rods are pushing down and there are tight clearances
when you let of, the rods begin to float, the clearances open up and oil pressure drops

Hope it's not that but the pressure Rises tho momentarily when I let off then decreases instead of decreasing instantly so I figure if it was under load with tighter clearances shouldn't pressure increase under load? The cam went in a little tight tho, when I installed it but was able to turn it by hand. Just took a little more effort.

 

[krazykuda]

Are there oil galley plugs under the camshaft thrust plate???

Are you running main bearing bolts or the studs??? The nut for the stud can hold the oil pump up and prevent it from sealing...

 

[diymirage]

I'm not sure
but i do know that when i had a rod bearing go my pressure would drop a few pounds when i got on it

 

[schwinger]

Ok must of misread it. I made sure the plugs were under the cam thrust plate and I'm running bolts on it instead of studs.

 

[jdehart]

Did you change cam bearings

 

[schwinger]

New ones were installed. I'm gona try a different filter today see if that works.

 

[yellow rose]

New ones were installed. I'm gona try a different filter today see if that works.

Buy a good filter, like a Wix, NAPA Gold or K&N and ditch that Rotella. You ain't burning diesel. You don't need all the detergents and crap it has.

Why use a diesel oil in a gas burner??

 

[schwinger]

And tried a Napa gold filter and still same thing... I might just have to take the pan off to check clearances again. Maybe somthing happened during break in or somthing but this gots me baffled and I was planning on taking it up to Minnesota next month but don't wanna drive it across country like this so ill dig deep in it and update later on.

 

[nm9stheham]

my oil level is on the full mark which I thought that was the problem to.

How much oil did you put in exactly? Dipsticks can get swapped around and you might have the wrong one....

You overall pressure at idle hot is decent. I think I would be trying another gauge at this point to make sure I was not chasing my tail.

 

[schwinger]

The dipstick was not the original one but I put 5 quarts in plus another one for the filter and made my own mark on the dipstick. unless these magnum engines take more oil I'm not too sure about that. I can try another gauge to see if that might be the problem.

 

[bobscuda67]

Shouldn't you have a 4 quart pan?

 

[schwinger]

Whoops my mistake. I forgot the that The Rotella oil jugs are sold in a gallon, 4 quarts not 5 like everybody else. Then I ad one quart to compensate for the filter so total of 5 quarts. It's the summit stock zinc coated pan which takes 4 quarts like you said.

 

[replicaracer43]

maybe the oil pickup tube is up too far from the floor of the pan, did you check that distance when you put it together?

 

[schwinger]

It was close. Didn't get an exact measurement but from what I recall its was just about an 1/8. I just used a piece of bubble gum to check it because I didn't have any clay.

 

[krazykuda]

It was close. Didn't get an exact measurement but from what I recall its was just about an 1/8. I just used a piece of bubble gum to check it because I didn't have any clay.

I tape two nickles to the bottom of the pick-up and set the height from the pan, then remove the nickles....

 

[krazykuda]

Buy a good filter, like a Wix, NAPA Gold or K&N and ditch that Rotella. You ain't burning diesel. You don't need all the detergents and crap it has.

Why use a diesel oil in a gas burner??

Nothing wrong with diesel oil in a gas burner. The diesel oil will hold up fine...

 

[racerhog]

Sounds like you got a bad pump or an internal problem.... Time to yank it back out and go find the problem.. Oh and the 15W40 works just fine in gas motors... Dont fall for that B.S.