Oil pressure holds steady on 40 pounds with mechanical gauge. Just started this. It was bench tested and showed a max of 60 pounds on the drill. Changed gauges and still no luck. This is the third oil pump I've had a problem with. I belive all Mellings. It's a stock pump. Probably going to pull the plug and remove the spring and piston next. Never done this in a big block A body.

Quit buying melling pumps, they have a sticky bypass issue and have had it for years across makes.

get another cup plug & you might polish the barrell and the piston just slightly plus a good visual

What would you use to polish the barrel?

some real fine sandpaper, for bodywork/painting it comes in 1000 grit etc & I ain't up on what grit I would use but I would be conservative & smooth things out a bit. it'd be hard to mess up that deal so I would not be afraid to tackle it as you just need the piston to be a slight bit freeer than it is now

Looks like the pump needs to come out. Looks to be a chore in a bIg block A body.

Not sure if that is a special size (dia) plug from Ma or if a parts house one can be obtained (I coulda swore it is a dealer item). I'd drill a hole in it & use a screw into it and slide hammer it out. Be greatfull you are a BB guy (pump on the outside!)

Remove the four 3/8 pump bolts and turn the pump sideways so the bypass valve plug is pointed up towards you and remove it and then the spring and then remove the bypass valve, I use a small pocket magnet to slide it out, if it is't stuck that is If it is stuck you may need to remove the pump from the motor and work on it on a bench to get it out Good luck Which Melling pump are you using, standard, high pressure or high volume? What oil temperatures are you seeing 40 lbs of pressure, hot or cold?

Know the process, been there, done that. Just haven't had to deal with removing a pump on a big block A body. The k member is slightly different that a b body K.

It's a Melling standard pump. It idles cold just below 40 pounds. It was idling at 25 with the electric gauge so I changed to a mechanical. With the electric gauge it wouldn't go above 45 pounds at 2000 RPM. Needle seems to hold steady. Like I said when we primed on the engine stand it held at 60 pounds. We did it again later since the engine sat in the engine compartment for some time. The initial fire up showed 60 pounds cold.

Busy time the next few days so I won't get back on it until next week.

You'll be drill priming it again so I would pull the dist/intergear first before removing the pump & when going back together I would suggest installing the pump and the bolts barely snug then installing the intergear then tightening the pump mounting bolts (VG plan on a SB so assuming it might be a good move with a BB). Holler how it turns out when all said & done. (we're sure it ain't a gauge prob correct?), I'm just wondering if 60 while priming (some passages might be closed) then dropping to 45 when running is OK but agreed that is quite a difference.

Have you changed the oil filter since breakin?

I agree with filter. I had a bad NAPA gold filter one time. Changed oil and it Worked fine for a day, then zero oil pressure. Checked for broken drive shaft and removed valve, all clean. Put on a new filter and back to normal.

It sounds like the electric gauge is goofy to me The standard pump have a different bypass spring in them so your cold oil pressure sounds dead on to me compared to the standard pumps I've used in the past

He has changed gauges already.

I have to ask a question, are you chasing ghosts??? or blaming the oil pump for another issue???
If I am understanding correctly you had 60lbs when priming the motor on an engine stand.
You had 60lbs cold on initial start.

You now have 45 lbs cold and 40 lbs warm at 2500 RPM. that is not a typical swing.

What is the pressure when idling warm???

you have changed the pump 3 times and gotten the same results. I am doubting that the issue is the pump.

one can change or shim the bypass spring to increase the pressure but I am wondering if the oil, clearances or something else may have you chasing your tail by blaming the pump?

have you changed the oil and filter??

Ok, lots of info being thrown around which I appreciate. First, I'll finish the change over to a mechanical hardline gauge. The oil filter change is in the plan. The next step will be to take it out and see what pressures it runs. Yes 40 pounds is not bad for a relatively stock 383. Again the pump is standard, it was primed with the drill which showed 60 pounds. Primed again before we fired the motor and again 60 pounds.

It wasn't driven much before I brought the car home to Mesa. Mainly driven to seat the rings. I'll keep everyone informed. As a note I talked with my buddy who owns the shop where I did the car. He had the same problem with a 440 recently. Ended up pulling the pump and polishing up the bypass. It too was a standard Melling. Problem fixed.

I guess my advice at this point is anyone running a Melling make sure to pull the spring and bypass and polish up the bypass tube. That way that possible issue has been addressed before installing the motor in the car. In fact it states just that in the shop manual.

Thanks again for all the input.


Forgot to mention I'm running a WIX filter and for oil I'm running 15/40 Rotello with a zinc additive

(1) thats what we do best! (2) smart move there (no opinion/expertise on the weight choice)

(1) thats what we do best! (2) smart move there (no opinion/expertise on the weight choice.

On the oil, given that the climate in the NW I found th 15/40 worked fine. Since I now live in the SW I need to consider changing from the 15/40, maybe a straight 30 wt?

I did not read the entire post, but I'm curious to how you are concluding that there is a problem? Priming oil pressure is not necessarily related to operating pressure. My hot idle and cruise pressure are considerably lower in my cars than the priming pressure, for several likely reasons.