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400 Oil Pressure question

Posted By: G_T

400 Oil Pressure question - 06/24/09 11:29 PM

1977 400, about 105K miles on it. Engine runs fine, no knocks, weird noises, etc. Mechanical oil gage.

2 months ago, it had 65-70psi cold, and ~30psi hot, ~10psi idle.

It has slowly dropped since. Did the usual oil changes (10W-40) and oil filter (puralator).

Now it is ~40psi cold, and ~5-10psi hot, 0psi at idle.

The top end was rebuilt about a year ago (head work, cam, manifold, etc.).

I'm not sure if the engine is just worn, or if a replacement oil pump is in order.

Other than leaking oil, it doesn't seem to burn/smoke.

Any harm with installing a high vol pump?

Other suggestions?
Posted By: Dougsmopars

Re: 400 Oil Pressure question - 06/24/09 11:34 PM

Pumps are an easy change. Better to be safe then sorry
Posted By: dOoC

Re: 400 Oil Pressure question - 06/24/09 11:36 PM

With all those oil-changes .. you might have loosened up some crud in-the-pan and elsewhere and it is now restricting the pick-up tube and screen.

Pull the pan.
Posted By: G_T

Re: 400 Oil Pressure question - 06/24/09 11:48 PM

last oil change was 2K ago. Pan was pulled the same time we did the top end to change gaskets and rear main seal. Nothing in the pan at that time (Actually I was surprised as it had the stock nylon timing set which we replaced with a dbl roller set at the time).

Engine was very clean inside - no crud/etc.

I guess a $65 high vol pump isn't a bad investment - very easy to change. Just seems odd that a pump would slowly go away like that over a 6 month period of time...
Posted By: dOoC

Re: 400 Oil Pressure question - 06/24/09 11:52 PM

Quote:




Just seems odd that a pump would slowly go away like that over a 6 month period of time...



THAT is very odd ...I would put another gauge on it to double-check the psi.
Posted By: Anonymous

Re: 400 Oil Pressure question - 06/24/09 11:56 PM

Pump is fine
drive it until it pukes
Yea ..maybe the cam bearings have gone away
maybe maybe maybe this maybe that--drive it! Have fun! when it quits THEN fix it--save that oil pump $$ for a tank of gas--
Posted By: Hoof Hearted

Re: 400 Oil Pressure question - 06/24/09 11:57 PM

Free advice from experience, cheap enough to do.

1) Replace oil pump with a Melling Hi-VOLUME (not pressure)

2) go with at least a 10/40 (I like Rotella 15/40)

3) Use a Napa Gold oil filter

4) consider changing the oil pump Input Shaft to a Mopar Perf. HARDENED Shaft.
Posted By: bboogieart

Re: 400 Oil Pressure question - 06/24/09 11:59 PM

Quote:

Pump is fine
drive it until it pukes
Yea ..maybe the cam bearings have gone away
maybe maybe maybe this maybe that--drive it! Have fun! when it quits THEN fix it--save that oil pump $$ for a tank of gas--

and carry plenty of freinds to push when it fails.
I say check with a mechanical guage and make sure of your pressure befor anything else. If your bearings are wiped out, a new pump wont do anything. you could try thicker oil and see what that does for you.
Posted By: G_T

Re: 400 Oil Pressure question - 06/25/09 02:23 AM

Quote:

Free advice from experience, cheap enough to do.

1) Replace oil pump with a Melling Hi-VOLUME (not pressure)

2) go with at least a 10/40 (I like Rotella 15/40)

3) Use a Napa Gold oil filter

4) consider changing the oil pump Input Shaft to a Mopar Perf. HARDENED Shaft.



Thanks Hoof... that is what I was planning. I really don't think it's the oil pressure gage...but, I can get another one to validate.

Worse case - if it blows, I have a spare 400 in the garage
Posted By: dave571

Re: 400 Oil Pressure question - 06/25/09 02:27 AM

Quote:

Any harm with installing a high vol pump?





Very good plan. This is actually what a hi volume oil pump was designed for. To restore pressure in engines with bigger clearance.
Posted By: dOoC

Re: 400 Oil Pressure question - 06/25/09 02:28 AM

SAVE your money on a new oil pump ! .... I have taken apart enough motors to see pumps that look totally grim ... put out pressure just fine.

But if your gauge swap confirms low pressure ... just put a couple of washers in with that relief spring IN the pump you have.
Posted By: G_T

Re: 400 Oil Pressure question - 06/25/09 02:29 AM

I thought the shaft on a big-block is integral to the distributor cam gear? I thought you only went with the hardened (bronze gear?) if you had a roller cam? Or am I off?
Posted By: stumpy

Re: 400 Oil Pressure question - 06/25/09 02:31 AM

Why didn't you check a rod bearing or two when you had the pan off? It takes 10 minutes and doesn't cost a dime. 105k miles you are ready for a rebuild. I don't think a new oil pumnp will do you any good at all.
Posted By: G_T

Re: 400 Oil Pressure question - 06/25/09 02:33 AM

No reason to at the time (12 months ago). Everything was fine. Motor ran strong, zero issues other than the leaking rear main seal. Engine only had ~70K on it at the time.
Posted By: stumpy

Re: 400 Oil Pressure question - 06/25/09 02:37 AM

No reason not to while the pan is already off.` I check mine every time I pull the pan. Like I said it's free and never hurts to know whats going on in the lower end.
Posted By: Hoof Hearted

Re: 400 Oil Pressure question - 06/25/09 03:29 AM

Quote: "I thought the shaft on a big-block is integral to the distributor cam gear? I thought you only went with the hardened (bronze gear?) if you had a roller cam? Or am I off?"

Yeah, you're a little off; Mopar Perf. makes an input shaft with a Forged(?) HARDENED End. With the heavier oil and volume of flow comes more of a chance you'll round off the tip, as we've all done with allen wrenches ...

The gear end stays the same.
Posted By: G_T

*UPDATE* 400 Oil Pressure question - 07/14/09 05:28 AM

Well the bandaid seemed to work. Swapped out the oil pump for a high vol unit, checked gage, new filter/oil & shaft as stated above. Primed it and fired it up.

75psi cold
25psi hot idle @ 195 degrees and 700 rpm

I'm sure it's a matter of time before a rebuild, but this seems to have cured it for a bit. Just a waiting game - so I can have some fun for a while.

I'll post again if/when a tap or knock develops

Btw, removing the oil pump shaft for priming/replacement was real fun (NOT). Did it with the manifold on - made a little tool to grab the gear and pull it out the distributor hole.
Posted By: RapidRobert

Re: 400 Oil Pressure question - 07/14/09 01:41 PM

Quote:

I thought you only went with the hardened (bronze gear?) if you had a roller cam?

yes the bronze gear one is for a roller cam & the hardened tip one is a regular one for non roler cams but has a hardened hex end
Posted By: furious70

Re: 400 Oil Pressure question - 07/14/09 04:25 PM

oil psi dropped out of the blue after racing 2 yrs ago in the 383 in my Fury, put a new pump on and it went back to normal and has been fine since. I did not tear down the old pump to diagnose, was happy it was fixed.
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