Oil Pressure advise please.

[AndrewP]

Hi brains trust.

OK, so bear with me on this one as this has been an ongoing 'issue' for years for me. Apologies for a lengthy description in advance!

Background

Initially when I purchased the car 8-ish years ago, it had had a tough life, and so when the oil pressure light used to 'flicker' at idle when hot I figured it was a bit tired and needed an engine refresh.
It had a standard Melling M-63 oil pump (non-HV) and standard pressure relief spring.
I`ll add, that my car also has a large-ish oil cooler up front (so more capacity in the oil system and what seems like metres of extra high pressure hosing! This was all renewed when the engine was rebuilt)

To get around the flickering oil light problem, I re-did the bottom end bearings and big ends and fitted a Melling M-63HV oil pump and the flickering went away (and the oil pressure gauge showed approx 50 lbs" when cruising).

A by-product of this new pump and bearings was a resonance that appeared somewhat randomly, but generally after a hard acceleration and when cruising back to normal speed.

Fast forward to last year the engine came out for a rebuild.
New crank, cam, cam bearings, main and big end bearings etc all done. Bearing clearances were checked and all around the 0.0025" - 0.0020" clearance so all good.

Admittedly I did use the old/new M-63HV oil pump back in again, re-dressed the front plate and everything went well when starting with oil pressure at ~ 70lbs" at idle when cold and settling on ~ 50 lbs" when hot (not moving much between on and off throttle)

On my first trip out though the damn resonance reappeared and subsequent trips its become more prevalent and now generally every time the car is cruising off throttle, the resonance appears.

This weekend I figured I'd try and 'sort it out' ..HA (fat chance)

Work done

This weekend I tried a new M-63 oil pump with its standard spring (white stripe), and the oil pressure was very low.
Reading around the 20lb" at idle and dropping to ~ 10lb" or less when hot. When sitting at the lights the oil pressure warning light came on solid, but went away when the throttle was blipped. Cam started getting just perceivably a little clattery.
BUT..no resonance! (mini hoorah)
So..I think this would indicate not enough pressure then with a standard pump + standard pressure relief spring.

Then...I tried fitting the HV pumps high pressure spring (slightly longer, thicker spring wire) to the standard pump body and immediately the pressure shot back to ~ 50lb" at idle. BUT..when hot and driving, after accelerating, the oil warning light comes on.
I think this means not enough capacity in the pump?
The other bummer is that with the high pressure spring, the resonance returns.

Ive tried 3 types of oil filter, big medium and small just in case it was an anomaly of the oil filter make/manufacturer..but no real difference.

So Im at a loss what to do.

In summary:

Standard pump + standard spring = too low pressure when hot @ idle (idiot light comes on), rises slightly when driving but no resonance
Standard pump + high pressure spring = pressure OK, not enough capacity and resonance returns
High Flow pump (HV) + high pressure spring = pressure OK, OK capacity but resonance returns

The resonance seems to be linked to the high pressure spring as it does it with both the standard and the HV pump bodies...

I have a new HV pump on order, but my only option now is to try:
High flow pump + standard spring = ???

Nothing else indicates any issues. There is oil at the top of the engine, oil is clear with no bits or swarfl, no clattering of the lifters, everything is new?

I have a separate oil pressure gauge coming to read the 'actual' oil pressure. This should confirm the oil pressure gauge is OK/out and if the oil pressure switch (idiot light) is working properly.

Perhaps its the oil cooler? (No idea why, but as its part of the system?)

I have recorded the noise, but unfortunately it wont let me attach to this post, but here is a link to Youtube with the noise audible.
https://youtu.be/8dHvctpz0Hg

Appreciate any help or opinions as Im after ideas of what to check next.

Thanks for any help/guidance in advance.

Cheers

Andrew

[slotcarone]

Hi Andrew
I listened to your video but really cannot hear anything except the lovely sound of the engine. Not understanding what you mean by resonance. That term is typically used for exhaust issues not engine issues. Remember these are tough engines and the cars that they originally came in in the USA almost never had an oil pressure gauge only the idiot light.

[AndrewP]

Hi Slotcar,

Thanks for the reply and reading the saga.

I listened to the recording and YouTube have reduced the quality a little when its been uploaded, but the noise is that buzzing/drone over the lower tones of the engine noise.

Its best described as a resonance that seems to be transmitted from the oil pump and up the hosing to the oil filter housing and then partly down the oil lines to my oil cooler up front.

I'd say almost definitely on the pressure side too as the return line from the cooler into the pump housing and onto the oil lines has little to no noises (using a mechanics stethoscope)

Amazingly, the oil pressure test kit I ordered a few days ago arrived (post on a Sunday!) and so for the first set of tests, I attached it to the oil pressure switch outlet and took some readings.

Nothing too amazing, but:

Standard pump body + high pressure spring

@ cold
pressure on external gauge = 70 PSI
pressure on internal gauge = ~ 65 PSI

@ hot
Pressure on external gauge = 55-60 PSI
Pressure on internal gauge - 50 PSI.

Very little movement of oil pressure on the external gauge when just revving so no apparent oil flow issues (but also no resonance this time round).
I may go for a drive with the gauge somehow connected and see if the resonance re-appears.

The next test I`ll do is to re-fit the standard pressure spring to the standard pump housing and see what that shows.

Thanks again for anyone reading this and any advise or even ideas what could be at play here.

Cheers

[DPP]

I would try it with the oil cooler out of circuit and back to standard pipework.

[slotcarone]

I agree with DPP. Bypass the oil cooler. Unless you are in very hot climate it is not needed for normal driving. Actually prevents the oil from getting up to operating temperature.

[Martin R]

I agree with DPP. Bypass the oil cooler. Unless you are in very hot climate it is not needed for normal driving. Actually prevents the oil from getting up to operating temperature.

I seem to recall that it can and does reach well over 100 degrees F in Perth, Western Australia....

[AndrewP]

I seem to recall that it can and does reach well over 100 degrees F in Perth, Western Australia....

Yeah it gets quite toasty here in summer (40C/105F ++). Think the hottest I've experienced is 47C/117F and that was hot hot.

Anyway..its a process of elimination, so I`ll sort out a bypass hose to see if the standard pump --> filter --> pump setup works and cut out the front mount oil cooler.

Silly question perhaps, but Im assuming there is no reason why a fresh rebuilt 383 shouldn't run quite nicely on a standard pump is there? Even with the remote oil filter and the ~1m of hosing that it adds?

Why do people add the HV pump? Is it just for extra capacity and belt and braces approach?

Thanks again everyone.

[slotcarone]

On a stock engine there is no reason to use anything but the standard oil pump.

[Grant]

High Volume pumps are for modified engines with bigger/bored out oil ways I believe Andrew,..Are you sure you have enough oil in this engine?..There seems to have been a little confusion over oil dipsticks and giving incorrect readings lately, 383 and 440 dipsticks are different, you don't think yours may be wrong and your low on oil do you?

[AndrewP]

Thanks gents for the replies.

Mines a stock engine, so sounds like there is no real reason to go for a HV pump.

Grant, its something that has crossed my mind as well having read (and contributed) to the posts I think you refer to.

Ive made sure the oil level is OK and my calculated value sees the oil 1/2 way on my dipstick so Im quite happy that its OK.
The resonance does seem to be linked more to pressure however as when the HV pumps pressure relief spring is fitted it makes the noise whether its fitted to the HV or standard pump bodies.
As you say !

Im just about to go and by-pass the oil cooler and see what effect that has on the noise and pressure. Fingers crossed it may give some indication of where to focus on next!

Thanks again.

Andrew

[PeterHume]

Hi Andrew
The oil filter is supposed to be rubber mounted, if you check the parts book they are shown.
This suggests Jensen had a noise issue, probably the same as yours.
It might be worth checking the mounting in case the rubbers are missing or age hardened.

Regards Peter

[AndrewP]

Hi Peter...

Holy moly...went to look and I have no rubber mounts at all. The filter is mounted directly to the inner wing on mine.

Id really like this fix to be the reason!...I will definitely owe you a beer or 10 if it turns out to be true!

I`ll try mounting it on some rubber blocks first and then go from there.

Fingers crossed!

Cheers

[Grant]

Hi Andrew
The oil filter is supposed to be rubber mounted, if you check the parts book they are shown.
This suggests Jensen had a noise issue, probably the same as yours.
It might be worth checking the mounting in case the rubbers are missing or age hardened.

Regards Peter

Good shout Peter, you can go to the front of the class for that thought my ole fruit

[AndrewP]

Hi everyone,

I've finally had the chance to fit some rubber blocks to try to mimic the rubber mounts originally and as Peter pointed out.

For those playing at home..these are the little blighters:

Screenshot 2021-10-19 181655.png (42.61 KiB) Viewed 3619 times

And...DEFINATELY a big improvement.

Its fair to say that the noise is still there (after all, the rubber mounts simply stop the noise being transmitted through the body of the car), but almost undetectable over the noise of the engine and general road noise.

I've since purchased a set of vibration/noise mounts where the main difference seems to be that instead of a long bolt through the mounting, these are 2 threads, completely isolated by a rubber block. The theory being is that there should be no noise transmission from one side to the other.

Anyway..a job for the weekend.

Still a little disconcerting that the noise is there, and related to the oil flow and Its not really what Id like on a freshly rebuilt engine, but all I can be is confident that having rebuilt the engine myself carefully and checking ALL the tolerances (twice in some cases!) that it must be something that (as Peter has mentioned) Chrysler occasionally experienced and so needing the rubber mounted oil filter housing.

Hopefully this may help someone else in the future with similar issues for reference.

Thanks everyone for their help.

Andrew

[PeterHume]

Hi Andrew
Great to hear things are improved with the rubber.
If it helps you are welcome to bring your stethoscope and have a listen to my interceptor.
It will either set your mind at rest if the same noise is present, or, add to your doubts if it's not
Regards Peter