CJ7 Fluctuating Oil Pressure Only 1000-1050 RPM New Motor - JeepForum.com
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post #1 of 52 Old 12-02-2019, 03:10 PM Thread Starter
sherlocktk
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CJ7 Fluctuating Oil Pressure Only 1000-1050 RPM New Motor

I just finished rebuilding the 258 motor in my jeep, and I have a strange issue. oil pressure is "good" (40 psi @ idle, 60 at RPM) Settles down to around 25 psi once the engine is warmed up, and increases with idle. I have about 200 miles on the motor at this point. I have a couple of weird things.

1. When the motor is warm, and the RPM is in between 1000 and 1050 the electronic gauge bounces around rapidly. (between 20-50psi) No other RPM range does it do this, the rest of it is linear. At this RPM range the engine ticks.

2. In this range of 1000 - 1050 The engine has a slight "tick" Just like after a oil change until pressure builds up, but not as loud.

3. Upon startup after sitting overnight, the engine "ticks" for about the first 1 second. Old motor did not do this unless it sat for a month or so. I have changed oil filters.

4. Analog gauge put in to verify #1 above, and it does bounce up and down rapidly but only around that RPM range.

5. I do have a gasket between the oil pump and the block

Thoughts:
1. Possibly the oil filter bypass spring (The one your can access via the filter) is broken on the new motor. I cant see how this would effect pressure as the plumbing of both seem to go to the same spot.

2. Possible "Bad" oil pump. If one of the impellers have a defect, I would think it cant pump properly but only 1/6 or so of the time on the bad spot. Its a new melling pump.

3. Leak in the pickup tube. I presume I could have not pressed in the pickup tube properly and there is a leak there, which is adding air/cavitation into the system but only under certain pump speeds


Any good ideas on how to test for #2 or #3? It seems I am going to be dropping the oil pan for this. I guess its possible a bearing could have some issue but I would think this would happen at all RPM's instead of just a small amount.

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post #2 of 52 Old 12-03-2019, 10:24 AM Thread Starter
sherlocktk
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I was doing more research. When I put in my oil pickup tube, it was a press fit (but by hand, not a hammer). I am suspecting this was not enough of an interferance fit and the pump will suck air at certain RPM's. Anyone who is installed this before how hard should it be to put in the oil pickup tube to the pump? It is a hand tight thing, or should I have needed to use a hammer and a creative use of a wrench.
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post #3 of 52 Old 12-03-2019, 12:46 PM
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Quote:
Originally Posted by sherlocktk View Post
Anyone who is installed this before how hard should it be to put in the oil pickup tube to the pump? It is a hand tight thing, or should I have needed to use a hammer and a creative use of a wrench.
I installed a Melling oil pump not to long ago and had to use a hammer... I took the closest fitting wrench and put it around the collar that stops the tube from going in to far and hammered on that. I also put the oil pickup tube in the freezer overnight so it would go on easier. It was still a press fit with the pump warm and the tube pretty cold but easier than it was when they were both at room temperature.

They make a special tool for oil pump tubes and it was expensive in my mind for something I was doing once.
That's my experience, I'm no means an expert so I hope someone else can back me on here!

Good luck!

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post #4 of 52 Old 12-03-2019, 08:03 PM
BagusJeep
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FSM mandates a new tube if the old one is disturbed and that a light film of Permatex No. 2 be applied:

If position of inlet tube in pump body has been disturbed, install replacement tube and screen assembly.
Apply light film of Permatex No. 2, or equivalent, around end of tube. Use Tool J-21882 to drive tube into
body. Ensure support bracket is properly aligned.


It is possible you have a leak here, the fluctuating gauge suggests air not oil. It says "drive" so yes, the factory thought a hammer was needed which, with a sealant applied, is logical.

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post #5 of 52 Old 02-05-2020, 04:25 PM Thread Starter
sherlocktk
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I finally got around to dropping the pan and installing a new pickup tube into the oil pump. Unfortunately this changed nothing. I still get the fluctuations at this particular RPM. There is a gasket between the engine block and the oil pump. That looked to be in good condition and appeared to be sealing properly based on contact points.

Further reading is pointing to either a bad oil pump (Specifically the pressure relief valve doing something weird) or possibly a spun bearing. I dont think it would be a spun bearing as it only seems to be bad at lower RPM.

How do I test the oil pump. I presume its possible that one of the impellers is out of spec but that seems unlikely to me if this is a new build. I am currently thinking:

1. Getting the jeep warm.
2. Remove the distributor, and install my distributor without the cam gear.
3. Spin the drill @500rpm. Which would mimic ~1000 rpm at the crank. See if I can "feel" anything while watching the manual oil pressure gauge.
4. If I don't feel anything and pressure looks good, I am thinking to crank manually while spinning the drill to see if there is a drastic oil pressure drop given the same power levels. I would guess this would point to a bearning / tolerance issue somewhere.

Thoughts?
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post #6 of 52 Old 02-05-2020, 09:47 PM
Cutlass327
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What brand oil filter? What weight oil?

Rick

1978 CJ5 5.0HO/T177/D300, '86 D30/D44 WT axles, 'glass body, 31x10.5 BFG A/T, TDK galv'd frame - DD and weekend toy


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post #7 of 52 Old 02-05-2020, 11:43 PM Thread Starter
sherlocktk
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Running valvoline 10w30. acdelco oil filter (second one)

I maybe have 300 miles on this engine and about 8 miles on this oil change

Oil pressure on cold start (50 degrees) is around 60. Climbs slightly when increasing rpm. The noise and fluctuation do not happen until after the heater starts to blow warm (about 3 miles) once engine is warm oil pressure goes to 25-30. Except at this lower rpm range (1000-1100) then it bounces between. 15-40psi

Before this oil change I was running rotella t5 15w40 for the higher zinc. No difference between the 10w30 vs 15w40
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post #8 of 52 Old 02-06-2020, 08:08 AM
Matt1981CJ7
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I would check to see if you have at least 3/8" between the oil pickup and the bottom of the oil pan.

An easy way to check is tape a ball of foil to the bottom of the pickup. Then reinstall the pan with just a few bolts. Remove the pan and measure the thickness of the foil. Should be 3/8-1/2".

If that's not the problem, I'd suspect the oil pump.

Matt


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post #9 of 52 Old 02-06-2020, 12:28 PM Thread Starter
sherlocktk
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Matt,

I will check the clearance when I drop the pan next. I already orderd an oil pump as I believe this the most likely failure mode. I originally installed the original pickup tube (an oversight) which was a press fit but without a hammer, so I dont think its likely that the pickup tube is in the wrong spot. The new tube and old look to be identical.
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post #10 of 52 Old 02-06-2020, 12:51 PM
LouC
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Have you tried checking the gauge reading with a manual gauge? Sometimes aftermarket oil pressure sensors do not read consistently right.

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post #11 of 52 Old 02-06-2020, 01:03 PM Thread Starter
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Yes I have used a manual gauge. Its a similar story. The gauge confirms what the electric one says. In addition to this there is a noise to coincide with the oil pressure fluctuations.
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post #12 of 52 Old 02-06-2020, 01:14 PM
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Assuming that the screen is the Melling-recommended 3/8" to 1/2 "

https://www.google.com/search?q=oil+...GkggfS8ZXoCw17,

and there is no side-wobble in the gear shafts of the pump with the cover off, you could consider sanding the mounting surface slightly to reduce clearance between the ends of the gears and the cover IF THE CLEARANCE IS MORE THAN .005.

If that doesn't help and there's no 'trash' inside, I guess it's new pump time.
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post #13 of 52 Old 02-06-2020, 04:05 PM
oldschool74cj5
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hello


i remember years ago when rebuilding a engine that i found the oil pump didnt fit that great. after dry fitting without a gasket i found that the body of the oil pump was hitting against the block. keeping it from sitting flush against the block. i had to grind a little off the body to give it some clearance. if i remem right the pump hit near the webbing for the main bearing.

some other points of leaks are.

one thing i would look at also is the cover installed to the pump. there is a gasket between the cover and the body.

i would also look at the plug in the oil gallery under the timing cover. you could be leaking there



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post #14 of 52 Old 02-09-2020, 06:24 PM Thread Starter
sherlocktk
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I just finished spinning the distributor manually with a drill when the engine was off, along with a manual gauge hooked up at the same time. (Engine was warm)

I get about a 15 psi fluctuation at ~1200 rpm and around a 5psi fluctuation @450 rpm. (This is drill RPM, so double that for "fake" engine speed) Since I am getting fluctuation without the egnine spinning, I am sincerely hoping this points to it not being a bearing issue as nothing is moving but the oil pump.

In addition to this it "feels" like each revolution with the cordless drill ramps up and down. I understand this is entirely subjective but all signs are pointing to something being out of clearance with the pump.

Would it be worth it to spin at a constant RPM then turn engine by hand to see if there are pressure differences first to eliminate or find a bearing issue?

My new pump comes on tuesday I hope to get that in next week.
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post #15 of 52 Old 02-10-2020, 10:59 AM Thread Starter
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I waited until late last night so the car can cool off. Around 70 degrees. Spinning the "Thicker" oil because of temperature the pressure doe not vary as much but you can both see and feel the pressure difference based on where you are in the gearset of the oil pump. I think this explains why it is not as bad until the vehicle warms up.
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