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High RPM Oil Pressure Drop

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Old 06-16-2013, 08:41 PM   #1
daz_au
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Default High RPM Oil Pressure Drop

Well this just started happening.... first noticed on highway pressure would drop from 60 ->40psi only at full throttle above 4000rpm, off throttle at 4000rpm was fine....

Yesterday, gauge dropped right off (almost zero !) when pushing over 4500rpm in 1st, but returned to 60 after changing into second... super weird. Any ideas ?
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Old 06-16-2013, 08:46 PM   #2
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Keep it below 4k and you will be fine . Dumb question but is your oil level correct and reading full
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Old 06-16-2013, 08:50 PM   #3
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Keep it below 4k and you will be fine . Dumb question but is your oil level correct and reading full
Yep, everything appears totally normal below 4000rpm, very weird, also not much fun

Oil level is all good and even when pressure drops, no strange noises or otherwise.... I hope its the gauge, but its the stock mechanical one so probably not !
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Old 06-16-2013, 08:51 PM   #4
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What oil weight you running and how old is it
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Old 06-16-2013, 08:55 PM   #5
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What oil weight you running and how old is it
10w30 Penn Grade, less than 6 months old.
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Old 06-16-2013, 09:04 PM   #6
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Oil running away from the pickup under hard acceleration.
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Old 06-16-2013, 09:17 PM   #7
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Oil running away from the pickup under hard acceleration.
Would certainly fit the symptoms... but why all of a sudden ? If the pickup fell off, would I get any oil pressure at all ?
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Old 06-16-2013, 09:31 PM   #8
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How about a clogged pickup and cavitation in the pump?
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Old 06-16-2013, 10:01 PM   #9
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Originally Posted by daz_au View Post
Would certainly fit the symptoms... but why all of a sudden ? If the pickup fell off, would I get any oil pressure at all ?
Some of the pickups aren't too far below the hole in the oil pump and you would still get oil when sitting still or accelerating slowly. It could also be a cracked pick up tube

Try slowly getting up to speed and dropping back a gear to make the engine rpm come up without acceleration involved. If the pressure stays up I'd say the oil is running away from the pickup.

I had a setup in one of my engines that would drop pressure under hard acceleration. I had to build some baffles in the pan to keep the oil around the pickup.
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Old 06-16-2013, 10:30 PM   #10
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Quote:
Originally Posted by claysmoker View Post
Some of the pickups aren't too far below the hole in the oil pump and you would still get oil when sitting still or accelerating slowly. It could also be a cracked pick up tube

Try slowly getting up to speed and dropping back a gear to make the engine rpm come up without acceleration involved. If the pressure stays up I'd say the oil is running away from the pickup.
I like this. Nice simple trouble shooting method.
the cracked pickup tube sounds plausible.

However, under hard acceleration, the oil is going to "pile up" at the rear of the pan where the oil pump is, and (I'm just guessing here ) you probably wouldn't even need a pickup tube to get oil into the pump.

Bad filter, or somehow bypassing back to the pan???


Gerry
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Old 06-16-2013, 10:40 PM   #11
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Drain the oil and put a scope in through the hole and see if the pick-up is still on the pump .
A fair bit of oil will be suspended in the top end as the RPM's rapidly increase . Bill
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Old 06-16-2013, 10:42 PM   #12
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I like this. Nice simple trouble shooting method.
the cracked pickup tube sounds plausible.

However, under hard acceleration, the oil is going to "pile up" at the rear of the pan where the oil pump is, and (I'm just guessing here ) you probably wouldn't even need a pickup tube to get oil into the pump.

Bad filter, or somehow bypassing back to the pan???


Gerry
The oil really doesn't just "pile up" at the back of the pan. I goes right up the back of the pan, around the rear main cap and keeps going into the rear counterweight on the crank. No matter, it gets away from the pump, pickup and the place you need to trap it in any case.
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Old 06-16-2013, 10:54 PM   #13
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Quote:
Originally Posted by 63split63 View Post
Drain the oil and put a scope in through the hole and see if the pick-up is still on the pump .
A fair bit of oil will be suspended in the top end as the RPM's rapidly increase . Bill
He has oil pressure at idle, and up to 4K rpm, so I would think the pick up is still on the pump. A partially plugged pickup might fit the scenario though. The next question would be "how does, or why would a pickup become partially clogged?" I've seen excess silicone sealant on the pickup, but that would happen pretty much right after a rebuild.
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Old 06-16-2013, 11:16 PM   #14
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Quote:
Originally Posted by claysmoker View Post
The oil really doesn't just "pile up" at the back of the pan. I goes right up the back of the pan, around the rear main cap and keeps going into the rear counterweight on the crank. No matter, it gets away from the pump, pickup and the place you need to trap it in any case.
Didn't know that. So, the OP says the oil level is good. The normal operating conditions dictate that under hard acceleration, the bottom of the pickup is submersed in oil, but if there is a crack in the pickup near the top, you might be sucking air. Wouldn't you be sucking air at less than 4K rpm also? (I'm not doubting you. Just trying to understand)

In your scenario, the crack in the pickup tube would be a bit lower than the static oil level in the pan, but at hard acceleration, the oil level at the pickup tube drops to a point where a crack would be sucking air.

I guess that means that if in your earlier troubleshooting method the OP retains oil pressure, it's time to drop the pan and look at the pickup.


Gerry
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Old 06-16-2013, 11:23 PM   #15
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Here is my 2 cents:::

Put in a temporary gauge where it comes out of the block...
Start it up and see if it fluctuates when going through the RPM'S...

That way you can eliminate a faulty gauge and go from there....
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Old 06-16-2013, 11:27 PM   #16
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Originally Posted by Mossy66 View Post
I guess that means that if in your earlier troubleshooting method the OP retains oil pressure, it's time to drop the pan and look at the pickup.
I was a little afraid to experiment, but I tried with just gently rising rpm and it seems acceleration is a factor. I first noticed that jumping on the gas on the highway dropped the oil pressure by 20psi, but then discovered its even worse in 1st when running to red line.

Inspection camera is a good idea, dont have one but have been looking for an excuse to get one Pulling the pan (and replacing/sealing it) from under the car doesn't seem like fun....
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Old 06-16-2013, 11:28 PM   #17
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Run some rislone cleaner in the oil you have in it and drive it around easy for a bit. Something is plugged (something loosened and is blocking something. It may be your drain back holes. Since you have pressure to 4000rpm at 40 and this is only happening at rpms, the oil is trapped in the upper part of the engine at rpms. I also did not like that you said your gauge completely hit zero. If accurate that is a big problem. Thus first clean/tighten the connections on that gauge!
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Old 06-17-2013, 08:06 AM   #18
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Add an extra Quart of oil and run the car up to problem zone. If this fixes the problem drop the Pan and do a visual inspection. Al W. (Back in the day we always ran an extra Quart of Oil because these cars leaked so much! lol).
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Old 06-17-2013, 09:09 AM   #19
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Appreciate all the feedback... I will drop the oil and filter this weekend, see if I can get an inspection camera into the pan and hopefully find a cause that makes sense.

It still has the old canister oil filter which I changed about 6mths ago (wix), I was thinking of getting one of the conversion plates to run a modern filter... not sure if that is recommended.

I did learn something with all the focus on my oil pan today, looks like I still have the stock L76 6qt pan on there based on some photos I found here on the forum of 5qt vs 6qt pans ! It is also leaking front and back surprise surprise.....
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Old 06-17-2013, 09:31 AM   #20
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Quote:
Originally Posted by daz_au View Post
I was a little afraid to experiment, but I tried with just gently rising rpm and it seems acceleration is a factor. I first noticed that jumping on the gas on the highway dropped the oil pressure by 20psi, but then discovered its even worse in 1st when running to red line.

Inspection camera is a good idea, dont have one but have been looking for an excuse to get one Pulling the pan (and replacing/sealing it) from under the car doesn't seem like fun....
it could be that the pickup has fallen off, however usually it is noisy as the crank hits the pickup....
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