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Old 07-21-2004, 12:03 PM
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Oil Pressure Drop with Higher RPM

My Mustang has a 351W - recently rebuilt (3000 milies). All clearances are right on the money, so the drop in pressure at higher RPM is a real mystery to me. I took the Mustang on a road trip abd had to run at 60 mph to keep the pressure in the middle of the gauge. If I pushed it to 70, down goes the oil pressure. It never drops below the "Normal" range, but get close, especially if the engine temperature is up a bit. It also seems to lose pressure under load, such as pulling a long hill. In a move of some desperation, I pulled the pan and checked main bearing condition and clearances. They look good, and clearances are all right at 0.002. Any help would be appreciated. Also, I use 10-40 synthetic oil, and a windage tray is in it.

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Old 07-21-2004, 12:21 PM
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Windsors have huge mains and bearing clearance is an issue. I would say it is parting line clearance, where the shells meet. King bearing is what I would recommend.

Chris
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Old 07-21-2004, 01:48 PM
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chris,
It sounds to me that it might be to much oil like the wrong dip stick or he has a windage problem crank picking up the oil.I have seen this on the dyno with stock pans and the first thing every one does is put more oil in and it gets worst.Oil temp would be a good indicator.





mike
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Old 07-21-2004, 08:51 PM
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Does it have a high volume pump?

Do you have stock oil pan on it?

If so you may just be pumping all your oil into your heads and your pick up may be losing its prime.

If you have a different pickup tube on it it might not be at the correct height in the pan and is losing its prime.
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Old 07-21-2004, 09:59 PM
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if it pumped all the oil out of the pan it would go to 0, not just lower a little.

K
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Old 07-21-2004, 11:58 PM
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Quote:
if it pumped all the oil out of the pan it would go to 0, not just lower a little.
Hmm didnt see where the post says pessures drops a little....nor does he have a gauge where numbers are being used.

K

Giving suggestions for him to think about....unlike someones post.

To much oil being pumped to the heads when a high volume pump is used is a common problem on sbf. I had a similar problem with my 302 the needle would jump around at times when engine is warm. Problem was solved with restricted pushrods.

Something to think about.
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Old 07-22-2004, 12:17 AM
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oil press. drop

what kind of oil pump and pick-up tube do you have and did you weld the pick-up tube to the pump with the spring with the spring in the pump?
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Old 07-22-2004, 07:51 AM
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pressure

I have seen chevy motors with high volume pumps and tight bearing clearences do this same thing. It has to do with the pump bypassing all the un-needed oil. It starts a rope looking kinda thing and none of the oil winds up going to the motor...

We had a motor on the dyno that did allmost the exact same thing as you described, switching to astandard pump fixed the problem.But like i said it was a chevy.

Keith
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Old 07-22-2004, 01:22 PM
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The pump, pan and pickup are all stock. Oil level was checked and is 5 quarts. I installed a mechanical gauge to see if there is correlation between the stock electrical gauge and a mechanical. There appears to be some difference. The mechanical shows about 50 psi at idle and 65 at 3000 rpm. This is with new 20-50 oil in it. The stock gauge does not move. It sits there at "high normal". I have not taken it up to highway speed or put it under a load yet, so I haven't determined if I still have pressure issues. I will post the results of my efforts as soon as I give it the acid test. Thanks for your input. Anything else from what I added?
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Old 07-22-2004, 01:36 PM
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Re: Oil Pressure Drop with Higher RPM

Quote:
Hmm didnt see where the post says pessures drops a little....nor does he have a gauge where numbers are being used.

Quote:
Originally posted by nova69
It never drops below the "Normal" range, but get close, especially if the engine temperature is up a bit. It also seems to lose pressure under load, such as pulling a long hill.

Uhh, did ya miss that part? His pan is obviously not being pumped dry, as alluded to in your first post. There's no use making a suggestion that doesn't follow the q, that's all I'm saying.

And yes, considering that I eliminated an incorrect possability, my post was useful.

K
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Old 07-23-2004, 03:37 AM
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low oil preasure

My 4 banger van did this very thing. My first attempt worked; it was a faulty gauge. I just put a mechanical one on. Then, with my '69 Elco 355, I noticed that my preasure went down when it got warm. Preasure at idle got dangerously low (7-10 lbs. w/a high volume pump). This time I had digested some cheap push rod tips and all that metal went to work on my rod bearings. I spun #4 a couple of days later. Hope you had a bad gauge.
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Old 07-30-2004, 04:11 PM
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I took the pan off and checked bearing clearances. Right on. Then I noticed the pan was caved in a bit, so I pushed it back out to where it looked right. I put everything back together with a mechanical gauge. The mechanical gauge and the stock gauge both read normal and stay there. It holds 40 at idle and 70 at cruising speeds. Anyway, it looks like I got it. Thanks for your help.
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