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  #1  
Old 04-07-2003, 12:11 PM
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Default OIL PRESSURE GOES DOWN WHEN HOT???????????????????

I have a 78 jeep cj7 with a 360 amc engine in it. I am having all kinds of trouble with oil pressure, and we can't figure it out. I have good oil pressure untill the engine gets hot. Then when i rev the engine, or down on the gas pedal the oil pressure drops instead of goes up? If i kept the gas pressed it will go to zero slowly. I am just stumped!! And for some reason my engine gets to hot. it runs around 210 temp or so. Does anyone out there have any suggestions???? It only seems to do it when when the engine is warmed up. Please help me out. I don't wanna rebuild this engine if there is something little to fix. We put a new oil pump on and it does the same thing. Something is wrong somewhere for the oil pressure to go down when pressing on gas when warm. I am open to all options. Just keep em coming! Thanks. it's gonna be summer soon, and i gotta have my jeep fixed...lol [img]images/graemlins/thud.gif[/img]
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  #2  
Old 04-07-2003, 12:20 PM
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Default Re: OIL PRESSURE GOES DOWN WHEN HOT???????????????????

Change the oil pressure guage if you havent already. Did you put a new pump in or did you rebuild your old one. Sometimes the oil pump housing can be worn and the rebuild kit only replaces the guts inside. I think it's normal to have less pressure when warm but it should increase with rpm. LEVE says 10 psi for every 1000 rpm, LEVE know what hes talking about. I dont think you should be over 195 deg. when warm. Check you thermostat and check what is recommended for your year, but 15 deg's is most likely unrelated to the oil pressure drop. That is just my $.02 I'm sure others know more.
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Old 04-07-2003, 12:28 PM
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Default Re: OIL PRESSURE GOES DOWN WHEN HOT???????????????????

Hrm, that makes no sense whatsoever. If you have good oil pressure at idle, then the pressure should go UP when you rev the engine! The oil pump is driven off of the Dist. gear that is driven off the cam, so when you spin the engine faster, the cam spins faster, the Dist. spins faster, and the oil pump spins faster, creating MORE oil pressure.

Maybe check the rod that connects the Dist. to the oil pump? Maybe it is warn enough that when enough force is applied to it (When the engine revs up) it slips inside the oil pump? Make sense? Pull your Dist. off and pull the rod out that goes to the oil pump...attatch that rod to a drill and stick it back in (Probably need an extension...I usually use a long extension with a socket that fits the rod) and spin the oil pump with the drill. That should simulate the engine reving, and if you've got a mechanical oil pressure gauge, you should see the oil pressure rise. Try different speeds with the drill and see if you can tell if the rod is slipping inside the oil pump. Also check the end that goes into the Dist. as that side might be the one slipping.

That is the ONLY thing I can think of that would cause oil pressure drop above idle...good luck!

Mike
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Old 04-07-2003, 12:32 PM
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Default Re: OIL PRESSURE GOES DOWN WHEN HOT???????????????????

You'd better install a mechanical oil pressure gauge to see what is really going on. If you have no oil presure at rpms, you motor would be toast in short order. First, see if what appears to be happening, really is.
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Old 04-07-2003, 12:46 PM
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Default Re: OIL PRESSURE GOES DOWN WHEN HOT???????????????????

I have a mechanical oil guage in my jeep, and that works fine. Thats how i know it's really going down when i rev the engine. I'm not driving it at all till it is fixed! I don't need something happening to it. This is my second one...lol And yes the oil pressure goes down when it gets hot and i rev the engine instead of rising. Thanks for the quick responses. i gotta figure this out SOON! Any other suggestions will all be looked into. Thanks all!!
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Old 04-07-2003, 04:18 PM
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Default Re: OIL PRESSURE GOES DOWN WHEN HOT???????????????????

As your RPM's go up, so does the oil pressure and oil consumption out of the oil pan. Is it possible your pickup tube isn't the right one/too short and you are pumping so much oil into the engine that the pan is getting empty enough to raise the pickup tube above the oil line before the oil can drain back to the pan? That is about the only reason I can think of that would make the oil pressure drop as RPM's increase.
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Old 04-07-2003, 04:39 PM
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Default Re: OIL PRESSURE GOES DOWN WHEN HOT???????????????????

1. It may make sense,
2. IF....
[*] The oil's been overfilled[*] There's Gas in the oil to raise the level,[*] There's water/coolant in the oil to raise the level,

5. And is caveatting, or
6. Foaming as engine speed increases.
7. So is it really a problem or not?
8. I'd be checking the sender,
9. And double checking with heavier weight oil,
10. To see if the symptoms change.
11. Is there any noise associated with this,
12. Like cam or crank noise?
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Old 04-07-2003, 04:44 PM
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Default Re: OIL PRESSURE GOES DOWN WHEN HOT???????????????????

I think Barfnick is on the right track. Three possibilities:

1) Oil level is too low
2) Pickup is too high
3) The return passages are blocked, filling the valley and valve covers with oil
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Old 04-07-2003, 05:01 PM
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Default Re: OIL PRESSURE GOES DOWN WHEN HOT???????????????????

There is no noise at all in the engine. Engine sounds good, and oil pressure is good untill hot. If ya rev the engine it goes down instead of up. And if ya hold the gas pedal down, i'm sure it wold slowly go to 0 on the oil pressure guage. The engine does seem to run too hot too. the temp is usually around 210 degrees. I have'nt drove this much at all. I NEED to find out whats up first. Gettin the itch now that it is gonna get warm. I will check out all these options, and get back to ya. Keep em coming. Thanks ALOT!!!

Mike [img]images/graemlins/40BEER.gif[/img]
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Old 04-07-2003, 05:28 PM
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Default Re: OIL PRESSURE GOES DOWN WHEN HOT???????????????????

I hope this isn't your problem, but bad bearings and lack of oil pressure can in and of themselves generate extra heat from the added friction.

I'd be dropping the oil pan and looking at the pickup screen, position, oil pump and finally bearings (if no problem is found with the above.). Maybe also pull the valve covers and look for obstructions to oil draining back. I've read that even having the pickup too close to the bottom of the pan can cause cavitation of the pump or vortex sucking in air. Possibly some obstruction causing the cavitation of the pump when it tries to increase volume of flow. Is the oil pan dented upwards near the pickup?
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