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Tractor Talk Discussion Forum

oil pressure and engine RPMs

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Jonathan

07-06-2004 15:23:36




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Hello, as I was driving my pickup today, I noticed that when I idled the engine (800rpms), my oil pressure dropped to about 40lbs, and would go back up to around 60lbs when the engine rpms were increased (around 1,650rpms)and would stay there until the engine was idled back down again. Is this normal, had I just not noticed that my truck did this or is something wrong?. I think it might possibly be my guage too, because when I shut the truck off the guage stays right where it was when the ignition was turned off, and when I turn the switch back on with the engine stopped, the guage will shoot back down to zero, but then will rise up to 20lbs.
thanks in advance

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txblu

07-08-2004 06:13:34




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 Re: oil pressure and engine RPMs in reply to Jonathan, 07-06-2004 15:23:36  
You gotta chevy. My Ford and Dodge hold pressure without budging regardless of conditions (except engine off). My chev is all over the place and if you use that stupid 10w-30 you can't find it on the gauge when hot (new truck).

Yuck!



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G-MAN

07-08-2004 10:55:43




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 Re: Re: oil pressure and engine RPMs in reply to txblu, 07-08-2004 06:13:34  
First, if you're really concerned, don't believe what that factory "gauge" says. The only sure way to check the pressure is with a known good mechanical gauge hooked into the system. Those factory "gauges" can be WAY off, and some of them don't even "gauge" the actual pressure at all - they read such and such pressure as long as there is enough pressure to activate the switch - basically just a pretty idiot light. But, as was previously stated, 10 lbs per 1000 rpm is a good rule of thumb. Specific pressures rely on many factors - oil viscosity, at what pressure the pump bypass opens, clearances, oil temp, etc. Although I don't put much stock in good oil pressure indicating good tight clearances. Most oil pumps move a lot more oil than the lube system actually needs, with the rest going to bypass. Even if the main clearances are .005" and spec is .002", if the pump can move enough oil to keep up, you'll still have good pressure. Like I said, if you're worried, get a good gauge and check it. Years ago, I noticed a slight dropoff in oil pressure in my '92 Dodge Cummins (no numbers - only marks on the "gauge"). I plumbed in my test gauge and found 100 psi at the top of the filter housing, and the "gauge" barely went past half.

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Mark - IN.

07-06-2004 19:35:16




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 Re: oil pressure and engine RPMs in reply to Jonathan, 07-06-2004 15:23:36  
Jonathan, I guess it depends on what it is that you're driving. A few years back, 40 lbs was real good, even at highway speed. Some imports were a lot higher. 60 lbs sounds real good too. But with some of the tight tolerances of today's engines, that's low. And a 20 lb swing is a pretty good swing, and I'm not saying that's bad. Oil pumps are mechanical and like anything else, the higer the RPM, the more oil that's going to be moved, and the more pressure is created. Want to sleep better? Locate the specs on your truck. Stop in a parts store and leaf through a manual on your truck (Chilton's, Llyod's, etc). If you do your own work, it'd be a good idea to have one anyway. And, if your local parts store sells oil pumps, it's entirely possible that the parts book may have the specs in it (they used to). Every engine has a minimum and maximum oil pressure when it rolls off the assembly line (stock), and the real question is whether or not 40 - 60 lbs pressure is correct for your engine. It just might be. Besides, all parts stores have that one thing that you realized you needed until you stopped in and saw it setting there calling your name, so just stop in as you're driving by, and don't let that one thing happen to be an oil pump you don't need, if you don't need it. Just my thought. Mark Krzyzanowski.

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wdTom

07-06-2004 18:36:44




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 Re: oil pressure and engine RPMs in reply to Jonathan, 07-06-2004 15:23:36  
When I was in the navy back a while ago an old chief engineman told me all you need is 10 lbs. per 1000 rpm. I take this to be a minimum, but it works out as a guide.



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rustyfarmall

07-06-2004 16:04:15




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 Re: oil pressure and engine RPMs in reply to Jonathan, 07-06-2004 15:23:36  
I would say everything is normal. Those electronic guages are supposed to work that way.
Your oil pressure is fine.



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Jonathan

07-06-2004 17:15:58




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 Re: Re: oil pressure and engine RPMs in reply to rustyfarmall, 07-06-2004 16:04:15  
Ok thanks, thats a load off my mind!, I wasn't for sure what was going on.



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