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Liberty Oil pressure sending unit?

6 messages,  Last post on May 07, 2009 at 9:53 AM

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#1 of 6 Oil pressure sending unit? by rickc38 May 06, 2009 (8:19 am)
Our 2004 Jeep Liberty has a problem where (usually when cold) the low oil pressure indicator will illuminate but when you shut off the engine and restart it will shut off. Is this a problem with the sending unit sending an incorrect code? Or maybe the oil pressure could be low? I'm seriously thinking of getting a gauge and testing the pressure. I know low oil pressure can mean BIG problems. I don't want to know about engine bearings being bad. But I know when I change the oil it takes a few seconds for the new oil in the pan to get to the crank because the engine ticks a bit for a few seconds. I've even tried putting oil in the new filter to "prime" it and it still seems to do the same thing. I don't like to hear those noises when I change the oil probably causing some unneeded wear. Any help would be greatly appreciated. -Rick Replies to this message: caribou1 (May 07, 2009 2:18 am) rickc38 (May 07, 2009 4:53 am) caribou1 (May 07, 2009 7:40 am) and 2 more...
#2 of 6 Re: Oil pressure sending unit? [rickc38] by caribou1 May 07, 2009 (2:18 am)
Replying to: rickc38 (May 06, 2009 8:19 am) I can see two things: - either the ECU does not change the status of the "at pressure" bit (low probability) and sends an engine malfunction alarm, - or you may have a leaking check valve (oil filter bypass) that lets the pressurized oil return into the sump via the pump after a few minutes when the engine is not running.   The absence of oil film normally explains the ticking sound of your engine but if you use mineral oil that is at the end of it's life, the engine will produce the same sound. This is a typical 4 stroke lawn mower engine issue: my wife doesn't know there is oil in there, she just pushes the thing Replies to this message: rickc38 (May 07, 2009 4:53 am) caribou1 (May 07, 2009 7:40 am) rickc38 (May 07, 2009 8:10 am) and 1 more...
#3 of 6 Re: Oil pressure sending unit? [caribou1] by rickc38 May 07, 2009 (4:53 am)
Replying to: caribou1 (May 07, 2009 2:18 am) No I don't use mineral oil. I always use new oil every 3000. But the check valve idea is a possibility though. But doesn't the check valve bypass the filter when it is clogged when the engine is running? I always use a new filter when I change the oil. Because if it was the sending unit sending an incorrect code wouldn't it signal the MIL light? I'm thinking about getting myself a scan tool and see if any fault codes come up even though the check engine light (MIL) isn't on. Might have something in memory. Replies to this message: caribou1 (May 07, 2009 7:40 am) rickc38 (May 07, 2009 8:10 am) caribou1 (May 07, 2009 9:53 am)
#4 of 6 Re: Oil pressure sending unit? [rickc38] by caribou1 May 07, 2009 (7:40 am)
Replying to: rickc38 (May 07, 2009 4:53 am) If you put in series: sump * pump * check valve-&-filter * engine   when the check valve cancels the filter you may get: sump * pump * engine   I think the time and pressure needed for the oil to circulate backwards through the filter is long enough to give you a noise free start even after a few hours. Replies to this message: rickc38 (May 07, 2009 8:10 am) caribou1 (May 07, 2009 9:53 am)
#5 of 6 Re: Oil pressure sending unit? [caribou1] by rickc38 May 07, 2009 (8:10 am)
Replying to: caribou1 (May 07, 2009 7:40 am) Ok that is true but if there is oil available in the filter it should start pumping right away. I mean there are no problems with oil pressure as far as I can tell after the oil is changed just that initial start after I have changed the oil and the pump pumps oil back into the system. That's the reason I tried filling the filter so that crucial time when the filter is filling up is eliminated. I don't know if the bypass will allow oil into the main gallery while the filter is filling up I don't think so. Replies to this message: caribou1 (May 07, 2009 9:53 am)
#6 of 6 Re: Oil pressure sending unit? [rickc38] by caribou1 May 07, 2009 (9:53 am)
Replying to: rickc38 (May 07, 2009 8:10 am) You would be surprised to see the time and initial effort it takes for oil to go through a dry membrane. Once the oil made it's way, it's purely friction. Before penetrating the filter it's a surface tension problem, and oil is repelled.

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