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Old 11-10-2004, 09:45 PM
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Location: Toronto,On,Canada
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oil pressure drops to zero at idle?bad battery?

Recent cold weather but not too cold.Recent oil +filter change ,a mix of 5-50W synthetic (1.5 litres),4 litres of Penns oil high mileage 10-30W.That is what is handy in my garage.
Now on start-up(high idling),pressure at 3.Running on highway and above 60km(40mph),pressure around 3 bar(max).
However idling,oil pressure drops to 0.2, 0.3 sometimes zero today,ie nil.
Peeping thru oil filler hole,there is oil gushing into crankcase with engine running,not dry.
No unusual noise.
my car's alarm consumes one battery per year(battery is now 11 month old),Idling voltage 13.95v.At rest witheverything off(except alarm) ,voltage across battery=12.25-12.40 volts.

Could this low oil pressure be due to
(i)bad oil pressure sender
(ii)bad battery going south.
(iii)wrong grade oil,I've sucked out 2 litres of old and put in 2 litres of 20-50W tonight just in case,Tomorrow i'll know whether thatis the culprit.
I suspect the battery cos last yr right before the engines dies with the bad battery,the oil gauge would fluctates and drop to zero then engine died.Replaced battery ,problem gone.However,now there is no fluctutation in the oil pressure,just low or zero pressure when hot.
one previous poster suggest that his VR was responsible while others says oil in crankcase means pump is good and likely culprit being oil p sender.
Any experience or opinion?
Tom 2010 C250 4-matic Sport (Canada)
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Old 11-10-2004, 11:24 PM
compress ignite's Avatar
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Join Date: Feb 2004
Location: 32(degrees) North by 81(degrees) West
Posts: 5,554
1. The 13.95 V figure you quote at idle for (I assume the alternator) does not "GEL" with the 12+ V figure you get ( I assume [across battery terminals] at idle with no load. (Battery has a solid double ought gage connection to a huge power draw)
2. Per SteveBFL electrical gauges are dependant on steady regulated voltage.
anything else makes the guages "Chicken Bones" thrown on the ground
as a prognostication of what is actually going on , on the other side of the
3. "If it ain't electrical , check the rubber O-rings on the inner shaft that the
basket oil filter fits on. If they are "Hard " + NOT FLEXIBLE replace."
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Old 11-11-2004, 12:08 AM
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Join Date: Mar 2003
Location: Southern California
Posts: 2,066
Normal system voltage with the engine running should be 13.5-14.5 volts. Open circuit voltage (engine off) for a fully charged battery should be about 12.5 at room temp.

The sending unit is probably the least reliable part of the oiling system. Since it's not easy to test, you might just go ahead and replace it, but check the connector first to make sure it doesn't have high resistance.

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Old 11-11-2004, 12:16 AM
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Join Date: May 1999
Location: Toronto,On,Canada
Posts: 280
Hello Duke,
The v across battery posts with engine off (12.35 with alarm light flashing0)seems a bit low compared to my 740 volvo's 12.6(no alarm)
Is the sender unit on the oil filter housing itself or more near the firewall.Is it simple diy: a disconnect -loosen - replace- tighten- job.,as easy as oil filter change?
Do I need the oil filter off?likely
Do i need the air filter cover off? as i searched and found.
Tom 2010 C250 4-matic Sport (Canada)
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Old 11-11-2004, 12:20 AM
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Join Date: May 1999
Location: Toronto,On,Canada
Posts: 280

Does anybody has a picture of where the oil pressure sender?
Lino,are you out there? ha ha ha
Tom 2010 C250 4-matic Sport (Canada)
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Old 11-11-2004, 08:07 AM
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Join Date: May 1999
Location: Toronto,On,Canada
Posts: 280
Unhappy bad battery

this am after a colder night with engine off,outside temp 6 celsius,42 F,voltage across battery=11.93 V,

must be battery.

oil pressure fine now,start-up 3,1+ at idle. 3 at 60kph(40mph).(though not completely hot sl below 80 C on the engine coolant temp gauge)

guess i have to go to Costco for a new battery again(kirkland branded interstate group 41---only 50 US$,cant complain)
Tom 2010 C250 4-matic Sport (Canada)
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Old 11-11-2004, 10:33 AM
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Location: Dallas/Fort-Worth
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I think you are dealing with two issues...really.

But let's wait until you do the battery replacement first.

The sender will either register close to zero, or peg at 3 on the gauge dial when it's on its way out.

Cold oil is thick, and should register a LOT more than near zero at idle.
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