oil pressure sensor or oil level sensor

mrjean

Original poster
Member
Jul 15, 2012
110
i feel like this might be a no brainer but i just want to make sure.

the oil gauge on my dash fluctuates between 40 and 0 when im at iddle and triggers the "check gauges" light when it hits 0. in a 10 second mark, it goes to 0 to 40 like 3-4 times. does not matter if im in park or drive, its weird. started happening a few months ago and then stopped and had not happened in a while. now its happening a bit more often. i am NOT seeing any changes in RPM and my actual oil level is within range (almost to the full mark), on the dip stick.

im wondering if the issue is the oil pressure sensor or the oil level sensor...or (hopefully not) the oil pump.

one thing that i did find weird is that when i am picking up speed or with my foot on the gas above 2500 or 3000 rpm my oil gauge goes to like 50 or 55. usually goes back down to 40 once im cruising. any ideas?
 

AtlWrk

Member
Dec 6, 2011
674
My money is on a flakey pressure switch. The 4.2L engines don't have a true pressure sensor, just a simple switch that trips around 12psi IIRC. That means that the oil pressure gauge on the dash is entirely fabricated by the PCM. GM even went so far as to make it wiggle around a bit to deceive drivers that they're seeing the actual oil pressure--that's why you'll see it move up a bit at higher RPMs.
 

mrjean

Original poster
Member
Jul 15, 2012
110
any idea where the stupid thing is located? passenger or driver? im trying to see if i could get to it myself. pictures would be nice! :smile:
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR

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mrjean

Original poster
Member
Jul 15, 2012
110
aha and what exactly is on the driver side? where you have to take the intake manifold off?

btw...pictures of the cracked rear axle assembly coming tomorrow..(diff post i have here)
 

IllogicTC

Member
Dec 30, 2013
3,452
Here's a question not asked - How does he test the switch for proper operation? And how does he test the oil pump for proper operation? It'd be a shame to drop cash on a new switch and it be totally unneeded.
 

IllogicTC

Member
Dec 30, 2013
3,452
mrjean said:
aha and what exactly is on the driver side? where you have to take the intake manifold off?

btw...pictures of the cracked rear axle assembly coming tomorrow..(diff post i have here)

I believe that is the coolant temperature sensor. Someone please correct me on this? Behind the alternator (roughly)?
 

IllogicTC

Member
Dec 30, 2013
3,452
I'm seeing further-back on the driver's side of the block installed into the block is the EVAP Emission Canister Purge Solenoid. It's directly under the holes for the intake on the block, lines up right under the intake for cylinder 4 or betweeen 4 and 5. I would imagine this needs the intake removed to access.

Toward the bottom of the block there's two engine knock sensors, one lines up about with cylinder 2, the other betweeen cylinders 5 and 6. Near the rear knock sensor is the crankshaft position sensor. Removing the intake may facilitate ease of access, but isn't strictly required for these components.
 

IllogicTC

Member
Dec 30, 2013
3,452
Also to stay a little more on subject, to test the oil pump there is a tool available. Specifically:

J 42907 Oil Pressure Tester Adapter (screws in where the oil filter goes)
J 21867 Pressure Gauge and Hose"

Problem is, the adapter alone costs $100+, which is ridiculous considering it's not even nearly as complicated as the $10 that you screw on there every oil change, but whatever.
 

AtlWrk

Member
Dec 6, 2011
674
IllogicTC said:
Here's a question not asked - How does he test the switch for proper operation? And how does he test the oil pump for proper operation? It'd be a shame to drop cash on a new switch and it be totally unneeded.

Normally I would agree but at $30, the age of the car and how trivially easy it is to replace it wouldn't be a waste even if it wasn't the problem.

Another (much cheaper) option for testing: there is a threaded oil galley plug on the front face of the engine block right next to the filter and sensor that can be removed. It's an M16 x 1.5 thread for which you can get an adapter like this: http://www.summitracing.com/parts/atm-2268?seid=srese1&gclid=CK66iJ_Xo7wCFZDm7AodLGkAbA

It provides the de facto 1/8-27 NPT thread that any cheapo, off-the-shelf oil pressure gauge will fit.
 

mrjean

Original poster
Member
Jul 15, 2012
110
thanks guys, i guess my main concern is wanting to change the correct oil pressure switch (by correct i mean right location). the switch or sensor the guy held up on the youtube video resembles the one i need to change. i just dont know if its on the driver side towards teh rear like the video or passenger side like The roadie said. (im gearing more towards that side anywho)
 

AtlWrk

Member
Dec 6, 2011
674
mrjean said:
yea im talking like close to the wall behind the engine.
how to change gmc 2005 Oil Pressure Sensor - YouTube

not saying this is my car since i have a 6 cyl not an 8cyl

I can't see the video but are you saying it's of an 8cylinder? That would be the 5.3L engine which is entirely different than the 4.2L six cylinder that you have. The oil pressure switch is where Roadie's picture shows it: front passenger side directly above the oil filter. Easy to get to from the top or bottom. Five minute job really.
 

mrjean

Original poster
Member
Jul 15, 2012
110
*update*
ordered the switched and changed it (Also did an oil/filter change). while my mechanic is changing the filter and the switch he tells me that he does not think the switch is faulty or spilling oil. he says its coming from a big patch of glob that was put before i bought the car on the splined disconnect/oil pan. i took a picture. best way to remedy?View attachment 32819

i have a feeling someone is going to say remove cv axle, remove spline, remove oil pan, replace oil plan, and work in reverse. if that is that case, the car can stay like that. ill make it a warning for the next owner. i cannot keep dumping money in this car if im getting rid of it in a few months.
 

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NJTB

Member
Aug 27, 2012
612
Flemington, NJ
It isn't so bad as 'remove the oil pan'. Clean it off and find out where the oil/grease is coming from.
As far as I know, the only thing in that area that has grease is the axle disconnect. You may want to wiggle the axle (look for up and down play) and make sure the bearings in it are OK. It should have a slight amount, no slop.
 

mrjean

Original poster
Member
Jul 15, 2012
110
guessing u didnt read the whole post lol.

theres a patch or attempted repair done right above the spline disconnect with the oil pan. this is the oil that i keep seeing under the spline.
 

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