No oil pressure!

GunnyIa

Member
2012 GMC Sierra 1500 oil pressure dropped to almost zero at 15 mph, jumped up a little with throttle increase, then back to almost zero at idle.

Checked oil level, it's at the full mark.

Oil pump? (where is it?) or pressure sending unit? (that's lost to me, too). Any experience with this occurance?

Appreciate all suggestions!

Gunny, in Iowa
 
You have to determine actual oil pressure. Remove the sending unit and install a pressure gauge and get readings. Usually the service manual will say to run it at idle then at 2,000 RPM and take both readings. Hot idle and cold idle low readings are telling. Post back
 
Couple of possible issues u may be
dealing with. Either a faulty oil psi
sender, or the gauge is quirky. There is
a filter screen by the psi sender that
gets plugged and will cause the sender
to have a false reading. Does the engine
die on you? Does the engine light come
on? If it doesn't I'm betting the gauge
in your dash is goofy. GM has had
numerous issues with this over the
years.
 
Not a GM, but the same issue on a Dodge with LOTS of miles on it. I would be driving down the road and the pressure would drop to nearly nothing, gauge go to zero and light come one. Then it would come up to something less than normal. Much worse when cold. After much discussion as to spend the time or not, we dropped the pan to find the pickup for the oil pump pretty much stopped up. It was apart, so a new pump and screen went in. Fixed the problem and is going with nearly 300000 miles on it. Damage done??? Unknown, but it's not consuming any oil to speak of (maybe a quart every 2000 miles) and runs pretty good.

As I said, not GM, but similar description.
 
I had a Ford truck that I bought new and it idled at 5 lbs. and ran at 45 lbs. at 2,000 RPM. Every time you shifted gears the oil pressure gauge looked like a tach going up and down. Dealer put 2 pumps in it and last time they tore the bottom end down and check bearings and found every think ok. The guy that tore it down told me to run it and if it started to make any noise run till it blew because Ford would put new engine in under warranty. Had the truck for seven years and engine never went bad and never used any oil.
 
Took truck to dealer to diagnosis problem. Will post back with results. Thanks for the replies!

Gunny, in Iowa
 
If it is a LS variant (4.8, 5.3, 6.0, or 6.2) the oil pump is actually behind the front timing cover and slips over a keyway that is part of the cam sprocket. The late 99 early 2000 engines were actually common for doing this, but GM fixed that in 01-02. The pickup tube actually slips into the pump and is sealed with an O-ring. Tube is held in place with a single bolt.

As far as the factory dash gauge goes. The oil pressure sensor is located in the very back of the engine, where the distributor would be on an old chevy small block. It's a pain to get to BTW and you will need a really deep 21 or 23 mm socket to get it off. Check it there with a manual gauge, maybe the sender has failed

I doubt there is anything crazy going on with the gauge. Long story short the sender does not go the gauge but to the Power train control module (PCM). Which in turn tells the microprocessor in the dash cluster what to tell the operator. So basically your dash computer is being told what to show you the operator by another computer which is receiving the input from the pressure sensor IE nothing there you can trouble shoot other than seeing is the sensor is bad.
 
Got my truck back today. Was told the oil was wrong viscosity and oil filter was a very cheap one, not the filter needed for this GMC.

They changed oil & filter, and fix a burned out headlight. $150 total cost. Apparently the filter has a check valve in it. Didn't know there was a filter like that!

Truck runs great with 50+ oil pressure. I'm feeling beter now. Thanks for your posts!

Gunny, in Iowa
 
Glad you got it fixed with no big problems. Shows not to jump to conclusions, and don't use cheap filters and oil. Check valve anti-drainback operation is important.
 
(quoted from post at 21:50:08 12/17/15) Got my truck back today. Was told the oil was wrong viscosity and oil filter was a very cheap one, not the filter needed for this GMC.

They changed oil & filter, and fix a burned out headlight. $150 total cost. Apparently the filter has a check valve in it. Didn't know there was a filter like that!

Truck runs great with 50+ oil pressure. I'm feeling beter now. Thanks for your posts!

Gunny, in Iowa

What brand was that filter?
 
Showcrop I would say that his problem was the filter more than the oil. I would almost bet it was a Fram filter.
 
(quoted from post at 07:52:08 12/19/15) Showcrop I would say that his problem was the filter more than the oil. I would almost bet it was a Fram filter.

That's what I am thinking.
 

That is the latest deal with "New engines"....they are using far SMALLER oil pick-up tubes and they cannot flow enough oil if it is a heavier Viscosity...

That and the chances of a bad oil filter could be the problem...
There is Nothing better than a Mechanical (Stewart Warner) oil pressure GAUGE....

Ron..
 
The oil filter is your problem. I was a GM
Service Advisor for several years. Always use
original equipment, it does make a difference!
The GM oil filter has a drain back valve that will
make the difference!

Scott
 

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