Oil Pressure

[John Snyder]

In the glove box is a sticker, your RPO Sheet, with all the codes or options your truck is equipped with. It will show probably show LMG and you can also see this on the emissions sticker under the hood. Ethanol is cool to run the engines love the stuff, free horsepower. I run it when it makes financial sense to or just for the extra power. Mine gets its best mileage on low alcohol percentages, between 15% and 20%.



Your engine has a variable displacement oil pump, pretty cool tech that is worth looking up and learning about.

cool so if it is LMG which it probably is then the oil pressure i described and sent in that pic are normal?

 

[John Snyder]

In the glove box is a sticker, your RPO Sheet, with all the codes or options your truck is equipped with. It will show probably show LMG and you can also see this on the emissions sticker under the hood. Ethanol is cool to run the engines love the stuff, free horsepower. I run it when it makes financial sense to or just for the extra power. Mine gets its best mileage on low alcohol percentages, between 15% and 20%.


It is an LMG i found it in the glovebox

 

[swathdiver]

cool so if it is LMG which it probably is then the oil pressure i described and sent in that pic are normal?

Yes, once hot, after driving a while, it will drop into the 20s on the gauge at idle or stopped at a light. I forget exactly but the bypass spring on the LMG is somewhere in the 40s.

Aluminum blocks see a little bit lower pressures but they pump more volume because of tolerances.

 

[John Snyder]

Yes, once hot, after driving a while, it will drop into the 20s on the gauge at idle or stopped at a light. I forget exactly but the bypass spring on the LMG is somewhere in the 40s.

Aluminum blocks see a little bit lower pressures but they pump more volume because of tolerances.

thanks for all your help much appreciated

 

[John Snyder]

Yes, once hot, after driving a while, it will drop into the 20s on the gauge at idle or stopped at a light. I forget exactly but the bypass spring on the LMG is somewhere in the 40s.

Aluminum blocks see a little bit lower pressures but they pump more volume because of tolerances.

Learned a few things I never knew today as well

 

[JC 707]

Sorry guys didn't realize this was the 2007-2014 forum.

 

[Thebesta94]

sensor might just be bad. I have had to replace 2 of them since I bought mine. They are a ***** to get too (back side of engine block wedged by the firewall) with my big hands but other than that not too difficult. Can get a all parts and custom socket for like $30 in total.

I only say this as my guage was tweaking out for about 2 weeks before it just read 0 pressure all the time. Brought it immediatly to the shop and it was holding pressure just fine... sensors just seem to go to shit pretty often

 

[tjoyce81]

The most likely cause of a low oil pressure issue in a 5.3 is a blocked oil pressure unit screen or an oil pump o-ring failure. HOWEVER - there is an often overlooked and very common issue that puts many of these engines in the junkyard FOR NO REASON. It is a weak or failing oil pressure relief valve inside of the oil pan. If ALL of the above does not fix the oil pressure issue - it IS the relief valve inside of the oil pan. The spring wears out in these valves, which causes oil to simply dump into the pan - and not feed the upper part of the lifter feed circuit. The oil pressure sending unit is located in this circuit - which is the reason you get a low oil pressure indication - when in fact oil pressure is good. The fix is to either replace this valve, or to simply install a plug so the oil does not dump into the pan.... When you block this off - oil pressure will be better than before....
Also, the tell tale sign of a failing oil pressure relief valve spring is a constantly fluctuating oil pressure indication, and pressure falling to zero after a few minutes - or low enough to set a "stop engine low oil pressure" message. If all of the above does not work, drop the oil pan and replace this valve or just block it off...

 

[daves07 tahoe]

The most likely cause of a low oil pressure issue in a 5.3 is a blocked oil pressure unit screen or an oil pump o-ring failure. HOWEVER - there is an often overlooked and very common issue that puts many of these engines in the junkyard FOR NO REASON. It is a weak or failing oil pressure relief valve inside of the oil pan. If ALL of the above does not fix the oil pressure issue - it IS the relief valve inside of the oil pan. The spring wears out in these valves, which causes oil to simply dump into the pan - and not feed the upper part of the lifter feed circuit. The oil pressure sending unit is located in this circuit - which is the reason you get a low oil pressure indication - when in fact oil pressure is good. The fix is to either replace this valve, or to simply install a plug so the oil does not dump into the pan.... When you block this off - oil pressure will be better than before....
Also, the tell tale sign of a failing oil pressure relief valve spring is a constantly fluctuating oil pressure indication, and pressure falling to zero after a few minutes - or low enough to set a "stop engine low oil pressure" message. If all of the above does not work, drop the oil pan and replace this valve or just block it off...

My 2007 5.3l Tahoe w/225k has been suffering from fluctuating oil pressure, I replaced the screen and sending unit, no change. The pressure is very low (10psi or less) on startup, it climbs when engine RPMs are above about 1,000, but then quickly drops back at idle, I wonder if this could be the pressure relief valve, in the oil pan, you mention above. I did not know that existed. Could it be that sludge is causing the valve to stick? I am considering dumping a quart of ATF into the motor, running it at idle for 15-20 minutes, then changing oil to see if it removes sludge and frees the valve. A whole lot easier than dropping the pan. Thoughts?

 

[wjburken]

My 2007 5.3l Tahoe w/225k has been suffering from fluctuating oil pressure, I replaced the screen and sending unit, no change. The pressure is very low (10psi or less) on startup, it climbs when engine RPMs are above about 1,000, but then quickly drops back at idle, I wonder if this could be the pressure relief valve, in the oil pan, you mention above. I did not know that existed. Could it be that sludge is causing the valve to stick? I am considering dumping a quart of ATF into the motor, running it at idle for 15-20 minutes, then changing oil to see if it removes sludge and frees the valve. A whole lot easier than dropping the pan. Thoughts?

I would suspect a bad o-ring on your oil pick up tube before a bad pressure relief valve. Either is possible, but based on the number of folks posting issues with oil pressure like yours, the majority solve it with a new o-ring on the tube.