Tahoe idle oil pressure

[JPVortex]

Hi so my 05 tahoe with the 5.3 seems to have lowish oil pressure while idling. At idle it has around 25-27psi of oil pressure, compared to a few months ago where it was a steady 35-40psi. Oil was low the other day and I topped it off, but the oil pressure stayed the same.

 

[CLSVT]

I'm curious to hear the comments you receive. On a related subject, I've never been very comfortable with the accuracy of these dashboard oil pressure gauges in our Chevys. If I'm going to diagnose an issue, I want to be sure my data is accurate. Has anyone verified the accuracy of these dashboard oil pressure gauges? What method did you use to verify? Sorry, I don't mean to hijack your question, just feel better knowing we are looking at real readings.

 

[OR VietVet]

Two things, quick PITA to change possible fix is the oil pressure sensor and use a Genuine GM replacement part when you do. If you do change it, attach an oil pressure gauge and check it. My 05 does idle at close to 40 PSI.

 

[Sam Harris]

What kind of oil filter do you use?

 

[JPVortex]

I'm curious to hear the comments you receive. On a related subject, I've never been very comfortable with the accuracy of these dashboard oil pressure gauges in our Chevys. If I'm going to diagnose an issue, I want to be sure my data is accurate. Has anyone verified the accuracy of these dashboard oil pressure gauges? What method did you use to verify? Sorry, I don't mean to hijack your question, just feel better knowing we are looking at real readings.

I haven't verified with hooking a gauge up yet, just going off of the one on the dash, and yeah I'm not sure I believe it either.

 

[JPVortex]

Two things, quick PITA to change possible fix is the oil pressure sensor and use a Genuine GM replacement part when you do. If you do change it, attach an oil pressure gauge and check it. My 05 does idle at close to 40 PSI.

Will def do this soon, thanks!

 

[JPVortex]

What kind of oil filter do you use?

I think it may have a Supertech right now, not sure why I cheaped out on it a few months ago. I plan on changing it soon, 3500 miles into a full synethetic change, but the oil looks pretty dark brown so I'll change sooner than later with probably a Mobil 1 or ACDelco filter.

 

[Fless]

If the tach gauge is correct the idle seems a bit low, FWIW. You might want to get a scanner on it to see what the desired (commanded) idle speed is and compare it to the actual per the scanner PID. Not sure if the gauge is off or not.

 

[iamdub]

Hi so my 05 tahoe with the 5.3 seems to have lowish oil pressure while idling. At idle it has around 25-27psi of oil pressure, compared to a few months ago where it was a steady 35-40psi. Oil was low the other day and I topped it off, but the oil pressure stayed the same.View attachment 389361

Don't take this lightly. Treat it as a serious matter, diagnose it THEN determine from that if it's not so serious.

First off- verify the condition. As the others mentioned, the gauges and sensor can be faulty. Use a mechanical gauge to verify the pressures. You can connect the gauge to the sensor port. If you do, you might as well have a new sensor on hand to replace it while you're at it.

If the pressure is indeed low, and it onset rather abruptly, dive in to the common cause(s). Low quality oil breaks down and has wilder viscosity swings and a low quality filter can cause a drop in pressure. Or, if the filter clogged up and you're now bypassing it. The Supertech should be okay since it's synthetic, but you still have to start with the easy stuff first. Change the oil and filter with good stuff and observe.

If no change, do the O-ring test. Add two extra quarts to the crankcase and drive somewhere, preferably close and not requiring high RPM, you can put the front into a nosedive, like a shallow ditch or back it up a hill. If the pressure suddenly jumps up to its previously normal range, then you've diagnosed a leaky O-ring. Drain the extra two quarts and plan your repair.

Another possibility with this generation is a cracked head allowing the coolant to mix with the oil in amounts so small that it goes undetected. It sludges up the inside of the engine. Eventually, the pickup screen gets choked off, reducing oil pressure. Do you have to add coolant ever so often, like once a month?

 

[JPVortex]

Don't take this lightly. Treat it as a serious matter, diagnose it THEN determine from that if it's not so serious.

First off- verify the condition. As the others mentioned, the gauges and sensor can be faulty. Use a mechanical gauge to verify the pressures. You can connect the gauge to the sensor port. If you do, you might as well have a new sensor on hand to replace it while you're at it.

If the pressure is indeed low, and it onset rather abruptly, dive in to the common cause(s). Low quality oil breaks down and has wilder viscosity swings and a low quality filter can cause a drop in pressure. Or, if the filter clogged up and you're now bypassing it. The Supertech should be okay since it's synthetic, but you still have to start with the easy stuff first. Change the oil and filter with good stuff and observe.

If no change, do the O-ring test. Add two extra quarts to the crankcase and drive somewhere, preferably close and not requiring high RPM, you can put the front into a nosedive, like a shallow ditch or back it up a hill. If the pressure suddenly jumps up to its previously normal range, then you've diagnosed a leaky O-ring. Drain the extra two quarts and plan your repair.

Another possibility with this generation is a cracked head allowing the coolant to mix with the oil in amounts so small that it goes undetected. It sludges up the inside of the engine. Eventually, the pickup screen gets choked off, reducing oil pressure. Do you have to add coolant ever so often, like once a month?

I'll check with a mechanical gauge ASAP. I will also change the oil and filter with high quality stuff if it actually has low oil pressure. From there I'll test the o ring if needed.

As for the cracked head theory this truck has never used any coolant whatsoever, I've never had to even top off the coolant at all. Only time I've lost a bit was when removing the lines at the throttle body lol.

One thing I'm worried about is oil consumption. My oil was very low the other day, and this truck has never consumed oil, I checked it about a month and a half ago and it was nearly full, yesterday I had to add a quart. Underneath is slightly wet around the pan, but no more than it was before. So I'm not sure if its burning it or what.

 

[iamdub]

As for the cracked head theory this truck has never used any coolant whatsoever, I've never had to even top off the coolant at all. Only time I've lost a bit was when removing the lines at the throttle body lol.

One thing I'm worried about is oil consumption. My oil was very low the other day, and this truck has never consumed oil, I checked it about a month and a half ago and it was nearly full, yesterday I had to add a quart. Underneath is slightly wet around the pan, but no more than it was before. So I'm not sure if its burning it or what.

This is good news! After what my brother's '05 Sierra experienced, I had to mention it. It was the typical Castech head failure. He lost all oil pressure one day. After I questioned him, he said he's been adding a little coolant every month for months. He also said the oil pressure range had steadily been dropping. The coolant was mixing with the oil through the crack in the head. But, being such a small and slow leak, the water part of the coolant would steam off when the truck was at operating temps, so there was no telltale milkshake in the oil. The rest of the coolant's chemicals remained and gunked up the oil and made a mess inside the engine. That day, a flat, thick chunk of sludge in the oil pan broke free and was sucked up by the pickup tube, blocking the flow and causing the loss of oil flow and pressure.

As for the consumption, a quart over six weeks isn't terrible, but should still be investigated. Done any towing during the past six weeks?

 

[JPVortex]

This is good news! After what my brother's '05 Sierra experienced, I had to mention it. It was the typical Castech head failure. He lost all oil pressure one day. After I questioned him, he said he's been adding a little coolant every month for months. He also said the oil pressure range had steadily been dropping. The coolant was mixing with the oil through the crack in the head. But, being such a small and slow leak, the water part of the coolant would steam off when the truck was at operating temps, so there was no telltale milkshake in the oil. The rest of the coolant's chemicals remained and gunked up the oil and made a mess inside the engine. That day, a flat, thick chunk of sludge in the oil pan broke free and was sucked up by the pickup tube, blocking the flow and causing the loss of oil flow and pressure.

As for the consumption, a quart over six weeks isn't terrible, but should still be investigated. Done any towing during the past six weeks?

Wow that sucks for that Sierra! Were you able to salvage the engines lower half without any major troubles?

Also I never tow with the Tahoe at all, it has a hitch receiver so the previous owner before 2019 when my mother owned it probably did, but not in years now.

Would this oil pressure testing gauge work alright for what I need? The oil pressure sending unit is all the way by the firewall behind the intake correct?

 

[iamdub]

Wow that sucks for that Sierra! Were you able to salvage the engines lower half without any major troubles?

I was. Pulled it out, tore it down to the short block and scrubbed it clean by hand. Replaced the lifters, push rods, rockers, timing set and all seals/gaskets. Got some low-mile 799 heads from a newer truck and added a high volume oil pump to the mix. All this was almost four years ago and at 181K miles. He's now around 220K miles. It hasn't been his daily driver since he bought a Camry about a year ago. He just uses it to haul his toys to the camp and general hauling duties around his town.

Also I never tow with the Tahoe at all, it has a hitch receiver so the previous owner before 2019 when my mother owned it probably did, but not in years now.

Was asking cuz high loads (high manifold vacuum) can make it consume more oil through the PCV system. I strongly recommend a catch can. You can get one for about $20 off Amazon. It would at least let you see if the oil is being consumed through the PCV system, while catching most of it so that's it's not actually burnt in the cylinders.

Would this oil pressure testing gauge work alright for what I need? The oil pressure sending unit is all the way by the firewall behind the intake correct?View attachment 389389

Sure and yes. There's a special socket available for it if you need it.

 

[JPVortex]

Diagnosis is going to happen ASAP, oil pressure at idle is down to about 21 today, was like 27 yesterday. Did a rev test to see how high I could possibly go, at 5k rpm I had just below 50psi oil pressure, so definitely going to keep it at 4k rpm or below.

As for an oil filter, how do you guys think this ACDelco one would do with full synthetic oil? As for oil not going to use Supertech, I'll probably go with Pennzoil or something.

 

[JPVortex]

Let me know what you guys think. I'm on a budget and I'm thinking about catching the oil that is in the engine, putting in a better filter and reusing the oil for now, as it's not very old at all. The oil looks okay on the dipstick so I see no reason not to unless theres like metal chunks in it.

 

[JPVortex]

So I got the oil pressure tester. But I dont believe any of these are the right size? Reading online it seems like it's a 16mm male into the threads where the oil pressure sending unit goes.

 

[ScottyBoy]

So I got the oil pressure tester. But I dont believe any of these are the right size? Reading online it seems like it's a 16mm male into the threads where the oil pressure sending unit goes.
View attachment 389437

I bought that same oil pressure gauge kit from Harbor Freight. It does NOT fit LS engines out the box. You need to buy or make an adapter. Since I replaced my oil sending unit just prior to buying this gauge, I used my old oil pressure sending unit to make an adapter. I drilled it out and tapped it so that the threads on the hose in that kit would screw right into the base of the old send unit. Harbor Freight sells a cheap tap and die set that has the correct size tap you need. I believe it was about 10 bucks or so. But it's a CHEAP set. The tap handle broke as I was using it. But it served it's purpose, to tap that one hole I drilled in the base of my old oil sending unit. After you make that adapter, it will screw right into the intake manifold where the oil sending unit screws in. And it will also screw into the block at the oil access port right above and behind the power steering pump after you unscrew the pipe plug from the port.

 

[JPVortex]

I bought that same oil pressure gauge kit from Harbor Freight. It does NOT fit LS engines out the box. You need to buy or make an adapter. Since I replaced my oil sending unit just prior to buying this gauge, I used my old oil pressure sending unit to make an adapter. I drilled it out and tapped it so that the threads on the hose in that kit would screw right into the base of the old send unit. Harbor Freight sells a cheap tap and die set that has the correct size tap you need. I believe it was about 10 bucks or so. But it's a CHEAP set. The tap handle broke as I was using it. But it served it's purpose, to tap that one hole I drilled in the base of my old oil sending unit. After you make that adapter, it will screw right into the intake manifold where the oil sending unit screws in. And it will also screw into the block at the oil access port right above and behind the power steering pump after you unscrew the pipe plug from the port.

I think I'll buy an adapter on Amazon.... lol. I'm also considering just running a thicker oil like 10w40 for now to buy me some time because I'm low on funds at the moment.

 

[Fless]

M16-1.5 male to 1/8" NPT female:

Pardon Our Interruption

https://www.amazon.com/GlowShift-Female-Sensor-Adapter-Reducer/dp/B00NWZZBS6

Swap Male M16x1.5 to Female 1/8 NPT Oil Pressure Sensor Adapter for GM LS Engine | eBay

Male M16-1.5 to Female 1/8"-27 NPT Adapter. Compatible with: All GM LS Series Engines. 1 x Oil Pressure Sensor Adapter. This adapter installs most commonly in the top-rear, or front-driver side of the engine block to access pressurized oil of the engine.

www.ebay.com

 

[ScottyBoy]

I think I'll buy an adapter on Amazon.... lol. I'm also considering just running a thicker oil like 10w40 for now to buy me some time because I'm low on funds at the moment.

I was going to originally do that, just buy an adapter. But it would have taken 2 or 3 days to arrive, and I was ready to get it done. After I couldn't find anywhere local to buy one, that's when I decided to just drill out my old oil sensor and just make my own adapter.