Oil pressure slow to build at startup

[Matthew Jeschke]

Okay, so I thought I had a post on this somewhere but cannot find it. My 2001 Z71 Tahoe is at nearly 240,000 miles. I bout at 225,000 miles. Has 5.3L v8. I'm wanting to swap out for a 6.0L and hoping this motor holds together until then. It's had some minor annoyances but this is the only one that concerns me...

I'm running 5w-30 oil and is pretty hot where I live.

1. I start up the truck... after which it takes a little while to build oil pressure. Oil pressure fluctuates a bit as well once idling. But seems to maintain a good pressure.

2. I turn off truck and wait about 30 seconds... then restart it. Same symptoms persist, leading me to believe block is quickly bleeding oil pressure somewhere.

I thought might be a bad oil filter / drain back valve so I bought a Wix filter and swapped it on but seems to continue to have same problem.

I'm wondering if this might be a sign of heavily warn main bearings.

 

[rockola1971]

oring at your oil pickup tube in the pan.

 

[Matthew Jeschke]

And like an idiot I redid oil pan gasket but not that :/

I doesn't seem to be too bad right now though but maybe you can tell from this video...

Ps, can that pickup tube gaske be changed by removing front cover?

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[SnowDrifter]

Can you read live data or check with mechanical gauge? Honestly that just looks like normal gauge behavior to me. If memory serves, that year has an air core stepper motor, which is prone to clogging / lubrication failure with age. It's not an encoder like the later trucks. Hence why I question if it's a real concern or one of gauges.

As far as bleed off: there's no air, accumulator, or other source of elasticity in the lubrication system other than the small amount offered by the irom block, steel filter housing, and maybe some flex on the rear cover. But at the pressures these are at, those are negligible. The short answer is oil Pressure is related to engine rpm with essentially no delay once the system is primed and full. Engine turns off? Oil Pressure gone in an instant. Rev to 5k? There's full oil Pressure immediately

 

[SnowDrifter]

Also, yes you can get to the gasket by removing only the front cover but it's not my chosen route. You might have to trim / bend a wrench, and do NOT drop that bolt or you'll be ripping pan off anyway

 

[Matthew Jeschke]

Can you read live data or check with mechanical gauge? Honestly that just looks like normal gauge behavior to me. If memory serves, that year has an air core stepper motor, which is prone to clogging / lubrication failure with age. It's not an encoder like the later trucks. Hence why I question if it's a real concern or one of gauges.

As far as bleed off: there's no air, accumulator, or other source of elasticity in the lubrication system other than the small amount offered by the irom block, steel filter housing, and maybe some flex on the rear cover. But at the pressures these are at, those are negligible. The short answer is oil Pressure is related to engine rpm with essentially no delay once the system is primed and full. Engine turns off? Oil Pressure gone in an instant. Rev to 5k? There's full oil Pressure immediately

I have a scan tool with live data. However better like your mechanical reader.

Although, maybe i am fine if that looks like standard behavior.

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[Rocket Man]

It looks normal to me. I see nothing to worry about.

 

[HiHoeSilver]

Mine acts exactly the same as your video.

 

[Chris2144]

Mine primes just a hair quicker than yours but I also only have 170k miles. Mine also is a little twitchy at idle. And every GMT 800 I've owned is that way. Like what had already been stated I think you're fine but the pick up gasket is common on these so keep that in mind

 

[SnowDrifter]

For what it's worth

@62f ambient

 

[SnowDrifter]

edit: Double post

 

[Matthew Jeschke]

For what it's worth

@62f ambient

Thanks! That is super helpful. That pump is pretty awesome. Mine is around a second or 2 slower but you're right is probably fine

I became really attentive to startup pressure as I pulled valve covers off and cleaned up lifters. I was worried running all that cleaner through motor might change my clearances on main bearings. (Probably just rumor that it could do that on high mileage motor).

I just want motor to last till I can find a 6.0 to swap in


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[SnowDrifter]

Not unless ya washed the oil out of the main bearings, which would be difficult. In which case put the pedal to the floor and crank it for 15 seconds. Barring that, an couple short oil changes to get the solvent out and Bob's your auntie

 

[rockola1971]

Oil pressure looks good but that delay in the pressure coming is weird. Ive never had a GM (And thats just about all ive ever owned) do that. My (2) 2003 Tahoes and my 2005 Yukon Denali do not do what yours is doing. Mine come up immediately without any delay. That looks like it could possibly be in the oil pressure gauge. If it were me I would get a mechanical gauge on it to check to see if the oil pressure is actually doing that. Could be the oring on the pickup tube getting ready to dump on you.

 

[Matthew Jeschke]

Good points. I think I'll start with the sensor.

 

[rockola1971]

Good points. I think I'll start with the sensor.

Oil pressure sending unit, wire connection at sending unit check for corrosion, oil pressure gauge itself, connection to instrument cluster for oil pressure gauge check for oxidation or corrosion then the nasty stuff like pickup tube oring, bypass device in oil filter adaptor, internal engine fault (bearings) or ????.

 

[dougo]

Typical varnish build up in the oil passages I would add Marvel Mystery oil at your next oil change some people use sea foam use per the directions ,

 

[cam3439]

Based on your oil pressure and oil weight that you’re running, I don’t think your bearings are shot.

If you’re going to tear the front apart to change the o-ring on the pickup tube, I’d recommend changing the oil pump, since you’re already in there. The pump does eventually wear out and can allow oil to bleed through; not to mention the pressure relieve valve possibly being slightly stuck open (debris or a scratch along the cylinder can cause this).

My 2005 Tahoe historically sat at 30-32psi when I bought it, but I changed out the pickup tube, o-ring and pump. Now my oil pressure picks up and idles like normal.