Post your “ cold start “ oil pressure and oil details.

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I thought this might interesting during the current cold snap.

I started my 2008 Chev 6.0 LS engine at -4 F and got around 20 psi indicated on the pressure gage. Once fully warm at 200 F on the water temp gage, it was idling at just under 40 psi. The oil is Pennzoil Platinum Euro 5w40. The oil pressure gage is high up on the engine and monitors the oil pressure after it goes through the filter and climbs up the oil galleys to the top of the engine.

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That's an excellent setup, and useful to determine oil filter loading. When the pressure drops with nearly the amount of the bypass valve, it's filter change time.

Don't have an oil pressure gauge or sensor on my car.
 
I can’t say that I’ve ever seen that behavior. Oil pressure should peg and be highest at cold start.

Dropping so low seems odd too because I’d expect that any mechanical bypass would close long before that.

That gauge may wel be buffered or not real.

The only delays I see are on my Cummins trucks where the filters don’t stay full for whatever reason, so it takes a second to pump up, or similarly on the mechanical gauges on my MB diesels which have a pipe that needs to be pumped up. And that’s like a second. Then pegged. They’ll drop when the oil is warm.

Here’s an example of the gauge pumping up after sitting for five months. Usually it’s much faster.



Here’s my high mileage Cummins after I got it. With two mismatched old batteries. You can see the oil pressure build up because the filters drain back about 1/3.

 
Don't forget that your mercedes gauge tops out at 45 psi, quite low.

What's the bypass valve pressure on those LS engine filters, and what is the oil pump bypass? I suspect his filter was a big restriction when cold, reducing pressure up top but likely similar pressure at the pump.

My car's oil filter has a 2.5 bar bypass so 35-ish psi.
 
The positioning of the oil pressure sensor is important to interpreting results. Here is the diagram for the oil system on a LS engine. Oil enters the pump at the front of the engine, travels the length of the block, goes through the oil filter then climbs the height of the block where the sensor is exposed to the flow of the oil. The oil then travels through the galleys to the cam and lifters and down to the main bearings while some goes up into the heads and lubricates the rockers and valve stems.

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This. It should be highest on cold start, and lowest at hot idle.
It depends on where the oil pressure gage is mounted. What you said is certainly true if the reading is taken between the oil pump and filter. But even with a pressure sensor mounted at the top of the engine, everything goes out the window at -4 F ( -20 C ). The oil viscosity is no long in the 2 to 16 cSt at 100 C. It’s 10’s of thousands of cSt at -20 C and suddenly that oil is trying make it through the gallery’s and filter, even if the bypass opens. With this potential record breaking weather I’m encouraging folks to observe their oil pressure upon start up ( if they have an oil pressure gage). It should be quite interesting. :)
 
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I thought this might interesting during the current cold snap.

I started my 2008 Chev 6.0 LS engine at -4 F and got around 20 psi indicated on the pressure gage. Once fully warm at 200 F on the water temp gage, it was idling at just under 40 psi. The oil is Pennzoil Platinum Euro 5w40. The oil pressure gage is high up on the engine and monitors the oil pressure after it goes through the filter and climbs up the oil galleys to the top of the engine.

View attachment 131647View attachment 131648
Early during my time here - I made mention of flow distribution (path of least resistance) and got blasted by the PD pump (pumps are part of my job btw) and pumpable crowd … Of course it varies for a short period at cold start …
 
It appears that the oil pressure sending unit is in the same place as the older small blocks but on the original small block the oil pump was at the rear of the engine. There could be other differences that I'm not aware of too.
On the boat (GM 4.3 pre-vortec) the pressure jumps up to 40 psi or a little higher after a cold start (but this engine has 25/40 marine oil in it). This will idle at 40 psi except with after running the boat on plane and then slowing down, then it drops to about 25 psi, till the engine is idled for while and the oil starts to cool off, then it goes back to 40 psi.
On our other vehicles that have oil pressure reads outs (98 Jeep has a gauge, 17 Wrangler has a read out in the menu in the instrument panel) the oil pressure jumps up to their normal levels as well right after a cold start. The 98 will run at 40-50 psi after a cold start and idles at 30 psi, the 17 Wrangler will jump up to like 65 psi and this will drop down to about 35 psi after it warms up.
 
It appears that the oil pressure sending unit is in the same place as the older small blocks but on the original small block the oil pump was at the rear of the engine. There could be other differences that I'm not aware of too.
On the boat (GM 4.3 pre-vortec) the pressure jumps up to 40 psi or a little higher after a cold start (but this engine has 25/40 marine oil in it). This will idle at 40 psi except with after running the boat on plane and then slowing down, then it drops to about 25 psi, till the engine is idled for while and the oil starts to cool off, then it goes back to 40 psi.
On our other vehicles that have oil pressure reads outs (98 Jeep has a gauge, 17 Wrangler has a read out in the menu in the instrument panel) the oil pressure jumps up to their normal levels as well right after a cold start. The 98 will run at 40-50 psi after a cold start and idles at 30 psi, the 17 Wrangler will jump up to like 65 psi and this will drop down to about 35 psi after it warms up.
Lots of things in motion here. I don’t suppose you started your boat engine at -4F? What I see is that the oil viscosity gets bizarre at -20 C ( -4 F ). People hand ring over a 2 cSt vs a 16 cSt oil at 100 C. Try 50,000 cSt at -20 C.
 
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It depends on where the oil pressure gage is mounted. What you said is certainly true if the reading is taken between the oil pump and filter. But even with a pressure sensor mounted at the top of the engine, everything goes out the window at -4 F ( -20 C ). The oil viscosity is no long in the 2 to 16 cSt at 100 C. It’s 10’s of thousands of cSt at -20 C and suddenly that oil is trying make it through the gallery’s and filter, even if the bypass opens. With this potential record breaking weather I’m encouraging folks to observe their oil pressure upon start up ( if they have an oil pressure gage). It should be quite interesting. :)
Now you’re throwing ideas out there.

Does it do this at normal temperatures?

-4F isn’t that cold frankly. Heck, Daimler allows 10w- oils at those temperatures.

How long do you observe this “phenomena”? You said once full warm it idles at 40 (notionally fully warm, regardless of ambient it will still drop when the oil is hot); what about in between? When does the oil pressure raise to an appropriate level while the engine is still cold? Seconds? Minutes? What about under elevated rpm/load?


 
Now you’re throwing ideas out there.

Does it do this at normal temperatures?

-4F isn’t that cold frankly. Heck, Daimler allows 10w- oils at those temperatures.

How long do you observe this “phenomena”? You said once full warm it idles at 40 (notionally fully warm, regardless of ambient it will still drop when the oil is hot); what about in between? When does the oil pressure raise to an appropriate level while the engine is still cold? Seconds? Minutes? What about under elevated rpm/load?


Good questions. Yes, sometime when it was idling it warmed up enough to climb just to less than 40 psi. When I got onto the highway, it continued to climb to just above 40 psi. I’m doing another cold start this morning at about -4 F but I’ve been plugged in for the last 3 hours. I’ll watch it closely.
 
@Snagglefoot Looks like you could use a new pickup tube o-ring. Very common on Gen III and Gen IV LSx motors. With time, the seal shrinks and hardens. Upon startup, lower pressure. After some run time, the o-ring swells from heat and the oil and expands. A common test for this is to jack the rear of the motor up and overfill the engine to effectively submerge the pickup tube/pump joint in oil -- if the pressure if higher, then you know that o-ring needs replacing.

On my 2005 Suburban, it was hard as a rock, and I'd have 30psi at cold start -- it wouldn't budge with RPM much until it would warm up. Now, a cold start is 55psi with hot idle anywhere from 38-42psi.
 
My '04 and '08 GM pickups (work trucks) with the 5.3 both showed high oil pressure at cold start, and it took about 20 mins in cold weather for the oil pressure to drop to the normal operating range.
 
@Snagglefoot Looks like you could use a new pickup tube o-ring. Very common on Gen III and Gen IV LSx motors. With time, the seal shrinks and hardens. Upon startup, lower pressure. After some run time, the o-ring swells from heat and the oil and expands. A common test for this is to jack the rear of the motor up and overfill the engine to effectively submerge the pickup tube/pump joint in oil -- if the pressure if higher, then you know that o-ring needs replacing.

On my 2005 Suburban, it was hard as a rock, and I'd have 30psi at cold start -- it wouldn't budge with RPM much until it would warm up. Now, a cold start is 55psi with hot idle anywhere from 38-42psi.
It very well could be. It’s the original O ring and the truck has 240,000 miles. I’ll carry on with my findings from earlier this afternoon.
 
With the ambient air at about -4 F and the water temp not registering I fired it up and the oil pressure registered and slowly build to 20 psi. When the water temp rose to 160 deg F the oil pressure started rising above 20 psi to a high of about 38 psi. Once the oil pressure hit about 38 psi it stayed there while the water temp finally rose to 210 degrees F. On the highway the oil pressure was about 42 psi.
 
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