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I have a 2003 Chevrolet K2500HD crew cab, short box with the LB7 (of course) and my oil pressure at idle when the motor is warm only reads 125KPA (18psi). The oil pressure at idle when the truck is cold is 400KPA (58psi) or so. However as soon as the accelerator is touched the oil pressure shoots up as more gas is applied ie. the oil pressure can get as high as 600KPA (87psi) when the motor is cold, when the engine is warm it can read as high as 425KPA (62psi). What could be causing this problem?
 

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What problem? Those sound like proper readings. Cold oil results in higher resistance, you are pumping molasses. The pump bypass is kicking in at the high level, and pumping (some) oil back to the sump.

Be real easy on it till it no longer pegs at 87, then you know the motor is getting the benefit of full flow. The low readings at idle, are not low, they are exactly what the motor needs with no load.

BTW, if you use a 5W- syn your truck will be happier, just don't worry about slightly lower readings when warm.
 

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So you are saying 18psi oil pressure is not low at idle?:confused: My '01 idles at 40psi and 60-70 psi when accelerating. Is this a guage issue or maybe a oil type thing? (I have Rotella 5w-40 in right now).
JP
 

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They dropped the pressure on the 03's and up. My 03 runs the same pressure readings as yours - max of 90 when cold @ 2000 RPM's, 55-60PSI when hot, and only 20 or so when idling hot. Your truck is fine.
 

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HH

As usual, an opinion is an opinion. I come from a background that lends more credibilty to the gauge that actually moves, and find that the gauges with little movement to be outright liars. What comforts me greatly, is that when cold idle the gauge rises to the right, showing me that that pump is working hard to get the cold oil through. With warm oil, that effort is just not required, and you should get lower readings.

These readings tell me that we have a strong, high volume, pump. This tends to be the difference in gauge movement. Where many vehicles are designed to a 4-8 gpm system, we are moving 8-15 (or more) gpm. RPM dependent naturally.

The pressure reading is a measure of the pump work performed, and is equal to the oils resistance to flow, the higher the gauge reading, the harder the pump is working. This number is directly related to oil viscosity. Oil viscosity is a function of oil temperature.


What does concern me, is when 2000 rpm oil pressure drops to 40 or less. This has been happening a lot, with those that really work the truck, and reporting very excessive oil temps, so hot that the required viscosity cannot be maintained (charted values at specific temps), even with synthetic.

You can look at a typical oil for our vehicles, this is delo 15W-40

200 18 cP 55 psi
220 14 cP 50 psi
240 11 cP 45 psi
260 8.5 cP 40 psi

Ballpark gauge readings based on 2000 rpm


The lubrication system is based on a figure of 12-18 cP, it is hydrodynamic film science dealing with surface tensions, etc, very boring. It is enough to see that hot oil is a problem, and you can see it on the gauge when it happens.

It is the basis for my oil cooler project.
 

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Mine idles down low, too. below 30 at idle for sure.
 

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HH

As usual, an opinion is an opinion. I come from a background that lends more credibilty to the gauge that actually moves, and find that the gauges with little movement to be outright liars. What comforts me greatly, is that when cold idle the gauge rises to the right, showing me that that pump is working hard to get the cold oil through. With warm oil, that effort is just not required, and you should get lower readings.

These readings tell me that we have a strong, high volume, pump. This tends to be the difference in gauge movement. Where many vehicles are designed to a 4-8 gpm system, we are moving 8-15 (or more) gpm. RPM dependent naturally.

The pressure reading is a measure of the pump work performed, and is equal to the oils resistance to flow, the higher the gauge reading, the harder the pump is working. This number is directly related to oil viscosity. Oil viscosity is a function of oil temperature.


What does concern me, is when 2000 rpm oil pressure drops to 40 or less. This has been happening a lot, with those that really work the truck, and reporting very excessive oil temps, so hot that the required viscosity cannot be maintained (charted values at specific temps), even with synthetic.

You can look at a typical oil for our vehicles, this is delo 15W-40

200 18 cP 55 psi
220 14 cP 50 psi
240 11 cP 45 psi
260 8.5 cP 40 psi

Ballpark gauge readings based on 2000 rpm


The lubrication system is based on a figure of 12-18 cP, it is hydrodynamic film science dealing with surface tensions, etc, very boring. It is enough to see that hot oil is a problem, and you can see it on the gauge when it happens.

It is the basis for my oil cooler project.
Wow! Now that's what I call a post! That was some good info and apparently I wasn't aware of the need for a higher capacity/better performing oil cooler. I have wondered why an oil temp guage is not included in trucks that obviously will be towing or hauling. I had the oil temp checked on my '94 7.4L dually and it was running around 254*(much hotter than I thought), but I did not expect the Duramax, especially with better oils now available, to be in the 260* range. Now let me get this straight, you are saying that the drop below 40psi @ 2000 RPMs is due to an oil viscosity drop resulting from elevated engine heat and not because of pump or engine malfunction? If true, then that means anyone of us could be at risk of poor oiling performance when "working" the truck. Hence, the oil cooler project you are embarking upon. It takes awhile, but eventually I'll catch on.
JP
 

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Now let me get this straight, you are saying that the drop below 40psi @ 2000 RPMs is due to an oil viscosity drop resulting from elevated engine heat and not because of pump or engine malfunction? If true, then that means anyone of us could be at risk of poor oiling performance when "working" the truck. Hence, the oil cooler project you are embarking upon.
Correct JP, but 260 is nothing, there is a lot of over 300+ going on.

Viscosity drop allows the same amount of oil to flow, but the ability of that oil to lubricate is severely diminished, as film thickness's reduce to metal-metal contact in more places. Then there is the issue of oil breakdown to consider at these temps, not to mention coking potential where "local" temps are much hotter than the "bulk" readings.
 

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You're correct about the temp drop with hot oil, I can always tell when I'm working the dmax as the oil pressure drops from 55-58 to about 40-45. Very scary the first time it happened I thought my injectors were dumping fuel, but after climbing the hill and the coasting/cool-down the other side, PSI came right back up. What I DON'T like is that the engine temp never goes up so there really is no sign that the oil is hot other than the PSI drop.
 

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From what empirical data I have been able to gather, when empty, the oil leads coolant by 10-40 degrees.

When under heaviest load on the hottest days, oil can lead coolant by 100 degrees. These are bulk readings. Purely speculating, but I think we should add another 30 for some local hotspots, like the turbo. 400 degrees? I think so. When towing. The LB7 should be better off than the LLY, but from reports like yours Fred, looks like it is very similar.
 

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These temperature levels are why I will spend more on synthetic oil. It may not do any better under normal conditions, though it does handle the temperature extremes better.

I started using Syn when I lived in Minnesota where engines have it rough on cold starts. Now that I live in Texas the heat makes life tough.

On a related note - I was surprised to learn that heat kills batteries faster than cold does. A cold battery may not have full power when cold, but the heat kills batteries dead in less time.
 

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Mine does around 35psi idling and [email protected] 2000RPMs warm 190*. I run syn oil as well.
 

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Mine runs around 20 hot idle either city driving or towing the 5th wheel. Similar highs as the others here. I do notice that when pulling a grade while towing the pressure drops a bit. Seems like the harder it's working and more boost it's making the more it drops down to around 45 PSI. I brought this up with my dealer and they replaced the oil pressure sending unit. Didn't change things one bit. I run synthetic. If I run dino I notice a bit more pressure drop at high idle than with syn.
 

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Your oil pressure is normal. 20-25 PSI at an idle 55-60 at crusing speed.
 

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Checked mine today:

cold: idle 75psi

warm: idle 25psi; 1800 rpm 60psi
 

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I believe the oil pressure guages in these trucks are a small step up from what we used to call "idiot lights." The little light that would go on after your oil was completely drained. My original guage, that came new with the truck, read 40 psi warm at idle and 65 psi warm above 2000 rpm. Just replacing the cluster and guage, with no change to the motor, changed the readings to 25 psi and 60 psi. I doubt there was any real change at all. Just a different guage.
 

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Idle I get 40 at operating temps 60 cold. On the road at 1800rpm I get 60 at operating temperature.
 

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I really like the gauge compared to others. The absolute values may be innacurate, as many oem gauges have little precision and are never really "calibrated". What I like is that we have the benefit of real time changes, as the signal is spread wide and not manipulated with some long time averaged construct by GM. IOW, changes are now.

My main complaint is the sensor location. It is downstream of most of the lub system components, so we can't see the effects of things like failed filter bypasses, etc.
 
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