Discussion - Oil pressure discrepancy over an oil change interval

[thefrey]

For some context, I recently did a DOD delete along with a new HV oil pump.

I am not sure if I am noticing this just because I’m staring at the oil pressure gauge more often, but…

I noticed that as I drove more miles on my oil that my cold start and cruising oil pressures dropped over time.

For instance, when I had new oil + a new filter, my cold start psi was around 65 and my crusing psi was around 43-45.

When I started getting around the 4500-5000 mark on my oil, I noticed my cold start pressures were mid-high 50s, and my cruising psi was about 38 at the same speed. They had slowly gone down (I initially thought it was temperature difference given it’s been 20-30s usually and then it spiked to 60+) but it’s not temperature related.

My idle PSI stayed the same the whole time around 25psi.


I got an oil change + filter yesterday and whadya know, my oil pressures are back up to 65 cold start, 45 cruising.

Now… this got me thinking what this might be. I don’t know if this is a normal phenomenon, but I figured I would pick some brains on here to see if this was normal.

I don’t know if this was an oil degradation (perhaps the oil’s shear properties), fuel dilution, or a filter issue. When cold my oil psi will spike to 75 if I am accelerating (I try to baby it when it’s cold) but I am curious if perhaps that it caused some filter degradation over time?

I am using 5w30 and was using a Fram Good filter.

Would love to hear any thoughts and learn something new.

 

[Doubeleive]

I would change the oil more often around 3000, you could also order a oil sample kit from blackstone labs, it's around $40 when that next oil change time rolls around take a sample and send it in, That will give you a more definitive answer as to what may be happening. If there is fuel or any kind of excessive wear it will show up in the test.

 

[Marky Dissod]

... noticed that as I drove more miles on my oil, that my cold start and cruising oil pressures dropped over time.
For instance, when I had new oil + a new filter, my cold start psi was around 65 and cruising was around 43-45psi.

Motor oil ages even if it's just sitting there (and do NOT forget to shake it before pouring!).
Motor oil ages moreso as it's used, with variances as to HOW and WHERE (6000 all-highway miles are almost as rough as 3000 all-Manhattan rush hour miles).
Since motor oil is also exposed to the environment (unlike ATF), dirt and fuel contamination are part of the equation too.
Also I've not yet met one person that can convince me that 0.5Qt of oil consumption = change oil this week, & 1.0Qt of oil consumption = change oil tomorrow.

Long stories short:
1. some 5w30s are better than others, even among Group4 synthetics. I'm of the 5w30 Valvoline Restore & Protect cult,
but there are several Group4 synthetics that pass muster even if they did not pay GM for a DEXOS sticker.
2. I prefer to use the 'larger PF61'-type oil filter; I'll use nearly any brand, but I NEVER use the cheapest 'basic' oil filter, anything over that is fine.
3. When I was leasing a 2012 Yukon XL for NYC taxi / livery / chauffeur driving, I changed it pretty damn close to every 3000 miles/monthly,
and am STILL wondering if there were times when I should've changed it a bit sooner / more often than that.

 

[Joseph Garcia]

I have seen this change in oil pressure as the oil ages in my previous truck. I cannot tell for sure with my current truck, as I've made many mods related to oil pressure.

I would recommend an oil change every 5000 miles MAX.

 

[strutaeng]

I think we (truck enthusiast) need to start dissecting our oil filters after oil changes...I'm kinda curious what the media would look like, on a normal and healthy engine? I've never done this myself, except this one junkyard engine I was trying to rebuild which had a spun main bearing and turned out to be junk.

1. I can't imagine oil breakdown would cause oil pressure to go down. Oil shear would be a characteristic of the oil and lubrication, but should not affect the system pressure.

2. I don't personally feel that the guages on these trucks clusters are "that" accurate. I like what Ford does and just has a Low and High, LOL. Note the guage does not have "psi" on the scale. A calibrated mechanical guage comparison would be a legit comparison though.

3. Would a restricted or partially restricted oil filter cause oil pressure drop? Yes, I think so. BUT it would have to be really restricted? Think bearing materials, which would be bad news. Similar to a transmission with so much clutch material that the oil filter gets clogged and cuts lubrication to the hydraulic circuits (I'm assuming pressure drops, eventually to zero if it gets really bad.) At some point the bypass valve would open, right?

4. Otherwise I got nothing, but interested in responses.

Edit: I think a direct reading of the oil temperature is also important, because that affects viscosity and pressure. I know there's a temperature guage for the coolant, but I don't know that correlates exactly to the oil temperature. I think ambient temperature also affects oil temperature.

 

[mikez71]

Fuel dilution you mentioned is the best sounding explanation to me so far...
(maybe contributing to oil breaking down?) Dunno!

 

[Scrappycrow]

What are your driving habits? Do you just do short trips around town or do you ever take sustained drives of 30+ minutes at highway speeds? Fuel dilution is mentioned, which leads me to wonder if: A) you ever get the oil hot enough, and B) what is the pressure behavior the next cold start after a sustained drive?

 

[Coveman]

I have not noticed my oil pressure falling over the life of the oil but it makes sense that viscosity breaks down over time (oil gets ‘thinner’) due to the viscosity index improvers that are broken down by engine shear and high heat, fuel dilution and oil additive consumption

The oil filter bypass is triggered by the oil filter inlet/outlet pressure differential (usually 7-15 psi) so cold starts along with some full throttle acceleration will trigger the bypass.

Since there is no actual monitor of the differential pressures on the oil filter we dont have feedback for when the bypass valve is opening and its effect on oil psi.

 

[thefrey]

What are your driving habits? Do you just do short trips around town or do you ever take sustained drives of 30+ minutes at highway speeds? Fuel dilution is mentioned, which leads me to wonder if: A) you ever get the oil hot enough, and B) what is the pressure behavior the next cold start after a sustained drive?

This oil cycle consisted of (2) 1100 mile trips (both trips we completed in 1 day), multiple 2-3 hour trips, and a handful of daily driving trips. I was a little over the 5.5k mark when I changed my oil for this one, longer than I would have liked, but there was a ton of highway driving, so I know the oil got plenty hot multiple times

Restart psi seems to be a function of how long I’ve left the car off, but if it’s been about 30 mins it’ll cold start at 45ish psi. Overnight is always 65 psi and is pretty consistent

 

[thefrey]

This would be a question for an oil test perhaps, but I wonder if there’s a difference in oil solution running e85 vs pump gas? I run e85 often but sometimes will blend e85 with 87 octane when e85 isn’t available to get an e30-e50 mix

 

[thefrey]

I'm of the 5w30 Valvoline Restore & Protect cult,

Something of note is that I was using 5w30 R&P

 

[rdezs]

This has been my experience going back to 1979..... Oil seems to lose its viscosity over time. And I still change my oil every 3,000 miles, even though I'm running a full synthetic.

 

[donjetman]

For some context, I recently did a DOD delete along with a new HV oil pump.

I am not sure if I am noticing this just because I’m staring at the oil pressure gauge more often, but…

I noticed that as I drove more miles on my oil that my cold start and cruising oil pressures dropped over time.

For instance, when I had new oil + a new filter, my cold start psi was around 65 and my crusing psi was around 43-45.

When I started getting around the 4500-5000 mark on my oil, I noticed my cold start pressures were mid-high 50s, and my cruising psi was about 38 at the same speed. They had slowly gone down (I initially thought it was temperature difference given it’s been 20-30s usually and then it spiked to 60+) but it’s not temperature related.

My idle PSI stayed the same the whole time around 25psi.


I got an oil change + filter yesterday and whadya know, my oil pressures are back up to 65 cold start, 45 cruising.

Now… this got me thinking what this might be. I don’t know if this is a normal phenomenon, but I figured I would pick some brains on here to see if this was normal.

I don’t know if this was an oil degradation (perhaps the oil’s shear properties), fuel dilution, or a filter issue. When cold my oil psi will spike to 75 if I am accelerating (I try to baby it when it’s cold) but I am curious if perhaps that it caused some filter degradation over time?

I am using 5w30 and was using a Fram Good filter.

Would love to hear any thoughts and learn something new.

Purchase a used oil analysis kit from Oil Analyzer Inc/Amsoil, send in a sample of your old used oil. Results in about a week.
There are many reasons viscosity of oil can thin out thus resulting in lower pressue.
But you'll need to spend time at BITOG forum doing homework.

 

[Marky Dissod]

I think we (truck enthusiast) need to start dissecting our oil filters after oil changes...I'm kinda curious what the media would look like, on a normal and healthy engine? I've never done this myself, except this one junkyard engine I was trying to rebuild which had a spun main bearing and turned out to be junk.

1. I can't imagine oil breakdown would cause oil pressure to go down. Oil shear would be a characteristic of the oil and lubrication, but should not affect the system pressure.

Oil viscosity does have a small effect on oil pressure; 0w20 will tend to show less pressure than 10w50.
And yes, 0w20 is no longer 0w20 by the time it needs changing (it approaches 4w16).

2. I don't personally feel that the gauges on these trucks clusters are "that" accurate. I like what Ford does and just has a Low and High.
Note the gauge does not have "psi" on the scale. A calibrated mechanical gauge comparison would be a legit comparison though.

Biggest reason why they are not 'that' accurate is because GM placed them where it was convenient for GM to place them,
not where the most accurate reading is possible. If you want a more accurate GM gauge, use GM's 60psi vs GM's 80psi sender.

3. Would a restricted or partially restricted oil filter cause oil pressure drop? Yes, I think so. BUT it would have to be really restricted?
Think bearing materials, which would be bad news.
Similar to a transmission with so much clutch material that the oil filter gets clogged and cuts lubrication to the hydraulic circuits
(I'm assuming pressure drops, eventually to zero if it gets really bad.) At some point the bypass valve would open, right?

We ought to know / be told plainly what the bypass valve's psi rating is. Note that this info is NOT readily available ...

Four to come ...

 

[Marky Dissod]

Edit: I think a direct reading of the oil temperature is also important, because that affects viscosity and pressure.
I know there's a temperature guage for the coolant, but I don't know that correlates exactly to the oil temperature. I think ambient temperature also affects oil temperature.

I've always wondered why the temperature pressure AND level of motor oil, coolant, ATF, and fuel are not ALL available to driver.
Come to think of it, what would be the electrical analogs of those? What about brake fluid?
ANYWAY
As an IronBlock LT1 enthusiast and tuner who has considerable experiences measuring and altering them by turning on the radiator fans sooner than GM intended ...
Motor oil and coolant temps seldom if ever directly correlate, although the disparity tends greatest during the first 0-20min of the first cold start of a given day.
Coolant usually warms up quicker than motor oil. In some cases partially blocking the radiator for the winter does help reach intended operating temp more quickly.

After the first 20min, ambient temp & weather is less of a factor; the various heat exchangers and the radiator have pretty much established their rapport.
By then the driver's tasking of the powertrain makes the weather less or more important in proportion to demands.
Motor oil starts out warming up slower than coolant, and gets some help warming up from the coolant, but eventually motor oil winds up warmer than coolant.

 

[ianbis]

Funny that you posted this, I was contemplating posting this exact "experience". I live in the North-East and have a 2011 Suburban equipped with the 5.3l Flex fuel engine (stock engine with Range AFM plug in disabler) with an aftermarket Catch Can, I use synthetic 5W30 and the OEM AC/Delco short filter. I will switch to the larger filter as soon as I'm out of short filters. I have approximately 185K on the clock. I hardly ever get anything in the Catch Can and she does not smoke.

After a fresh oil change my oil pressures are pretty standard, however, as I approach 3K miles and approximately 60% oil life (per the oil life monitor) the engine becomes louder and requires the addition of a 1/2 quart of oil. The addition of the 1/2 quart of oil at this point does not change the oil pressure behavior listed below but the engine does return to its quiet nature. I imagine 1/2 quart of fresh oil cannot "improve" 5.5 quarts of oil with 3K miles on it. Or at least where oil pressures are concerned.

So on to the meat and potatoes: when I change the oil and approach/put 3K miles on the truck my cold start oil pressure is lower (down from 58 to 45), and my steady state driving at 60 mph oil pressure is lower (down from 39 to 36). My hot idle oil pressure is always pretty steady at 20-22 regardless of the age/mileage of/on the oil.

After a fresh oil change the engine is back to being quiet and the oil pressures are back to 58 cold start, 39 steady state 60mph and 20-22 hot idle.

All oil pressures above are per the OEM Oil Pressure gauge.

After noticing this I decided that my OCI was going to be 3K miles.

I have changed the oil approximately (5) five times now and the oil usage and pressure behavior have been consistent.

She runs pretty strong but that said, I can only hope she will make it to 300K.

An engine builder once told me that healthy oil pressure is 10 psi per 1K RPMs and double that at idle so that gives me some comfort. Said another way 20psi at idle and plus 10 psi for every 1K RPM thereafter (up to max oil pressure)

 

[dgjtools]

For some context, I recently did a DOD delete along with a new HV oil pump.

I am not sure if I am noticing this just because I’m staring at the oil pressure gauge more often, but…

I noticed that as I drove more miles on my oil that my cold start and cruising oil pressures dropped over time.

For instance, when I had new oil + a new filter, my cold start psi was around 65 and my crusing psi was around 43-45.

When I started getting around the 4500-5000 mark on my oil, I noticed my cold start pressures were mid-high 50s, and my cruising psi was about 38 at the same speed. They had slowly gone down (I initially thought it was temperature difference given it’s been 20-30s usually and then it spiked to 60+) but it’s not temperature related.

My idle PSI stayed the same the whole time around 25psi.


I got an oil change + filter yesterday and whadya know, my oil pressures are back up to 65 cold start, 45 cruising.

Now… this got me thinking what this might be. I don’t know if this is a normal phenomenon, but I figured I would pick some brains on here to see if this was normal.

I don’t know if this was an oil degradation (perhaps the oil’s shear properties), fuel dilution, or a filter issue. When cold my oil psi will spike to 75 if I am accelerating (I try to baby it when it’s cold) but I am curious if perhaps that it caused some filter degradation over time?

I am using 5w30 and was using a Fram Good filter.

Would love to hear any thoughts and learn something new.

Doing a DOD Delete with a new Camshaft can affect oil pressure. The tighter the cam to bearing clearances, the higher the oil pressure. That why it's a crap shoot when changing a cam without replacing the cam bearings. Some guys have inadvertently spun or knocked out a cam bearing during a cam swap. This results on Zero oil pressure.