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Reading Engine Oil Dipstick Level 3.6L

2689 Views 34 Replies 11 Participants Last post by  Digger84
The images below are of the engine oil level on the dipstick after cooling down for several hours. The dipstick enters the sump at an angle, so one side is showing the level at full while the other shows the level between full and minimum. I purposely reduced the amount of oil I filled with this time, but I have usually filled it so that both sides show up at least at the full level on the dipstick. I had been wondering if this actually resulted in me overfilling it this entire time, because I typically notice more oil than I would like to see passing through the PCV system and into the intake. I have read in multiple places that overfilling the 3.6L can lead to it blowing oil into the intake. What is the proper way to read the dipstick when both sides don't show the same level?
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Personally, I would add oil 1 cup at a time until both sides of the dipstick reflect full. I am a firm believer of a little too much oil is much better than not enough oil.
If that does not work for you, measure the amount of oil you put into the crankcase and keep within the capacity limits reflected in your owners manual.
Second point is it sounds as if you might have too much blow by and might need a new set of piston rings!
 

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Discussion Starter · #3 · (Edited)
Personally, I would add oil 1 cup at a time until both sides of the dipstick reflect full. I am a firm believer of a little too much oil is much better than not enough oil.
If that does not work for you, measure the amount of oil you put into the crankcase and keep within the capacity limits reflected in your owners manual.
Second point is it sounds as if you might have too much blow by and might need a new set of piston rings!
I don't think it's excessive blowby because it doesn't burn any oil that I can detect with 5,000 mile oil changes. I just did a compression and leakdown test when I replaced the oil cooler assembly, and all cylinders are within 5% compression at approximately 155psi with leakdown less than 1% on each cylinder. I took images of the cylinders with a borescope, and they all have a very well defined deep crosshatch which would indicate minimal wear. I also replaced the PCV valve at around 80,000 miles with a new Mopar. I usually fill the sump with a hair under 6 quarts, but I'm wondering if there is enough residual oil left after draining for a few minutes that it leads to overfilling with the specified quantity of oil.
 

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It always reads one side higher than the other when its parked on a level surface whether I check it hot or cold.
The dip sticks can be a pain to read, I always check mine at a minimum after sitting overnight. I wouldn't be too concerned if one side covered half the hash marks and the other side was totally covered. You are talking about 1/2 quart max. Your engine is still well protected. Me, yes, I top off to top of hatch marks when I'm midway down them, been doing that forever with all my vehicles, no ill harm yet.
 

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Discussion Starter · #7 ·
The dipstick tube does not enter the oil pan vertically, so it's expected that the upper side of the dipstick will read less than the lower side, but my question pertains to which side is correct for taking the reading. The dipstick seems to self align for rotation when I push it into the tube such that the "engine" letters are always read when looking at it from the driver side of the vehicle. This would ensure that the side of the dipstick tip without the crosshatch would always point up, and show a lower level just as I showed in the picture from my initial post.
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The dip sticks can be a pain to read ...
Agreed. On both my JK and JT, I find that I have to clean off the 'bullet' end of the dipstick with brake parts cleaner and let it dry in order to actually see the oil level.

I also find that you will pick up oil on the 'bullet' from the inside of the dip stick tube, making it difficult to tell the real level sometimes.

On my JK, I have always drained the oil when hot/warm and put in 6 quarts. This has always resulted in an oil level near the top of the hatched area on one side of the 'bullet' and a little over half way on the other. However, if I let it sit overnight, it always reads to the top of the bullet (slightly overfull) because of all the oil draining back to the pan.

If I crank it with the gas pedal to the floor (not starting the engine) until I see oil pressure, then pull the dipstick and let it sit for 10-15 minutes, it reads normal when I check it.

Here is what the top side of the 'bullet' looks like:
(the bottom side reads to the top of the hatched area)

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Do the math the dipstick front reading side to back reading side is less than 1/4”
Now multiply that by sin of a generous 30 degree overestimate from how far you are off vertical and your concern that that angle makes a difference falls apart

or if you still have doubts take a pan of liquid (even dirty oil) and submerge dipstick tip at your estimated angle and compare level on sides once removed
 

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You’re overthinking this. After a complete drain and filter change add a 1/2 a quart less than the capacity and go from there.
I have never noticed the discrepancy from one side of the dip stick to the other. If it bothers you split the difference. A SLIGHT over or under fill isn’t likely to be an issue. Personally I would rather be slightly low than high.
 

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Discussion Starter · #11 · (Edited)
Do the math the dipstick front reading side to back reading side is less than 1/4”
Now multiply that by sin of a generous 30 degree overestimate from how far you are off vertical and your concern that that angle makes a difference falls apart

or if you still have doubts take a pan of liquid (even dirty oil) and submerge dipstick tip at your estimated angle and compare level on sides once removed
I did the math. Sine is not used for this problem, and the angle of the dipstick measures 40 degrees from vertical. The relevant parameters are the angle of the dipstick = 40 degrees, the thickness of the dipstick = .115", the area of the upper oil pan = approximately 16" length X 9" width, tangent and cosine of the dipstick angle. The pan is not exactly rectangular, but this is a pretty good approximation.

At a 40 degree angle with a .115" thick dipstick, there will be a difference of .096" on the dipstick between the upper and lower side level. This would result in an oil level height difference of .074" in the 16" X 9" pan, which equals an oil volume difference of 10.7 cubic inches or .19 quarts. This is hardly a trivial volume of oil, and certainly could be enough extra to cause oil to be blown through the PCV system after an oil change.

The question still stands as to what side of the dipstick reads the correct level, but our best assumption may be that the manufacturer intends for the reading to be taken off the side with the crosshatching. The side with the crosshatching always points downward due to how the dipstick is inserted into the tube, so filling until the side without the crosshatching is at the maximum level would result in overfilling by .19 quarts as I showed. This could result in oil being blown into the intake manifold which is a common complaint.
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You have way too much free time. :ROFLMAO:

Also, you didn't include barometric pressure and elevation from sea level, which may (or may not) affect the reading. I know there are special instructions for baking a cake at higher altitudes and barometric pressure has an effect on the weather, so there must be something to them.
 

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Discussion Starter · #13 · (Edited)
You have way too much free time. :ROFLMAO:

Also, you didn't include barometric pressure and elevation from sea level, which may (or may not) affect the reading. I know there are special instructions for baking a cake at higher altitudes and barometric pressure has an effect on the weather, so there must be something to them.
Funny. My hypothesis is that filling the sump until the dipstick reads max. on the non crosshatched upper side results in some excess oil being blown into the intake past the PCV system, and I think I just showed above that this is a possibility since the sump could be overfilled by .19 quarts. I will monitor the intake now that I have reduced the fill volume so that the upper side of the dipstick is about midway between min and max. I suspect that I won't see as much residual oil in the intake as when I was filling to the max. level on the upper side of the dipstick.
 

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I did the math. Sine is not used for this problem, and the angle of the dipstick measures 40 degrees from vertical. The relevant parameters are the angle of the dipstick = 40 degrees, the thickness of the dipstick = .115", the area of the upper oil pan = approximately 16" length X 9" width, tangent and cosine of the dipstick angle. The pan is not exactly rectangular, but this is a pretty good approximation.

At a 40 degree angle with a .115" thick dipstick, there will be a difference of .096" on the dipstick between the upper and lower side level. This would result in an oil level height difference of .074" in the 16" X 9" pan, which equals an oil volume difference of 10.7 cubic inches or .19 quarts. This is hardly a trivial volume of oil, and certainly could be enough extra to cause oil to be blown through the PCV system after an oil change.

The question still stands as to what side of the dipstick reads the correct level, but our best assumption may be that the manufacturer intends for the reading to be taken off the side with the crosshatching. The side with the crosshatching always points downward due to how the dipstick is inserted into the tube, so filling until the side without the crosshatching is at the maximum level would result in overfilling by .19 quarts as I showed. This could result in oil being blown into the intake manifold which is a common complaint.
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So you calculate that one side is less than 1/10 of an inch different than other side
Compare to original
Dipstick pictures and like I said that was NOT the cause for the difference in levels on the two sides he pictures no matter how hard you manipulate it
The angle of the dipstick makes no significant (less than .1” difference on two sides and to get that small difference you assumed the dip stick was rotated to exact position to place the two sides on highest an lowest side of slope when probability is against that specific rotation

again a insignificant problem with a falsely proposed etiology
No matter how much you wish it could explain the op pictures
 

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Discussion Starter · #15 · (Edited)
So you calculate that one side is less than 1/10 of an inch different than other side
Compare to original
Dipstick pictures and like I said that was NOT the cause for the difference in levels on the two sides he pictures no matter how hard you manipulate it
The angle of the dipstick makes no significant (less than .1” difference on two sides and to get that small difference you assumed the dip stick was rotated to exact position to place the two sides on highest an lowest side of slope when probability is against that specific rotation

again a insignificant problem with a falsely proposed etiology
No matter how much you wish it could explain the op pictures
The difference between top and bottom of the dipstick in the original picture is .170" and the calculated difference is .096". That could be explained by my vehicle not being perfectly level. The dipstick pretty much self clocks to the same orientation with the crosshatched side down each time its inserted unless you purposely install it with the lettering pointed the opposite direction. The main points are that the angle of the dipstick will cause a different reading between top and bottom, and that seemingly small .096" difference results in nearly 1/4 of a quart oil volume due to the size of the oil pan.
 

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You can really overthink this by taking into account surface tension & energy and contact angle of the oil along with the angle at which the end of the dipstick enters the oil.

Or, you can drain the oil when hot/warm, letting it drain for 15-20 minutes. Install a new filter & pour in 6 quarts of oil, accept whatever the dipstick reads and go have fun with your Jeep. This method has never failed me.
 

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Discussion Starter · #18 · (Edited)
Adding an accurate amount of oil at the time of the oil change doesn't do much for those who don't change their own oil, or those who have to add oil between changes because the engine leaks or uses oil, so I believe that establishing best practices for reading the oil level at any time is important on these vehicles to determine if the sump is overfilled. I also understand that I could wait an additional 20 minutes or more for the oil to drain, but I like to keep the entire oil change to around 10 minutes.

My main concern though is to account for the oil that I and many others find in their intakes with no apparent cause. My engine has stellar compression and leakdown numbers, as well as perfect looking cylinder bores and a relatively new Mopar PCV valve, so I believe the most likely cause is excess oil in the crankcase being blown through the PCV system into the intake from inaccurately reading the dipstick and potentially not being on a completely flat surface when topping off the oil level after a change. I have always seen some oil in the intake pretty much since the first time I had the intake off at around 15,000 miles, but I also have always topped off the crankcase so the level was at or above maximum on both sides of the dipstick until just recently.

I appreciate that there are multiple other factors that could slightly influence the reading, but the reality is that the basic geometry of how the dipstick enters the oil pan will be the most influential factor. To show that the discrepancy between the dipstick level in the OP picture and the calculated level was caused by taking the reading on my uneven gravel driveway, I decided to take another reading in a parking lot 30 mins after running a couple errands. This time I picked out the most level parking spot I could find, and confirmed this with a bubble level on both the stock rocker guard as well as the bottom of the metal part of the stock front bumper. I paid specific attention to ensuring that the dipstick was clocked so that the crosshatched side was pointing down in the oil pan, and the difference between the top and bottom side of the dipstick match the previously calculated difference almost exactly at .1" after retaking the measurement with the vehicle on a level surface. I encourage anyone who is interested to verify for themselves.
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Rotate dipstick 90 degrees on long axis should zero out and difference

but. Ice to know you prefer the straighter Block entry of the dipstick tube on the minivan and journey 3.6 engine

plus they use a flat blade dipstick no cable and special added tip
 

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I will say it's been an interesting read catching up on this thread, but @RedRubi2012 , I have a question as to how you think 1/2 a pint of fluid diff in the sump would lead to excessive blowby at the PCV. The sump is a storage area and the oil pump is responsible for moving the oil to the top of the motor. 1/2 a pint of fluid difference in the sump is not going to impact how much the pump sends to the top of the motor. It may cause a touch more splashing for the crank, but the valves and PCV will see the same amount of oil. I appreciate the math and effort to prove the volume difference, but don't see how that translates to more blowby. Do you have a theory on that?
 
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