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Reading Engine Oil Dipstick Level 3.6L

2709 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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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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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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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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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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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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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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Discussion Starter · #22 · (Edited)
The theory is that overfilling leads to excessive crankcase pressure even before getting to the point of the crankshaft making contact with the oil and causing it to froth, which would be really bad. Now clearly the oil sitting in the pan isn't getting directly blown out the PCV which is in the valve cover, but the higher crankcase pressure could be pushing more oil from the upper valvetrain into the PCV system than it would be otherwise, as well as lead to a higher concentration of oil vapor in the escaping gases both of which end up coating your intake plenum over time.

I showed through calculation and measurement on a level surface that you could be .19 quarts high with the difference in readings on either side of the dipstick, but I also showed that volume could be practically doubled to .38 quarts just from parking on a mildly unlevel gravel surface and taking the same reading. We don't know for sure how much additional oil is required to cause this on a 3.6L, but I cleaned the intake on mine and will attempt to test by reducing my oil fill and monitoring over a period of time. I could be wrong, but I see no other good explanation for the presence of oil in my intake. You can find plenty of people in various automotive forums reporting oil in the intake from an overfilled crankcase, and Izuzu acknowledges it below.
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Discussion Starter · #24 · (Edited)
Isuzu may admit it in this snippet, but we don't know that the system for the motor this applies to operates the same as the 3.6. It could be, but we don't know. I will also point out that even in the snippet, there is some room between full and over-full. They are allowing for a range from ideal both plus and minus. We don't know what the 3.6 engineers set for a range for comparison, but it's safe to assume they did. 2.5mm seems like a pretty reasonable value for a range, but that is a guess.

By all means, please test, I am curious how it turns out, but also please keep in mind that there could be other things in play which you seem to have ruled out by default. The PCV you installed could not be to spec, it may have picked up a ding during install, a piece of debris could have lodged in the seal, etc.
I suppose that could be a possibility, but then two separate Mopar PCV valves that were manufactured around 4 years apart and installed by different people would have to be malfunctioning for that to be the cause. I mentioned I have found oil in the intake throughout the ownership period, so that would mean both the factory installed PCV valve and the OE replacement were malfunctioning, which seems unlikely.

I also mentioned that I just recently did compression, leakdown, and borescope tests all of which returned textbook results, so that rules out excessive blowby past the rings. The vehicle doesn’t burn a detectable amount of oil between 5,000 mile change intervals, the spark plugs showed no oil buildup, there is no blue smoke out the tailpipe, and the engine performance seems good other than pinging on 87 octane at low rpm high load that is eliminated with 89 octane fuel, so I think that rules out leaking valve seals. I am open to other theories, but oil buildup in the intake from overfilling still seems like the most likely explanation to me.
 

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Discussion Starter · #26 · (Edited)
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
Good point that the front wheel drive 3.6L models have a more vertical entry dipstick tube and a different design dipstick. I think that the ultra thin flat blade dipsticks are the best design for measurement accuracy, but I see no reason why the bullet on ours couldn't have been designed to eliminate the round cross section on the very end, and reduce down from the wire to a rectangular cross section near half the current thickness in the measurement region, which would significantly reduce the effect of the dipstick angle on the top to bottom reading. A purely theoretical zero thickness dipstick would read the same on top and bottom regardless of the angle it was inserted.
 

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Discussion Starter · #28 · (Edited)
If you held it upright like that to read it then you got a false reading
That picture was only intended to illustrate the clocking of the yellow handle on the dipstick in relation to the non crosshatched side of the measurement region on the bullet tip. When the dipstick is inserted so that the "engine" lettering can be read while standing on the driver side of the vehicle, the non crosshatched side of the bullet will be pointed upward in the oil pan. The dipstick is able to be inserted with the handle at any rotation, but I find that it will realign itself if you attempt to insert it with less than a 90 degree rotation from this position. If you try to insert it clocked 90 degrees in either direction from this position so that the "engine" lettering is read from the front or back of the engine compartment, it takes much more force to insert it. Unfortunately the picture in the owners manual that points out the location of the engine oil dipstick doesn't show any detail of the handle clocking, but mine was delivered with the dipstick clocked this way as well as the majority of them I have seen in person or in photos.
 

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Discussion Starter · #30 · (Edited)
WOW. Interesting read. Talk about going down the rabbit hole. My JEEP 2015 JKU-R Hard Rock is a toy, not a daily driver. If it rolls out, we are likely going out to play, or heading out for an extended expedition to some location where we'll make camp and then go out exploring daily. We retired fairly well-off, so the only thing holding us down is two retired Great Danes (former show dogs). If we can convince the daughter to house-sit, we are going somewhere.
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Going by the manual (something I do a lot) for my JEEP, it seems clear enough.
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Check level 5 minutes after a warmed-up engine had been shut off.

After an oil change:
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Since I do my own oil changes on the JKU-R Hard Rock, I'll drive it some to get everything up to operating temperature, then park it in the LEVEL portion of the driveway. I'll remove the drain plug and allow the old oil to drain. While it is draining, I'll pull the oil filter and replace it with a stock JEEP (MOPAR) filter, taking care to lube the O-ring and not over-torque the filter cap. While the oil drains I'll quickly check the front and rear differentials for proper levels, check the transfer case for proper level, and check all suspension bolts (marked with a paint stripe) to ensure none are loose or mis-aligned. By this time the oil pan is just a drip every second or so. I put the drain plug back in and torque it to spec. I fill in 6 quarts of my choice of oil. After filling I will always check the dip-stick and it always reads over-full. This is expected, but I just feel better seeing the oil level on the dip-stick before starting. The motor is mostly still warm since parking it, but the oil is not. So I'll let the motor idle while I clean up the tools, then shut it off and let it sit while I put away the tools. That takes about 5-minutes. I'll pull the dipstick and clean it, then check the oil level. It is always right at the full mark. I've never cared if it looked like a slight amount above or below the full mark.

We are at 65,000 miles now (just did an oil change after our Big Bend trip). At 50,000 miles I needed to replace the thermostat. While in there working, I also decided to replace the spark plugs. Probably unnecessary, but I did it anyway. As you know, you need to open the intake manifold to get to 3 of the spark plugs. The inside of the manifold was clean. NO OIL POOLS.

I'll never laugh at folks who IMHO over-maintain. I lean that way myself..... But this thread - WOW! Still, it made me realize that maybe I want to check my PCV. Something else for me to over-maintain? YUP !!!
How long do you estimate you let the sump drain before you put the plug back in and refill with oil? You say no pooled oil, but did you see any presence of oil on the back of the throttle plate and in the plenum?
 

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Discussion Starter · #32 ·
I agree that it would be unlikely that 2 oem parts were bad, but things happen. Could be debris in the oil as well. I just don't see how such a small change in oil level in the sump would cause an over-pressure condition. I know a way over-fill will and I see where it sure looks like you have an over-pressure issue, I just don't see where the 2.5 mm of extra level is the cause of it. On the other hand, I don't have any better suggestions for you either. It's an head-scratcher.
Well at this point it doesn't cost me anything further to test the effect of different oil levels in the sump on the amount of oil found in the intake plenum. I have exhausted pretty much every other avenue, so I want to rule this out before considering spending $80 on a third PCV valve.
 

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Discussion Starter · #34 · (Edited)
Over pressure would suggest the oil pump. Seems fairly common on here with them failing to high pressure. Usually a code is thrown though. It would seem more plausible. Maybe in time it will generate a code.
Crankcase (air) pressure is caused by the combustion gases that leak past the rings into the crankcase which all engines have to a degree, and by the airflow that is generated within the crankcase by the movement up and down of the pistons and rotating assembly. The oil pump generates pressure within the liquid oil, but does not affect the crankcase pressure that is vented through the PCV system.

My understanding is that overfilling the crankcase with oil reduces the air volume in the crankcase, and that leads to the higher crankcase pressure everything else equal. This higher pressure air then has to vent from the crankcase into the upper valvetrain where it can push additional oil from this area into the PCV system as it escapes to the intake. The higher pressure air is capable of holding more oil vapor which will also be transported to the intake.

If the crankcase is significantly overfilled, then the crankshaft will start to make contact with the oil and cause alot of foaming and aeration in the liquid oil. Aerated oil full of bubbles is harder for the oil pump to distribute, and has reduced ability to lubricate and cool critical engine parts. You are in real trouble if it's overfilled to that point, but there are typically windage trays installed that can help mitigate this aspect.
 
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