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Reading Engine Oil Dipstick Level 3.6L

2708 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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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?
I agree, also I would think if there was more splashing due to excess oil you would see some foaming or aeration in the oil too. Got me thinking that the hash mark side is the one to read and as long as it's in that range checked cold you are good. Could run it an oil change just at he bottom of the hash marks and see if it makes a difference,
 

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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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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.
 

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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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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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If you held it upright like that to read it then you got a false reading
 

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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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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 !!!
 

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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.
View attachment 4570531
Check level 5 minutes after a warmed-up engine had been shut off.

After an oil change:
View attachment 4570532

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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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.
 

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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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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.
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.
 

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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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