3.6 oil cooler fail

[Judd]

Leaking oil cooler. What is the normal failure mode on these?
1. Cracked body
2. O-Rings leaking due to hardening or bolts loosening over time due to heat cycling.

If it's the o-rings leaking, anyone try Blue Devil seal sweller?????

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[Maximus Gladius]

Leaking oil cooler. What is the normal failure mode on these?
1. Cracked body
2. O-Rings leaking due to hardening or bolts loosening over time due to heat cycling.

If it's the o-rings leaking, anyone try Blue Devil seal sweller?????

You’ve got some good milage on your vehicle at 100k miles (160 kms), maybe a bit more by now. Have you replaced your PCV valve and are you confident it’s allowing the pressure out of your crankcase?

From everything I’ve read concerning the OEM oil cooler, people blame the plastic parts for breaking, and maybe so but this post has me intrigued to question crankcase pressure and I’m questioning if the PCV is causing pressure build up and the weakest link are the seals at the oil cooler. ??

When ever I’ve heard about a “rear main seal” leak, the next thought has always been to blame or change out the PCV but in my short years of having my 21 JTR, and all the reading of oil leaks we tend to have, I’ve not read where the rear main seal was a problem but rather the oil cooler or valve gaskets and then we can take it a step further to determine from those 2 areas, which one leaks the most and is it crankcase pressure/PCV related?

To your question though about the blue devil sealant, I’m not a fan of pouring anything like that in the oil as it will affect all gaskets and seals and is that something that’s necessary or a good thing? @ShadowsPapa would certainly have an opinion based on experience here but I’m betting he’d say just go in and fix the leak instead of pouring in that stuff. (I’m feeling lucky he’ll agree with me, do I buy that lottery ticket today?)

Let’s say your leak is a pressure related issue and you toss in that seal swell stuff and it fixes the oil cooler leak, the pressure has to come out at the next weakest point, so all you do is chase leaks and make your situation worse.

I’ve also read up on complaints of the aluminum oil cooler upgrade lasting about a year before leaks show up again so some research into why that’s happening is necessary.
Good luck!

 

[Lost1wing]

Over tightening!
O-rings installed wrong.

When installing the cap, you want to make surd the cap and housing are clean. You want to be sure that the old o-ring has been removed. Lubricate to new o-ring and put it in the correct place. Screw in the cap until it just stops. If you must torque it, use a quality torque wrench that is calibrated. These caps are NOT the tighter you get them, the better they seal. The tighter you get them, the more chance of cracking the housing. Same goes for doubling the o-ring. You end up forcing the cap in expanding the housing until it cracks.

 

[ShadowsPapa]

Over tightening!
O-rings installed wrong.

When installing the cap, you want to make surd the cap and housing are clean. You want to be sure that the old o-ring has been removed. Lubricate to new o-ring and put it in the correct place. Screw in the cap until it just stops. If you must torque it, use a quality torque wrench that is calibrated. These caps are NOT the tighter you get them, the better they seal. The tighter you get them, the more chance of cracking the housing. Same goes for doubling the o-ring. You end up forcing the cap in expanding the housing until it cracks.

Exactly. The o-ring seals, not the tightness of the cap. Once that o-ring is down where it belongs, the cap could even be loose and it won't leak The cap only needs to be tight enough that it can't back out on its own

When ever I’ve heard about a “rear main seal” leak, the next thought has always been to blame or change out the PCV but in my short years of having my 21 JTR, and all the reading of oil leaks we tend to have, I’ve not read where the rear main seal was a problem but rather the oil cooler or valve gaskets and then we can take it a step further to determine from those 2 areas, which one leaks the most and is it crankcase pressure/PCV related?

To your question though about the blue devil sealant, I’m not a fan of pouring anything like that in the oil as it will affect all gaskets and seals and is that something that’s necessary or a good thing? @ShadowsPapa would certainly have an opinion based on experience here but I’m betting he’d say just go in and fix the leak instead of pouring in that stuff. (I’m feeling lucky he’ll agree with me, do I buy that lottery ticket today?)

If the PCV was non-functional, you'd have fumes backing up into the intake rather than a leaking seal.
These seals and seals like them for decades are "wedge" types - meaning a bit of pressure forced the seal lip against the shaft - some even have springs to preload the lip against the shaft.
You'd have to build up some real pressure for a lip type seal to leak (unless it was a sort of seal installed in halves, then they are generally leaking at the joint between the halves, not at the seal lip itself.

Most of the leaks with these are valve covers or oil filter housing/cooler leaks that appear as rear main because of windage and the path the oil follows to find the course off the engine.
I'd bet most rear main leaks are misdiagnosed leaks from another source, or, if it is that seal, it was damaged by grit, dirt, sand and so on.
Lip type seals can take some pressure - upwards of 7 psi or more, before a leak. You are more likely to see oil mist being forced into the intake because these aren't really closed systems- there's a tube allowing fresh air into the crankcase as the PCV evacuates the crankcase of "fumes". Pressure will go back out that tube, leading to oil consumption, not leaking

 

[Maximus Gladius]

Exactly. The o-ring seals, not the tightness of the cap. One that o-ring is down where it belongs, the cap could even be loose and it won't leak The cap only needs to be tight enough that it can't back out on its own



If the PCV was non-functional, you'd have fumes backing up into the intake rather than a leaking seal.
These seals and seals like them for decades are "wedge" types - meaning a bit of pressure forced the seal lip against the shaft - some even have springs to preload the lip against the shaft.
You'd have to build up some real pressure for a lip type seal to leak (unless it was a sort of seal installed in halves, then they are generally leaking at the joint between the halves, not at the seal lip itself.

Most of the leaks with these are valve covers or oil filter housing/cooler leaks that appear as rear main because of windage and the path the oil follows to find the course off the engine.
I'd bet most rear main leaks are misdiagnosed leaks from another source, or, if it is that seal, it was damaged by grit, dirt, sand and so on.
Lip type seals can take some pressure - upwards of 7 psi or more, before a leak. You are more likely to see oil mist being forced into the intake because these aren't really closed systems- there's a tube allowing fresh air into the crankcase as the PCV evacuates the crankcase of "fumes". Pressure will go back out that tube, leading to oil consumption, not leaking

But I’m not sure the OP is talking about the “O ring” as in the cap we screw down. I think (I could be wrong) he’s talking about the cooler leak where the multitude of seals are where the cooler bolts down to the block. Are these “lip seals” like a rear main seal. I’d like clarification from the OP what he’s referring to when he says “O ring” seal.

 

[ShadowsPapa]

But I’m not sure the OP is talking about the “O ring” as in the cap we screw down. I think (I could be wrong) he’s talking about the cooler leak where the multitude of seals are where the cooler bolts down to the block. Are these “lip seals” like a rear main seal. I’d like clarification from the OP what he’s referring to when he says “O ring” seal.

If I recall correctly, there was a design change for the seals where that cooler mounts............ my head and face are throbbing like a SOB right now, fluids have migrated down the side of my head under the scalp into my right temple area so gotta bow out for now - DAMN, this hurts!

 

[Maximus Gladius]

We got your back, we’ll figure it out. Take it easy Bill

 

[Maximus Gladius]

2. O-Rings leaking due to hardening or bolts loosening over time due to heat cycling.

To me, what you’re referring to here are the seals under the cooler that seals it to the block. Please clarify your use of the term “O-ring” and where this is for you.
You mention maybe this leak at the O-ring due to “hardening”, ..that wouldn’t happen in the cap with regular 5000 mile oil changes.
You also mention “O-rings”, plural, more than one, so I think it’s the seals at the base of the cooler you’re talking about.

I’ve not looked at the design or seal grooves or what some say is the flaw with OE except we’re dealing with plastic to aluminum and you have a solid point with the heat cycles you speak of, …and you’ve done a few in your 100k + miles.

 

[Lost1wing]

It maybe that those seals or even the housing would fail. I think the culprit it still at the installation. Over tightening and double O-rings will make it awful hard to remove, thus breaking twisting the housing.

I noticed on a Mopar parts web site that the Dorman cooler is available with a Mopar part number. That would be the one Jethro would order when replacing his broke plastic one.

If you struggle getting a cap off, something went wrong on the installation.

 

[Medical_Bartender]

Not exactly apples to oranges, but I replaced the oil cooler on my 2015 JK with the 3.6 around 105k miles. I'd changed my own oil every 5k miles since I bought it with 13k on the odometer. I don't recall seeing exactly where the failure point was though. I gave it a look-over after removing it and everything looked normal, so it may have been some type of pressure related failure of the o-rings or plastic that only showed up under running oil pressure.

Of note, I distinctly remember when it went. I turned over my engine when the jeep was cold and left outside during a cold night shift...heard a noise I hadn't heard before - almost like a low pitched squeal for a split second or two that then went away. Drove home and found a puddle of oil under and all down the sides of the transmission. I think mine was related to fatigue over the years and the higher pressure associated with a very cold start. No basis for this conclusion, but nothing else jumps out as the cause for me.

Best of luck. It's not a terrible job to DIY. I'd recommend changing out driver spark plugs and coil packs at the least since you'll be right there once you take the plenum off.

 

[Stan H]

Not exactly apples to oranges, but I replaced the oil cooler on my 2015 JK with the 3.6 around 105k miles. I'd changed my own oil every 5k miles since I bought it with 13k on the odometer. I don't recall seeing exactly where the failure point was though. I gave it a look-over after removing it and everything looked normal, so it may have been some type of pressure related failure of the o-rings or plastic that only showed up under running oil pressure.

Of note, I distinctly remember when it went. I turned over my engine when the jeep was cold and left outside during a cold night shift...heard a noise I hadn't heard before - almost like a low pitched squeal for a split second or two that then went away. Drove home and found a puddle of oil under and all down the sides of the transmission. I think mine was related to fatigue over the years and the higher pressure associated with a very cold start. No basis for this conclusion, but nothing else jumps out as the cause for me.

Best of luck. It's not a terrible job to DIY. I'd recommend changing out driver spark plugs and coil packs at the least since you'll be right there once you take the plenum off.

In my Uncle Ricks Chrysler Van his oil cooler started leaking and it wasnt the housing it was the O-ring on the bottom side of the cooler . He actually saved it showed it to me last time I was over there. The O-ring had wore flat. Not blowed out. @Maximus Gladius

 

[Maximus Gladius]

In my Uncle Ricks Chrysler Van his oil cooler started leaking and it wasnt the housing it was the O-ring on the bottom side of the cooler . He actually saved it showed it to me last time I was over there. The O-ring had wore flat. Not blowed out. @Maximus Gladius

Wild! Wore flat! Just like the O ring failure in the connector under the coolant tank. It wore flat too and caused my coolant leak.

 

[Stan H]

Wild! Wore flat! Just like the O ring failure in the connector under the coolant tank. It wore flat too and caused my coolant leak.

Wonder if the O-rings they are using in those oil coolers are coming from Temu ?

 

[Stan H]

Most common failure on the 3.6 Pentastar is a cracked oil cooler housing, the plastic body loves to split from heat cycles.
Blue Devil? Wouldn’t waste the time. It won’t fix a cracked housing, and swollen o-rings on the cooler isn’t a reliable or clean solution. Most folks just replace the cooler (preferably with the updated aluminum unit).

Unfortunately the cooler won't fail but you would have the same Cheap-o-rings. Imagine replacing with that aluminum Dorman from Amazon and it failing 6 months later .

 

[Hootbro]

The housing cracking at the body where the oil filter sits was primarily a pre PUG Gen 1 thing with most being 2013 and prior with the old oil filter design.

Most times nowadays it is the o-ring(s) blowing out from the housing assembly base to the upper block. Most shop mechanics that see it say you could get away with a just a new o-ring set but most up-sell the whole new housing and cooler assembly since they are there anyway and the lesser risk for customer pay work and comebacks.

The last outlier is the actual metal cooler assembly that sits on the plastic housing block of the whole assembly will sometimes blow out a o-ring but getting replacements for those can be tricky as MOPAR does not show those as a serviceable separate part.

If one has time and looking to save money, they can do the teardown and see what specifically failed and order just the repair parts needed, but like the shop mechanics, the easier and quickest path is to just replace the whole oil filter/cooler housing assembly with new provided o-ring(s) and be done with it.

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