Status: SOLVED!

I believe I have found a rare defect in the casting process for the 6G72 block. After days of searching off and on, I have only been able to find what sounds like two other instances of this defect on other forums. I have had a pesky oil leak since I swapped in this engine and I have tried hard to fix it. Before moving on with this thread, I must note that there are "ZERO" leaks anywhere else on this engine, no antifreeze leaks, no oil leaks(asides from this one). Front/Rear camshaft seals are replaced/not leaking, valve covers are dry as a desert/not leaking, rear main is not leaking, front main is not leaking, confirmed head gasket is not compromised/leaking.

Symptoms: Strong oil burning smell accompanied with smoke emanating from the lower driver side down pipe(the one that routes underneath the bell housing inspection plate) and two oil splotches the size of a quarter under the vehicle after a few short minutes of parking/turning off the car.

I have replaced the lower oil pan gasket twice thinking I messed up and it didn't solve anything, my next thought was that it had to be an upper oil pan gasket leak. I pulled the engine out of the monty last week and reapplied both the lower and upper gasket using black rtv for the lower pan and red rtv for the upper as per the manufacturers recommendation. Still leaking, since everything is clean enough now to see where the leak is coming from, I crawled underneath with the monty running and observed oil actively seeping out from the point shown below.






Another angle shows where it originates and how it flows to a single prominent point and it drips/flows down onto the upper and lower oil pan and then everywhere else, Something else to note is how the oil flows from that point down onto the A/C bracket and drips off. This cannot happen if the leak was below the point I am suspecting. The below image was taken upon first start up after reinstalling the engine, I had yet to even put it in gear. There's no way it could have blow oil anywhere around from wind. My second thought is that it may be coming from the bolt hole itself, perhaps during the machining process, the bit tapped into an oil galley of some kind?







Now some of you may be wondering why it appears it's leaking from that one spot in the above picture. I physically saw it seeping/running from the spot I'm suspecting. I will cleaning up that area thoroughly once the weather is a bit more agreeable. I have two options at my disposal to fix it. The spot in question is accessed by removing the driver front tire, A/C compressor, and A/C bracket.

(1): Blue Devil stop leak (add to oil per instructions and run until either (A): it stop leaking, or (B): 1,000 miles after adding) at which point I'll drain the oil and refill to make sure the stop leak doesn't become an issue later down the road.

(2): JB Weld. Clean up the area, remove paint, etc and apply the jb weld to the spot.

Any other thoughts regarding this is greatly welcomed as this is surely an odd problem.

 

Naevis, that is an interesting thing you've stumbled across. I can't imagine that a slight divit/depression shown in the first photo would result in this leak. The whole point of the oil pan gaskets and RTV sealants is to seal those micro defects. What is interesting to me, is that on the next generation of engines (6G64) Mitsubishi has committed the oil pan gasket and only used their orange RTV sealant.i wonder if that reduces number of possible "failure points".
Anyhow, the two likely possibilities I see is the actual hairline crack in the block (not the line on the pan mating surface), or your other suggestion - oil leaking from the bolt hole near by.
You can start by testing the idea of the bolt hole. Take out that bolt, clean everything. Then put a blob of RTV on the end of the bolt and on few threads. Let it set a little (3-5 min), then install it back in.
As far as the hairline fracture possibility - they do have special dyes that when applied to cast metal with a suspected defect. will penetrate the crack and make it visible. I've never worked with them myself, so unfortunately I can't point you in the right direction there. I'll look around and if I come across it, I'll add to this post.

Here is a link to dye penetrant testing info:
https://duckduckgo.com/?q=dye+penetrant+inspection&t=fpas&ia=web

 

Great suggestion with the dye penetrant, I've actually worked with the stuff a few times, but it's leaking fast enough I should be able to see it with the naked eye once I clean everything up. I just have to wait for it to stop raining. Also it's not the divit/depression itself that I'm suspecting, If you look at the picture below, you'll see a faint line across the gasket surface on the block that is a leftover from the casting process, interestingly enough, this line corresponds with the divit you mentioned, it runs perpendicular to that casting mark on the gasket surface, which is why I'm suspecting it to be where the crack in the block may be (The picture below has an orange line showing how the angles line up and how I suspect that spot). Sorry I don't have any better pictures, I didn't think to take a closeup of this spot as in a million years I wouldn't have suspected a block defect when I had the engine out. (I got lucky with this shot being as detailed as it is because the original picture was taken about 6 feet away with my phone)



 

That is a tough spot to get any photo while on the vehicle. BTW, when you clean up that spot, spray some baby powder or talcum powder there. It will help to see exact spot where it's leaking.
I honestly don't know what to do once you confirm the presence/absence of the crack. Perhaps take a dremmel to it, grind down the spot to make a little deptession/channel along the crack, then JB Weld that spot. The trick will be to fully degrease the crack before JB Weld is applied. It's very impressive that you got the rest of the oil leaks under control. Nice job with that.

 

Oh man that is a brilliant idea, talcum powder to find the leak, I love it. The plan was/is to try and JB weld it like you said, I plan on trying to reverse flush the crack with brake clean if possible. Yeah it's been a roller coaster trying to get them all taken care of. I've learned a lot over the years about the quirks of this engine. I even figured out a way to keep the valve covers from leaking whatsoever, tested over 20K combined miles(two engines w/each having 10k on the covers). If you're interested I could tell you how I did it.

I may be able to to do this work tomorrow if the weather holds out (I despise working in the rain or on wet ground).

 

Yes please!!! I have a set of new gaskets installed on my 3.6L after the engine rebuild. They are not leaking, but knowing how common this issue is, I'm keeping an eye on them. If there is a good trick to help them last longer, I'd like to know it.

 

The problem with the valve covers leaking stems from how the valve covers gasket surface is made. If you take the gasket out of one of the valve covers, you'll notice that it's not flat, rather it has creases everywhere from the stamping/rolling process. These create spots on the gasket where it gets pinched or doesn't allow even pressure across the gasket, which creates weak spots that are prone to oil seeping past.

The fix:
When you go to replace the gaskets, remove every trace of the old gasket from the valve covers and thoroughly clean as much oil and residue from the gasket mating surfaces in the valve covers as possible. When you are ready to reinstall the covers, place a generous bead of red or black RTV along the valve covers gasket mating surface(I must note that I used pressurized black RTV to perform this process but I'm sure a regular tube would do just fine.), wait a few minutes then carefully place the valve cover gasket into it's position, gently press down on the gasket and run your finger along the surface of the gasket, applying even pressure as you do it, this allows the RTV to fill the troublesome areas and create a better sealing surface by molding it to the gaskets shape. Wait at least 15 minutes after the last step, then place the valve cover onto the head, tighten down the bolts finger tight, wait 30-60 mins and tighten to spec.

At this point you can either return the engine to service or better yet, wait over night to let it cure more. I've done both so far and haven't seen an issue thus far. Before I figured this out, I was lucky to make it 5k before they started up again. I've replaced the valve covers about 7 times now, 5 of those were before finding out this trick. the last two where for two different engines. My next step was to strip the paint from the valve covers and JB weld the gasket mating surface of the valve covers to create a smooth flat surface but I haven't had to resort to such barbarism as of yet.

 

Update:

I ran Blue Devil brand oil stop leak for about >600miles and it has slowed the leak so much that I don't even get drops of oil on the ground anymore. The burnt oil smell is no longer detectable inside the vehicle anymore either. I'm changing the oil shortly after posting this so I'll update if the leak gets worse again, but for now I'd say it's not a problem anymore.

I know some of y'all will scold me for running stop leak but hey, call me a guinea pig for science.

Edit / Update: (11/10/21)

It's been awhile because I forgot about this thread. Firstly the stop leak didn't work, it quickly started leaking again after my next oil change and I'm not about to keep adding stop leak every oil change so now it just leaks. Secondly, I found the source of the leak while I had the engine torn part way down on the front to replace a bad timing tensioner. The leak is located in between the oil pump and block so I was right about the leak location but not about a defect being the cause, here is a picture for your viewing pleasure:

1998 6G72 Oil Leak