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Hole in rear of oil pan

Old 01-12-2019, 02:47 AM
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Default Hole in rear of oil pan

I tried to find more information on this, but I couldn't find any. I have had a small oil leak since I reassembled my engine. It is a 1.8 from a 1997 and was bored over, hot tanked, and decked.
The leak was a few drops after hard driving with a t2560 at 12psi. But now I am running an EFR6758 and the leak has become significantly worse. The oil appears to be coming from the transmission weep hole and clutch fork shift boot. I have replace my rear main seal twice now, and the second time I used an OEM Mazda seal with FM install tool. I have also replaced my oil pan gasket and the leak persists. So I am now replacing the steel(?) oil galley plug with an OEM Mazda brass plug.

I have also replace the CAS o-ring and I am certain it is no longer leaking(back of head and tops of trans is dry).

But upon looking at the oil pan, I spotted a hole in it. Is this normal?



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Old 01-12-2019, 02:58 AM
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Got the same hole in mine. That leak is almost always the CAS though, rarely the rear main seal. Have you modified your valve cover PVC passages to help reduce crank pressure?
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Old 01-12-2019, 09:07 AM
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Yeah that’s the dowel pin I’m fairly certain
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Old 01-12-2019, 01:01 PM
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Originally Posted by gooflophaze View Post
Got the same hole in mine. That leak is almost always the CAS though, rarely the rear main seal. Have you modified your valve cover PVC passages to help reduce crank pressure?
Yes, I have replaced the CAS O ring twice and I used an anaerobic sealant on the cap. It stopped leaking once I used the sealant.

Thank you Curly, I checked my old motor in the daylight and found the same hole. I can't believe I never noticed it before.
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Old 01-12-2019, 10:47 PM
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I replaced the galley plug the machine shop used. This is a comparison of he plug and the OEM Mazda part. The plug came out very easily.


The brass plug has a tapered end and the block has a machine surface for it to mate to. I added a little anaerobic sealant and made sure it counter sunk a little.

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