1966 427/390 Coolant in Oil on Break In

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Jun 27, 2020 | 4:11 PM

jeggers93

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1966 427/390 Coolant in Oil on Break In

Just started freshly rebuilt L36. First start/break-in was interrupted after 10 minutes because I had a leaking fuel bowl. Fixed that overnight and started again today. Set rpm at 2500. Ran fine for 10 minutes then I noticed some knocking so I shut it down. Dieseled for a stroke or two after I turned off ignition. Pulled LH valve cover and sure enough see signs of coolant in oil.

Ideas on what to check next and potential source?

Jun 27, 2020 | 7:52 PM

Little Bear

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Pull the intake see what you see... I'm thinking head gasket or head so pay attention as you pull it back apart. Hopefully you didn't score the bearings.

Oct 29, 2020 | 8:53 PM

chevyboy@22

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From: Raleigh, North Carolina

Although initially listed as a 450hp engine, the solid lifter 427ci engine’s rating was later reduced to 425hp shortly after its introduction for reasons unknown. Similarly, the 390 horsepower engine was initially rated at 400 horsepower. When the official ratings were reduced, the decision to make this change was purely administrative and was not the result of any changes made to the engines.

Nov 2, 2020 | 12:44 AM

73shark

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From: KC, MO area

jeggers93: Welcome to the forum.

If it's not a head gasket, most likely place is the intake gasket where the coolant crosses between the heads. Should be sealant there.