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Perfect Seal for Head Gaslets?

Old 09-12-2020, 10:25 AM
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Default Perfect Seal for Head Gaslets?

I got one of my 502s out of the 311 last night and found that the head gaskets were seeping (again). When I did the top-end refresh in 2019, I replaced with 17048 Fel-Pros following their instructions for assembly. I was surprised to see this after what was probably twenty hours of running (if that).

Reading through OSO last night, I saw that Mercury Perfect Seal was recommended to stop this. How is it being applied and how successful is it at dealing with the problem?

Off to get the other one out now...
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Old 09-12-2020, 02:09 PM
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Tom,

Those gaskets really should not need any additional sealer. The black coating is a sealer in itself. When you did the freshen up were the heads resurfaced ? Where exactly are the gaskets seeping ?

Are you using bolts or studs ? If bolts, make sure they are not bottoming out in the bolt holes. I have seen it happen and it will fool you into thinking you are torquing the bolts correctly where in reality they are bottoming out.

Are you retorqueing the head bolts ? It really should not be needed but it cant hurt. When I do them I use this procedure that one of the Fel Pro performance techs taught me many years ago:

1. Torque the heads using your normal method. Then walk away for a few hours or even overnight.
2. Then starting with the first bolt in the sequence loosen it about 1/2 turn. Then torque it all in one pull to the final torque value. Go through the entire torque sequence like that doing one bolt at a time. Try marking one of the bolts before you loosen it and you will see how much further it moves when you retorque it.

The reason for that procedure is that if you just go back and try to retorque the bolts a lot of times the torque needed to just to get past the friction on the bolt head will make it seem like they are tight but they really are not.

Just thinking out loud. Of course if the head or block surfaces are less than ideal you just might have to use additional sealer.

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Old 09-12-2020, 03:36 PM
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Run the Cometics Tom.....
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Old 09-12-2020, 03:39 PM
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Perfect seal is great for a lot of marine sealing like drives and bellhousing coolers .. I would not use it on a head gasket .
I used to spray mine with Copper seal but they`re fine without that also. YOur problems probably not gasket related
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Old 09-12-2020, 08:00 PM
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Thanks guys.

An older similar thread on this (Merc 420s with seeping had gaskets... Water drips between head and Block...) had a response from MBam saying the sealing surface on the outer edge of the block was thin resulting in seepage. He recommended Perfect Seal to cure the problem. Both of my 502s show evidence of side seepage with the starboard engine being factory sealed. Neither engine show any issues with water mixing with oil, and both have compression of 150-155 psi (with exception of a valve issue on port side #7).

I had not heard of using anything to seal the ports outside of spraying the gaskets down with copper so I thought Id bring it up.
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Old 09-12-2020, 08:07 PM
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Originally Posted by seafordguy View Post
Run the Cometics Tom.....
Eric, I had not planned on going into the short blocks so Im thinking the Cometics wouldnt work for me unless I decked the blocks. I wish I could use them but I think Im stuck with the FelPros.
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Old 09-12-2020, 08:32 PM
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When I was drag racing, many of our motors LEAKED water when cold running cometics. Spraying them with copper seal fixed that.
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Old 09-13-2020, 07:44 PM
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Not using Perfect Seal anywhere after it failing to seal the fuel lift pump to raw water pump gasket on 7.4 LX MPI's. Definitely NOT on a head gasket. If you want anything other than copper spray as listed above, Indian Head Gasket Sealant. Press fit (hammer) a brass half sphere fitting into a removed freeze plug hole on an aluminum head and that thing never leaked in 10 years of ownership with IHGS!
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Old 09-13-2020, 09:23 PM
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Originally Posted by Tractionless View Post
Not using Perfect Seal anywhere after it failing to seal the fuel lift pump to raw water pump gasket on 7.4 LX MPI's. Definitely NOT on a head gasket. If you want anything other than copper spray as listed above, Indian Head Gasket Sealant. Press fit (hammer) a brass half sphere fitting into a removed freeze plug hole on an aluminum head and that thing never leaked in 10 years of ownership with IHGS!
I was considering cooper spray.

I took the heads off today and there was no evidence of water seeping between the gasket surfaces. A little stumped but all was clean. The head gaskets looked perfect.
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Old 09-14-2020, 12:53 PM
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I would strongly suggest upgrading to the Comtic (or similar) MLS steel head gaskets. They are expensive but said to be bulletproof and possibly reusable. Of course make sure your surfaces are straight and have the correct finish for sealing.

Hopefully you are in a situation where you can use them!

Last edited by 87MirageIntruder; 09-14-2020 at 12:58 PM.
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