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Old 10-14-2013, 10:22 PM   #1
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Default Question about gaskets and sealant

Hello all,
I've been reading the forums and I understand that when there's a groove, one uses sealant and when it's a flat surface, you use a gasket.

I've been taking apart a motor, and I noticed (maybe anomalous) that the circle bracket that held the rear main seal had a gasket AND a bead of silicone. The water pump had a gasket with some adhesive dressing (like a spray). The intake manifold gasket looked like it was adhered with a sealant as well....

Are there surfaces where you tag team sealing with both gaskets and sealants? Or did whoever built this motor just botch.

That being said, I've been trying to read through the PDF's and it didn't really specify. Any clarification is greatly appreciated.
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Old 10-15-2013, 01:38 PM   #2
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The Miata engine uses a combination of gaskets and sealants. For example, the oil pan rails and corners of the half round end gaskets get ultra Grey sealant. However, the half round gaskets don't need to be covered in sealant, just the ends. The rear main seal itself doesn't need any sealant, but the holder itself does get some.

In general, the sealing points were designed to use either a gasket or sealant, not both except at the ends, corners, or other transitions. There are times to use gasket cement or even a very light coat of sealant to help a gasket when the matting surfaces have been damaged. However, that isn't usually the case with the factory design as it would make assembly slower in the factory.

Search around for the factory workshop manual. It contains diagrams which show where to use sealant and the specific type.

FYI... The intake manifold should use the metal gaskets with no sealant.
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Old 10-15-2013, 01:43 PM   #3
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I was referencing the factory manual, but was thrown off since it didn't actually address the metal holder that bolts onto the block, it just mentioned pressing the main seal in itself. When I removed the holder on my block, I was pealing off a black gasket which was also bonded with silicone sealant. The holder itself was grooved for sealant.

I appreciate the response and clarification for the IM gasket. Thanks.
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Old 10-16-2013, 01:15 PM   #4
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That sounds right, though it should be ultra grey sealant, not black.

The factory manual is vague in places...
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Old 10-16-2013, 01:25 PM   #5
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Whenever there's a flat gasket, I use Indian Head Shellac. Sticks the gasket in place, and makes for a great seal. I've never done a water pump without it, and never had a leak, even on questionable surfaces (gouged, nicked, etc.).

If it's a rubber type seal, use a little oil and no sealant.
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Old 10-18-2013, 02:23 AM   #6
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Quote:
Originally Posted by noname4me View Post
That sounds right, though it should be ultra grey sealant, not black.

The factory manual is vague in places...
The black gasket was a paper gasket, the grey was silicone

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Old 10-18-2013, 12:17 PM   #7
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Quote:
Originally Posted by psyber_0ptix View Post

The black gasket was a paper gasket, the grey was silicone

Sorry, misread your post.

The black rubber gasket only gets ultra grey on the corners. Shouldn't be a need to goop the whole thing up with silicone.
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