Exhaust manifold gaskets on a 403?

Thread Tools
 
Search this Thread
 
Old May 29, 2026 | 06:46 PM
  #1  
MrEarl's Avatar
Thread Starter
Registered User
 
Joined: Aug 2019
Posts: 104
From: Athens, Georgia
Exhaust manifold gaskets on a 403?

79 Buick Estate Wagon, 148,000 mile, 403 engine. Noticing an increased exhaust noise in engine bay, can't tell exactly where it's coming from. Hopefully just at the manifold tailpipe connections. Will be taking to a shop but would like to know a bit more than I do such as are there gaskets (donut type or other) at the manifold tailpipe connections?

Last edited by MrEarl; May 30, 2026 at 03:11 AM.
Old May 29, 2026 | 08:18 PM
  #2  
olds 307 and 403's Avatar
Out of Line, Everytime😉
 
Joined: Dec 2006
Posts: 10,108
From: Melville, Saskatchewan
Yes on the passenger side rear outlet. Oldsmobile V8's didn't use exhaust manifold gaskets. I seen a few leak working in a garage. We installed a gasket and we never had any return.
Old May 30, 2026 | 03:54 AM
  #3  
MrEarl's Avatar
Thread Starter
Registered User
 
Joined: Aug 2019
Posts: 104
From: Athens, Georgia
Originally Posted by olds 307 and 403
Yes on the passenger side rear outlet. Oldsmobile V8's didn't use exhaust manifold gaskets. I seen a few leak working in a garage. We installed a gasket and we never had any return.
Thanks! Since the manifold ends are already shaped conically to fit into the tailpipe, are we talking about a flat fiber type gasket or ? Do you recall what size?
Old Yesterday | 07:44 AM
  #4  
olds 307 and 403's Avatar
Out of Line, Everytime😉
 
Joined: Dec 2006
Posts: 10,108
From: Melville, Saskatchewan
They were usually blue fiber with a metal ring built into the top. It is basically the shape of the metal cone built into the manifolds on the crossover pipes. Carefully tighten the three bolts by hand and don't go too tight.
Old Yesterday | 11:40 AM
  #5  
FStanley's Avatar
Registered User
 
Joined: Oct 2015
Posts: 677
have had good luck with RemFlex gaskets I cleaned up head and exhaust manifold surfaces as best I could while still attached to the exhaust pipes on the car. I used a flat file covered with 220 grit sandpiper then cleaned it off with brake cleaner and a paper towel. Remflex can deal with a lot of warpage.. 20lbs torque at most..
Old Yesterday | 09:04 PM
  #6  
MrEarl's Avatar
Thread Starter
Registered User
 
Joined: Aug 2019
Posts: 104
From: Athens, Georgia
Originally Posted by olds 307 and 403
They were usually blue fiber with a metal ring built into the top. It is basically the shape of the metal cone built into the manifolds on the crossover pipes. Carefully tighten the three bolts by hand and don't go too tight.
something like this


Old Today | 05:36 AM
  #7  
olds 307 and 403's Avatar
Out of Line, Everytime😉
 
Joined: Dec 2006
Posts: 10,108
From: Melville, Saskatchewan
No. The Felpro

60240 was what I always used. That picture is **** on Summit. This is what it looks like.

It could also be rotten bolts on the manifolds and crossover. You will have to narrow it down to where the leak is.

Old Today | 05:50 AM
  #8  
MrEarl's Avatar
Thread Starter
Registered User
 
Joined: Aug 2019
Posts: 104
From: Athens, Georgia
Originally Posted by olds 307 and 403
No. The Felpro

60240 was what I always used. That picture is **** on Summit. This is what it looks like.

It could also be rotten bolts on the manifolds and crossover. You will have to narrow it down to where the leak is.

Okay, thanks. I just know the shop will likely say 403s don't use gaskets and wanted to have something to suggest if the need arises. My hearing isn't very good these days so am having a hard time determining where the sound of the leak is coming from. I've read of a reverse airflow test where a shop vac is used to blow into the exhaust pipe and soapy water sprayed on the joints. I may try that. Thanks for your help!!!
Old Today | 10:19 AM
  #9  
olds 307 and 403's Avatar
Out of Line, Everytime😉
 
Joined: Dec 2006
Posts: 10,108
From: Melville, Saskatchewan
That sounds like a good plan. If everything is tight and not rotten, good chance it is one of the two gaskets needed to fix the leak. We had good luck with just slipping in a manifold gasket and leak was gone. Those donuts usually don't leak, unless they are disturbed.
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
Buick77
Big Blocks
11
Oct 17, 2025 01:01 PM
rpjr42
Parts Wanted
6
Dec 19, 2023 07:07 AM
Kennybill
Small Blocks
1
Oct 13, 2013 05:09 PM
RAMBOW
General Discussion
1
Aug 12, 2009 06:24 AM
toneypenna
Big Blocks
8
May 24, 2009 07:08 PM




All times are GMT -7. The time now is 08:44 PM.