Logo
Click for Chrysler parts and manuals!
Results 1 to 8 of 8
  1. #1
    Join Date
    Jun 2012
    Location
    Finger Lakes NY
    Posts
    70

    Default Replace intake manifold?

    Hello, I have a good running 340 in my old 74' century resorter. I have done all of the exhaust manifolds within my ownership, they had a couple hairline cracks so I did it to avoid having more serious issues.

    I am wondering if I should be thinking the same way about the intake manifold. It is original. Looking inside the thermo housing, it's very rusty and rough looking inside. Is this a point that will eventually rot out and cause engine damage? Anyone have a good source for a marine manifold? Is it the exact same manifold as a 318?

    Thanks,
    Steve

  2. #2
    Join Date
    Nov 2005
    Location
    Chi West, IL, USA
    Posts
    836

    Default Re: Replace intake manifold?

    Not sure, but I believe the ports on a 273/318 may be smaller than the 340/360.

  3. #3
    Join Date
    Dec 2014
    Location
    Ontario Canada
    Posts
    58

    Default Re: Replace intake manifold?

    The cast iron 4 bbl intake manifolds on these engines are heavy and not prone to rusting out. The bottom side is bathed in oil so rust free (picture 1). What you are seeing is the heat damage to the paint caused by the choke pot cavity exhaust passage (picture 2). You could clean it up a bit with a wire brush and repaint it if you like, but the heat will likely bake the paint off again.
    The intake manifold will have a casting number on it just forward of the distributor (picture 3) which should be used when and if a replacement becomes necessary.
    In short you are quite likely OK, unless your engine has been exposed to a the weather for some time.
    Click image for larger version. 

Name:	Bottom view.jpg 
Views:	12 
Size:	94.9 KB 
ID:	20956Click image for larger version. 

Name:	Top view.jpg 
Views:	13 
Size:	66.6 KB 
ID:	20957Click image for larger version. 

Name:	Casting number.jpg 
Views:	12 
Size:	62.2 KB 
ID:	20958

  4. #4
    Join Date
    Jun 2012
    Location
    Finger Lakes NY
    Posts
    70

    Default Re: Replace intake manifold?

    Thanks for the replies. I am not concerned with surface rust on the outside of the manifold but the corrosion from the water inside the manifold. When I open the thermostat housing there is rust inside the manifold and the surface is quite pitted. Has this been an issue for anyone?

  5. #5
    Join Date
    Dec 2014
    Location
    Ontario Canada
    Posts
    58

    Default Re: Replace intake manifold?

    My engines are closed loop and antifreeze runs through those passages. The inside of mine still looks good. Click image for larger version. 

Name:	Thermostat Housing c.jpg 
Views:	11 
Size:	73.4 KB 
ID:	20962
    I'm guessing yours must be an open loop system exposed to
    raw water or even salt water perhaps?

  6. #6
    Join Date
    Jun 2012
    Location
    Finger Lakes NY
    Posts
    70

    Default Re: Replace intake manifold?

    Quote Originally Posted by Toonl View Post
    My engines are closed loop and antifreeze runs through those passages. The inside of mine still looks good. Click image for larger version. 

Name:	Thermostat Housing c.jpg 
Views:	11 
Size:	73.4 KB 
ID:	20962
    I'm guessing yours must be an open loop system exposed to
    raw water or even salt water perhaps?
    Yes, mine is running raw water. No salt ever. Mine looks a lot worse than yours.

  7. #7
    Join Date
    Dec 2014
    Location
    Ontario Canada
    Posts
    58

    Default Re: Replace intake manifold?

    I'm afraid that is about as far as I can go then. Surface rust is not an issue, and should the condition be worse it is impossible to us know the condition of your centerhead without actually inspecting it. If you are uncertain, you could have a local mechanic give it a quick look. I hope it turns out to be OK.

  8. #8
    Join Date
    Mar 2007
    Location
    West Hartford, CT,
    Posts
    69

    Default Re: Replace intake manifold?

    It's pretty hard to pressure an intake manifold if you don't have blocking plates, so you may want to consider this.

    Find a local shop that will "boil" it in a cleaning tank. Then once it's clean, give it a good inspection (NDT mag-particle if you have capability).

    If you can't mag-particle inspect, give it the screwdriver and hammer test. Use screwdriver to try and poke a hole in clean cast iron manifold-pretty hard to do if it is in good shape. If it has been compromised, it'll likely give way.

    Then, hang manifold up in garage somewhere from a string tied through a bolt hole. Lightly tap areas with ball-peen hammer and make note of sound (resonance). Like any object that isn't cracked, it should have a certain "ring" to it. If you hear a thud, investigate that area and make a determination of integrity.

    Or, send it to a local NDT inspection shop.

    Good luck, Noel.

Similar Threads

  1. Replies: 1
    Last Post: 07-29-2013, 10:18 AM
  2. 318 intake manifold
    By trojanboater in forum Chrysler Inboard and Sterndrive Forum
    Replies: 3
    Last Post: 06-11-2013, 06:35 AM
  3. Replace intake manifold gastet?
    By scott_duerring in forum Crusader Marine Engine Forum
    Replies: 5
    Last Post: 06-13-2011, 10:00 AM
  4. 318 intake manifold
    By penn_yan_lover in forum Chrysler Inboard and Sterndrive Archive
    Replies: 5
    Last Post: 10-23-2007, 10:51 PM
  5. Intake manifold 43
    By Bob Ruiz in forum Mercruiser Sterndrive Archive
    Replies: 1
    Last Post: 04-22-2007, 10:26 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •