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348/409 Bypass hose question

Discussion in 'The Hokey Ass Message Board' started by dolsen37, Jun 8, 2013.

  1. dolsen37
    Joined: Mar 7, 2006
    Posts: 182

    dolsen37
    Member
    from Nebraska

    I have a 348 that I recently installed a stock 3x2 intake (set up by dickster27, thanks Dick), My question is can I plug the intake bypass port and the water pump outlet port and not run a bypass hose? I need to know if by plugging them off will the engine temperature be a problem (run hotter)? The tri-power intakes port is offset and dumps on the right side of the engine and the original 4 barrel port was straight forward and a simple 90 degree hose was an easy hookup. I cant find an original 3x2 fitting and have had trouble finding a 90 degree fitting 1/2 pipe to 5/16 hose end to install. I am not running a heater and am thinking of plugging the bypass system off. As I understand it the bypass works to provide temp to the thermostat. Feedback needed (especially from any of you who have plugged the bypass hose system on your engines.

    Thanks
    Dan
     
  2. willys1
    Joined: Oct 31, 2012
    Posts: 1,021

    willys1
    Member
    from South Ga

    I have run a BBC with plugged bypass, but I drilled the thermostat to have some water flow. Blower intakes don't utilize the bypass. Some water flow is necessary to prevent hot spots. You can also remove the center of the thermostat or by a restrictor plate. If you are not running a heater I doubt you will notice the longer warm up..I say plug it and try it..
     
  3. I have mine plugged and been driving it for 4 years now and never had any trouble not even when idling in a line. Just plugg it.
     
  4. krylon32
    Joined: Jan 29, 2006
    Posts: 7,996

    krylon32
    Alliance Vendor
    from Nebraska

    Many years ago I bought a polished aluminum water pump from Lamar Walden (348/409 Guru) and when he had them cast he eliminated the provision for the bypass? Motor seemed to not know the difference.
     

  5. dolsen37
    Joined: Mar 7, 2006
    Posts: 182

    dolsen37
    Member
    from Nebraska

    Thanks all for the replies, I am going to plug them off.

    Dan
     
  6. Lobucrod
    Joined: Mar 22, 2006
    Posts: 4,122

    Lobucrod
    Alliance Vendor
    from Texas

    Bypass's are designed to keep the coolant circulating through the engine when the t-stat is closed. That keeps hot spots from forming in the heads since that's where most of the heat comes from. The heads are far enough away from the t-stat that they could be many degrees hotter by the time the t-stat opens. I wouldn't take a chance on harming even one cylinder on a classic engine like a 348 or 409. I run nailheads and they just cost too damned much to repair.
     
  7. Lobucrod
    Joined: Mar 22, 2006
    Posts: 4,122

    Lobucrod
    Alliance Vendor
    from Texas

    I just ran into an issue with the 409 in my 38 Chevy coupe gasser so I thought I'd revisit this thread. I changed from an electric water temperature gauge to a mechanical one and wanted to have an idiot light also so I removed the bypass hose to use the only available water port on the intake for a sending unit. Went for a drive right after and noticed that the temp would jump up to 200-205 before the thermostat would open. After the thermostat opened the temp would drop down to under 180 then the cycle would start over again. I did some constructive plumbing and hooked up the bypass along with the sending unit and now it runs at a stable 180 degree temp without all the fluctuations. So my vote is to retain a bypass hose if your cooling system is designed for one.
     

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