upper radiator hose blows off

Discussion in 'Engine Topic' started by jimboz28, Nov 29, 2010.

  1. jimboz28

    jimboz28 New Member

    Nov 15, 2009
    washington, nj
    I did a quick search and couldn't find a thread with the same problem I'm having. If there is one, I must have missed it, sorry. So here goes- The car is an 81 Z28. I built an engine for it a while ago, and when I was breaking the cam in, after about 10 minutes, the upper radiator hose blew off. I was in the car when it happened, so I shut it off as soon as I realized what happened. At first, I thought the hose clamp was just loose, so I tightened it up, but the same thing happened again. I noticed that my upper radiator hose had a bend in it that went up higher than the radiator, so I changed it. I also noticed that the thermostat housing didn't have the same angle off of the block as the stock one, so I put the stock one back in. I talked to one of my buddies about it, and he suggested I take the thermostat out and see if it helps. I took the thermostat out, and started the car up again. After about 10 mminutes, both radiator hoses were rock hard so I shut it down before they flew off. I'm going to put the t-stat back in, with some holes drilled in it as some of you guys suggested in someone else's thread. I put a new 13lb radiator cap on it as well. I'm not sure what to check next, and I'm afraid my brand new engine might already be shot. There is no oil in the antifreeze, and there is no antifreeze in the oil pan. The only thing I haven't replaced yet is my radiator- new water pump, hoses, t-stat, radiator cap. Sorry for the long post, but I wanted to give as much detail as I could think of. Someone please HELP!:confused: :mad:
  2. tom3

    tom3 Veteran Member

    Aug 1, 1999
    Seems like it would have to be a bad cap. Try a lower pressure cap to test it.
  3. Blown Camaro

    Blown Camaro Veteran Member

    Dec 13, 2009
    Deltona, FL
    Start the car with the radiator cap off. Once the thermostat opens watch the coolant through the radiator neck. Is it frothy? You may have a blown head gasket or a cracked cylinder.
  4. COPO

    COPO Veteran Member Lifetime Gold Member

    Sep 15, 1999
    Ontario, Canada
    He's already at a 13 lb cap.
    You either have a bad cap or bad thermostat.

    Regardless of why your coolant system is being pressurized, if you are building enough pressure to blow off a hose, then it's either not clamping tightly enough, or the pressure relief system (the cap and overflow bottle) aren't working properly.

    I would pressure test the system to see when this hose pops off. You may need to borrow a tester or have the car towed to a rad shop to test it.
    If it pops off at a pressure below what the cap is rated, then it's not clamping tight enough. If it pops off above what the cap is rated for, then the problem would be the cap.
  5. jimboz28

    jimboz28 New Member

    Nov 15, 2009
    washington, nj
    Ok, I installed the 13lb cap but I haven't run the engine since then, so I'll start it up with no cap and if it looks ok, I'll put the cap on. I forgot to mention I installed a pressure gauge on the thermostat housing in one of the sensor ports to see how much pressure it's actually making, but I haven't started the car with it installed yet. Assuming I see bubbles or frothing in the radiator, is there any way to tell if it's the block/head gasket/cyl. head? Or am I going to have to take this thing apart again to figure out what it is?

    Thanks for the replies, tom3, blown camaro, high country z, and copo. I get out of work at 3, so I'll post an update after I run this thing again.
    Last edited: Nov 29, 2010
  6. High Country Z

    High Country Z Veteran Member

    You may have air trapped in the system.
  7. 73Camaro383

    73Camaro383 Veteran Member Lifetime Gold Member

    Oct 29, 2010
    Im intrested to see the outcome of this. Radiator cap would be my thought.
  8. warped

    warped Veteran Member Lifetime Gold Member

    Were you monitoring the coolant temp as the engine was running? What are you using for cooling? Flex fan, clutch, electric??? Do you have a shroud? Usually when breaking in a new engine, you need additional cooling to compensate for lack of forward motion and the additional heat generated by new parts breaking in. Make sure you have plenty of air flow through the rad and if possible use a garden hose to spray down the radiator if things start getting too warm. Good luck.
  9. Knuckle Dragger

    Knuckle Dragger Moderator Staff Member Lifetime Gold Member

    Nov 2, 2002
    Waddell AZ
    Absolutely has to be a bad cap, bad clamp, or poor fitting hose. Maybe a combination. Read Copo's post again he states the logical thought process.

Share This Page