Engine engine overheated, now idles high....why?

Discussion in 'Classic Mustang Specific Tech' started by craig3x, Dec 8, 2012.

  1. just as the title says. My 289 overheated the other day. (water pump went bad and leaked out of the weep hole) It got pretty hot, but I shut her down and filled the radiator back up to drive the 2 miles back home. It cooled down and drove fine, but the idle is high now. About 2500RPM. And idea why this would happen? Idle has been high every time I've started it since.
  2. Several things come to mind, none are good and some are less good than others:
    1>NEVER - NEVER put cool or cold coolant into an overheated engine while it is not running and circulating/mixing the different temperature liquids, as the shock of the cold water contacting the VERY, VERY HOT cast iron of the heads, intake, block, etc, can and often does cause cracking and or warpage. :( See below.
    2>Vacuum leak due to:
    A>Faulty intake gasket caused by warping of something.​
    B>Cracked or warped intake manifold.​
    C>Cracked or warped head.​
    D>Blown head gasket.​
    E>Cracked or warped block.​
    F>Any or all of the above.​
    3>MAYBE, just MAYBE (if you are really lucky, depending on your setup)you created a fairly substantial vacuum at or near the base of your carburetor.
    This is likey not the kind of stuff you were hoping to hear, but you asked!:shrug:
  3. Hi,
    Yes, depending on "how hot", lots of nasty stuff can go wrong. Seeing any white'ish smoke out of the exhaust? Any noticeable loss in coolant, that is, after replacing the pump, re-filling coolant, and purging of air pockets?
    Obviously, you re-checked the carb linkage is normalized, as 2500 Rs is a big swing?
    I'm a big proponent of coolant recovery systems, as they assist with purging air in the system, as well as, maximizing available coolant in the system.
    Good Luck!
  4. changing the water pump today. Will report back....hopefully with good news
  5. What kind of shape was the engine in before this happened? recent timing gear? Fresh rebuild? Or 150K + original?
  6. Can't say for sure. I recently bought it and the previous owner didn't know much. It ran strong though. No smoke of any kind out of the tail pipes before or after the overheat.
  7. Warped carburetor base/sticking throttle plates.
  8. glad to report that there was no damage! The high idle was due to a stuck choke. just a coincidence I guess
  9. You be one lucky SON-MA-BEACH!:nice:
    madspeed likes this.
  10. good to hear! That wouldnt have beed my luck
  11. Great news on the the choke. Can I suggest you buy yourself a lotto ticket ! Good luck.
  12. my winning lotto numbers are 289, 302, 351, and 460