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Old 05-12-2020, 11:16 PM
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GtoFM GtoFM is offline
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History - '64 389 78XW I acquired 40+ years ago. PO mods include tri power, 280 ISKY cam and valve guide seals.

I'm finally getting around to rebuilding it to replace the '66 in my '64 GTO. I have no history but upon disassembly discovered the heater hose connecction at the timing chain cover had a short hose with a plug in it. A pump flange with a 3/4" female pipe fitting is attached to the rear of the left head at the freeze plug.

I can think of no reason for this. Any ideas?

  #2  
Old 05-13-2020, 10:43 AM
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pfilean pfilean is offline
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Maybe someone was trying to stop blowing heater cores and got it all wrong. The solution is to put a restrictor in the hose out of the front of the manifold. A plug in the hose at the timing cover would only make the problem worse.

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Old 05-13-2020, 10:57 AM
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GtoFM GtoFM is offline
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What do you use as a restrictor?

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Old 05-13-2020, 01:46 PM
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On a stock engine the restrictor is build into the heater hose fitting on the cylinder head. It's a spiral piece of metal inside the fitting.

I've made a couple for people that fit into the inlet pipe of the heater core, just a turned aluminum plug with like a 1/4" hole in it, for when their engine for whatever reason doesn't have a provision for the stock type restrictor.

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Old 05-13-2020, 08:48 PM
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The spiral spring thing was a 65 and later after the heater connection was move to the back of the head. Before that when the heater take off was off the manifold water crossover the pressure could be so high at high RPM when the thermostat was closed it could blow the heater core. (I learned the hard way.) Oldsmobile had a different hose fitting with a restriction that was added as a fix. Pontiac was often fixed with an insert in the hose as previously described.

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Old 05-13-2020, 11:01 PM
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Thanks for the info! I found old threads with possible resolutions for the '64.

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Old 05-16-2020, 10:07 PM
tjs72lemans tjs72lemans is offline
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I never knew about a spring in a fitting. When I rebuilt my heads on my 72 I left the heater fitting in head. I don't remember seeing a spring in there. Does this just fall out and have to be put in? Motor is assembled, dyno and in car hooked up ready to run. Will I have a problem?

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