Can HG be blown or leaking and not overheat?
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Northstar Engines and System Technical Discussion Discussion, Can HG be blown or leaking and not overheat? in Cadillac Engine Discussion; Odd coolant behavior, but never overheats. -->...
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    blackx70 is offline Cadillac Owners Member
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    Can HG be blown or leaking and not overheat?

    Odd coolant behavior, but never overheats.

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    1969byrdman's Avatar
    1969byrdman is online now US Coast Guard: Semper Paratus
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    Re: Can HG be blown or leaking and not overheat?

    what is odd about it? Have you checked for flow through the surge tank? have you done a block test to see if HG is blown?
    Have you checked codes?

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    Re: Can HG be blown or leaking and not overheat?

    Welcome Aboard !!!

    What odd coolant behavior ?? Describe your symptoms exactly, please.

    As posted - purge line, cylinder block exhaust gas test, and water pump -drive tensioner pulley, coolant level sensor, correct coolant level, cooling system checks, pressure cap leaking - sure an engine can have a blown head gasket and not overheat.

    One cause of Northstar overheat because the cylinder block head bolt hole threads fail, the bolt(s) loosen, exhaust gas blows past the fire ring, eats the soft gasket material, over-pressurizes the cooling system, blows off coolant, the engine overheats.

    Other causes are cracked surge tank, rusted heater piping at the firewall, rusted thermostat housing, faulty water pump, improper heater circuit flow, etc..

    The Engines; Northstar forum - sticky threads on cooling system problems.

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    blackx70 is offline Cadillac Owners Member
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    Re: Can HG be blown or leaking and not overheat?

    Was losing coolant via overflow. Replaced cap and has stopped, though I check it daily. No codes, no overheat, have not block tested. Purge line flows, replaced water pump belt and tensioner and I replaced the thermostat when we first got it.

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    Re: Can HG be blown or leaking and not overheat?

    You should be good to go.

    Click my username, open the profile. Left column, scroll to Albums - 3 albums of stuff for your Northstar.

    The ticks on your temp gauge - and the fan settings - are the same as mine. Coolant surge tank about half full, cold.
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    Re: Can HG be blown or leaking and not overheat?

    He has a base Deville. Digidash, no analogue gauges.

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    Re: Can HG be blown or leaking and not overheat?

    Ah, so ........ Then the center "bar" on the temp indicator = the 12 o'clock range on my picture. Each solid tick that appears corresponds to the same ticks on the analog gauge.

    Both panels use the same coolant temp sender.

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    blackx70 is offline Cadillac Owners Member
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    Re: Can HG be blown or leaking and not overheat?

    Thank you very much.

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    Re: Can HG be blown or leaking and not overheat?

    On the same topic, would a very small piece or two of what appears to be gray 'foam' material floating in the surge tank constitute some of that 'Soft gasket material' that Sub mentions a few posts up?.....Incidentally, I'm trailering my 1996 Deville to Palatine, IL tomorrow to have the engine inserted, etc. based exclusively on the recommendations of this group. Undeniable evidence of HG failure in my case. I'll let you guys know how everything turns out.

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    Re: Can HG be blown or leaking and not overheat?

    Maybe - maybe ......... but that "soft gasket material" is actually a mat of graphite, fiber, organic material and sometimes extremely fine wire screen.

    Surf through the stickies on head gasket troubles at the top of this Northstar main threads page - plenty of photo history of the erosion of the edges of coolant passage holes in gasket material.

    Note that NO gasket material is missing from between clamped surfaces - only chips/chunks at the open deck areas or hole edges. Normal in ANY engine head gasket with coolant passage slots/holes.

    See those curved slots and other holes with a "rusty" look? Those exposed coolant passage edges are subject to erosion in ANY engine and are NOT, in any way, contributory to "head gasket failure" due to failed cylinder block head bolt hole threads.

    The cylinder (gas pressure) edges are sealed by the collapsible stainless steel fire rings.
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