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Equipment
fresh 455 60 over poncho, E-heads from Butler boys using thier head gaskets, new desert cooler copper rad, new and tested thermostat trie dd, new flow kooler water pump, new heater core, new hoses and belts, tried new 13 lbs and 16 lbs rad caps, no difference, 1 qt overflow can, water wetter, 50/50 antifreeze.electric fan in front of rad pushing towards engine, 15 inch flex on engine side(i know its not real efficent mostly for looks)The temp of the lower rad hose is 120 when the upper is 190 so I feel the rad is cooling ok, (opinions welcome here folks, is 120 degree water going into the block cool enuff?)
The plugs do not indicate a lean condition and I have tried varying the timing with little effect overall
Problem
At first it was overheating as the engine was getting its first 100 miles, 210-220 degrees
Now it will run 180-195 but heres where it gets bizarre.... as you let off the throttle to slow for a red lite, (at 185 or hotter) the overflow can sends a giant stream of coolant out the vent hole (like my Great Dane taking a pee)The pressure seems excessive and eventually this makes the coolant level low and the temp climbs.I am totally missing the connection between the de-acceleration and the spewing... the different pressure rated caps do not change anything.
at this point any ideas would be helpful and greatly appreciated
Thanxx
rob
 

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I have had caps that were grooved from age that did not fit tightly when turned down. I have also had rads that had deeper pockets where the cap sits so it did not seal properly. Just last week I repaired a customer car (98 Jeep) that had a rad cap that was only sealing if it was put on a certain way. I suggest you try a rubber disc cut out of inner tube and put that under the cap and see if it seals then, if it works then try going up to a 21 pound cap. Measure from the flange edge to the sealing edge with a vernier and then measure the rad spout, it should compress the inner sealing gasket at least 0.015".
 

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Well I wish I had a good idea for you but can't think of anything at the moment. One thing that did come to mind (weather it relates or not,don't know) is you mentioned the relationship between decelleration and spewing. I know that when we burp a cooling system, after filling it, to get the air out we bring up the rpm's for a bit to build pressure in the block then release to idle to force t-stat to open quicker. If you hold the rpm's up too long and there's still air in the system as soon as the rpm's drop the pressure shoots coolant out of the radiator like a fire hydrant. Don't know if something could be causing this effect in your car but figured I'd mention it.
 

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You did not say what your thermostat was rated at
195 degrees is what I would use also what is the year of your motor?1973 and on had EGR-valves, and the heads and intake for same year motor? most will all bolt-up but. Are you using a spacer between your water pump and radiator/ should be 2-inch spacer and do you have a schroud? all add up
If your in a high humity area(like Iowa) tourque your heads 20lbs more don't want a blown head gasket from overheating.Also get it up to temp without cap on be sure all air out of system.Is your new rad.have in and out in original location?

[ March 25, 2002: Message edited by: Pontiacman ]</p>
 

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parrothead69,howdy!only a month ago i got my sons 89 chevy p.u. back from the frame shop[bent bad] and when went to reassemble the front end[we had torn it down,fendersgrillbumperetc.,in order to assess damage and save some dough]icould'nt find the radiator cap.so naturally a quick run to the local auto parts store was next.listen guy!same symptons the new cap was not sealing, the length of the cap while uncompressed [is that a word?]was too short so when i screwed it on it was not touching the shoulder of the rad. neck where it seals!my son went through the old part bin we keep and found an old cap of same locking ears size,everything hunky-dory now.a friend experienced the same thing when trying to use a new cap fom the same "discount' parts store.hope this helps ,jimm
 
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