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Old 08-14-2003, 11:12 AM
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1967 pontiac 455 overheating

first off I would like to say hello to eveyone as this is my first time on the hotrodders bulletin board. I have a 1967 pontiac firebird with a rebuilt 1974 pontiac 455 that I bought last year. I have tried so many things to stop it from overheating. I have a friend who is a retired mechanic who is helping me. We have replaced the thermostat, put three electric fans on it,checked the water pump, put in water wetter and a few other things. We cannot get this car to stop overheating! We thought it might be boared out to much, but found out it is only 30 over. The car runs for about 25 minutes, gets up to 180-190 and cannot hold. It has a serpantine belt system with a standard flow pump that we just chacked yesterday. We are going to open it up this weekend to see if something is blocked inside. We found out through the previous owner that it has a homemade cam. If anyone can suggest anything it would be much appricieated. THANKYOU>

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Old 08-14-2003, 11:17 AM
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no, i really cant give you any ideas. some of the big block camaro guys probably can tho. i have a 66 tempest as you can see, so i just want to say welcome to another poncho man and i hope you fix your overheating problem. do you have headers? ceramic coated? that could help some. you shouldnt have to cut any holes in your inner fenders.
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Old 08-14-2003, 11:23 AM
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Make shure that your water pump is turning in the correct direction with the serpantine belt system. some of these need a reverse flow water pump.
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Old 08-14-2003, 11:39 AM
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Brisk, welcome. I had the same problem with a '65 GTO/444. In additiona to what EBlack36 recommended, you might want to check behind the water pump to see if the tubes that go between the water pump and the timing cover are in good condition. If they are bad or not there at all, the water will not circulate through the block.
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Old 08-14-2003, 07:33 PM
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Feel the radiator core. It should be uniformly hot across the top or inlet side. The outlet side will be slightly cooler with no cold spots anywhere in the core.

You could also use a thermometer inserted into the fins to do this.

If the outlet side is much cooler than the inlet then there is not much circulation.
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Old 08-14-2003, 11:42 PM
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Make sure the metal plate is behind the water pump.
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Old 08-15-2003, 01:01 AM
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Also if anyone has ever put stop leak in the radiator, which is a big no no in a poncho, the water jackets in the heads are only drilled 1/8 to 1/4 inch and the plug up quick with stop leak.
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Old 08-15-2003, 01:11 PM
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Lot's of good advice given so far.

Also check to see if the water pump has a stamped steel impeller instead of a cast one. If it's a stamped steel one, get rid of it -they're junk. I've even heard of them being stamped where the fins are bent in the wrong direction causing it to flow terribly. Get a good factory steel flex fan for it too. If it has an aftermarket fan it may not be hvy duty enough. I had one years ago that would flatten out when revved and it would block the flow of air through the radiator. What are the head casting numbers? What compression is it? What kind of gas are you using?
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Old 08-19-2003, 07:50 AM
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How did you make out this weekend Brisk? What did you find?
Just curious.
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Old 08-19-2003, 12:17 PM
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Thanks for asking but we did not do it last weekend but will open up the engine this weekend. After doing some research, and talking to whoever we could, we think it is in the heads, so were going to inspect them, we just don,t think we are getting any coolant to the engine or it isn't doing any good. Will let you know.
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Old 03-04-2007, 01:18 PM
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overheating

Before you spend money on water pumps ,radiators etc do a coolant check to see if you have leaking head gasket.
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Old 03-04-2007, 03:38 PM
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it is unlikely the cam is "homemade" but if it is a big long duration "rough idle" camshaft, say bigger than the factory Pontiac "Ram Air IV" cam, (larger than 230deg duration@.050) you would want to recurve the distributor for increased ignition timing at idle. A small, short duration "stock" like cam with high idle manifold vacuum and a smooth idle will idle fine with 6 to 12 deg BTC. But a big rough idle cam with reduced manifold vacuum has a lot of exhaust delution at idle. This ex delution creates a slower late fuel burn. The slow, late fuel burn at idle over heats the combustion chamber and cylinder walls and exhaust ports at idle instead of burning fast and pushing on the piston, This slow(er) late burn causes the motor to overheat at idle The fix is to advance the timing further at idle. As much a 20 to 24deg BTC at idle (sometimes more) is nessessary with big race cams. But you have to recurve the distributor advance curve so you have the same typical
maximum timing at high rpm. I believe its 33 to35deg for a Pontiac. If you just advance the idle timing on a typical stock GM distributor you'll have too much timing at high rpm. How much manifold vacuum is there at idle. Is the overheating problem only at idle and ok when driving on the hiway or get worse on the hiway? Or?

You could test this out for yourself (if your 455 has a big rough idle cam in it) by readjusting the ignition timing at idle to 25deg BTC. (vacuum advance disconnected) Then re-ajust the idle speed back to 800rpm. If the temp stablizes now, that was the problem, late timing at idle. Do not drive the car like this. the timing will advance too far at high rpm. You must recurve the distributor to reduce/limit the mechanical advance travel first.
This is a common problem on cars that someone installs a big "rough idle" hot rod camshaft without recurving the distributor for correct timing at idle that compensates for the difference in the fuel burn rate at idle.

Last edited by F-BIRD'88; 03-04-2007 at 03:50 PM.
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Old 04-03-2008, 10:17 PM
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overheating

in the end , what did you finally do to correct your problem. i have the same problem and i am looking for the answer.
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