68 Bird Overheating

Attempt #2
Last month on America's most overheated car...
No fan shroud, car got real hot down the road, and overheats when I hit highway speeds. It is a fresh rebuilt '68 Pontiac 400, I have a new radiator
(now 2nd), water pump (3rd), and I'm on the 3rd thermostat.
Decided to take it on the highway. As soon as I hit 4th gear, a small explosion and sparks greeted me with radiator fluid and smoke pouring out the end. Found my water pump (2nd one) had sheared off and cut my new $$$$ radiator to pieces.
The suggestion was to get a fan shroud. I did.
Same thing now, except my newest water pump has held all the way to 2000 RPM. Yeah, I'm actually scared to take it any higher. The gauge goes to 250 (rally gauges) and at 35-40 Mph I get 3/4 to Max on the gauge.
Could it be my timing? I have it set at 12 degrees, but when timing by sound, it ran better way out towards (I'm guessing) 30 + degrees. It has a street/strip cam, don't ask for numbers, it would take a month to find it in all the paperwork.
I'm trying the timing, and if it doesn't work, either take a gallon of $3.65 gas and end its evil hold over me, or pay someone to haul it to the crusher, (It really is an evil car, I have stories), or park it for another 10 years for another poor sap to sink $$$ into it.
Please help or send priest for an exorcism
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As far as the timing goes we always go by total advance ( eliminates sticking weights etc.). If the weights are sticking in the mechanical advance when you set your timing at 12 it's still 12 at higher r's... except when the vacuum pulls in which still won't help. On most of our small blocks we run total at around 38 degress... a couple of ours we run a little higher. We check it at about 3,000 rpms with a adjustable timing light or you can use a timing tape on the balencer.

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Did you ever replace the fan clutch? Believe it or not, but a bad one will cause overheating on the highway. I have seen it a couple of times myself. First time we about killed ourselves trying to figure out the over heating problem on ac '74 Olds Tornado. We fixed every thing else first, then replaced the clutch, recommendation from a crusty old GM wrench. Second time, different car, '74 Monte Carlo, same problem. I stuck a new clutch in it first thing and problem solved. Greg
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Yeah, brand new fan clutch, first one was destroyed by the 2nd water pump shearing off the shaft. The new one is for "with air conditioning", though I don't have A/C
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Brian wrote:

clutch new?
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It's really overheating. Can't touch anything, and I even used a laser thermometer and got over 250 shortly after turning it off. Everything is new. Radiator (2nd), hoses, water pump (3rd), fan clutch (2nd), fan shroud, thermostat (3rd), alternator, and a used power steering pump (3rd) from e-bay thats work when it wants to. By the way, a 1967-1969 power steering pump does NOT fit all those years. I have one for each year and a couple of doubles, but only one working (sometimes) and a leaking one for a 1968.
Tried the timing and fuel mixture screws yesterday, no help, so next chance I'll replace another thermostat. Advance auto seems to have bad parts.

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I'd be starting to wonder if I had some blockage in the water jacket. I had a SBC once that the previous owner drove the old freeze plugs into the water jackets rather than pull them out. Drove me crazy with overheating problems.
Brian wrote:

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I had it rebuilt at West Allis Machine in Milwaukee. They could have done almost anything. I had to clean out all the oil ports that were clogged with cotton.
"> I'd be starting to wonder if I had some blockage in the water jacket. I

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snipped-for-privacy@sbcglobal.net says...

Milwaukee..eh? Ever go to the Foster Pontiac car show?
What kind of impeller is on the water pump? Some of the rebuilders are installing cheap stamped steel impellers in place of the factory cast iron impeller. There have been a lot of reports showing up from people that have a stamped impeller water pump and overheating problems.
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I did a little reseach. The water pumps that were having problems are the '64-68 Pontiac water pump. There was a incorrect stamped steel impeller being installed AND the direction of the fins were going the wrong way! You'd think they would test the product when they make a design change!
The "fixed" version with the cast impeller is part number #58594 through NAPA Auto Parts. A1 Cardone supplies pretty much all of the auto parts chains with remanufactured parts.
There are also two metal plates that are sandwiched between the water pump and timing cover. If they are missing or there is excessive corrosion on the aluminum timing cover there will be overheating issues.
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I thought the impellers were going the wrong way at first, cause it looks backwards from how you'd swim through water using the back of your hands instead of the palm, but the old original pump is shaped that way also. I even thought (for a time) the motor was running backwards!
The metal plates are slightly worn, so I may try replace them next.
I fabricated metal radiator support filler panels and installed them to see if that helps, but time is my enemy, so I'll have to test ride it tomorrow.
Thanks for all the help/suggestions!
Brian
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Brian wrote:

    First, when setting the timing you need to disconnect the vaccume advance, set timing at idel. Your supposed to do it in drive (500 to 700 RPM's), simpler way is to dail back your idel speed.
    Next, go to NAPA or equivialant real parts house, buy a good water pump & thermostat. Then check your bottom hose, make sure it has the spring inside, if not aquire one. If your car Has a A/C condenser, pressure wash it from the back side, or remove it. If clogged it will block air flow. Then make sure you have the proper size GM clutch & fan blade. No Aftermarket fans! Make sure you have the blazes direction of rotation correct! Easy to tell, if wrong it will push air towards the radiator not pull air towards engine.
Charles
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Bought all the parts last week, no A/C installed and its a 4 speed. Fan rotation is correct. Drove it to the highway, where it had warmed up to a good 180 or so, and took the on-ramp. Temp was fine until 2 miles later I got off the highway and idled back home (3-4 miles) at 35+ MPH. It kept creeping up until it broke the 250 when I pulled into the driveway. Took a laser thermometer and read 300 on the exhaust and about 250 on the heads.
I might go with the idea that the old freeze plugs are floating around on the inside.
Hey just found out I don't have radiator support filler panels installed. Ordering them now!
Brian
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Brian wrote:

    If those don't help (you could make some test parts out of cardbord for a drive), go talk to the engine builder. They very well might need to dis-assemble the engine and clean it. Charles
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