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#1
06-05-2012, 10:55 PM
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Intermittent coolant leak
My 400 TA has been sporadically losing engine coolant for the past couple months. The radiator would be about a pint low every couple weeks. Crank case oil and transmission oil both look ok. Also passes antifreeze exhaust gas test so it does not seem to be an internal leak. No visible steam/exhaust from the tail pipes. Checked all the hoses, radiator and heater core as well. Engine runs great and maintains normal temps.
Finally a couple weeks ago I notice a spot on the driveway and in the drip pan on the garage floor. Seems to be coming from the rear passenger side of the engine block and the transmission. Weird thing is it comes and goes. One day it was dribbling out pretty fast and over the oil filter and onto the headers. But, once it warmed up it was dry as a bone. Not another drop for a week. Then Sunday while running it about 2k rpm in the driveway charging the AC system it leaked a 5" diameter spot onto the driveway. I am thinking rear freeze plug on the block or head. Any other ideas?
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1977 TA 400 9.5:1 CR 351hp 414LbFt, #13 Heads + 1.52 Roller rockers, 1968 Pontiac 400 intake, Holley 4165 650 DP #7054 Howards Hyd .447/.467 IN:288 EX:298 214/224@.050, MSD6A + MSD timing control + H2o/Meth 1-5/8" headers, Magnaflow 200CPI Cats + 2.5" Pypes X, Dynomax STs, TH-700R4 2200 stall, 3.42 Eaton 10-bolt, PS/PB/PW/PL/AC/Cruise 13.84@100.14mph 2.18 60' on P255-60-R15 radials, pump gas, mpg : 21.5 hwy 15.2 city 
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#2
06-06-2012, 12:08 AM
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I saw a 557 block crack right in the area your talking about about a 1 inch external crack that leaked intermittently. It was in a 77 T/A and you couldn't see it until we pulled the engine out for another problem. It never leaked enough that it was a concern for the owner, guess he just topped it off when it was low and never tried to find the leak.
I have never seen a Pontiac block crack there and I've worked on a bunch of them. I see your car doesn't have the original engine in it though so maybe a head core plug rusted through or a head gasket leaking externally only. A pressure tester will let you pressurize the cooling system cold and locate it for sure.
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Brad Yost 1973 T/A (SOLD) 2005 GTO 1984 Grand Prix 100% Pontiacs in my driveway!!! What's in your driveway? If you don't take some of the RACETRACK home with you, Ya got cheated    
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#3
06-06-2012, 11:52 AM
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Quote:
I sent the car to the shop where they can pull the transmission and hopefully get to the source. I am sure its going to be expensive, just a matter of how much. Hopefully just a head core plug you mention or a block freeze plug. Anything more than that and the wife is going to kill me....
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1977 TA 400 9.5:1 CR 351hp 414LbFt, #13 Heads + 1.52 Roller rockers, 1968 Pontiac 400 intake, Holley 4165 650 DP #7054 Howards Hyd .447/.467 IN:288 EX:298 214/224@.050, MSD6A + MSD timing control + H2o/Meth 1-5/8" headers, Magnaflow 200CPI Cats + 2.5" Pypes X, Dynomax STs, TH-700R4 2200 stall, 3.42 Eaton 10-bolt, PS/PB/PW/PL/AC/Cruise 13.84@100.14mph 2.18 60' on P255-60-R15 radials, pump gas, mpg : 21.5 hwy 15.2 city
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#4
06-06-2012, 09:25 PM
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I had a leak in the same area, traced it to the heater hose clamp at the head. Would leak sometimes and not other times. Was running down the trans. Tom
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#5
06-08-2012, 04:23 AM
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go with the cheapest and most simple fix first. also some block sealing products work very well
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#6
06-08-2012, 02:57 PM
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Talked to the shop today. Dumb thing decided to seal itself up again this week.
They have not been able to detect any water from it until today. He said it definitely looks like its between the block and tranny. They are trying their best to pinpoint the location before pulling the transmission. Likely a freeze plug, if not that it would have to be some sort of crack. Hope its bad a plug!
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1977 TA 400 9.5:1 CR 351hp 414LbFt, #13 Heads + 1.52 Roller rockers, 1968 Pontiac 400 intake, Holley 4165 650 DP #7054 Howards Hyd .447/.467 IN:288 EX:298 214/224@.050, MSD6A + MSD timing control + H2o/Meth 1-5/8" headers, Magnaflow 200CPI Cats + 2.5" Pypes X, Dynomax STs, TH-700R4 2200 stall, 3.42 Eaton 10-bolt, PS/PB/PW/PL/AC/Cruise 13.84@100.14mph 2.18 60' on P255-60-R15 radials, pump gas, mpg : 21.5 hwy 15.2 city
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#7
06-08-2012, 10:23 PM
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retorque your heads
check freezplugs and replace as needed that heeter hose nipple- check ti see if hose clamp is tight or too tight and if the hose has been cut through. block sealer |
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#8
06-23-2012, 05:35 PM
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Source located and cause found
Had the engine pulled.
Both left and right rear freeze plugs have been damaged by too long transmission bell housing bolts that protruded through the 700R4 BOP adapter plate. You can see the imprint of the end of the bolt in the plugs. The driver side plug was partially pushed into the block at an angle but not punctured. The passenger side plug was punctured by the bolt. Probably a tiny leak at first but corroded over time thus getting worse over time. The 700R4 was swapped in in 2007 so it took about 5 years.
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1977 TA 400 9.5:1 CR 351hp 414LbFt, #13 Heads + 1.52 Roller rockers, 1968 Pontiac 400 intake, Holley 4165 650 DP #7054 Howards Hyd .447/.467 IN:288 EX:298 214/224@.050, MSD6A + MSD timing control + H2o/Meth 1-5/8" headers, Magnaflow 200CPI Cats + 2.5" Pypes X, Dynomax STs, TH-700R4 2200 stall, 3.42 Eaton 10-bolt, PS/PB/PW/PL/AC/Cruise 13.84@100.14mph 2.18 60' on P255-60-R15 radials, pump gas, mpg : 21.5 hwy 15.2 city
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