Hey guys, I've recently put a new radiator in my 55 Pontiac with a stock 287. The original split at the core, and was leaking everywhere. I put in a Jegs universal aluminum radiator, and ditched the stock pulley fan for a 16" 2500cfm electric puller fan. I have a couple questions here: First, is that fan and radiator combo sufficient to cool this engine to begin with? What pressure radiator cap should I be running with this setup? I currently have an incorrect (I'm sure) 17lb cap on it that I had laying around. Also, I put a new 180deg thermostat in (Stant brand), but while running it in the garage with the engine up to temp, it never seemed to open! So I took it out, and am running with no thermostat for now to ensure full flow. Also, I have a mysterious coolant leak from the back of the block that I've been chasing. I noticed even with the old radiator, that I had a water leak dripping from the oil pan. It took this last drive to the Bean Bandits show on Saturday to really heat it up, and overheated when pulling into the driveway. Steam was escaping out of the rear of the passenger side cylinder head. There is a ~3/4" round plug at the back of the head there, and the coolant was leaking from it. This is where the leak has been coming from all along. So it doesn't seem like a head gasket, but what is this plug there for on the back of the head? I guess I'll have to pull the head off to look into it, but I'm looking for any info before I do that. Thanks! Evan
Probably a rusted out "freeze plug". If the engine leaks, then your pressure cap isn't doing anything, and the coolant will boil at a lower temp than it would if it held pressure. The cap pressure rating should kind of match what the radiator is capable of holding. With the stock radiator a 3 or 7 psi cap would be appropriate. With an aftermarket radiator a 13 or even 17 psi cap might be ok, but you'll find the weak points in the rest of the cooling system! Should have a thermostat in it...I suggest putting it back in, make sure the engine is full of coolant before running it (after you fix the other leaks of course) I'd use the stock pulley driven fan, but I'm weird like that, probably comes from living in AZ so long
That rusted freeze plug is so if you turn the heads around and swap them side for side. there is no right or left. With all of this overheating you might have compressionleaking into the cooling system. When its full of water and running do you see bubbles in the radiator? I would pull the engine out remove the heads and check for cracks and clean the water jackets and replace all of the core hole plugs. If one is rusty they are all suspect. OldWolf
The stock fan will cool better than the electric one. 5-6-7 Pontiac radiator is pretty close to a 5-6-7 Chevy radiator, I would think you could have put one of those in with a minimum of fuss. 55-59 Pontiac are reverse cooled, that can make a difference.
A couple of observations: First of all it sounds like the expansion plug in the head is the culprit if you can see coolant coming from it.Almost impossible to replace in the car so the head will have to be removed.I would check ALL of the expansion plugs and replace as necessary. I don't know how thick of a core a universal radiator has but the stock Pontiac has a 3" core and capacity(with heater)is about 3 gallons as I recall.Speaking of heaters;do you still have the underseat heater core?If so this could be a part of the problem.When coolant is lost or drained from the cooling system,it is extremely difficult to bleed air from the heater core.What usually happens is you refill the radiator and it seems to be full and then it starts overheating and you release the pressure cap and it spews coolant everywhere. I bleed the air out by filling it first with straight water and running the engine with the cap removed.It will eventually heat up and blow out the air(and a lot of coolant which is why I start with straight water).Once it seems to be free,I start loading it with regular coolant slowly and continue to run it at idle with the cap removed.It eventually bleeds out all the air. I would also run the stock fan WITH a shroud AND a 180 thermostat.The t'stat serves a dual purpose:It keeps the water in the engine during warm up to bring it to operating temperature faster and it also keeps the water in the radiator longer to cool it down.Leaving out the t'stat allows the water to circulate too rapidly and not cool enough.
When putting my '60 Pontiac (389) back together, I switched to a Weiand intake and had rear coolant leak. Reaplaced gasket and used ARP bolts. That radiator cap# should be lower, mines 13#, no issues. Good Luck Aslo, use the OEM style water pump, the after marker with the welded blades have gotten bad reviews. Check out: http://forums.performanceyears.com/forums/forumdisplay.php?f=418 Ken
Thanks alot for the info guys, that's all a big help. I'm gonna pull the head tonight I think and see what I'm dealing with. I need to fix that plug leak first before moving on over to cooling issues with the new radiator. Are these plugs a common size and easy to find? Also, how do you get them out? I honestly didn't know there were freeze plugs like this in the cylinder head, I thought it was just in the block. I'll probably pull both heads to check them out and replace both plugs anyways. Any tips or things to look for as far as overall engine health when I have the heads off anyways? Also Safariknut, I do still have the underseat heater, but since I'm running a new radiator without a fitting for it, I don't have it hooked up at all. It should be dry. I may put the stock fan back on, with the shroud, and move the e-fan to the front as a pusher. I'm gonna fix the leak first, and see where I'm at though, because I've already put a lot of work into building the e-fan mount.
If you are talking the plug just below your valve covers there shouldn't be any coolant coming out of that. Check to see if it's not running out the back of the intake. Where the fulcrum for the throttle/transmission rod goes can be a bitch to get tight. You can get to it by removing your dist cap and use a long extension. I thought mine was leaking out the back also but it was coming out at the back of the intake running down the block.
Also, sheesh, I guess I need to know this also. These Pontiacs are as noted reverse flow. I had an LT-1 that was reverse flow and you have to get a specific thermostat for that application. Is it the same on these Pontiacs? If so, not just any thermostat will work.
Uh Oh...I've heard that mentioned!? What exactly does reverse flow mean? I bought the thermostat that RockAuto had listed for this specific year/engine. The leak is definitely coming from the plug on the passenger side head. There is no leak at the driver side where the pivot for the throttle linkage is. I put my finger into the depression where the plug is, and can feel it wet there. That is definitely where it is coming from.
Reverse flow means that it flows backwards. LOL Sounds like you got the correct thermostat though. Most flow cool water from below, the Pontiac flows the cool water into the top. Again, the plugs just below your valve covers or the ones further down? I'm going to guess the lower ones as the upper ones just access into the rocker arms. I've never had good luck running a car that was supposed to have a radiator shroud without one.
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