1970 318 Coolant Leak

1970FuryConv

Old Man with a Hat
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I have a 1970 318 original engine in a Fury. The engine is leaking coolant on both sides of the block. I thought that the problem could be fixed by removing the old rusty freeze plugs and replacing them with 4 rubber expansion plugs from Advance. Did the job, I pressure tested the cooling system, and the test was perfect at 16 psi. Drove the car. No leaks. Came back a few days later, coolant on the garage floor under the engine. A few months passed, always the same thing, drive the car, no leaks when I parked it, puddle a few days later. I drained the cooling system again, including removing both block drain plugs. I then removed the rubber expansion plugs, so the block was completely drained. I hammered in new brass freeze plugs and DID NOT add antifreeze. A day later, I have the leak at the center of each side of the block, even though the block is drained. There are droplets on each side of the block at the oil pan rails, oil pan, auto trans cooling lines, and right side exhaust pipe, plus small puddles on the floor below side of block. I'm wondering if the heads could have warped upward in the center just enough that coolant pooled somewhere in the heads is draining out the between the bottom of the head and the top of the block and then down the side of the block - masquerading as a freeze plugs leak, but actually a much larger problem. Could coolant have pooled somewhere in the heads and be draining out as I described? Could a block with this slow leak pass a pressure test? The block was completely drained when I installed the freeze plugs. It's hard to believe that the coolant is coming from the block. Left side of block below, but leaking both sides.

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Sure it's not the bypass hose? A leak there could drain down both sides of the block.
 
Refill the engine, get everything cleaned off and pressure test again. I think Big John may be on to something with the bypass hose, I would look over everything it is amazing how coolant can travel making you think something is leaking when it's not.
 
Check that timming cover. I've seen many a leaking smallblocks. May be the gasket. I got a cover from a 68 if you need one
 
Try the pressure test again without the coolant. Air will escape faster and spray over engine with soapy water, look for bubbles.
 
I tried the pressure test with no coolant in system. I sprayed soapy water around the brass freeze plugs I installed. 2 of them had air bubbles. Guess I need to remove them, dry off the circular seating area, add some silicone to that area, and then install new plugs. OTOH, I may have been better off with the rubber expansion plugs.
What I don't understand is, Where is the coolant coming from? I drained the whole block. I added no coolant, but I still have a leak. I sprayed the soapy water on the bypass hose. I didn't find any leaks. I sprayed around the timing chain cover, although that needs a more thorough spraying with soapy water, but I didn't find any leaks there either. IMO, neither the bypass hose or timing chain cover explains where this coolant is coming from. Could it be hung up in the heads somewhere, slowly draining down, and coming out around the brass freeze plugs?
 
Even with removing the block drain plugs you will still have some coolant that is in the engine. Replace the leaking freeze plugs, and make sure you use a freeze plug installer. Then repeat the procedure until the system holds pressure.
 
Not that it explains where your leak is coming from but are you aware there are Freeze plugs on the back of the block? If your side plugs were bad the rear ones could be bad also
 
He has to fix the leaking ones on the side of the block first. Then he can remove the inspection cover on the trans and listen for air escaping. To repair those he would have to remove the transmission. But again make sure you use an installer because even the slightest deforming will make a new freeze plug leak.
 
He has to fix the leaking ones on the side of the block first. Then he can remove the inspection cover on the trans and listen for air escaping. To repair those he would have to remove the transmission. But again make sure you use an installer because even the slightest deforming will make a new freeze plug leak.
Yeah, I get all that. If he had bad plugs there's a reason for it. He may have been unaware of the plugs on the back.


Again, where's the shruggy icon?
 
Not that it explains where your leak is coming from but are you aware there are Freeze plugs on the back of the block? If your side plugs were bad the rear ones could be bad also

Good point! I am aware of the plugs at the back of the block. I removed the starter, RS support strut, and the torque converter cover. I felt around both of them. The metal feels smooth. Also, I didn't come up with any moisture on my finger tips. So far, I can't find a reason to remove the trans and replace them. But, you made a very good point. The car is originally from Connecticut. Maybe road salt on the outside and weak coolant on the inside finished off the side freeze plugs, while the rear plugs were protected? The front freeze plugs were covered with a layer of oil sludge, plus the front sub frame might have protected them. They don't seem to be leaking either. I bought the car with the side freeze plugs rotted thru. The owner had been starting the car twice a year and had let it sit outside for 2 years, so I don't think he would have noticed the problem. All I had to do was start driving it (after a lot of brake and electrical work) and the leaks started making puddles on my garage floor.
 
Even with removing the block drain plugs you will still have some coolant that is in the engine. Replace the leaking freeze plugs, and make sure you use a freeze plug installer. Then repeat the procedure until the system holds pressure.

I don't know what a freeze plug installer is. I used a 15/16 socket and a 10" extension as a driver. I used a 3 pound BFH to hammer the freeze plugs into place. Do you have a picture of a freeze plug installer? Do you think it could be used in tight confines under a car engine? I was really having trouble keeping the driver perpendicular to the block.
 
View attachment 70742 This is what I use on the soft plugs prior to driving in place

This is a good idea too. I'm having trouble keeping the bottom of the surface of the mounting area dry. Coolant keeps dripping down from somewhere up in the engine. I think maybe passages from the head to the block are partially blocked, either due to the way a replacement head gasket was configured or due to rust particles partially clogging the passages. Once I can get a dry surface area, I like your idea.
 
I don't know what a freeze plug installer is. I used a 15/16 socket and a 10" extension as a driver. I used a 3 pound BFH to hammer the freeze plugs into place. Do you have a picture of a freeze plug installer? Do you think it could be used in tight confines under a car engine? I was really having trouble keeping the driver perpendicular to the block.
I don't have a picture available, but they are sold by Snap-on, and Matco. It has adaptors to fit the plugs on the rim, not the center with a installation handle, and yes they do work
 
Forgot to explain one thing, If you hammer the freeze plug in with a socket in the center of the plug you can distort it and nine time out of ten not get them in deep enough to seal correctly.
 
You want to hammer on the outer edge of the freeze plug not the center

I see that now. On YouTube, there are people with how-to videos using a socket just large enough to fit inside the rim. To see if I could avoid the YouTube solution, I called Advance Auto to ask if I could rent/borrow a freeze plug install tool. He said that they didn't have one and recommended that I use a block of wood. Thanks for nothing.
I'm going to keep trying to find an install tool or use a socket that is larger than the diameter of the freeze plug. I bought the #2 Form-A-Gasket, BTW.
 
An update, I cleaned up each hole with 240 grit sandpaper. Coated mounting surface with Permatex #2 Non-Hardening Form-A-Gasket Sealant. It’s like the brush-on Aviation sealant. Then coated the mounting surface of the Dorman 1635C Brass Freeze Plug with the same sealant. I purchased the Proto 2314-4 driver on eBay for $8 including shipping (see below). I used a 10” long 1/2" extension with duct tape over end and NAPA 48 ounce sledge with Proto 2314-4 driver to drive the freeze plug in, using the outer lip of the freeze plug. I stopped when the front of the driver was flush with the side of the block. I repeated this procedure for the other holes on the side of the block. The only variation is how long I had to make the extension in order to hit it with the hammer. So far, the repair seems to be holding. Thanks 65 Sporty and Train Tech for your help.
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