Coolant will not return to rad from overflow tank
Thread Starter
Instructor
Joined: Oct 2000
Posts: 115
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From: Roanoke, VA 24018
Coolant will not return to rad from overflow tank
I posted this a few weeks ago and am still having the problem. The coolent that expands into the overflow tank will not return to the radiator. All hoses have been replaced and the pressure cap. I don't believe there is a hose in the overflow tank on a 79. Any ideas?
Team Owner
Joined: Aug 1999
Posts: 30,995
Likes: 99
From: Ontario
Re: Coolant will not return to rad from overflow tank (Todd Mabry)
I have seen this from time-to-time but quite frankly it has never worried me as the cooling system seems to operate just fine. If the rubber hose from the rad to the bottom of the coolant tank sucks air then the suction back to the rad breaks down. You can partially see the air block at the connection tube on the tank actually. Remove the rubber hose at that end and fill the hose with water, carefully re-connect and you are back in business. I find that a small ring clamp on the hose connection prevents a re-occurrence of the problem.
Drifting
Joined: Jan 2002
Posts: 1,645
Likes: 11
From: Schaumburg IL
Re: Coolant will not return to rad from overflow tank (Todd Mabry)
If the two earlier posts don't solve your problem, go to AutoZone and borrow their radiator pressure checker. Pump it up to about 20-25lbs and see it there is air or bubbles pushing back into the tank. Should be. This device does work as a siphon and there has to be a path back to the rad. that is clear. Also, make sure the fluid level after running is at least at max. Good luck.
Thread Starter
Instructor
Joined: Oct 2000
Posts: 115
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From: Roanoke, VA 24018
Re: Coolant will not return to rad from overflow tank (bigvette1)
Thanks for the posts. Paul79, I have the overflow hose clamped on both ends. Doesn't leak at all there. I'll try filling the hose with water to eliminate the air gap. Car runs right at 180 until it pushes all the coolant out of the rad! BigVette1, I do check the level after running and it's low in the rad. About 6-8 inches low. My problem is, if I keep filling the rad up, it starts to push out of the top of the overflow and onto my pipes. This has been a pain in the butt :) We'll get it though.....
Team Owner
Joined: Aug 1999
Posts: 30,995
Likes: 99
From: Ontario
Re: Coolant will not return to rad from overflow tank (Todd Mabry)
Quite frankly I have never seen what you are describing: all the coolant being pushed out of the rad?? The tank serves only for expansion of the coolant under high-heat/pressurized conditions. In the old days the anti-freeze was simply vented to the pavement. Now it is drawn back into the tank as cooling occurs.
Let me describe the behaviour of my 1979 using the pic below. The black magic marker line is my cold reference point. (I am a little low today as the car has been sitting for six months and I have not topped up.) You will note it is the typical Canadian compromise: half-way between the hot and cold extremes<g>. My thermostat is 192F. Even in the heat of July the coolant never rises more than 1 1/2" above that reference mark. And returns to it when the engine is shut down. I have never seen the level even approach the top of the tank....
Again, I have never had your experience and cannot offer a solution. But perhaps the pic will generate comments from others.
Let me describe the behaviour of my 1979 using the pic below. The black magic marker line is my cold reference point. (I am a little low today as the car has been sitting for six months and I have not topped up.) You will note it is the typical Canadian compromise: half-way between the hot and cold extremes<g>. My thermostat is 192F. Even in the heat of July the coolant never rises more than 1 1/2" above that reference mark. And returns to it when the engine is shut down. I have never seen the level even approach the top of the tank....
Again, I have never had your experience and cannot offer a solution. But perhaps the pic will generate comments from others.
Burning Brakes
Joined: Apr 1999
Posts: 1,161
Likes: 0
From: Texas
Re: Coolant will not return to rad from overflow tank (Todd Mabry)
Todd:
I had close to the same problem on my car. It would not push water to, or pull from the overflow tank. I couldn't find any pressure leaks in the system. I put on a hotter thermostat, from 160 to 180, (no change) and went to a lower pressure radiator cap than stock, from 16 lbs to 13. It now works but I have since developed a small leak in the water pump shaft seal. It could be that I was losing pressure thru the pump all along but it has acted this way thru 2 different (rebuilt from Hi-Lo) water pumps. I am about to put on a Stewart stage II pump if I can find the time in the next couple of weeks. I've got the pump already. I will probably try my old 16lb cap to see if the overflow tank works after the pump swap. good luck
dr
I had close to the same problem on my car. It would not push water to, or pull from the overflow tank. I couldn't find any pressure leaks in the system. I put on a hotter thermostat, from 160 to 180, (no change) and went to a lower pressure radiator cap than stock, from 16 lbs to 13. It now works but I have since developed a small leak in the water pump shaft seal. It could be that I was losing pressure thru the pump all along but it has acted this way thru 2 different (rebuilt from Hi-Lo) water pumps. I am about to put on a Stewart stage II pump if I can find the time in the next couple of weeks. I've got the pump already. I will probably try my old 16lb cap to see if the overflow tank works after the pump swap. good luck
dr
Drifting
Joined: Jan 2002
Posts: 1,645
Likes: 11
From: Schaumburg IL
Re: Coolant will not return to rad from overflow tank (Todd Mabry)
Todd,
The cooling system is a closed system. Once you fill the radiator and it purges the air out it will draw what it needs from the overflow tank to completely fill the system. Only coolant that is expelled due to heat expansion when you are running goes to the overflow tank. As the engine cools it creates a vacuum and it draws the expelled fluid back into the radiator. From what you said - I keep filling the radiator and it gets 6-8" low. Somewhere these is a leak. Coolant can't just disappear without a cause. Possible:
- The hoses or waterpump
- Leaking from the block via the frost plugs
- Into the engine (your oil level will go up and there will be a milky foam in the the radiator)
- Being burnt due to a bad head gasket.
I would make sure the system is full and purged of all air. Run it with the cap off for 15 minutes, then cap it, fill the overflow tank and let it cool.
Then run a system pressure check. If that shows nothing, run a leak down check and if you have a bad head gasket allowing fluid to be burnt, you wil hear an air hiss out of the tail pipes and/or bubbles in the radiator. Good luck.
The cooling system is a closed system. Once you fill the radiator and it purges the air out it will draw what it needs from the overflow tank to completely fill the system. Only coolant that is expelled due to heat expansion when you are running goes to the overflow tank. As the engine cools it creates a vacuum and it draws the expelled fluid back into the radiator. From what you said - I keep filling the radiator and it gets 6-8" low. Somewhere these is a leak. Coolant can't just disappear without a cause. Possible:
- The hoses or waterpump
- Leaking from the block via the frost plugs
- Into the engine (your oil level will go up and there will be a milky foam in the the radiator)
- Being burnt due to a bad head gasket.
I would make sure the system is full and purged of all air. Run it with the cap off for 15 minutes, then cap it, fill the overflow tank and let it cool.
Then run a system pressure check. If that shows nothing, run a leak down check and if you have a bad head gasket allowing fluid to be burnt, you wil hear an air hiss out of the tail pipes and/or bubbles in the radiator. Good luck.
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