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Coolant Boiling in Recovery tank

TopBanana72

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I have a 72 Charger with rebuilt 318 and a Cold Case aluminum radiator added about 3 years ago. The cooling is great. Guage never gets to half most times. Sometimes though on a hot day, if idling for a long time (10 minutes or more) and the gauge goes say a little more than half, I will get a lot of coolant in the recovery tank boiling away. Recovery tank is a plastic O'reilly's one. Once cooled off, the recovery tank is empty.

Any ideas?
 
The recovery should fill up hot and contracting back cold. Are you actually percolating coolant in the tank? Any coolant loss over time?
 
check your radiator cap. Sometimes they go bad.
Why ?? If it fills when hot and empties when cold then the cap is working as it should. If its getting hotter than normal when idling, that's pretty much normal too - think of cars stopped in heavy traffic on a freeway - water flow through the rad slows down and there is less air moving through the rad so temps rise. I think your cooling system is performing as it should.

Fill the rad only to the recommended level. The top of the rad is the "expansion chamber". When initially filled (to the top of the fins) the remaining air-filled area creates the pressure that keeps the coolant from boiling. However, it does expand, pushing air out first and then coolant if it reaches the overflow level.
 
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I have a 72 Charger with rebuilt 318 and a Cold Case aluminum radiator added about 3 years ago. The cooling is great. Guage never gets to half most times. Sometimes though on a hot day, if idling for a long time (10 minutes or more) and the gauge goes say a little more than half, I will get a lot of coolant in the recovery tank boiling away. Recovery tank is a plastic O'reilly's one. Once cooled off, the recovery tank is empty.

Any ideas?
1-There needs to be coolant at the proper level cold in the expansion tank with the radiator full. Thats the way it is designed. Right now it sounds like you are low on coolant.
2-Water alone boils at around 225. With a 50-50 mix that raises the boiling point. A proper functioning radiator cap also raises the boiling point. I doubt you are boiling with the gauge at 1/2 in the normal range. You should verify this is correct and find the actual coolant temperature.
 
You could be getting a vacuum in the recovery tank, is the hose sucking closed or something?
 
Blown head gasket pushing air in the coolant system?
That occurred to me, too. That's why I asked if he is losing coolant. But with a blown head gasket I would suspect massive overheating on the temp gauge, etc.
 
A weak cap can let coolant or air past it. Perhaps its not boiling and just bubbling. Take a temp of the coolant in the recovery tank when it appears to be boiling. You say the car is not overheating.
 
The recovery should fill up hot and contracting back cold. Are you actually percolating coolant in the tank? Any coolant loss over time?
Yes, percolating. Yes, some does make it out of the drain part of the recovery tank (tube at top of tank routed to ground.)
 
A weak cap can let coolant or air past it. Perhaps its not boiling and just bubbling. Take a temp of the coolant in the recovery tank when it appears to be boiling. You say the car is not overheating.
Not overheating according to the dash gauge (factory). It could be bubbling, looks pretty dramatic when it's happening. I'll take temp of coolant if it happens again.
 
Why ?? If it fills when hot and empties when cold then the cap is working as it should. If its getting hotter than normal when idling, that's pretty much normal too - think of cars stopped in heavy traffic on a freeway - water flow through the rad slows down and there is less air moving through the rad so temps rise. I think your cooling system is performing as it should.

Fill the rad only to the recommended level. The top of the rad is the "expansion chamber". When initially filled (to the top of the fins) the remaining air-filled area creates the pressure that keeps the coolant from boiling. However, it does expand, pushing air out first and then coolant if it reaches the overflow level.
ya, could be it radiator was over-filled. It's down to just above the fins now, but I'll keep watching it.
 
That occurred to me, too. That's why I asked if he is losing coolant. But with a blown head gasket I would suspect massive overheating on the temp gauge, etc.
pretty sure head gasket is ok
 
Let's start from the start..
If you're using a recovery bottle system, the rad should be FULL. And maybe 1/2 in the bottle. At this point, there should be NO BUBBLING in the reserve. It will go up and down with use.
 
Let's start from the start..
If you're using a recovery bottle system, the rad should be FULL. And maybe 1/2 in the bottle. At this point, there should be NO BUBBLING in the reserve. It will go up and down with use.
Recovery bottle keeps all air out of the system. You are correct here.
 
That occurred to me, too. That's why I asked if he is losing coolant. But with a blown head gasket I would suspect massive overheating on the temp gauge, etc.
I've had this happen before. I didn’t have overheating but I did pressurize the cylinders doing a leak down test and bingo the coolant started bubbling and foaming. A coolant recovery tank should never be hot enough to boil antifreeze. A 50/50 mix should have a boiling point well above 212f.
 
Well, I put the cap on from my old radiator, a 16 psi unit that looks better made than the Cold Case one. I drove around for a half hour and let it do about 15 minutes of hot idle. This time, gauge never reached half, and no rumbling and bumbling coolant in the recovery tank. Really only a small amount in the bottom of the recovery tank was there after shutdown. It was not as hot out today (about 75), so I will test in hotter weather, but I'm thinking it was the cap. If this problem returns, I'll post. Thanks to all for the great suggestions!
 
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