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Old 05-17-2017, 12:25 PM   #1
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Lehman 120 heat exchanger cap seeps antifreeze

I am new to the forum and new to my 1983 CHB 41 and could really use some guidance on this issue. The heat exchanger cap seeps antifreeze from the expansion tank. I have replaced the cap but no change. The expansion tank is mounted 2' above the exchanger. It holds pressure fine just leeks from the expansion tank tube. Any ideas?
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Old 05-17-2017, 01:14 PM   #2
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Greetings,
Welcome aboard Mr. 41. I'm a bit confused...(nothing new). The only "caps" on the heat exchanger I'm familiar with are the end caps held on with a 1/2" or so brass/bronze bolt with a rubber gasket between the cap and the exchanger body. This "joint should NOT leak, at all.

The expansion tank has a radiator style cap designed with a specific "release" pressure (can't remember the # but about 7 psi, I think). On the side of the neck this cap screws on is a 1/4" diameter (or so) hose nipple which is the expansion tank overflow and there should be a small hose connected to that nipple. Thereafter there is one of two things....the hose is either open and drains excess anti-freeze away or the hose goes into a jug/reservoir.
IF your expansion tank is totally full, when the coolant heats up, pressure builds up in the cooling system, the radiator cap then allow excess coolant to vent through this above mentioned tube. So what's the problem?
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Old 05-17-2017, 02:06 PM   #3
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You are over filling your expansion tank.

Keep the level of the fluid about 1" below the lip when cold.
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Old 05-17-2017, 02:06 PM   #4
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Quote:
Originally Posted by RT Firefly View Post
Greetings,
Welcome aboard Mr. 41. I'm a bit confused...(nothing new). The only "caps" on the heat exchanger I'm familiar with are the end caps held on with a 1/2" or so brass/bronze bolt with a rubber gasket between the cap and the exchanger body. This "joint should NOT leak, at all.

The expansion tank has a radiator style cap designed with a specific "release" pressure (can't remember the # but about 7 psi, I think). On the side of the neck this cap screws on is a 1/4" diameter (or so) hose nipple which is the expansion tank overflow and there should be a small hose connected to that nipple. Thereafter there is one of two things....the hose is either open and drains excess anti-freeze away or the hose goes into a jug/reservoir.
IF your expansion tank is totally full, when the coolant heats up, pressure builds up in the cooling system, the radiator cap then allow excess coolant to vent through this above mentioned tube. So what's the problem?


On the exchanger there is a radiator style cap 4psi. Stant TR101.
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Old 05-17-2017, 02:39 PM   #5
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Greetings,
Mr. 41. Well, I'm at a loss. I've never seen a heat exchanger with a rad cap. Sorry...
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Old 05-17-2017, 02:59 PM   #6
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I really appreciate everyone's feedback. I'll get it figured out. Thanks Again !!
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Old 05-17-2017, 03:01 PM   #7
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Pokey,

I think the seepage you see not unusual. Cbill's advice to maintain level 1" down when cold is good. I suggest you route the end of the tube to a container, like an antifreeze jug, with the hose all the way to the bottom.

That way, when the motor cools off, it can suck some fluid back into the expansion tank, all normal stuff. I'm in PDX today/tomorrow if you want to discuss further. I suspect you are still in the bay area, internet it is.
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Old 05-17-2017, 05:04 PM   #8
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Lehman 120s without the expansion tank neck modification dont have normal radiator caps as they will release pressure but will not allow fluid back up as the caps only have one spring for overpressure only.

The bottle is a good idea for catching fluid, but it will not return unless you do the mod with tbe newer style caps
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Old 05-17-2017, 06:13 PM   #9
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The expansion tank has a metal tube inside it which leads to the overflow tube. If the tube blocks the nearest exit for pressurized coolant is the cap.
Your cap may be ancient and need replacing, undo it and check the seal. But most likely the tube is blocked solid, and needs clearing, remove the tank and go for it.
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