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Old 04-10-2020, 15:57   #1
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Coolant leak at Filler Neck or Cap on 3YM30

I am leaking a tiny amount red coolant from either the radiator cap or the neck on top of my heat exchanger. The cap looks perfectly fine and the top of the filler neck is smooth without imperfection. Is it possible that the filler neck has developed an imperfect connection to the heat exchanger? Is the filler neck removable? It only leaks a very small amount and only when the engine is warmed up well.
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Old 04-10-2020, 18:13   #2
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Re: Coolant leak at Filler Neck or Cap on 3YM30

If in doubt, read the manual .
Yes, the filler neck is replaceable. This page details how and gives the part number.
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Old 04-10-2020, 18:23   #3
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Re: Coolant leak at Filler Neck or Cap on 3YM30

Have you replaced the cap recently, is the correct pressure cap fitted.they usually have the capable pressure stamped on them.
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Old 08-10-2020, 06:43   #4
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Re: Coolant leak at Filler Neck or Cap on 3YM30

Let me expand on aclmck's wisdom. You've got a pressurized coollant system. That means that the cap seals the system with its spring and gasket up to a certain pressure, which allows the coolant to keep working above its base boiling temperature. If it gets hotter than that, some steam/coolant is released and makes a red mess. If the spring is weakened by age or the gasket has hardened, it releases and makes a red mess at a lower temperature.

Failure of the cap in one of these modes is much more likely than failure of the neck that the cap sits on. It is also much cheaper than replacing the neck. So, make a cap failure your first hypothesis, inspect it, and even if it is just old, replace it with one marked for the same pressure before investing in less likely repairs. Here's to a clean engine room. I wish that I had one.
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Old 20-10-2020, 19:05   #5
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Re: Coolant leak at Filler Neck or Cap on 3YM30

I guess I asked the wrong question previously. Instead of asking if filler neck was removable I should have asked if it was common that the bond between filler neck and exchanger fails. I would have thought not common but talking to a few others they said not as strange as it seems. I did replace the cap multiple times. The top of filler neck appears uniform so the slight leak seems to be coming from the filler neck connection. Tomorrow, I plan on putting a bead of JB Weld around it to see if that does the trick. Seems like filler neck replacement involves going medieval to remove original so I figured trying to patch it won't be a set back. My 73 year old slip mate says he has done it a couple of times.
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Old 20-10-2020, 20:38   #6
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Re: Coolant leak at Filler Neck or Cap on 3YM30

Quote:
Originally Posted by EmeraldCoastSailor View Post
I guess I asked the wrong question previously. Instead of asking if filler neck was removable I should have asked if it was common that the bond between filler neck and exchanger fails. I would have thought not common but talking to a few others they said not as strange as it seems. I did replace the cap multiple times. The top of filler neck appears uniform so the slight leak seems to be coming from the filler neck connection. Tomorrow, I plan on putting a bead of JB Weld around it to see if that does the trick. Seems like filler neck replacement involves going medieval to remove original so I figured trying to patch it won't be a set back. My 73 year old slip mate says he has done it a couple of times.
Hi, loctite used to make a wick in version that was really good, it was green in colour and if there was a gap it would wick in and set, sealing up the gap.
I believe that it is 290.
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