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Old 02-06-2026, 01:23 PM   #1
wsurf4me
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Aluminum Radiator Leaking

Noticed the aftermarket aluminum radiator in my truck is starting to let go. It appears it's starting to seep where the tubes meet the end tanks. I've always ran 50/50 mix AC Delco coolant water, 180 degree thermostat. I'm in Florida so no issues with severe cold. The previous owner installed it so I have no idea of manufacturer or how old it is. My question is why is this happening? Cheap-o radiator or something else?
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Old 02-06-2026, 03:01 PM   #2
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Re: Aluminum Radiator Leaking

Can't tell you why it's happening. I'll get push back from what I have done in the past. Alumaseal powder and not the liquid. It stops seeping. Heck a long time ago when we were teenagers my buddy put an old firetruck radiator in his 37 chevy with a 409. Pinhole leaks everywhere. Don't know where he got the suggestion (way before internet), but he used black pepper. It worked! Not saying to try it. Best bet is a new radiator. Tight on cash try the alumaseal powder.
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Old 02-06-2026, 04:31 PM   #3
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Re: Aluminum Radiator Leaking

Bars leaks has always worked for me. I’ve heard of the black pepper working too back in the day
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Old 02-06-2026, 05:35 PM   #4
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Re: Aluminum Radiator Leaking

Just a note on alum radiators. On my LS swaps I always use the rubber stock? upper and lower radiator mounting system.
Brackets welded to the side tanks bolted to the the rad support can flex a bit and over time cause leaks.
Pic of my LS swapped 68 with an aftermarket generic LS Afco rad using the stock rad mounts upper and lower.
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Old 02-06-2026, 06:34 PM   #5
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Re: Aluminum Radiator Leaking

Quote:
Originally Posted by howzzzit View Post
Can't tell you why it's happening. I'll get push back from what I have done in the past. Alumaseal powder and not the liquid. It stops seeping. Heck a long time ago when we were teenagers my buddy put an old firetruck radiator in his 37 chevy with a 409. Pinhole leaks everywhere. Don't know where he got the suggestion (way before internet), but he used black pepper. It worked! Not saying to try it. Best bet is a new radiator. Tight on cash try the alumaseal powder.
I searched for Alumaseal, looks like they stopped making it. It is still available on ebay.
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Old 02-06-2026, 06:35 PM   #6
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Re: Aluminum Radiator Leaking

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Originally Posted by leddzepp View Post
Bars leaks has always worked for me. I’ve heard of the black pepper working too back in the day
I ordered up some Bars for now.
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Old 02-06-2026, 06:52 PM   #7
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Re: Aluminum Radiator Leaking

That's too bad they stopped making it. Does anyone remember the original Bars Leak that looked like chucks of licorice is some fluid?
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Old 02-06-2026, 09:53 PM   #8
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Re: Aluminum Radiator Leaking

My dad was born in 1924. He told me stories of way back when they would use horse manure, black pepper or raw egg. The bits would plug the holes and the egg would gum it up. It only kinda worked because cooling systems were very low pressure. They did what they had to during the depression.
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Old 02-06-2026, 09:58 PM   #9
leddzepp
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Re: Aluminum Radiator Leaking

Quote:
Originally Posted by howzzzit View Post
That's too bad they stopped making it. Does anyone remember the original Bars Leak that looked like chucks of licorice is some fluid?
I do
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Old 02-06-2026, 10:48 PM   #10
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Re: Aluminum Radiator Leaking

We used to call those chunks in the Bars Leaks "rabbit turds". Anyone remember "dog turds" for stopping radiator leaks? They were some sort of grayish pellets about 3/4" thick and 1" in diameter. Black pepper actually will work, short term. I bought a '40 Chevy from a guy who had used Bars Leaks. The heater didn't work all that well after a glob mostly closed off one of the adapter pipes at the water pump. About froze my keister off, driving it in Idaho.
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Old 02-06-2026, 11:12 PM   #11
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Re: Aluminum Radiator Leaking

I've used these... just relabeled Bar's Leak.
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Old 02-07-2026, 10:24 AM   #12
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Re: Aluminum Radiator Leaking

Quote:
Originally Posted by howzzzit View Post
That's too bad they stopped making it. Does anyone remember the original Bars Leak that looked like chucks of licorice is some fluid?
I remember, I had to use some back in the early 80's because that's all I could afford at the time. Later I fixed the radiator right. The Bars Leak helped.
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Old 02-07-2026, 10:30 AM   #13
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Re: Aluminum Radiator Leaking

That is a common place for them to leak. Hard to say if the radiator is cheap or not. It could be due to vibration or worn mounts. If the radiator gets twisted a bit from the worn mounts, it will break the tubes away from the header panel.
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Old 02-07-2026, 10:56 AM   #14
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Re: Aluminum Radiator Leaking

Stop leaks good to get you by till you have time for proper repair on daily driver. Not good for second or play vehicle. If the radiator or other cooling system passages are tightening up with corrosion, what do you think all those extra partical in the coolant are going to do.
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Old 02-07-2026, 12:37 PM   #15
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Re: Aluminum Radiator Leaking

Quote:
Originally Posted by LS short box View Post
Just a note on alum radiators. On my LS swaps I always use the rubber stock? upper and lower radiator mounting system.
Brackets welded to the side tanks bolted to the the rad support can flex a bit and over time cause leaks.
Pic of my LS swapped 68 with an aftermarket generic LS Afco rad using the stock rad mounts upper and lower.
Quote:
Originally Posted by Joyridin View Post
That is a common place for them to leak. Hard to say if the radiator is cheap or not. It could be due to vibration or worn mounts. If the radiator gets twisted a bit from the worn mounts, it will break the tubes away from the header panel.
Thanks for that. Looks like the previous owner fabricated some top mounts with flat bar and 1/8" sheet rubber. I popped one off and the rubber is hard as a rock. Not sure what's holding the bottom but seems to be in the middle of the radiator. I put the Bars in to get me by for the moment.
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Old 02-07-2026, 12:43 PM   #16
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Re: Aluminum Radiator Leaking

Is this something that can be repaired or am I looking at a new radiator? Either way I can either purchase or fabricate better mounts.
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Old 02-07-2026, 01:29 PM   #17
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Re: Aluminum Radiator Leaking

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Is this something that can be repaired or am I looking at a new radiator? Either way I can either purchase or fabricate better mounts.
No repairs on an aluminum radiator. You will make that leak 100x worse if you touch it with heat.
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Old 02-07-2026, 04:56 PM   #18
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Re: Aluminum Radiator Leaking

A pepper shaker from a fast-food restaurant got me home from the drag strip in my 55 Belair in the wee hours of the am.
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Old 02-07-2026, 05:58 PM   #19
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Re: Aluminum Radiator Leaking

It being Florida, I'd wonder if the environment attacked and pitted the aluminum from the outside, since the inside was fully protected from corrosion
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Old 02-07-2026, 06:12 PM   #20
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Re: Aluminum Radiator Leaking

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Originally Posted by Sicklajoie View Post
I've used these... just relabeled Bar's Leak.
Yup, look like the old dog turds. I think we had a different brand, though? It has been over 50 years...
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Old 02-07-2026, 09:31 PM   #21
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Re: Aluminum Radiator Leaking

For what it's worth I'll attest to the black pepper "fix" as a temporary to get you home again. I was in the US Army 3rd Armd. Div. serving in Germany in the late 60's. Yup, I'm old, LOL. On maneuvers for Cold War training and one of our jeeps sprung a leak in the radiator. Our old time Motor Pool Sgt. who had served in WW2 told the driver to stop by the Mess tent and grab some black pepper from the cook. Let the radiator cool enough to open the cap and throw in a couple teaspoons of pepper. Topped off the radiator coolant and it never leaked any more during our training field time. Got back to the post and then the radiator was changed out. It does work for a small leak and in a tight situation,
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Old 02-07-2026, 11:55 PM   #22
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Re: Aluminum Radiator Leaking

Quote:
Originally Posted by howzzzit View Post
That's too bad they stopped making it. Does anyone remember the original Bars Leak that looked like chucks of licorice is some fluid?
So that's the reason I don't leak as much as I used to. I think I ate some of those chucks of licorice. There was no warning on the can.
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Old 02-08-2026, 12:57 AM   #23
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Re: Aluminum Radiator Leaking

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Originally Posted by Ironhorse View Post
For what it's worth I'll attest to the black pepper "fix" as a temporary to get you home again. I was in the US Army 3rd Armd. Div. serving in Germany in the late 60's. Yup, I'm old, LOL. On maneuvers for Cold War training and one of our jeeps sprung a leak in the radiator. Our old time Motor Pool Sgt. who had served in WW2 told the driver to stop by the Mess tent and grab some black pepper from the cook. Let the radiator cool enough to open the cap and throw in a couple teaspoons of pepper. Topped off the radiator coolant and it never leaked any more during our training field time. Got back to the post and then the radiator was changed out. It does work for a small leak and in a tight situation,
My eldest sister had a car that had a serious radiator leak, and I told her to use pepper as a temporary fix. But she kept using it and eventually trashed the engine. She was going through a divorce, and I really wish that she had asked me for more help, but I had recently gotten married, and I guess she was afraid to ask. Sad.
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Old 02-08-2026, 11:44 AM   #24
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Re: Aluminum Radiator Leaking

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So that's the reason I don't leak as much as I used to. I think I ate some of those chucks of licorice. There was no warning on the can.
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Old 02-08-2026, 11:57 AM   #25
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Re: Aluminum Radiator Leaking

Aluminum radiators will have problems with electrolysis if not isolated. After mounting and before hoses are attached, check for grounding. If there IS continuity to ground look for metal to metal contact and correct. Not only will you avoid electrolysisdamage, you will eliminate a possible rub point were vibration could create a hole.
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