MTFCA Forum

I was looking at my 21 Touring today and noticed the replacement flat tube radiator has a couple of damp spots on it and very small leaks. These are very slow and not dripping. The radiator was a flat tube recore bought on eBay years ago when I was assembling parts to build the 21. I haven’t use any radiator stop leak in any of my cars for years.
Yes I know the best way is to remove the radiator and either pinch off the leak area or solder it.
Before I resort to doing that any recommendations would be appreciated for a pour in stop leak would be appreciated.
Thanks

If you are using coolant/antifreeze, that will find the smallest of faults and leak. Perhaps it should be called leak finder. A change to water and some soluble oil may make the "leaks" go away. Others will have different ideas.

Allan from down under.

"egg keep" sodium silicate aka Water glass. Had success with this stuff.
I would go with Allan's recommendation first.

I have had good results with a product called K Seal.
Craig.

Thanks for the tips. I may change the radiator coolant. I have antifreeze in it since the shop isn’t heated for winter. Maybe I should use less antifreeze in it. It’s got over 1/2 antifreeze in it. We dont get long weeks of below freezing in central Texas. Maybe 1/4 antifreeze and the rest water might do. Since the shop is enclosed and out of the wind and weather hat be enough even really cold. But I will get one of the radiator sealants mentioned.
Any thoughts about using a weakened radiator coolant? In other words not much antifreeze?.?

I believe any antifreeze will find a way to leak as Allan says. I run water & water soluble oil. But, I never see temps below 40 where I am.

John kuehn wrote: ↑

Sun Jul 06, 2025 9:41 pm

Thanks for the tips. I may change the radiator coolant. I have antifreeze in it since the shop isn’t heated for winter. Maybe I should use less antifreeze in it. It’s got over 1/2 antifreeze in it. We dont get long weeks of below freezing in central Texas. Maybe 1/4 antifreeze and the rest water might do. Since the shop is enclosed and out of the wind and weather hat be enough even really cold. But I will get one of the radiator sealants mentioned.
Any thoughts about using a weakened radiator coolant? In other words not much antifreeze?.?

John, antifreeze can be mixed to give protection down to specified temperatures. I do believe a 50/50 mix is ideal but the ration can be changed to provide protection to designated freezing points. I would recommend mixing for a temperature at least 20 degrees colder than you usually observe in the winter. Better option may be to just take the radiator to a shop and have the leaks soldered.

You'd probably be OK with a 40/60 mix of antifreeze and water. But.... Texas weather can be unpredictable...

Anyone ever try black pepper? A few tablespoons? Radiator
Shop says use pepper! Also, the bars leak tabs have
always gotten me home.

An old radiator man told me to use ground ginger, I have used it on many vehicles and it always works. Those seal tabs that come with a new GM water pump are ground ginger, I some times find it at the Dollar Store, I use about 1/2 a jar (about 3 1/2 in tall) for a T. Put it in a hot engine and dissolve it in a cup of hot water before adding and then drive for a while.