# Mechanics, thoughts on radiator stop leak? **URL:** \ **Category:** Factual Questions\ **Created:** [May 8, 2009, 4:52am UTC](https://boards.straightdope.com/t/mechanics-thoughts-on-radiator-stop-leak/495723 "2009-05-08T04:52:13Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![Magiver](https://avatars.discourse-cdn.com/v4/letter/m/4491bb/32.png) [@Magiver](https://boards.straightdope.com/u/Magiver)\ **Post date:** [May 8, 2009, 4:52am UTC](https://boards.straightdope.com/t/mechanics-thoughts-on-radiator-stop-leak/495723/1 "2009-05-08T04:52:13Z")
I’m fully prepared to replace my heater core but the leak is so small as to be unnoticeable. I’m talking about maybe a drop a week. It’s been like that for a year. There is no visual loss of radiator fluid and I rarely smell it. Is radiator stop leak bad for the car? I’ve always thought of it as evil but I’m on a money diet and would like to put off the repair for awhile. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [May 8, 2009, 5:32am UTC](https://boards.straightdope.com/t/mechanics-thoughts-on-radiator-stop-leak/495723/2 "2009-05-08T05:32:57Z")
The leak will get worse. Maybe tomorrow, maybe next month, but it will get worse. Stop leak is a stop gap measure. Your call as to when to bite the bullet. ---
**Author:** ![Leaffan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leaffan/32/299_2.png) [@Leaffan](https://boards.straightdope.com/u/Leaffan)\ **Post date:** [May 8, 2009, 5:37am UTC](https://boards.straightdope.com/t/mechanics-thoughts-on-radiator-stop-leak/495723/3 "2009-05-08T05:37:53Z")
I had a leak in my radiator a few years back and used the stop leak stuff. It worked fine, but eventually the radiator needed replacing. In the mean time the stop leak stuff clogged up my heater core. I needed to get the core flushed out a few times and to this day the heat output in my car has suffered. The stop leak stuff will work on small leaks and do what it’s advertised to do. However it may cause other unintended problems and therefore I do not recommend it. It should be viewed as a stop-gap measure and not a permanent solution. ETA: What Rick said. ---
**Author:** ![Magiver](https://avatars.discourse-cdn.com/v4/letter/m/4491bb/32.png) [@Magiver](https://boards.straightdope.com/u/Magiver)\ **Post date:** [May 8, 2009, 6:12am UTC](https://boards.straightdope.com/t/mechanics-thoughts-on-radiator-stop-leak/495723/4 "2009-05-08T06:12:43Z")
That is what I was worried about, clogging up passages making the radiator(s) less efficient. Dang. At least it’s easy to get to. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [May 8, 2009, 1:31pm UTC](https://boards.straightdope.com/t/mechanics-thoughts-on-radiator-stop-leak/495723/5 "2009-05-08T13:31:26Z")
Stop-leak products as a group raise concerns about clogging passages in heater cores and radiators. Said clogging has been known to occur (ask at any radiator shop for horror stories). Nevertheless, there is one brand I have used for decades without any clogging issues that I know of, and that is Bar’s Leaks. They have several products; I am referring to the original [Bar’s Leaks Radiator Stop Leak](http://www.barsproducts.com/C16_R6.htm). It has been used as a factory-applied product by some vehicle manufacturers. I have no qualms about using it in my cars or in my customers’ cars. As for actually stopping the leak, it often works, but not always. I have seen it stop a “pissing a stream” leak from a water pump; six months later the leak recurred and the pump had to be replaced. It worked on a leaking radiator in one of my cars; two years later the leakage recurred and the radiator had to be replaced. Its value is in buying time. I can offer no guarantees that it will stop the leak or that it won’t clog the heater core, but it has performed well enough for me that I have confidence in it. I do not have that same confidence in most other brands or types of stop-leak products. ---
**Author:** ![Magiver](https://avatars.discourse-cdn.com/v4/letter/m/4491bb/32.png) [@Magiver](https://boards.straightdope.com/u/Magiver)\ **Post date:** [May 8, 2009, 7:16pm UTC](https://boards.straightdope.com/t/mechanics-thoughts-on-radiator-stop-leak/495723/6 "2009-05-08T19:16:07Z")
> [@Gary\_T](#): > > Stop-leak products as a group raise concerns about clogging passages in heater cores and radiators. Said clogging has been known to occur (ask at any radiator shop for horror stories). Nevertheless, there is one brand I have used for decades without any clogging issues that I know of, and that is Bar’s Leaks. They have several products; I am referring to the original [Bar’s Leaks Radiator Stop Leak](http://www.barsproducts.com/C16_R6.htm). It has been used as a factory-applied product by some vehicle manufacturers. I have no qualms about using it in my cars or in my customers’ cars.. This is what a mechanic told my brother in law. He had problems with a GM 3.8L. What factory applications use this? I’m curious. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [May 8, 2009, 7:30pm UTC](https://boards.straightdope.com/t/mechanics-thoughts-on-radiator-stop-leak/495723/7 "2009-05-08T19:30:21Z")
> [@Magiver](#): > > This is what a mechanic told my brother in law. He had problems with a GM 3.8L. What factory applications use this? I’m curious. I don’t know specifically. [Here’s](http://www.barsleaks.net/barsstory.html) the source, but all it says is “Now Bar’s Leaks is factory installed in 3 out of 4 new cars made in USA by such as General Motors, Ford, and Chrysler…” ---
**Author:** ![AskNott](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/asknott/32/5790_2.png) [@AskNott](https://boards.straightdope.com/u/AskNott)\ **Post date:** [May 8, 2009, 8:07pm UTC](https://boards.straightdope.com/t/mechanics-thoughts-on-radiator-stop-leak/495723/8 "2009-05-08T20:07:30Z")
Here’s one thing that’s sure. If you’re looking over a used car for sale, and you find a can of Bar’s Leaks in the glove compartment, walk away.:smack: ---
**Author:** ![zwede](https://avatars.discourse-cdn.com/v4/letter/z/ac91a4/32.png) [@zwede](https://boards.straightdope.com/u/zwede)\ **Post date:** [May 8, 2009, 8:39pm UTC](https://boards.straightdope.com/t/mechanics-thoughts-on-radiator-stop-leak/495723/9 "2009-05-08T20:39:46Z")
Bar’s leak was factory mandated on the Cadillac HT4100 engine found in various Cadillac’s back in the 80’s. Reason was the HT4100 was an early aluminum block engine and the casting was so porous that it would leak coolant into the combustion chambers unless you pured some sealant in the coolant. ---
**Author:** ![snailboy](https://avatars.discourse-cdn.com/v4/letter/s/97f17d/32.png) [@snailboy](https://boards.straightdope.com/u/snailboy)\ **Post date:** [May 8, 2009, 11:00pm UTC](https://boards.straightdope.com/t/mechanics-thoughts-on-radiator-stop-leak/495723/10 "2009-05-08T23:00:08Z")
If you don’t need the heater for a while, you can disconnect the hoses leading to it and connect them together using a coupling. I’d never use any stop-leak substance in any car I planned to keep a while. ---
**Author:** ![sendmestufff](https://avatars.discourse-cdn.com/v4/letter/s/f04885/32.png) [@sendmestufff](https://boards.straightdope.com/u/sendmestufff)\ **Post date:** [November 26, 2013, 6:59am UTC](https://boards.straightdope.com/t/mechanics-thoughts-on-radiator-stop-leak/495723/11 "2013-11-26T06:59:27Z")
:eek: 3 months. I’ll confirm or negate this finding over time, but added it 3 months ago, the leak got worse and worse and now it’s gone 😕 one thing of stop leak is all I used. I was wondering though if this sealant stuff I found for $5 that withstands temperatures of over 500 deg F and neg 100 deg F would work, it even mentioned on the package, for radiators. I’ll update this and let y’all know what I find, but please comment. ---
**Author:** ![bluezooky](https://avatars.discourse-cdn.com/v4/letter/b/e8c25b/32.png) [@bluezooky](https://boards.straightdope.com/u/bluezooky)\ **Post date:** [November 26, 2013, 7:10am UTC](https://boards.straightdope.com/t/mechanics-thoughts-on-radiator-stop-leak/495723/12 "2013-11-26T07:10:22Z")
> [@Gary\_T](#): > > I don’t know specifically. [Here’s](http://www.barsleaks.net/barsstory.html) the source, but all it says is “Now Bar’s Leaks is factory installed in 3 out of 4 new cars made in USA by such as General Motors, Ford, and Chrysler…” It’s specified by GMH for my vehicle but only a couple of pellets, not the whole can, I use a tiny bit of Bar’s when changing the fluid.