Dye Penetrant Testing

and What it Can Do For You and Your Jeep

by Rich Mylar

Being a millwright/welder I ran into this method of testing for cracks and metal defects about 15 years ago, and I have been sold on it ever since I first used it. There are three parts to this aerosol system: the dye, the cleaner and the developer.

CansIt's great stuff and can be purchased at any welding outlet for around 30 bucks. I recently used it to check for cracks I knew were somewhere in my old overheated F4 block. This stuff found the cracks within 10 minutes, and I did it all in my little backwoods shop.

To use the system all one has to do is follow the instructions on the cans; it is that easy to use. The first thing that needs to be done is clean the part or parts in question as best you can. I scraped my block with a putty knife and then wire brushed it carefully. I then wiped down the area to be tested with clean rags and alcohol.

ApplyAfter the alcohol evaporated, it was time to apply the red colored dye to the area to be tested. The directions say to let the dye dwell on the test area for five minutes -- I usually leave it for up to ten minutes. The more time you give the dye, the deeper it will penetrate the crack.

The dye can also be sprayed into a small expendable cup or can and then be applied with a small paint brush. Remember the 5-minute dwell time -- this is very important for finding the micro cracks.

Note: If you decide to try to use this method for checking for cracks, be sure and wear old clothes because if you get the dye on cloth it will never wash out. If you get the dye on your hands, forget trying to wash it off, but it will wear off eventually.


After the dye has been given enough time to penetrate the suspected area of defect or cracking, use clean rags and wipe the area clean of dye as best you can. I use the rags repeatedly to wipe away the excess dye. Once the test area is free of visible dye, I spray the aerosol cleaner on another clean rag and wipe the test area thoroughly and then let the cleaner evaporate.

The third step is to spray the developer on the test area. The developer is white in color, and only needs a few minutes to pull the red colored dye from the crack (or cracks, in my case.) A red line, usually a meandering red line, will show the crack or cracks. The red dye and white developer have a very high contrast, making the smallest of cracks easy to see. But if the area looks like a field of snow, your part is good and acceptable for service.

DeveloperThis is a good F-4 block that will be bored out. Noticed the dye being pulled out of the outside center head bolt hole at the top of block. I left a little extra dye in that bolt hole to show how well the develpoper can pull out the dye.

CracksThis F-4 block is cracked. The head bolt hole has a vertical crack running to the small water jacket hole above it that is between the valves, and also has cracks running to the valve seat inserts. It is plain to see that the developer did a good job of pulling the dye out of these cracks so they clould be seen.

If your part has red lines, the part will need to be repaired or replaced. It is that simple. You can get a good idea how deep the crack goes if you leave the developer on for a few hours. This gives the developer more time to pull all the dye out of the crack and the red line will grow even wider.


This shows the developer sitting on a block after 24 or so hours, giving a good idea how well the developer works at pulling the dye out of the holes. When the dye is wicked out of a deep crack by the developer, the crack will continue to be easier to see.

I am inclined to think that the dye penetrant system is better than magnetic particle testing. Always remember to follow the directions of each manufacturer, although I have found that the different manufacturers are pretty much the same. I have read about a fluorescent dye penetrant that is used with a black light to find the cracks, but I have never used it.

I hope all your parts turn out like a field of wind-driven snow. -- Rich Mylar

Thanks to Rich for suggesting and writing this article, which could save somebody a lot of trouble. -- Derek Redmond

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Last updated 2 November 2007 by Derek Redmond redmond@cj3b.info
All content not credited and previously copyright, is copyright Derek Redmond