Has anyone had any luck getting heads(GMC in this case) checked for cracks this way? How much is charged for the service? Thanks,

Ed Pruss
Longmont, CO

I have never had it done but I know it is not very expensive. The local shop out here charges about $20 to $30 per head for the V-things.

Just picked up a "848" head and they did a magnaflux check for $30.

Dear Ed;

Yes; The Magnaflux process is a standard part of rebuilding heads & almost all automotive Machine Shops have the equipment.

If your working on a head your familar with then It's not necessary.

Good luck.

a mag. test is not as good as you think. a pressure test would be better.

Hello Bob,

I assume you must have had a bad experience with mag particle testing results. Would you please elaborate on your reservations of the mag particle test. With fluorescent dye, a UV lamp, and a qualified tech its should be very effective.

Also inexpensive dye penetrant tests kits (cleaner, red dye, and, white powder developer) available from your local welding or industrial supply are much better than a unaided visually inspection. Dye penetrant testing is considered less effective than the mag particle testing by industry.

A mag test will not tell you if you have a internal LEAK.It will only show a surface issue.
This is why a pressure test is better.

Larry,

Are you pressurizing the coolant passages to detect cracks/leaks in one of the internal head passages? Makes sense.

Tested right from The Thermo housing Mount. This will also tell you if you have seats installed and there is any Leaks around the seat area as well. Pressure Or Vacum Is much the same Test.
But a simple answer is YES This is how I found out a had a very small Leak Under one of my exhaust seats. (#1 for that matter)

After my experience with a porus casting earlier this year, from now on I'll always get a used head pressure tested before I get it rebuilt.

larry and efi-diy have answered the question.

Thanks for the replies guys. Those are good examples of the limitations of mag particle testing.

Good stuff.Guess I better have my head tested.