# Cracking ceramic on plugs

**URL:** <https://community.cartalk.com/t/cracking-ceramic-on-plugs/68736>\
**Category:** Maintenance/Repairs\
**Created:** [October 17, 2011, 11:45pm UTC](https://community.cartalk.com/t/cracking-ceramic-on-plugs/68736 "2011-10-17T23:45:01Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![byronkirby](https://avatars.discourse-cdn.com/v4/letter/b/cc9497/32.png) [@byronkirby](https://community.cartalk.com/u/byronkirby)\
**Post date:** [October 17, 2011, 11:45pm UTC](https://community.cartalk.com/t/cracking-ceramic-on-plugs/68736/1 "2011-10-17T23:45:01Z")

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what is causing cracked porcelain on my plugs about every 2000 miles. third time 99 ford contour 2.0 cvt. I’m not overtightening.

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**Author:** ![keith](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/keith/32/5518_2.png) [@keith](https://community.cartalk.com/u/keith)\
**Post date:** [October 18, 2011, 12:18am UTC](https://community.cartalk.com/t/cracking-ceramic-on-plugs/68736/2 "2011-10-18T00:18:11Z")

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Are you loosing coolant?

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**Author:** ![Triedaq](https://avatars.discourse-cdn.com/v4/letter/t/65b543/32.png) [@Triedaq](https://community.cartalk.com/u/Triedaq)\
**Post date:** [October 18, 2011, 12:27am UTC](https://community.cartalk.com/t/cracking-ceramic-on-plugs/68736/3 "2011-10-18T00:27:00Z")

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If the ceramic around the firing tip of the spark plug is cracking, this may be an indication of coolant getting into the cylinder. I had this happen on a 1990 Ford Aerostar. The cylinder head had a crack. Fortunately, the vehicle was under warranty and Ford replaced the engine.

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**Author:** ![waterboy](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/waterboy/32/764_2.png) [@waterboy](https://community.cartalk.com/u/waterboy)\
**Post date:** [October 18, 2011, 2:42am UTC](https://community.cartalk.com/t/cracking-ceramic-on-plugs/68736/4 "2011-10-18T02:42:54Z")

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Where is the cracking occurring?

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**Author:** ![the\_same\_mountainbike](https://avatars.discourse-cdn.com/v4/letter/t/c89c15/32.png) [@the\_same\_mountainbike](https://community.cartalk.com/u/the_same_mountainbike)\
**Post date:** [October 19, 2011, 6:28pm UTC](https://community.cartalk.com/t/cracking-ceramic-on-plugs/68736/5 "2011-10-19T18:28:53Z")

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And is it on the same cylinder(s) repeatedly?

Fracturing of the ceramics is caused by

1. thermalshocking (see Triedaq’s post)
2. lateral stressing of the center electrode during gap adjustment
3. mechanical shock, generally caused by pinging or preignition
4. undertorquing, causing poor heat-sinking from the plug housing to the head
5. overheating. Causes can be myriad, including lean operation.

Your car has an OBDII system. Have you checked for any stored codes?  
Have you had any other operating problems?