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Spark Plug Replacement

I have a 1997 Ford Ranger truck V6 4L engine, automatic. A few years ago, I was informed by my Ford dealer mechanic that I had a cracked cylinder head and that the crack was near or at the threads of the #4 spark plug port. The cost would be $5K to fix it and a few hundred to band-aid it. I took the band-aid method. They told me the fix was replacing the #4 spark plug, no details beyond that. Since then I had it band-aid one other time when the truck began acting up, rough idle, bucks at any speed. Well it is doing it again but me trying to save $$, I’m thinking I can do the band-aid myself this time. I got the spark plug and tools ready at hand. However, I wanted to know if I should wrap the spark plug threads with teflon tape or something to maybe make a tighter seal? Or would I chance getting shreds of tape into the engine? Any ideas? I really want to make this truck last a few more years till I can save up for another vehicle. Thanks ahead for any ideas/solutions!

Teflon tape won’t withstand anything close to those temperatures.

I cannot see how a new spark plug would alleviate a crack in the head…which, in and of itself, would be extremely rare. I suspect something is missing in the decripion, and without that I can’t ponder a guess.


Teflon tape etc. is ill advised. It would be helpful to know what the band aid repair was. The head can be retapped with an insert for spark plugs, perhaps that is what they did, see what the old plug looks like and get back to us.

The part that I find most interesting is that the dealership allegedly wanted to charge $5k to replace the cylinder head. I wonder if those guys wear masks like most thieves.

You paid a few hundred dollars for a spark plug (band aid #1)?

Gee, what can I sell you?

Teflon tape won’t do anything, positive or negative. When installing spark plugs you put anti-seize compound (extreme high-temperature grease) on the threads, not teflon tape. Teflon tape is for plumbers.

I think you need to find a good independent mechanic (NOT a chain store) and find out if there really is a crack in the cylinder head. Don’t say you think there is one, just ask why the truck is running rough, etc.

Please don’t put teflon tape on the spark plug threads. Go buy some anti-seize compound. Then go find a mechanic.

First, lets determine if the threads are stripped (and have been repaired) or is the head cracked?? I’d like to see these work orders where they apply band-aids and charge hundreds of dollars…

Thanks for the input thus far…

My original paperwork from Ford dated 7/31/07 says “Found cyl 4 misfire removed plug found fouled with coolant replaced plug vehicle no longer misfiring. Cylinder head is cracked in #4spark plug port. Replacing spark plug is temporary fix, and plug will again foul. Customer advised.” That service cost $179.95 labor and $8.27 for the spark plug. Mileage was 132,310.

The misfiring issue occurred again on 8/26/08 but this time I decided to get a non-Ford shop’s opinion/fix. Their work order is not as detailed and says “Check and advise: Misfire”. That service cost $85 labor and $9.66 for a platinum plug. Mileage was 145,339.

Current mileage is a little over 156,000. I am money to these mechanics since I don’t know much about the mechanics unfortunately! Base on the feedback and what the previous work orders say, I think I’ll replace the #4 spark plug and not use the tape but instead get the recommended high-temp anti-seize grease. I like the idea of having the cylinder retapped which might get rid of the crack if it is in the right place. Any ideas what that should cost? One other note, the independent mechanic that did the second band-aid, said for a few hundred and keeping the truck for a few days, he could try running some type of liquid solution that coats the internals, solution is drained, then it cures for 24 hours. No guarantees it would patch the crack but it was the only option he gave me besides the repair he did that day.

Retapping will not repair a crack. I think what Waterboy was thinking was that there was a misunderstanding of the diagnosis and the plug hole was stripped rather than cracked. Tapping and helicoiling would fix a stripped hole. I too wondered if that was the real problem, as cracks in head are so very rare.

It sounds like the engine runs fine as is but with a need to replace the #4 plug occasionally. There are products out there that are fluid enough to propogate into a crack that will cure and might provide temporary relief. If the crack is into the plug hole you’ll want to let the product cure and chase the hole with a tap, then definitely use anti-seize to prevent the product from bonding he plug to the head.

Let us know how you make out.

Oh, and wear rubber gloves when using the anti-seize and use it sparingly. That stuff gets everywhere and is the messiest stuff ever created by mankind. A little dab will spread itself over an entire steam locomotive.

I had a similar experience with a 1990 Ford Aerostar with the 4.0 liter V-6 engine. I purchased the vehicle used but with some factory warranty remaining. When I would first start the van, it would idle roughly for about 30 seconds and then smooth out. The dealer diagnosed the problem as a bad head gasket and the head gasket was replaced. All was fine for several months and then the van started missing out. It turned out to be a spark plug–the ceramic insulator around the center electrode had broken away. The dealer replaced the spark plug, but the misfiring reoccured a couple months later. The dealer pulled the cylinder head again and did find a crack. The service manager said that enough coolant had gotten into the cylinder to score the cylinder wall. The entire engine was replaced, fortunately under warranty.

With your twelve year old Ranger, would a used cylinder head be a cost effective repair that might be less than $5000?

Ok I didn’t do the brightest thing and ended up pulling spark plug #6 rather than #4 on my initial repair. #4 port is the one with the crack. So I included shots of both #4 and #6 spark plugs plus the port for #4. The truck runs much better now with the new spark plug. I’m guessing I’ll have to replace #4 again in about 10K miles or so.

Thank you all for your comments. Triedaq and mountainbike, I’ll have to pass your ideas over to my newly found mechanic to see if it would be worth the cost. I posted some pics above of the old plugs. I did a short test run with the truck and it seems to be running alot better now, no rough idling or bucking when moving. I figure I can continue replacing the plug every 10K miles or so, or have the mechanic install a used cylinder head. Then again I was considering California’s new program Cash for Clunkers if I qualify. Not sure I can get $4500 in a private sale with the truck’s current problems. The California program gives you that if you purchase a new vehicle with better MPG. I might not even qualify due to the truck might exceed the MPG limits for the California program. Anyways, thanks all again for the input…