Who the hell puts the wrong spark plugs in a 3.8L?

snowstang · Mar 25, 2026

Hi all, I’m new to the car scene and even newer to mustangs. I recently picked up a 2001 3.8L coupe with the 460 in it for 3000 bucks. (Only has 70k miles!! Hell yeah!) anyhow, I live in a desert state and like the idiot I am on the FIRST bit of maintenance I did on the car (which I have since subbed the snowstang) I cracked the oil pan using a bolt extraction kit. Oil leak needs to be taken care of but is not that bad. Since I didn’t learn from my mistakes the first time, I noticed I was getting HORRIBLE mpg, (15- 16 mpg!) and took off the air box. The air filter was trashed and the SKU number said it was from 2011. Anyhow it was still getting bad gas mileage so I popped off the spark plug wires, and lo and behold I see Denso IT16TT spark plugs on my drivers side, and NGK TR55 spark plugs on my passenger side. (What the ??) I tried replacing the passenger side first, and was able to replace the first two cylinders, then got to the final one. Would not budge, grabbed my breaker bar. Would not budge. Grabbed an extension. Would not budge. Grabbed my impact. Stripped the whole ing plug. Anyhow, now it’s not driving and I need tips on how to fix this and how much this would cost. Is this a fix it myself situation or should I bite the bullet and get charged 2000 dollars at my local auto shop?

TLDR
starter gearhead, minimal knowledge with no mentor, cracked oil pan and **** up the spark plug threading on cylinder six. Any and all tips appreciated.

Forgot to add, saved up all of my money since highschool to buy this car and have worked a ton of hours to get this car for me to get through college. Selling/scrapping is not an option

gkomo · Mar 25, 2026

Did the plug break off in the head or is it out but the threads are jacked up?

LILCBRA · Mar 25, 2026

You'll need to be careful doing this and try to make sure your tap starts straight, but stripped spark plug holes are a fairly common occurrence.

https://www.oreillyauto.com/detail/c/performance-tool/tools---equipment/hand-tools/cutting---drilling-tools/thread-repair/spark-plug-thread-repair-kits/8dc812c8c340/performance-tool-m14-spark-plug-rethread-kit/pfm0/w83164/v/a/5466/automotive-car-2001-ford-mustang

A couple tips - load the flutes of the tap with grease, that should catch the chips from the rethreading procedure. An alternative, if you're able, is to get a shop vac as close as you can to the tap, but that's most likely going to be tricky at best. And, once you're done, try to blow the hole out as best you can to try to get any scrap out of the cylinder. Another thing that I'd suggest - get yourself some red Loctite to apply to the outer threads of the insert to try and ensure it doesn't back out.

I'm sure someone will be along to either correct me or add whatever I may have missed, but it is repairable.

snowstang · Mar 25, 2026

gkomo said:
Did the plug break off in the head or is it out but the threads are jacked up?

Plugs out, the thread is just shot. Old plug is shattered as well

snowstang · Mar 26, 2026

LILCBRA said:
You'll need to be careful doing this and try to make sure your tap starts straight, but stripped spark plug holes are a fairly common occurrence.

https://www.oreillyauto.com/detail/c/performance-tool/tools---equipment/hand-tools/cutting---drilling-tools/thread-repair/spark-plug-thread-repair-kits/8dc812c8c340/performance-tool-m14-spark-plug-rethread-kit/pfm0/w83164/v/a/5466/automotive-car-2001-ford-mustang

A couple tips - load the flutes of the tap with grease, that should catch the chips from the rethreading procedure. An alternative, if you're able, is to get a shop vac as close as you can to the tap, but that's most likely going to be tricky at best. And, once you're done, try to blow the hole out as best you can to try to get any scrap out of the cylinder. Another thing that I'd suggest - get yourself some red Loctite to apply to the outer threads of the insert to try and ensure it doesn't back out.

I'm sure someone will be along to either correct me or add whatever I may have missed, but it is repairable.

Yay! Would you take the engine out? I still have to replace the oil pan and If I need to vacuum out the cylinder head anyway it might just be better. Plus that cylinder is a bitch to reach.

LILCBRA · Mar 26, 2026

I don't know how easily the oil pan would be while the engine is in the car, but the spark plug hole could be repaired without removing it. It would definitely be a lot easier on a stand, so if you're planning on pulling it for the oil pan that would definitely be something I'd do while the engine was out.

Have you called any shops for an estimate? $2k seems a little steep imo. But they will absolutely do this while the engine is in the car. They may have the advantage of a lift which may give them a better angle.

snowstang · Mar 26, 2026

LILCBRA said:
I don't know how easily the oil pan would be while the engine is in the car, but the spark plug hole could be repaired without removing it. It would definitely be a lot easier on a stand, so if you're planning on pulling it for the oil pan that would definitely be something I'd do while the engine was out.

Have you called any shops for an estimate? $2k seems a little steep imo. But they will absolutely do this while the engine is in the car. They may have the advantage of a lift which may give them a better angle.

Called a few local shops . Local project car shop said they couldn’t give me an estimate until I bring the car in and the cheapest estimate I got was around 1700 dollars for both.

gkomo · Mar 26, 2026

They make spark plug thread chaser kits. I feel like that would be the easiest to try first. Would just need to make sure the threads are lined up correctly before going too deep with it. Unless i'm misunderstanding what the actual problem is.

So did the previous owner cross thread the spark plug in the hole when they installed it? I guess i'm confused on how the threads got jacked up if you were able to remove the plug without breaking it off in the cylinder head.

Noobz347 · Mar 26, 2026

Here is one of those kits. Had to dig just a little bit to ensure this one works for you 3.8L.

https://www.summitracing.com/parts/lil-65200

Even if you're not comfortable doing it, you could certainly take the tool to your general mechanic. They might even give a discount if you toss the tool in as part of deal (assuming they don't already have one).

Oh... Causes cancer but only in Cali.

LILCBRA · Mar 26, 2026

snowstang said:
Called a few local shops . Local project car shop said they couldn’t give me an estimate until I bring the car in and the cheapest estimate I got was around 1700 dollars for both.

How bad is the leak? You said the pan is cracked? Do you have access to the crack? If so, has a shop given you an idea on the cost to just repair the spark plug threads? You could definitely MacGyver the oil pan to get you by, but the plug hole is a make or break deal as far as driving the thing goes. I think they're labor costs wouldn't be completely out of line for an engine removal, but I'll bet that cost would drop significantly if you didn't have them repair the pan at the same time. So, if you can access the crack you speak of, I'd suggest having a shop take care of the spark plug threads if it's something you're not comfortable doing yourself. If you can access that crack, you can drain the oil, thoroughly clean the area - maybe do some light grinding there - and give it some JB Weld. I suspect that would give you a down and dirty repair to get you by until you can afford to do something more permanent. Then, once it's cured, refill the oil and see where you're at.

For the record, I went and read some of the reviews on that thread repair kit that I linked, it sounds like the other one that @Noobz347 linked is probably a better bet. But if you take it to someone, that will be most likely be up to them anyway....

apple99Mustangdude · Apr 3, 2026

LILCBRA said:
You'll need to be careful doing this and try to make sure your tap starts straight, but stripped spark plug holes are a fairly common occurrence.

https://www.oreillyauto.com/detail/c/performance-tool/tools---equipment/hand-tools/cutting---drilling-tools/thread-repair/spark-plug-thread-repair-kits/8dc812c8c340/performance-tool-m14-spark-plug-rethread-kit/pfm0/w83164/v/a/5466/automotive-car-2001-ford-mustang

A couple tips - load the flutes of the tap with grease, that should catch the chips from the rethreading procedure. An alternative, if you're able, is to get a shop vac as close as you can to the tap, but that's most likely going to be tricky at best. And, once you're done, try to blow the hole out as best you can to try to get any scrap out of the cylinder. Another thing that I'd suggest - get yourself some red Loctite to apply to the outer threads of the insert to try and ensure it doesn't back out.

I'm sure someone will be along to either correct me or add whatever I may have missed, but it is repairable.

couldn't you get a specialty vacuum to slip down into the spark plug hole when done to vacuum out any particles that may be left behind? At least a boroscope when done should show any left, right?

apple99Mustangdude · Apr 3, 2026

snowstang said:
Hi all, I’m new to the car scene and even newer to mustangs. I recently picked up a 2001 3.8L coupe with the 460 in it for 3000 bucks. (Only has 70k miles!! Hell yeah!) anyhow, I live in a desert state and like the idiot I am on the FIRST bit of maintenance I did on the car (which I have since subbed the snowstang) I cracked the oil pan using a bolt extraction kit. Oil leak needs to be taken care of but is not that bad. Since I didn’t learn from my mistakes the first time, I noticed I was getting HORRIBLE mpg, (15- 16 mpg!) and took off the air box. The air filter was trashed and the SKU number said it was from 2011. Anyhow it was still getting bad gas mileage so I popped off the spark plug wires, and lo and behold I see Denso IT16TT spark plugs on my drivers side, and NGK TR55 spark plugs on my passenger side. (What the ??) I tried replacing the passenger side first, and was able to replace the first two cylinders, then got to the final one. Would not budge, grabbed my breaker bar. Would not budge. Grabbed an extension. Would not budge. Grabbed my impact. Stripped the whole ing plug. Anyhow, now it’s not driving and I need tips on how to fix this and how much this would cost. Is this a fix it myself situation or should I bite the bullet and get charged 2000 dollars at my local auto shop?

TLDR
starter gearhead, minimal knowledge with no mentor, cracked oil pan and **** up the spark plug threading on cylinder six. Any and all tips appreciated.

Forgot to add, saved up all of my money since highschool to buy this car and have worked a ton of hours to get this car for me to get through college. Selling/scrapping is not an option

Not applicable in your case, but it was mentioned that parts catalogs have been known to give the WRONG spark plug info, so they said to make sure you measure the NEW plugs against the OLD plugs coming out - in at least one case, the spark plugs installed that the auto store parts catalog said online was correct - was not - they were too long - damaged the engine when the spark plug stuck out too far into the cylinder. Kind of like never forget that a brand new part can still be bad.

LILCBRA · Apr 3, 2026

apple99Mustangdude said:
couldn't you get a specialty vacuum to slip down into the spark plug hole when done to vacuum out any particles that may be left behind? At least a boroscope when done should show any left, right?

Chances are actually kinda slim that enough particles would fall into the bore to cause a real problem, but better to be safe than sorry. As far as a vacuum goes, I really have no idea if there's anything made for the automotive world for this purpose, though I wouldn't be shocked if there is. But loading the tap flutes with some grease is fairly effective for catching the scrap, so if that's done, and you pull the tap out regularly to clear it, there shouldn't be a big problem.

Who the hell puts the wrong spark plugs in a 3.8L?

snowstang

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gkomo

now i can hopefully expect to receive the shaft

LILCBRA

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snowstang

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snowstang

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gkomo

now i can hopefully expect to receive the shaft

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Who the hell puts the wrong spark plugs in a 3.8L?

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