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Discussion Starter · #1 ·

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I am wondering, how does a larger bolt head reduce cross-thread risk? Even if the strengthening of the metal was to the whole bolt, not just the head, I think that might make it easier to slice through the threads on the pan via a cross thread.
 

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2018 Forester XT Limited CVT
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The TSB shows photos of the old and new parts. The new bolt has a section of shaft that is not threaded, on the end opposite the head. I guess you put that into the hole and then it's more difficult to cross thread. But, if you are not starting the bolt with your fingers, then it's more likely it will get cross threaded.

Maybe a lot of people get oil changes done by people with poor workmanship, and they tell the customers that there is something wrong with the bolt.
 

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I can't say I have never messed up a procedure as seemingly simple as putting a bolt on. But when a bolt covered in oil starts to meet resistance and not turn as you put it back on, I would think that would set off some major red flags to the person doing the work.
Although I could easily see myself, under the right circumstances; losing my temper, cursing, and cranking the bolt on anyway in snit.
It isn't logical ... or smart .... but since when do those two descriptors have anything to do with human beings.
 

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2011 Subaru Forester
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So does this mean that Subaru dealers will swap out the old oil drain bolt for the new larger cap-sized one on all their cars when asked? It doesn't seem to be a recall.
I guess this must have happened to mine at some point because the oil drain pan plug in mine is a hefty 19mm.
 

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2022 Forester Sport
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So does this mean that Subaru dealers will swap out the old oil drain bolt for the new larger cap-sized one on all their cars when asked? It doesn't seem to be a recall.
I guess this must have happened to mine at some point because the oil drain pan plug in mine is a hefty 19mm.
It's not a recall and it's not a warranty item. As the last couple lines of the TSB point out, the fault cannot occur without improper torque, poor workmanship, incorrect tool usage, etc.

As someone that was once a tech, I'm seen the pictured oil pan bolts many times, on all manner of vehicles. Usually caused by DIY owners that think a crescent wrench makes a complete tool set.
 

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Is the 17mm bolt on the TSB the same as the older EJ series plugs? If so, they are beefy and easily sourced online for a few bucks. The key with any plug to avoid over torquing (thus rounding out) is to use the collapsible drain plug washers.
 

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I am wondering, how does a larger bolt head reduce cross-thread risk? Even if the strengthening of the metal was to the whole bolt, not just the head, I think that might make it easier to slice through the threads on the pan via a cross thread.
They cite the changed design at the bottom of the threads, not the larger bolt head, as reducing the cross-threading risk. See Item 1 under the picture of the new and old bolts.
 

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Sahuarita, AZ 2018 Forester Limited
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Discussion Starter · #13 ·
I am wondering, how does a larger bolt head reduce cross-thread risk?
The larger bolt head addresses the rounding of the head as shown in the TSB photo. The TSB refers to rounding as wear:
"These changes were developed to reduce excessive oil drain plug wear after performing multiple maintenance services".

Rounding/damaging the drain plug head was the biggest complaint in several threads on this forum, including this one:
('14-'18) - 2017 - Another rounded oil drain...

I've been DIYing oil changes on my cars for decades - Hondas, Toyotas, Subarus and a Suzuki - using the same wrench set. Never once did I damage a drain plug head until the first oil change on my 2018 Forester with the 14mm head. I immediately installed this 17mm drain plug and have had no problems since.
 

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2015 Forester 2.5i CVT
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Great info and about time, thanks but the Subaru techs at our local dealership love to use impact tools on everything and one of the reason's I've reverted to doing my own maintenance, they over torque, strip and break lug studs, diff and engine drain bolts on my Forester too many times.
 

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I was just reading the TSB a bit more closely and I'm glad that Subaru knows that if the bolt or pan is damaged, it's the workmanship that is causing the problem. From page 4:

Font Circle Number Art Rectangle
 

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2015 Forester 2.5i Limited CVT
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I saw that TSB two weeks ago. Subaru also updated the cvt drain plug. I’ve never rounded a drain plug or any Subaru fastener for that matter. I switched to a Stahlbus drain plug a while back anyway.

Using good quality sockets is very important. The tolerances on cheap sockets are too loose. Good sockets will push on the side corners and not on the points. Same with a good quality box wrench. I’ve used both 6 and 12 point without issue.

Cheap sockets, bad technique and improper torque can still round even the new updated plugs. A bad mechanic can still over torque the new plugs.

Zero chance with a Fumoto or Stahlbus. Hopefully the metal used on the updated drain plugs is tougher. Size won’t matter if it’s soft.
 

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Yes but the key thing is the damage was done by the last person who put the plug in and either cross threaded it or overtightened it and stripped the plug. I am actually a bit surprised this happens with the 14mm plug, as you are more likely to use a bigger ratchet and apply more force to a bigger plug. Do quick lube shops or garages use an impact gun on the plugs? Could a failure to use a new crush plug gasket also be connected?
 
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