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Seized oil drain plugs


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i have seized oil drain plugs on the engine and diff and the oil fill plug on the gearbox. The car is a 1971 1300 Spitfire that hasn’t run for 22 years. It is now running and I want to change the diff and gearbox oil.

The engine has been solved by a vacuum pump through the dip stick tube but I am stuck with the diff and gearbox.

I have been using a 7/16” spanner and a hammer along with plus gas but no effect so far. I have also tried a bit of heat from a blow torch. I have been looking for 8 point sockets but cannot find the right size in the uk.

Can anyone advise how best to loosen the plug. Does anyone have experience with one of the universal sockets?



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The 8 point socket you need is a 7/16" one.

For example a Snap-on SW414 in 1/2" drive or an F314 in 3/8" drive.

Works a treat getting the stubborn drain plugs undone - but not really suitable for the engine drain on a GT6 (and possibly a Vitesse) as there is minimal clearance between the chassis rail and the drain plug, so getting the tool in place is almost impossible.



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I've always recommeneded heat, but you've tried that!   How hot?    Did you let the torch really get at the plug?   In fact, it won't get that hot if the sump is full of oil, as like a pan on the stove, it can't get hotter than the liquid boiling in it.   That's only 100C for water, but a healthy 300C for sump oil, so worth while.

Another way to get heat into the plug it to weld a bolt onto it.    Very concentrated heat!

Then, violence. HIT the hot plug with a BFH.  Not so hard as to dent the sump, but give it hearty whack.      Then Stillson's.    Order a new plug first!


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... but make sure that you get the correct plug before you start. I have a tapered, no washer, plug on my Spit. I was sent a straight one with washer. Only found out it was the wrong one when the plug came out. I had forgotten that my engine is a Herald 13/60 not a Spitfire.

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This one is REALLY mishapen!!  Mole wrench was needed to get it out which did it no good whatsoever. Didn't need to treat it carefully did I,... I had a new one... oh yeah. Of course, had to get it back together quickly for a trip out. Listed the C*nley's one for next spares order.

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25 minutes ago, Gadgetman said:

What thread is the sump plug, is it 3/8 BSP or NPT ?

i need to get a new magnetic one for my Vitesse

I bought the magnetic one from Canleys for my vitesse . Don’t forget to use the copper washer . Got the t shirt !

nb same one fits the diff level plug 



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is there a case for case-hardening the across flats part? they would not "round off" or get distorted.

Could get a few done at work gratis if useful mod? Would be no good for plugs with attached magnets.

I can't remember the last time I drained thru the sump plug. Syphon thru the dipstick is way easy compared to a cat litter tray inside two HD bin liners.




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Why is the plug a square head when just about everything else is hex. There must be a logical reason for it?

Pete - If the C*nleys plug fits all, why does the plug I got from P*ddocks not fit. If one plug fits all, then all the plugs made should be the same.. if you get my drift.

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well std plug  114774  fits these 

and mag plug 155660     https://www.canleyclassics.com/demoapp/?ptno=155660

if the supplers get the thread pitch incorrect its  wrong  maybe paddocks have a problem

note on rimmers part   

Product Description

The two types of drain plug are interchangeable.
It is advisable to use the magnetic type for safety’s
sake, to attract and collect any unwanted ferrous
particles in the gearbox lubricant.


so that aligns with my brain waves 





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