Sump nut torque

[Luxobarge]

Originally Posted by ASt85

I think the sump plug is supposed to be fitted dry @ 35Nm - copper greased at 36Nm is too low a torque and could work loose as copper grease dissolves in hot oil.

If I may, I'd disagree - a lubricated thread will do up much tighter (nore tensile strain on the bolt) before arriving at the specified torque (i.e. twist)figure, so with copper grease it will be too tight, not too loose.

The figures are indeed for a dry thread, and in many places leaving the thread dry is going to lead to problems later on, so I like to lubricate threads generally. For this reason on things like sump plugs, wheel nuts etc. I use "mechanic's feel" - do it up until it feels right. Never had one come undone so far!

Cheers!

[huron]

PTFE tape every time. Never had one come undone on its own or leak and they don't seize.

[StatusRed]

Originally Posted by ASt85

I think the sump plug is supposed to be fitted dry @ 35Nm - copper greased at 36Nm is too low a torque and could work loose as copper grease dissolves in hot oil.

I thought when you torque with grease on it it actually increases the grip it has? I did the same thing with my S40's sump plug and it hasn't come loose at all in a year.

[DaveNP]

How does one get a dry thread on a sump plug? you might clean off the plug but I've never managed to wait long enough for the last little drip of oil to come out so I could clean and dry the hole.

[StatusRed]

Originally Posted by DaveNP

How does one get a dry thread on a sump plug? you might clean off the plug but I've never managed to wait long enough for the last little drip of oil to come out so I could clean and dry the hole.

That's a good point!

[ASt85]

Originally Posted by StatusRed

I thought when you torque with grease on it it actually increases the grip it has? I did the same thing with my S40's sump plug and it hasn't come loose at all in a year.

The torque is a measure of the tension in the bolt so although the bolt is over stretched at 36Nm instead of 35Nm - the grease causes it to have less grip on the thread. Vibration and the presence of hot oil can, under some circumstances, cause the bolt to work loose.

A similar argument applies to wheel bolts/nuts which should always be fitted dry. Having said that, I would make an exception in the case of those awful Mcgard security bolts which have a habit of seizing.

Originally Posted by StatusRed

That's a good point!

I usually wash the sump plug in petrol, then dry it and the threaded sump hole with kitchen roll.....however, you are probably right in that the last drop is always a problem

[StatusRed]

Originally Posted by ASt85

The torque is a measure of the tension in the bolt so although the bolt is over stretched at 36Nm instead of 35Nm - the grease causes it to have less grip on the thread. Vibration and the presence of hot oil can, under some circumstances, cause the bolt to work loose.

A similar argument applies to wheel bolts/nuts which should always be fitted dry. Having said that, I would make an exception in the case of those awful Mcgard security bolts which have a habit of seizing.



I usually wash the sump plug in petrol, then dry it and the threaded sump hole with kitchen roll.....however, you are probably right in that the last drop is always a problem

Yeah I also do that but a drop refills the space within 1 second, I'd of thought manufacturers are aware of this and would take it into account when specifying the torque.

[ASt85]

Originally Posted by StatusRed

Yeah I also do that but a drop refills the space within 1 second, I'd of thought manufacturers are aware of this and would take it into account when specifying the torque.

You are almost certainly right - a friend used to use blue thread locker "just to make sure" - but if you use a new crush washer each time you change the oil the chances of a leak are pretty small.