Should re-installed fasteners be oiled?
 

I am of the school that all fasteners should be perfectly clean, all threads chased and lightly lubricated with oil. I've followed this for years and never had a fastener strip, fall out or a component leak or come loose using this method.

However, Porsche torque specs call for dry fasteners unless it specifically says to lubricate them. But, all the Porsche fasteners I take off my car are coated with a greenish blue coating, which is some sort of anti-corrosion compound, but wouldn't this compound also be a lubricant?

So does it make sense when re-installing a fastener after its been cleaned, to oil the threads and use the Porsche spec, since the new Porsche fasteners were lubricated to begin with?

Hi San
You are a bright fellow technically - suggest you google "MEC bolts"
My conclusion was to do all you mention but pay particular attention to cleaning the threaded holes. Then use green Loctite ,sometimes blue depending on the situation.
ARP have some very interesting reading on this subject.No motor oil - just their moly Assembly Grease with a customised torque figure.
The reason is the torque spec of 10nM for short(long is a different story) M6 bolts is perilously close to thread-stripping torque when bolting into aluminum.
So I use slightly less torque with an old aircraft mech. dial torque wrench.Plus loctite and always a thin s/s washer to prevent galling giving a false reading.
If the threads seem likely to strip or are a vital clamping point I have substituted s/s studs+red loctite .Then it is no risk to use the full spec torque because both nut & stud are s/s thread+ an oiled s/s washer.
S/s fasteners are so cheap and easy to find now on EBay.
I hope this helps.It is just what I do, not saying it is an expert opinion.

I was under the impression that the greenish coating acted similar to a loctite.

Newart,
yes it does but it wears off when you r/r the bolt.

If it is loctite, then it would still have some lubricating properties during installation. So if thats the case,then i guess the oiling the threads wont affect the corect torque value, but i should use a thread locker instead of oil, as gelbster suggests.

Im probably overthinking this. Guess i have too much time on my hands.

I use the green loctite instead of oil because :
1.It has some lubricity when you do the initial install/torque
2.10nM is insufficient to avoid the fastener backing out with heat-cycling/vibration
3.Consistent clamping force is essential to prevent warpage(like sump plate) and weepage(cam covers)
4.It is easier to remove than blue/red.
In critical locations s/s studs+red loctite with s/s nuts+green are a better solution.

It depends on the materials which cleaner/lubricant I choose. I always want clean threads and so a quick squirt of WD-40 and wipe with a rag will often be enough. In places requiring loctite I will clean and apply without other lubricant. Never-seez is often used in marine applications where bolts are subject to salt water or chlorinated water. Where galvanic corrosion is a possibility (steel into aluminum threads) I always use an oil based lubricant/cleaner to reduce corrosion. In high heat areas like brake calipers the oil will boil off but enough residue will be left behind to inhibit corrosion.

So yes, I prefer to clean/lube threads rather than to apply dry fasteners.

More than you ever wanted to know about fasteners and lubricants from an engineering standpoint:
The Engineer's Companion/Fastener Design Manual, Part One

Great reference but I doubt many will read that manual.

There is a quick & smart solution.
On which fasteners on the M96 would the correct grade of Loctite be harmful/problematic ? Answer -None.
So just understand the 3 basic types of Loctite and you are done.

That is why Porsche used MEC bolts ?

If you want to upgrade the fastners -use stainless+loctite -cheap and easy to find.
Oiled fasteners - at the low torque specified, how are you going to prevent them backing-out with vibration and heat-cycling ? Answer,you can't.
Lubricated fasteners in steel+steel situations - great -see ARP.
Hope this clarifies it.

I would caution anyone changing to stainless fasteners to consider the application and do your homework. Stainless is typically not as strong.

I know it's harder to cut a stainless bolt in half. Can you elaborate regarding hardness, toughness etc.?

I must admit, publicly, that I have never cleaned or lubed threads nor have I heard of green thread locker. I just got better thanks to you guys. I'm thinking I'll always put a dab of blue on but will this prevent oxidizing?

Here's a reference chart. Take a look at the metric portion of the chart to compare strength. I'm not saying never use stainless, but that one should be aware of the properties when changing critical fasteners. It is -not- a 'no brainer'.

https://www.boltdepot.com/fastener-information/materials-and-grades/bolt-grade-chart.aspx

I think you are confusing mPa and psi?
Aluminum threads will strip long before s/s in any normal application. We are only talking 10Nm for an M6 bolt !
The limiting factor is not the s/s fastener. The limiting factor is the threads in the aluminum part.