Swapping out snow tires and tightening down this one bolt...
 

I have a helicoil on one lug bolt on the front tire on the '99 turbo and it started spinning when I applied 80 ft lbs to it. It's been there for about 5 years and the four other bolts tightened up nice and snug. Do you think I can drive this way for a couple weeks and get it fixed or is it dangerous to drive the car this way?

I would just take it out before it flies outta your wheel on the highway and goes through someones windshield.

You'll be just fine with 4 lugs in the meantime.

Replace the hub lug bolts are kinda important to the car. I would never use a helicoil on a bolt like that. Used hubs are cheap

Properly installed Heli coils are just as strong as the parent material.

While not optimal, a car can be run with 1 missing lug as design standards consider this possibility but it isn't advisable.

wow I need a hel coil for my w140,I did not no they made them.Where did you get one.To replace the axle is a awful job.

Wrong heli coil is a spiral wound strip of metal that is easily deformed and is in no way as strong as the hub metal. The only repair that i would use on my families car is a timesert which is a full metal sleeve with threads inside. heli coils pull out all the time when removing the bolt in them timesert wont do that

Heli coils are made from stainless steel not soft metal. Once installed, the coil can't escape.

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I will give that heli coils are not optimal for frequently removed bolts and more for occasionally removed bolts ( Vs never removed bolts ) and require some care when inserting the bolt.

If the insert was installed too close to the surface, it will pull the top thread out during careless assembly. Ideally, the top of coil should be 1 turn below the surface assuming there isn't a deep chamfer.

If the new thread was not tapped deep enough, the bolt will bind and tend to unscrew the insert. All of these failure modes can be traced back to improper instillation.

I have personally validated that you can drive for extended periods with only 4 lug bolts without issue.