Oil Cooler leak on a 2008 ML320 CDI. New E bolts from mercedes. Attempted to torque down first cooler bolt. Kept spinning. Removed cooler and found that front and rear bolt holes didn't have upper threads. Checked old bolts and found threads came out with two of the bolts. Assuming front and rear bolts. I inserted new bolt in just the whole and found I could tighten it. Not sure if I'll strip out the rest of the threads.
What should I do next? Drill and tap the holes? Use a longer bolt with a nut?
Let me know if you've run into this and what did you do.

Thanks in advance for your assistance.
RayK

 

This is a tough call for someone else to make without seeing the damage.

How long are the bolts? How long is the bolt hole? Compare these two questions with undamaged bolts and holes.

Were the bolt holes damaged or the bolts were or both?

Using new bolts, do they grab the threads at the bottom of the hole?

Where would you put this nut? If I were you, I would use a tight fitting copper washer.

 

Holes are 17.88 mm to 18.44 mm deep
Cooler tab thickness = 5.10 mm
Cooler Torx30 bolts used to tighten cooler down have thread length of 19.06 mm
This means approximately 14 mm of thread is holding the cooler down.
Inspection of old bolts reveals thread came out with the bolts when removed.
I tried using a longer bolt with 33.06 mm of thread. Hand insertion seems to hold.
I was thinking of installing nut on the longer bolt, insert into hole with locktite, waiting for hardening,
and then trying to tighten the nut down to see if torgue can be reached. Praying that the longer bolts will hold.
New bolts with new thread were tried. Could not reach torgue. The more I turned, the easier it was. I was striping the hole threads.
Do I try this or do I drill and tap?
Hoping that someone out there may have run into this previously.

 

Do you have photos? Helicoil is an option for stripped threads, but I don't know this application well enough to know if it is feasible. Then there are the metal shavings to consider. Drilling and tapping a helicoil is a final, or near final option because of the shavings/debris.

 

I agree with Chassis using a Helicoil and there shouldn't be any problem with torquing the bolts to 12Nm.

Make sure you blow out the chips after drilling.

 

FWIW.....IMO

Install Time Sert they are much better than a Helicoil

Review

https://www.time-sert.com

Time Serts are solid bushings, Helicoil's are a spring insert.

Regards

Joseph~