Who's Retapped The Lower Theromstat Housing Hole?

Kind of specific I know... but, I have the heli-coil kit, a tap handle and am ready, I think. Drilling it out would be a PITA without removing the rad, cooler, and grill. There's more than enough room to sink in a coil. I have the 3/8 kit as a 5/16's was too small and an M8 was probably what was used by the previous owner. Did I mention this was to fix a screw up??

How CRITICAl is drilling the hole smooth if I have enough depth already? Can a reaming with a Dremel bit be enough?? Never re-tapped a hole in my life and I don't want to be towing this thing in to have the dealer do it. I know I need to go very slow, back it out, oil, back in, back out, etc... I'm assuming this is correct?

I need the master Jedi on this one, replacing a head to fix this would kind of ruin my day...

A drilled finish will work well for a threaded hole in an automotive application. If you are really worried, you could drill the hole undersize and ream it, but that's too much work for what you want to do.

The original size of the hole was 5/16"-18, and if you are going to go the next size up you are probably going to have to open up the hole in the housing. Check it for fit before you do the job - or see if you can get away with a 5/16" coil insert. There are also threaded bushings that can be used (solid, not coiled wire,) but I think the 5/16" bushing needs a 9/16" or 3/4" hole!

Since that hole opens into the water jacket, I would probably go so far as to install a short stud, and seal it into the hole well before putting the whole thing back together.

If you have an "angle" drill, you will have an easier time getting the drill work done. For tapping, you aren't going too deep (relatively thin casting) so you should find that work going fairly easily.

Still, I'd prefer to stick with the original bolt size if I could get away with it. Check quickly by running the drill specified for the 5/16" kit (no power - just fingers) and see if there is any resistance. If it goes too easily, you are probably going to have to go 3/8"

It's too bad you're way out there, or I'd give you a hand. Isn't Beezil out there somewhere? I'm sure you could find someone to give you a hand on this - if you're not sure you can do it, you'll likely need it and it can't hurt. Should only cost a couple beers or so to get help, and you'll probably learn from the experience.

5-90

Thanks... I'll try the angle drill first. I know I'll have to ream out the housing hole as well. I love fixing other peoples screw ups...