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Repair Coolant Leak

I’ve been working with my son to get a 92 Honda civic LX running. When finished, it was running fine except for the temp gauge always showing Hot.

My son replace the Thermo sensor for the gauge but over tightened an snapped it off. I had to drill out the remaining piece and clean the threads to install another sensor.

When we started the car, white smoke was pouring out of the exhaust and when rev’d, coolant came out. I think I may have drilled in too far and created a leak.

How can I repair this??


The temp sensor hole goes completely through the outer wall and into the water jacket, so in order to have “drilled too far” you’d have had to keep going after penetrating the water jacket’s outer wall and drilled through the inner wall. I can’t envision someone continuing to drill after the bit breaks through, so I suspect that the coolant burning problem may have already existed and its cause be also reaponsible for the constant hot reading.

In short, I suspect that you have a blown headgasket and/or a warped head.

Whether I’m correct or not, the head will have to come off to see what’s going on. You can always run a pressure leaksown test to find out which cylinder to look at, but IMHO you might as well just pull the head and go at it. Check the gasket for evidence of a breech, check the block upper surface for erosions, and send the head out for checking and planing. I’m not sure I’d recommend doing so on a 19 year old engine.

Or, this being a 19 year old Civic with unknown mileage, start looking for a boneyard motor to put in it.

Thanks for the reply. Yes the drill did go into the inner wall, just enough to cause a leak. I pulled the head and verified it. The coolant is leaking into cylinder #4. I’m going to see if a local automotive welding shop can TIG weld it. If not, I’ll start looking for a replacement head.
The car is 19 years old but only has 80K miles on it, so I’m going to try and salvage it.


Drill stop. There are many drill stops but one of the best ones I saw was a broken drill bit that stuck out a half inch from the chuck. So, if you are ever drilling out a rivet on a nut plate on the aft fuselage of a tanker aircraft, use a short drill bit but keep it down to three eighths. When the Colonel has to ask “where was his drill stop?” it gets embarrassing.