OK, so...I had a ten minute job to pull off the thermostat housing on a 300-6, and swap in a new thermostat. One bolt came loose, and THEN...the other bolt snapped-off the head. I watched a lot of youtubes, and there seems to be three methods to get the remaining threaded stud out.

Number one: Spray penetrant, heat up the block around it to loosen the rust. Put on a nut and tap it "left and right" to loosen it. Then set a "stud extraction tool" on it and use a impact with the power set on low to "rattle it" and hopefully break it loose instead of breaking it off even shorter.

https://mobileimages.lowes.com/produ...pg?size=pdhism

Number two: If the previous didn't work, slide a washer onto the stud, then slide a LARGE nut onto the stud, and then WELD the nut onto the stud. Again, use an impact to rattle it on low-power, and slowly raise the power until it breaks loose.

https://www.hagerty.com/media/mainte...a-broken-stud/

Number three: If the previous two didn't work, cut the stud flush with the block, center-punch and drill it with a 1/4-inch cobalt bit (the bolt is a hair bigger at 5/16). Then tap-in an extraction bit like this:

https://cdn11.bigcommerce.com/s-k9nv...583937.jpg?c=1

The big question is...will welding on the stud damage the electronics on the 1994 F-150??

Any advice is welcome.

 

Put the ground lead on the engine block, no harm done. For extra peace of mind, unhook your battery.

See thread

 

i always put ground cable as close to work as possible, and use an OTC anti zap auto surge protector hooked to the battery.
in 40 years of automotive welding i have never harmed any electronics. before the anti zap was released for purchase, i used to disconnect the battery positive cable and connect it to ground with a jumper cable. i can not say the same for others that did not use one though.
unfortunately they are A LOT more expensive than when i bought mine in 2004. if i remember correctly it was only around $25 back then.

 

Thanks, Messofatruck and tc transport, I appreciate the responses...

 

I always unplug the ECU welding on anything.

Every major company I've delt with from lil'-bitty circuit boards to full size PCs & control units say do it.

Stinger says specifically they won't warranty a repair on a unit connected to a chassis by harness that was welded on & say they can tell.

Induced voltage through the harness grounds will fry an ECU.

 

Some of our DA guys were welding frames for the "huck rivet" repair that was to take and pay 5.5 hours
They fixed them in 5 minutes with a DC stick welder (never disconnected anything)
I did them the old fashioned way with hard work and toil
Never fried anything myself welding frames and things for wreck damage
ALLWAYS disconnect the battery

 

Not a cheap option but I borrowed one of these once and they worked great for what you are doing. You can bend the elements as needed to get to where you have to.

1KW Magnetic Induction Heater Hand-held Induction Heater for Bolts Removal | VEVOR US


And yes, I have always unhooked the ground when welding.

 

Ditch the penetrant and use a crayon or candle wax on the broken stud . Use a little heat to melt the wax... that and a small flat or cape chisel will get thst stud out.

You can also use alum if the housing is aluminum and the broken bolt is steel.

Just build up a dam around the broken bolt. Use alum powder like you would use in the kitchen.
Mix with water and make a paste. Put the paste in the area above the bolt and go to bed. The next morning the bolt will be almost gone eaten away by the chemical reaction between the aluminum and steel. Nothing else will be touched.

You can find videos of this process on youtube.

 

Thank you @Scndsin, @manicmechanic007, @spurredon, and @krooser.

Time for an update. I have achieved great success! Sometimes the good guys win. I must confess that when the bolt head broke off without warning, I said a bad word...even though I am sure that poor bolt was doing the best that he could. Some past wrench-head examined the thermostat and re-installed a soft hardware store bolt with no anti-seize. The rusty bolt was visibly dug-in there like a hungry tick, and the soft recycled steel was forced to submit to the leverage of my "double wrench" Kung Fu.

At that moment, I could see that at the very least, there was a stub sticking out that I might be able to work with. I posted my dilemma here, and while waiting for the helpful suggestions, I did some research to see if there was some new magic wand that I did not know about yet. Here is what I found.

We are all familiar with the common 4-flute spiral "easy out", and I day-dreamed about using one and decided that if I broke it off in the hole I was going to drill down the center of the stub, I could still weld a big nut around the stub, so my lack of a welder would not delay my ability to try something (The truck is a fourth vehicle, which makes me feel decadent with my 2013 sedan, a bicycle, and my wife's SUV).

There are a couple of types of extractor that attempt to grab the outside of a stud, and back it out. I do not not know which works better than the other. They seem to be in the $25-$35 price range. Sometimes the shape and size of a solution can be a factor. I was able to disconnect the lower radiator hose at the bottom and then lift the radiator out of the way without disconnecting the other three hose joints. The thermostat housing can also lift out of the way without disconnecting the heater hose. I feared I might be forced to remove the fan, but...the widest gap between the blades was wide enough to get a cordless 18V drill in there. I decided my first effort would be with a $5 4-flute easy out that is a tapered spiral with a left-hand twist, because it was immediately on the shelf, and the other styles would have to be ordered, so I'd have to wait.

I gently tapped the tip of the stub with a Dremel to remove any jaggedness. I then managed to get a 5/16 nut onto the stud. I slowly spun the biggest drill bit that would fit through the 5/16 nut (1/4? 9/32?) in the hopes that doing that would form a centered dimple on the tip of the stub. I then used a 1/8th drill bit to make a pilot hole. I only wanted to go deep enough to allow the easy-out to fit, because I feared every moment that the drill bit I was driving would break off. The 1/8th made it all the way through. Then I used the 1/4-inch drill bit as instructed, to make the final hole. It seemed big when compared to the new bolts I had, and the remaining "bolt" shaft would be only threads. I suspect that the removal of 80% of the bolt shaft definitely relieved any torqued-in stress the bolt had previously enjoyed.

Mere words could not convey my joy, when the easy-out removed the hollow shell of a stud that remained. I used an angle-grinder with a thin cutting disc to slice the tip of a "too long" 5/16 hardened bolt I had bought (They didn't have the correct length at the store). I split the tip down the center about three threads, and then cut-in from one side. This left an odd tip that would act as a thread-chaser with some air-space to allow spoils to collect instead of compacting debris deeper into the hole. I inserted my "thread chaser" into each hole all the way, marked it with a felt marker, and then counted the turns as I removed it. Both holes had 8-turns of air-space inside, and the stock bolts had been using 6 turns.

I spun on nuts and then cut the two new grade-8 bolts to a length that gave me 6 turns, plus a little more to allow for split lock-washers (which I like as visual indicators that full-compression has been reached when the split has been flattened). After the cut, I removed the nuts which straightened the burrs. I then used the grinder to soften the edge of the tips.

I spread a thin smear of Permatex on the composite gasket, a light smear of anti-seize on the bolt-threads, and snugged-up the bolts. Today I will see if it leaks.

The youtube channel "Project Farm" does a lot of shoot-outs, and they did a comparison of several types of easy-outs of the type where you drill a hole down the center of the stud (or broken bolt). The main result was that the typically short "multispline" extractors are the best-performing type for softer steel.

https://www.diamondtoolstore.com/pro...-extractor-kit

The common long-taper 4-spline extractor worked best for hard steel, because the force used is focused on only four splines, and the multi-spline extractors would not penetrate the steel enough to get a bite.

https://www.jugenheimersupplies.com/itemdetail/54660556