They are excellent for such jobs. Use penetrating oil and low torque to unfreeze the nut. Use short bursts of power and it if starts to move, slightly tighten it again and repeat the process. Extensions make it harder for the gun to do its job because they soak up some of the vibration. You may have to hold the extension with one hand to minimize shaking movement.

Use an impact gun, not an impact wrench.

In that circumstance, I would not use the impact wrench unless I was replacing the bolts. It is waaaaaay too easy for the impact to break the bolts. The exhaust heat makes them VERY brittle.

If the bolts need to be saved - heat is the only way to go. Heat up the bolts red hot and CAREFULLY turn them by hand. Replacing manifold studs is no fun!

Thanks, I do want to save the manifold bolts. I have used heat on other stuck nuts and was surprised how well it works. I am a little shy about fire around the engine nonetheless.

My interest in doing this job myself, I have moved away from exaust work years ago as it requires laying under a car, I do have oil change rams which help a lot in this case. But my "friendly" neighborhood mechanic I have hired over the years to do work on my older vehicles (I have four vehicles, only one now in the category of old a 90 Galant) has now been found to be a parts price gouger. The exaust pipe from the manifold to the Catalytic was priced out by him, after warning me, at $270. I said let me think (I may go back to Midus to see what high price they charge) it over. I then went home and looked on the web and found the price at RockAudo on the web delivered for $130, next I priced it out as a retail customer at one of the parts houses he check, they want $170 to me. So, I am now more interested in working it myself, even if I need to buy a few tools, and I've got loads of tools, including a HD air compressor (far more than I really need) to run air driven tools. I'm also looking into cutting the exaust pipe in front of the flexible connector this part has and behind and installing a joining pipe or one of the "replacement" flexibles sold by JCWhitney and others. The car has stainless steel "plumbing" and has held up for 15 years/150,000 miles and is good for who knows except for the failed flexible connector. Why it has a flexible connector is beyond me, other than for some give between the pipe hanger attached to the body and the manifold attached to the engine. Somehow other cars I've owned have managed to deal with that movement conflict without using a flexible connector.

It sounds as though you wish to use the 3/8" sockets you already own. Most impact guns require 1/2" or larger IMPACT sockets. You should NOT use the chrome coated sockets that came with your socket set. If you do, they will crack and/or shatter.

If you do get an impact gun, get impact sockets as well or you'll be sorry.

As for your repair, I wouldn't use an impact gun on those small manifold bolts. The gun will shear them off quite quickly and easily.

My emphasis is on low torque and short bursts. Trying to turn them when they don't move is asking for a break-off. Heating them red hot and letting them cool works well if you can get close by safely. An impact gun is standard practice on rusted boiler bolts, at least with our dealers.

I haven't even tried with just muscle and a socket, with some penitrating oil first. I have both 3/8" and 1/2" socket sets. I haven't tried to fit the 1/2" in the narrow space leading to one of the three nuts. It may go.

I don't have an immediate need for the car, and the heatwave we're having in NJ doesn't make me much interested in being outside under a car working.

I wonder what a place like Midas does, they're doing exaust work in several bays all day long, they must run into these old rusted bolts several times a day. I think I have seen the sparks of a cutting torch on visits in the past, but that was to cut a pipe off, not dealing with the rusted nuts. I may yet go to Midas, and see how much $$ they want. I don't recall if they'll give a price estimate over the phone, I know exactly what I want them to price. Of course if they get me in they'll try to sell me a new cat and muf, plus tail pipe.

Recently, I needed to replace the exhaust pipe from the cat back. It's too long to do without a lift and in the past I used to cut the pipe and install a coupler. I called Midas to see what they cost, because this would be the third time I had to do this and they offer the lifetime gaurantee. This pipe costs about $110 at Napa and lasts two years. They wanted about $250 and said they used an aluminized steel pipe. I was thinking out loud and wondered what Auto Zone used. He said Midas's pipes ARE Auto Zone pipes, ordered from their warehouse !! I thanked him and called Auto Zone. For $79, I could buy a lifetime pipe from AZ, which I did, and it's now awaiting installation.

More war stories, I called Midas to see what they wanted for the front exaust, they said pipe would be approximately $300. So the local guy's price of $270 was in the "zone", again I can buy it over the counter locally for $170 and shipped from RockAuto (I haven't checked AZ) for $130.

My survey result: they all price gouge.

So next time when you think the labor costs of $70 and up per hour are high, keep in mind you're likely paying parts mark-up that runs $100 per hour and up. For the case-in-point, Midas went so far as to estimate the labor at 0.8 hours, so $300-130= $170 price mark-up for the parts used, and I'll bet they'll get you/me for some extras, clamps/hangers... anyway $170/0.8 = $212.50 per hour just from parts mark-up. Now the poor hired hand is likely making $20 per hour, maybe $30 loaded labor cost, so you can see why the owners are still in business.

And that's the way they stay in business !

speaking of compressors, IÂve been looking to buy a compressor for the DIYÂr for small jobs around the house (wheel rotation, brake jobs, nailing, etc  nothing too major). However, IÂm having trouble deciding what to buy. I donÂt want something too over-powered but also donÂt want something too cheap. Some Craftsman models IÂve looked at online didnÂt seem to get good reviews (like the 15gal/1hp, 26 gal/2hp, etc). I found a Husky at Home Depot (26gal/1.7hp w/ tools) for under $300 that got good reviews that IÂm considering. Is that good? Any feedback would help. Thanks!

Here is a link that might be useful: husky @ Home Depot

The muffler shops just peel the ubolts off with an impact gun and replace them. They normally dont get into manifold work. As jtc001 said, replacing broken manifold bolts is a miserable job.
I have 2 half inch air impact guns. The CP gun gets all the use because the cheapo Chinese made Craftsman (still kicking myself over that one)is underpowered, heavy and awkward in tight spots. The three eighths inch butterfly impact is one of the most useful tools I have ever had.

The reason those businesses charge the prices you quote is because they are doing the job. So far you are getting quotes and clunking on your computer. I have a feeling before it is over you will wish you had paid your mechanic.

I would try heating the stud up first and use a breaker bar to remvove the nut. If that doesn't work go with the impact gun. I'm pretty sure if you use a impact gun to remove a nut on a manifold stud, the stud will break. Then the fun part of trying to remove the stud from the head begins.

This is probably a dumb question, but what is the difference between and impact wrench and an impact gun? I have used an air driven impact wrench for years with great success. What am I missing? Charles Ranheim

Cranheim same thing as far as I know ?

For nasty rusted exhaust manifold nuts, you can use a nut splitter - look it up in Sears or SnapOn catalog.

Auto repair DIY is definitely more satisfaction when you're done, but it can be a lot more aggravation along the way - for a first project you won't have a net saving of money, BUT some of the money you spend will go into tools you keep forever. I like that.