The prospect of either rounding off a bolt head or worse, snapping one off, is enough to keep a lot of people from messing around under the hood of their car. Car Doctor John Paul has some advice.
Q. I work on my cars and it never fails once I need to loosen a rusted bolt/nut more often I break it rather than get it loose. I purchased a rechargeable impact gun and that helps a little but still I’m braking bolts.
Do real mechanics heat everything with a torch or is this part of living in the Northeast? Here is my real problem: I need to replace the spark plugs in my Ford truck and from reading online I know these engines have history of seized sparkplugs, what can I do to prevent a disaster?
A. What I have found when encountering rusty fasteners is start with plenty of penetrating oil. There are several good ones: PB Blaster, Areo Kroil, Liquid Wrench and SeaFoam are a few that I have had good luck with.
If you’re so inclined, these guys did a 12 minute video on the best penetrant, including the acetone/trans fluid mix:
A couple of interesting notes:
- Aero Kroil is by far the most expensive product here, and did the least to loosen the nuts
- Liquid Wrench and a 50/50 mix of ATF/Acetone were the cheapest and did the most
- Heat was by far the most effective tool to remove a rusty nut
Before you try to loosen anything, soak the rusty faster and allow the penetrating oil to seep into the threads.
Once you have waited a few minutes (or longer if really rusty) always tighten a bit before you try to loosen the nut. Just backing off the rusty nut will cause rust to bind in the threads and then adding more effort just breaks the fastener. This video describes the method:
I have also had good luck using an impact gun. Depending on the fastener, it is the light impacts that do the work, not high torque. A cordless drill/driver can work well. These light duty impact guns seem to provide just the right amount of quick taps without exerting too much force.
For your Ford engine, soak the sparkplugs and let the oil sit overnight. Then using the same technique, tighten slightly, spray the penetrating oil, loosen and repeat. If things go poorly, there are kits to rethread/helicoil the cylinder heads without having to completely removing them.
When installing the sparkplugs, use an anti-seize compound on the threads, and make sure they are tightened properly using a torque wrench. Plugs that are loose will have carbon build up on the threads and too tight will stretch and damage the threads.
John Paul is senior manager of public affairs for AAA Northeast. A certified mechanic, Paul tests dozens of new cars each year and also hosts a radio show on AM 950 wrolradio.com