I've been having a few problems that might be electrical in my car.
Seeing as mechanics always want to replace parts first, I'm having to diagnose this problem myself.
It seems like replacing all the fuses would be cheap and preventative, and more effective than a voltmeter with my limited knowledge of electrical.
I drive a 2004 1.7L Honda Civic Si, the US version.
Could this cause problems for my car? Would it help with the diagnosis?
Fuses do not need to be replaced unless they have blown, so it's not a regular maintenance thing.
In terms of checking them, depending on your vehicle, many only require a visual check to see if the metal is present or missing.
If you do have fuses where their status is not obvious, a good multimeter is only a few dollars (probably cheaper than replacing all the fuses, anyway) - and you will find it useful round the house, and for other small jobs once you have one. Make sure you get a reputable brand.
Replacing all the fuses should not cause any problems with your car, unless you get the fuses wrong, or don't fully seat them etc. On balance, much better off just testing them all with a meter.
As a general maintenance practice or a troubleshooting method without having a particular reasoned approach, no. If it's troubleshooting, testing the fuses on their exposed blade tips is equivalent.
That said, replacing the fuses shouldn't create any risks so long as you're replacing them with the appropriate values.
It should be pointed out that fuses can exhibit cumulative degradation due to short-term overcurrents which were insufficient to open the fuse. This can reduce the fusing current, but until the fuse actually opens, it's not going to be producing any problem symptoms itself. Even if this were a concern, replacing the fuse wouldn't fix the source of underlying periodic overcurrents.
In other contexts, (e.g. large mains cartridge fuses), the fuse body is filled with an arc suppression filler such as calcium carbonate. In damp environments, this can absorb moisture and cause corrosion of the fuse elements. In these cases, maintenance fuse replacement might be a valid stop-gap approach to avoid replacement of the protection equipment. There aren't any filled fuses in typical automotive applications.
Replace them all? No. As others have mentioned, they're either working or they're not. Test them with a multimeter or fuse tester. Be sure to look for "fusible links" in the wiring on a newer car, not all fuses are in the fuse box anymore for some unfathomable reason...
Take them all out, one at a time, and clean them? I've had that help on some vehicles. It's especially worth the effort if your problems are intermittent. Between vibration and corrosion it's quite possible for the connection between fuse and socket to become unreliable. Pull it out, clean off the corrosion, coat the contacts with anti-oxidation grease like is commonly used in electrical panels, and put it back. Should last quite nicely after that.
