Cool Under Pressure Page 2
Q & A — August 2002
By Capt. Ken Kreisler
Cool Under Pressure
2: Gasket Sealants, Battery Charging Systems
there more than one type of gasket sealant, and if so, what are the differences
between them, and how are they applied? J.P., via e-mail
RTV is cured by moisture in the air, so the cap must always be put back on the tube as soon as possible. It has a shelf life of about one year, so always check the expiration date on the tube before you use it. If there is no expiration date on the tube, don't buy it.
When using RTV sealants, first remove all residue, dirt, and oil from the mating surfaces. Make sure to remove any gasket material from the blind attaching holes, which are used to position those parts, as it can cause hydraulic lock and prevent the bolts from properly tightening the parts.
Unless otherwise specified by your engine manufacturer, apply RTV sealant in a continuous bead of 1⁄8 to 3⁄16 inch thick, and apply sealant to the bolts where they contact the top of the head, as well as to the threads. Torque the bolts within 15 minutes after applying the sealant or it will have already started to cure and not seal properly. If this happens, you'll have to remove the old sealant, reclean the surfaces, and redo the process.
Anaerobic sealant cures only in the absence of air, as when it's squeezed between two machined mating surfaces, so it will not spoil if the cap is left off the tube. It should not be used if one of the mating surfaces is flexible.
As with applying RTV, first clean gasket material, grease, and dirt from the mating surfaces, and remove any gasket material from blind attaching holes. Unless otherwise specified, apply the material in a continuous bead no less than 1⁄3 inch to one sealing surface, as well as to the bolts where they contact the head and bolt threads. As with RTV, you should torque the bolts within 15 minutes of application or the sealant will start to cure.
am considering upgrading to a larger battery charging system. Will I have
to change my wiring? S.L., via e-mail
First, rewire when upgrading to a larger battery charger. If you use the same gauge wire as on your existing system and subject it to a heavier load, the result will be increased resistance, which reduces voltage and produces more heat and, in the extreme, fire. The U.S. standard for wire size is the American Wire Gauge, or AWG. The higher the number, the smaller the diameter; a #18 gauge wire is smaller than a #10 gauge wire. Your electrician can determine the proper gauge wire for you.
Also consider the length of the wire run. Long runs typically result in lower voltage due to increased resistance. A three-percent drop is fairly normal with long runs, so although your charging device may be set to the normal charging voltage of 13.8, your batteries will receive only 13.4 volts. That's why you should install the charger as close to the batteries as possible. (Remember, if the battery is 15 feet from the charger, the total run for both wires will be 30 feet.)
help with a maintenance problem? Write to Maintenance Q & A, Power
& Motoryacht, 260 Madison Ave., 8th Fl., New York, NY 10016. Fax:
(917) 256-2282. e-mail: firstname.lastname@example.org.
No phone calls, please.
This article originally appeared in the January 2003 issue of Power & Motoryacht magazine.