tank vent in a full tank due to expansion.
Further, hot fuel causes power loss, since
it’s less dense and thus packs less oomph
per unit volume. I highly recommend return
fuel oil coolers on all diesel engines. They
are shown on the piping schematics.
(Newer, high-output diesels often come
with return oil coolers built in. Check this
before ordering an unnecessary additional
external oil cooler.)
Oil coolers are no more than simple heat
exchangers. Raw seawater is drawn in for the
main engine cooling (or heat-exchanger cool-
ing) and passed through the sea strainer.
(Figure 4-10 shows a seacock leading to the
sea strainer, then to the Sen-Dure return oil
cooler. A Racor clear-bowl fuel filter with a
metal flame shield is located above the sea
strainer.) The cool raw water is then routed
down through the oil cooler and then to the
water pump on the engine. You can see in
Figures 4-5 and 4-7 that the return oil passes
through coils in the oil cooler before travel-
ing back to the fuel tank, now at lower
temperature. (Duplex sea strainers—-identi-
cal in concept to the duplex fuel filters—are
also highly recommended.) See Chapter 17
regarding seawater intake.
Hot Oil
In cold climates—as anyone who has ever
run a compression-ignition engine knows—
diesels are hard starting. Fuel heating ele-
ments are available that fit into the fuel fil-
ter. Typically, they can raise fuel temperature
from 0°F to 60°F (from –17°C to 15.5°C) in
5minutes at under 10 amps. These units are
switched on and off from the helm and auto-
matically reduce current draw as the temper-
ature increases. If you’re building boats for
Alaska, Newfoundland, or Baltic operation,
late fall through winter and early spring,
these heaters will make getting them going
in the morning more pleasant.Fuel-Line Valves
CFR Yacht, CFR Commercial, and the ABYC
are strangely silent on recommended valve
types for fuel systems. Technically, any valve
is acceptable if it will withstand the required
21 / 2 -minute burn test and has packing that
won’t break down from contact with the fuel.
For example, some Detroit Diesel manuals
recommend the use of gate valves for their
lack of restriction on fuel flow. In fact, how-
ever, gate valves, as well as anyvalves with
packing, are potential trouble. Even if the
packing doesn’t break down from the fuel, it
will wear out eventually. Accordingly, no
valves with packing for their primary seal
should be used in fuel piping.
The two best alternatives are globe
valves and quarter-turn ball valves. Globe
valves are acceptable, but they cause
restriction in fuel flow due to their construc-
tion. Also, you can’t tell if they’re open or
closed simply by glancing at them. Tw o
arguments in favor of globe valves are thatChapter 4: Fuel Piping and Fuel System Bonding
Figure 4-10. Return oil cooler
Figure 4-11. Ball
valve (Courtesy
Conbraco)