Kohler SFGLD480 Operation & Maintenance Manual page 105

PRODUCT INFORMATION INDEX DATE
Dep. 2
IT-C-A-25-030e G
January 2015
KOHLER POWER ENGINES
SUBMERGED OIL PREHEATING SYSTEM
O&M_2.002211.810_A_10_2016
1. INTRODUCTION
The aim of preheating oil is to raise the oil temperature before starting the engine up to the appropriate minimum
value (about 40ºC) that ensures adequate oil viscosity for loading the engine.
2. DESCRIPTION
For this purpose, we use a direct preheating system in which the heating resistance is in straight contact with the
fluid, i.e. oil, to warm up.
Direct heating offers the advantage that heaters' efficiency is near 100% because oil directly absorbs all the
generated heat. This contributes to faster warming up and suppression of thermal delay. There is no intermediate
medium giving rise to heat losses during heat transfer.
The oil preheating system is a monobloc unit that consists of a resistance, a thermostat and a protective cap.
According to the engine model and the crankcase capacity, there will be one, two or four resistances. See table 1.
For heating oil, we specify a 1500W resistance with a specific charge of up to 3.9W/cm². Fitting into the tank is
with a 1-1/4" gas stamped brass cap nut and a copper gasket to prevent oil leaking through the thread. The tube
is made of AISI 316L stainless steel, 8mm in diameter.
Fig. 1 - Heating resistance
3. ASSEMBLY
These monobloc units lie inside the crankcase (oil sump), in the lower front area. See Fig. 2, 3 and 4.
The resistance is connected to the mains through a plug-in thermostat with the power wires secured to the
special-purpose clamping screws.
The resistance must always lie horizontally and submerged in oil. Otherwise, it could break and fail to operate
correctly.
These so-called monobloc preheating systems have built-in thermostatic controls with temperature adjustments
from 30 to 90ºC. The thermostat must be set at 40ºC. When the preheating system switches on, the resistances
start warming up the crankcase and the oil temperature rises progressively. As the oil temperature reaches 40ºC,
the thermostat switches off.
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