Onan MDKBH Series, Service Manual

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4-6
MAINTAINING THE ENGINE COOLING
SYSTEM
Refer to Table 4-1 for scheduled maintenance.
Cooling System Overview
The engine is cooled by a pressurized, closed-loop
liquid cooling system in which coolant is pumped
through passages in the engine block, head and ex-
haust manifold (Figure 4-4). The exhaust manifold
also serves as the engine coolant reservoir.
The heat exchanger is mounted inside the exhaust
manifold. Raw water (the flotation water) is pumped
through tubes in the heat exchanger to cool the en-
gine coolant. The raw water then passes through a
hose into the exhaust-water mixer where it cools the
exhaust gases and is expelled. The V-belt drives the
coolant and the raw water pumps.
Recommended Coolant Mixture
See ENGINE COOLANT (p. 3-2) for recommenda-
tions.
Replenishing Normal Coolant Loss
Check coolant level in the recovery tank before the
first startup of each day and, if necessary, refill to
COLD when the engine is cold or to HOT when it is
running. The recovery tank is designed to maintain
coolant level, not to fill the system. If the tank is
empty, check for and repair any coolant leaks and
refill the system through the fill neck on the engine.
Make sure the two hoses from the recovery tank are
routed through the two holes in the right end of the
genset enclosure, that the coolant recovery hose is
connected to the fill neck on the engine and that the
overflow hose terminates in the drip pan where it will
not splash coolant on electrical components.
Pressure Cap
Replace the pressure cap every two years (seals
deteriorate and leak). Proper cooling system pres-
sure (10 psi) is essential for optimal engine cooling
and minimal coolant loss.
Coolant Hoses
Check for and replace hoses that leak or are dam-
aged.
Draining and Cleaning Cooling System
WARNING
Accidental or remote starting can
cause severe personal injury or death. Discon-
nect the negative (–) cable from the battery to
prevent the engine from starting.
WARNING
Hot coolant spray can cause severe
burns. Let the engine cool before releasing the
pressure cap or removing the drain cap.
1. Have towels and containers ready to wipe up,
collect and properly dispose of the coolant.
2. Disconnect the negative ( – ) cable at the battery
to prevent the engine from starting, let the en-
gine cool and remove the front and top access
doors and the coolant pressure cap.
3. Drain the exhaust manifold/coolant reservoir
by disconnecting the hose at the coolant pump
inlet (Figure 4-4) and twisting it down into a
container.
4. Drain the block by removing the cap on the
drain fitting on the left side of the block (Fig-
ure 4-4). Use an 11/16 inch socket on a swivel
and 12 to 18 inch extension. To catch the cool-
ant and direct it into a container, insert the sock-
et and extension through a piece of hose large
enough to fit over the socket but shorter than
the extension. The hose will catch the coolant
as the cap is being unscrewed.
5. Use radiator cleaning chemicals to clean and
flush the cooling system before refilling with
fresh coolant. Follow the cleaner manufactur-
er’s instructions.
Refilling Cooling System
CAUTION
Low coolant level can cause severe
engine damage. Make sure the system is full.
CAUTION
Filling a hot engine with cold water
can cause cracks in the manifold, head and
block.
Close the block drain cap and reconnect the pump
inlet hose and fill the system through the engine fill
neck. The system will fill only as fast as the air can
escape. Fill to the bottom of the fill neck. Start and
run the engine for a couple of minutes to dislodge air
pockets and shut it down. Add as much coolant as
necessary and secure the pressure cap. Then refill
the recovery tank up to the COLD mark.
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