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Old 28-05-2013, 16:35   #1
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Bleeding the cooling system - Yanmar 4JH4AE

Hello Everyone,

I've just replaced the domestic hot water heater which of course meant opening the coolant circuit. The aux coolant piping actually has 2 heat exchangers in the loop, one for the hot water heater and one for a small cabin radiator. They're plumbed in series.

I don't seem to be getting any flow through this loop, so I figure it's air locked. I pulled what I think is the return line to the engine off at the engine, and get no flow out (I also capped the engine port). Can someone confirm that the port on the thermostat housing is coolant out, and the adjacent port that connects on top of the line to the oil cooler is coolant return? I also put a hand pump on the return line, and with the engine running tried pulling coolant. I did get some (and drained the expansion tank by doing it), but after removing the pump I still got no flow. Occasional dribbles, but nothing significant.

Am I on the right track, and just need to persist in pulling coolant through with the hand pump?

Also, can anyone confirm whether there's a zinc in the cooling system on this engine? The manuals seem to indicate only for turbocharged 4JH engines, but there is conflicting information in the service manual.

Many thanks!
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Old 28-05-2013, 17:38   #2
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Re: Bleeding the cooling system - Yanmar 4JH4AE

Doug,
I don't know if this helps, but I disconnected the feed from the engine to the hot-water heater, raised the hose 6"-8" and poured coolant directly into the hose. Coolant worked its way through the system and I didn't have problems clearing the line. Good luck!
Don
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Old 03-06-2013, 21:44   #3
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Thumbs up Re: Bleeding the cooling system - Yanmar 4JH4AE

Don's post above got me thinking in a slightly different direction than my initial attempt, and I wound up with a full system will little mess.

I disconnected both aux coolant loop hoses from the engine, and stuck one in a jug of antifreeze (premixed). I attached a hand pump to the other hose, and stuck the output hose from the pump into the same jug. I then pumped, circulating the fluid until only antifreeze (no air) was being output by the pump. I did have to elevate the jug to prevent siphoning, but I pretty quickly wound up with a full system. Disconnecting the hose and pump and reconnecting the hoses to the engine went quickly, and it didn't look like much, if any air was introduced. After running the engine for 20 minutes or so I had hot coolant running in the aux loop.

For me, the key to reducing the work and mess was to use a single jug of antifreeze, rather than a source and drain bottle.

Hope this helps someone!
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Old 08-06-2013, 08:58   #4
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Re: Bleeding the cooling system - Yanmar 4JH4AE

I had the same problem when I repowered with a new small Caterpillar engine I put a small ball valve on the head beside the thermostat housing a extra hole for a tempture gauge.I then added a small hose to the valve started the engine and let all the air out till a steady stream of coolant was flowing I left it on the engine and use it after changing the coolant it works great.
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Old 08-06-2013, 17:47   #5
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Re: Bleeding the cooling system - Yanmar 4JH4AE

That sounds a bit more elegant than my solution. I'd tried a cruder version of your solution by pulling what I thought was the aux loop return off the engine but I never got anything out of the hose, even after running the engine for 15 minutes or so. I suspect the coolant pump doesn't have enough oomph to move the liquid if there's a large enough bubble of air in the line or heat exchangers.
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