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Last weekend I was going to replace antifreeze in my Yanmar 4JH2E but
couldn't find drain plug. I am afraid it is somhere not accessable. Went through manual but in the chapter about servicing cooling system it was not explained how to drain the old antifreeze.
Any suggestions will be greatly appreciated.
Nestor Tolstikhin
Bayfield 36' Miracles
 

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According to the Seloc manual (for '75-'98 4JH and 4JH2 series engines):

Most engines have the following drains:
> Engine Block: rear of engine above crankshaft centerline.
> Header Tank: at low point of tank
> Expansion Tank: at bottom of tank
> Header Tank: at low point of exchanger.

The book makes it sound like there are petcocks for draining. While they draw many components, there is no illustration of these petcocks. Let me know how you make out. If desired, I can scan the pertainant pages and attach to an email.
 

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If I remember correctly, there are two for coolant. One on each side of the engine. If you are staring at the belt, they are about 3/4 way back on each side. There are small hex head bolts that you turn to get the flow going.

I'll try and take some pics for u if I can remember. Good luck!
 

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If I remember correctly, there are two for coolant. One on each side of the engine. If you are staring at the belt, they are about 3/4 way back on each side. There are small hex head bolts that you turn to get the flow going.

I'll try and take some pics for u if I can remember. Good luck!
Thank you! That helps. The pictures will also help immensely!

Tod :)
 

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This was on my 3GM30 but the 4JH2E (which I have in current boat) has the same style. The drain is the brass fitting left side of photo next to my thumb.

Off the bottom of the exchanger is another drain, this one has knurled knob on it.



The drain might also be of the style that has a knurled knob that is turned to drain the fluid. Most of the time there will be a piece of clear plastic tubing from the drain to direct flow to the bilge/off the engine so maybe look for those tubes to help find the drains.

On my 4JH2 I haven't drained the coolant yet but have noticed one at left rear corner of engine (about even with the bell housing) of the knurled knob type.
 

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Great picture, and explanation. Thanks! I do have the same brass fitting, with a hose attached. I assume I can loosen the brass fitting to drain the heat exchanger into the attached hose?

What about the various pet-cocks? Is it necessary to loosen/drain these as well? I am looking over the manual now and trying to make sense of it so I can be ready to do this on the weekend.

Thanks again!
 

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Oh fun. So "which one's which" just became very entertaining. The manual didn't seem to identify the location(s) of any of them! Any pointers are appreciated!

Guess it won't hurt to just open them all. The impeller should fill the exchanger when we fire it up, and we'll be filling the coolant with distilled water a few times, then emptying.

Sound like the right process?

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S/V Sapphire
1992 Pacific Seacraft 37 #292
 

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Last weekend I was going to replace antifreeze in my Yanmar 4JH2E but
couldn't find drain plug. I am afraid it is somhere not accessable. Went through manual but in the chapter about servicing cooling system it was not explained how to drain the old antifreeze.
Any suggestions will be greatly appreciated.
Nestor Tolstikhin
Bayfield 36' Miracles
Suggest when re-filling you let it run a bit with the expansion tank cap off until it won't take any more coolant. Some engines may have an air bleed screw high up on the block, don't know about Yanmars?

Paul T
 
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