Coolant Change for a 4JH2-TE Yanmar

Aug 29, 2018
57
Hunter 420 Passage Sv
I am going to change out the coolant in our Yanmar 4JH2-TE motor.
I would like to get any tips, advice and tricks on how to do this. We also have hot water heating loops to deal with.
Any advice on how to drain the coolant would be appreciated.
 
Oct 22, 2014
20,993
CAL 35 Cruiser #21 moored EVERETT WA
Have lots of rags, and a container to catch the coolant. The water heater should be turned off. If the heater is higher than the engine it should drain back to the on engine tank. You can attach a hose and flush the lines with fresh water. Refilling is straight forward. Fill the engine tank with coolant mix. Turn on the engine to circulate the coolant through the engine and the water heater. Add more coolant to top off.

Some believe you need to loosen the return hose on the water heater to be sure the line is flushed and recharged. I am not of that school. If you have run a hose to flush the coolant system, then the flush water is throughout the system. When you add the coolant that water will get mixed with the coolant mix and the system will be purged. You can add a little straight coolant is you are concerned about the 50/50 mix standard.
 
Nov 9, 2004
110
Hunter Passage 420 Rock Hall, MD
You should have a drain cap on the hose leading from the engine just before the hot water heater and another one on the hose at the top of the engine. Use these too empty and fill the coolant with the petcocks located in a couple of places on the engine
 
Aug 29, 2018
57
Hunter 420 Passage Sv
Thanks for the advice. I do have the tee inlets at the engine and at the hot water heater tank. I thought about pulling the Hot water return hose off at the engine and blow through it to push the coolant out of the dip in the line. I was going to attach a hose with a funnel to the fill. I do have 2 drain cocks as well. Can I leave the thermostat in place or should I get the engine up to temp so it opens?

To Hot Water Heater.jpg
 
Oct 22, 2014
20,993
CAL 35 Cruiser #21 moored EVERETT WA
Leave the Thermostat. You do not need to heat the coolant it is 50% water.
That is unless it is frozen.:yikes:

Are those hoses soft?
Looks like they have had a chemical on them. The changed color and the bulging near the hose clamps indicates a replacement may be in their future.
 
Oct 26, 2010
1,883
Hunter 40.5 Beaufort, SC
I thought about pulling the Hot water return hose off at the engine and blow through it to push the coolant out of the dip in the line. I was going to attach a hose with a funnel to the fill. I do have 2 drain cocks as well.
I replaced my hoses after I sprung a leak in the heater hose connection at the water heater. Your hoses look worse than mine did before I replaced them. :yikes:

After I replaced my hoses and drained the engine through the two drain cocks at the aft end (low) on the engine, I filled the block with coolant, elevated both water heater hoses above the heat exchanger cap on the engine and filled with a funnel until coolant came out the other water heater hose. I then connected them both to the engine. Seemed to work out very well. I only had to add a pint or so to the overlfow tank after I ran the engine for a few minutes.
 
Oct 26, 2010
1,883
Hunter 40.5 Beaufort, SC
I also blew through the hoses before I filled with the funnel to ensure there was no residual coolant in the pipes inside the water heater heat exchanger.
 
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Aug 29, 2018
57
Hunter 420 Passage Sv
Great advice!! The picture doesn't do it justice due to the bright light and shadows. I do plan to change out 3 hoses on the engine (short little sections and expensive!!!), the engine temp sending unit, a new belt and the coolant fill cap while I am doing this task.
 
Aug 29, 2018
57
Hunter 420 Passage Sv
Coolant successfully changed out. Thanks for the support through this forum. Shop Vac with a custom end helped empty the Hot water Heater hose and Garden hose custom pieces (with Funnel attached) with quick couplings really helped in the fill up if the engine through the Hot Water Heater hose. Check this off the list.
 
Jan 4, 2006
6,444
Hunter 310 West Vancouver, B.C.
Coolant successfully changed out. Thanks for the support through this forum. Shop Vac with a custom end helped empty the Hot water Heater hose and Garden hose custom pieces (with Funnel attached) with quick couplings really helped in the fill up if the engine through the Hot Water Heater hose.
And wasn't it a bloody mess when you finished ? ? ?

I went through that when I first changed the coolant on my Yanmar 2GM20F. Disconnected hoses as I removed the coolant from the hot water heat exchanger. Every hose end seemed to be at the wrong elevation. Air everywhere in the system when finished. Kept filling the coolant reservoir for the next two outings before all the air was gone.

Swore never to do that again. Now I change ONLY the coolant that is contained in the block every two years and leave the remaining coolant in the hoses and HEX. Doing it every two years ensures that the corrosion inhibitors, seal lubricants, and other magic is replaced frequently enough to keep them up to strength. Two year old coolant coming out is indistinguishable from the new coolant going in.

Hardly have any top up until all the air is gone and not a drop of coolant is lost (on the floor, on the sink top, on the upholstery, and everywhere else imaginable).