Yanmar water heater loop questions

[4arch]

I have a Yanmar 2GM20F with a Raritan 6 Gal water heater connected to the coolant loop. The water heater is installed well above the engine. I would think that if I open the radiator cap, all of the coolant in the water heater coolant loop would drain back out. That doesn’t happen though. To my knowledge there isn’t any check valve or siphon break in the water heater lines though there is a plastic Prestone flush fitting in one of the water heater lines. The engine doesn’t overheat and the water heater makes very hot water off the engine. Some might say if it ain’t broke - don’t fix it, but I do want to understand what’s going on before I undertake replacing the coolant. Is there a check valve somewhere I’m missing? Does the engine have a built in check valve for the water heater lines? Is my system low on coolant and just circulating steam through the water heater loop?

[stevemac00]

You ask a lot of questions - I'll see if I can answer some. There is no check valve. It probably won't drain completely - you need to pump it out, flush, pump again then fill with a coolant mix like Halvoline Dex.

For my 3GM30F I took off output hose from the pump, then opened radiator cap and pumped out using a small Jabsco hand held pump. It has great suction and I was able to pump it dry. I used distilled water for flushing a couple times before re-filling. Also, don't forget to remove the expansion tank and empty/clean it.

For filling I put the hose back on and slowly poured in coolant waiting for air to bubble out. I let it stand overnight and topped off again the next day. My procedure worked great for me and I never had to add any more.

I doubt the water heater is above the exchanger fill cap. If it were then coolant would drain down into the expansion tank.

[4arch]

Thanks for your thoughts. The water heater is definitely entirely above the level of the fill cap and the expansion tank has always been completely empty. It's mystifying.

[SteveInMD]

My water heater is above my heat exchanger fill cap. I don't have any problems with coolant running out when I open the cap. I assume it has something to do with the location of the hoses going to the heater and the thermostat in the engine block.

When I changed my coolant I got pump (a drill mounted type) and a two buckets. I pumped water through the heater to flush it out. One bucket with clean water and one to catch the outflow. Then I did the same with distilled water. Finally I charged it with coolant. I used a pliers-type coolant line clamp on each hose to keep the coolant in and the air out. I had a helper close the clamps while I was still pumping. The pump surged the liquid through the heater fast enough where it was very unlikely any air could remain in the system. I had no problems with air-locks when I was done.

(I wouldn't try using a battery powered drill because they turn too slowly, or at least mine does. I used a high speed 120 volt drill. It was a fairly inexpensive at the home imp. store.)

[sailak]

Hmmm.

I filled mine until full then started the engine leaving the cap off to "burp" the air out.