Drain / Bleed Coolant - Yanmar 3GM30F

[Capt.Don]

I'd like to change the coolant in my Yanmar 3GM30F. I've located 2 drain petcocks: port side just behind the alternator; stbd side above the oil dipstick. These are 1/2 diameter screw knobs with clear plastic drain hoses. Fluid drains from the port side; not much drains from the stbd side. Also have 3' hotwater heater hose to flush.

Other posts are somewhat vague about 2 or 3 coolant drains on Yanmar engines - I've only found these 2 (can only find 2 in the Yanmar Service Manual too). Are these the only drains or is there another?

Also, there's a 3rd petcock between the heat exchanger and mixing elbow. This is ~1" rod for opening/closing the valve. What is this for (I think for draining/bleeding seawater)?

Thanks
Don

[ggray]

I think you have it right Don. 2 freshwater drains and 1 raw water drain.
Are you changing coolant type?

[Capt.Don]

Yes - had unknown green coolant. Research on the net recommended Texaco Long Life PC7991/7998), Havalon Extended Life (PC7994), Dexcool Long Life (GM) or Prestone Extended Life (PCAF888). Bought a gallon of Dexcool and distilled water. I'll attempt tomorrow!

[ggray]

Just make sure you thoroughly flush out the old. I'm told that if there is contact between the two, there is some undesirable reaction.

I flushed with a radiator cleaner and then freshwater.

[Capt.Don]

Good idea - I'll pickup radiator cleaner too. Do you know what temperature the 3GM30F should run at? I'm finding at 2800 RPM, the temperature is solid 180 degrees F. This is consistent with what I've read about the thermostat starting to open at 160 degrees and fully open at 180 degrees and the normal operating temps of around 185 degrees. This seems fine to me, but just wondering, as there are posts of this running at 160 degrees too.

[four winds]

I put Dexcool in my 3gm after a fresh water pump replacement. I did not completely drain the system, only what escaped via the pump removal. I believe this was the vast majority of the old antifreeze as it is now the color of Dexcool instead of the other color.

Can anyone say more about the issue of mixing different antifreeze please?

My water jackets were crystal clean behind the pump. So I should drain and replace if there could be a problem with my mistake of not completely draining the old stuff.

[Capt.Don]

You should not mix the green and orange coolants. The claim is that the different additives to ethylene glycol create a sludge that could block the flow of coolant. As per my original post, I've started this process, flushed a couple of times and still have a diluted green solution, which is why I didn't think I found all the drain valves. I want to make sure I completely drain the old coolant and will probably flush a couple more times just to be sure, before adding dexcool.

[ggray]

Originally Posted by Capt.Don

Good idea - I'll pickup radiator cleaner too. Do you know what temperature the 3GM30F should run at? I'm finding at 2800 RPM, the temperature is solid 180 degrees F. This is consistent with what I've read about the thermostat starting to open at 160 degrees and fully open at 180 degrees and the normal operating temps of around 185 degrees. This seems fine to me, but just wondering, as there are posts of this running at 160 degrees too.

I really don't know; i don't have a gauge!

[Capt.Don]

I completed flushing the unknown green coolant from my Yanmar 3GM30F and replacing with Dexcool (pink). I used a radiator flush product and repeated with water until the flush was clear. This took an additional 4 cycles. What I did was (1) open filler cap on top of the heat exchanger, (2) open two coolant drains, one on port side behind the alternator and the other on the starboard side by the oil dipstick, (3) let coolant drain (takes about 5 minutes), (4) remove water heater hose, blow coolant out of hose/heater, (5) close drains, (6) fill the heater hose with water and reconnect hose, (7) fill heat exchanger with a little over 1 gallon water, (8) run engine till reaches temperature (180 degrees F), monitor temperature gauge, run additional 10 minutes, verify water flow through heater by feeling temperature of hoses, (9) shut off engine, let cool, (10) repeat. Along the way, I cleaned out the overflow bottle.

Although this process is not difficult, it is time consuming. Each cycle took about 3/4 hour, running the engine 10-15 minutes, letting cool 10-20 minutes, drain and refill. The challenging part was filling the water heater hoses to avoid an air blockage and so there'd be circulation.

To complete this will be motoring at high RPM, monitoring temperature and coolant levels. Now to consider changing fuel filters and changing the oil!