4BY2 & 6BY2 coolant temperature-what a new owner should know

Vikie and Al,

I ran the engine several times while feeding antifreeze into the heat exchanger. I do not think it is air, she makes lots of hot water and ‘bus heater’ hot air.

On my R25, it is easy to inspect the flow of water by looking into the sea chest.

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where do the hot water line for the hot water heater and bus heater join"??????
 
It might be worth the cost to get a UV leak detector kit (dye, light, and glasses) to find or rule out leak locations. But, before that, I'd want to be sure the coolant recovery system is working right. The Yanmar spec sheet I found says that engine holds 10.6 quarts of coolant. Assuming that the external hoses and coils associated with the DHW heater and the "bus heater" bring the total coolant capacity up to 18 quarts and that the expansion factor of the coolant is 6%, that's about 1 quart of coolant that has to escape the pressurized system as the operating temp reaches max and then return as the engine cools. Is it possible the Yanmar expansion tank is too small to handle the extra capacity from the house system? On my R27, I would close the 2 valves that isolate the house circuit and see if the symptoms persist.
 
Crunch,

I'm quite sure the coolant recovery system is working. I filled it three times during the last three tests - essentially everything went into the engine.

I may be experiencing more than one problem????

I decided to remove the "bus heater" and hot water heat exchanger from the system to eliminate the possibility of leaks where I can't see then,

A true rat's nest. The engine has 19mm/3/4" tubing coming from the water pump and the return line. As expected, since these sizes are "taken", the bus heater and hot water heater use 5/8" line. Rather than employ a 3/4" to 5/8" adapter, or even two barbs and a coupling, the builder, previous owner, or a stranger on a bed that weighs 400 pounds came from the engine with a 3/4" barb to 1/2" NPT, a 1/2" NPT elbow, a 1/2" NPT to 3/8" barb, some strange 3/8" tubing, another 3/8" barb to 1/2" NPT and a 1/2" NPT to 5/8" barb - the mess held together with 4 hose clamps. There were two of these on my boat - and a total of 3 broken hose clamps - hard to inspect place that I messed during the yearly checkout.

I took the mess out and put in a 5/8" barb to 1/2" NPT elbow to 3/5" barb with two high quality hose clamps. I used one of these since I took the heater and water heater out of the circuit temporarily.

I added a can of radiator cleaner when I refilled the system and ran it for 15 minutes to circulate the cleaner. Later today or tomorrow I'll try it at speed to see if it overheats.

ONE QUESTION: I removed a 24 mm Brass washered plug from the lower part of the fresh water portion of the heat exchanged - expecting that to drain the coolant. Nothing came out - even though the heat exchanger was filled to the top of the cap. What does this plug do? It is near the flywheel end of the engine, below the heat exchanger with the head on the starboard side of the engine. the manual has this plug located near where they say is the coolant drain.

It would be nice to know what part of the engine has neither salt nor coolant behind it - maybe this is related to my overheat???
 
My only experience with Yanmar marine diesels is the 2GM20 in my old auxiliary sloop, so I can only speculate about the dry drain in the heat exchanger. Is it possible that the drain opening is buried under sludge or mineral buildup that has accumulated at what I imagine is the lowest point of an aft-raked exchanger. If the exchanger interior is a bunch of fresh-water tubes surrounded by sea water (or vice versa), it might be that some of them are blocked/plugged/embedded while some above them are open. That would probably reduce the engine's cooling capacity, but doesn't explain where the missing coolant is escaping from. Can you take an end plate off the exchanger to inspect it?
 
The only time I have overheating problems is when there is growth blocking my raw water inlet. I can see water coming out with the exhaust and it usually works at lower RPMs but the flow is restricted enough that if I go at turbo speeds we overheat. A quick dive and cleaning has solved the problem twice.

You've done so many other things on the system I'm guessing that you already checked this but I didn't notice it in your postings. So, just in case, I mention it.

Jeff
 
The loss of coolant and over heat may be two issues . Loss of coolant if all exterior connections are confirmed to be leak free could be a tube leak in the exchanger. It may not leak when running slower because of cooler and lower pressure in the cooling system. The higher temp At high speed could be caused by a blockage in raw water system ,reverse gear cooler. After cooler, thru hull pickup, exhaust elbow, I have seen a coolant hose deteriorate from the inside causing a blockage. A heat gun can help in trouble shooting a blockage. It is most likely something simple but hard to find. Good luck!
 
The Yanmar parts manual shows a series of hoses and valves labeled "hose, air bleeding". Are these the hoses necessary to bleed the heat exchanger after I put in new antifreeze?

I have run the engine with the cap off - several ties - and filled it to the top. I also filled the overflow bottle 3 times - only to have the antifreeze drawn into the heat exchanger when it cools.

This is the sign of a small leak. Leaks out under pressure and sucks water back when the engine cools.

I don't know where the antifreeze is going - I'm on my second gallon - but it isn't going into the engine (oil level not rising, looks normally black), not going into the hot water (no water flows out of the domestic hot water valve when the engine is running at speed) and I don't think it is going into bilge but I'm not sure since I spilled a bit when filling the engine.
 
If it is an exchanger tube leak it is mixing with raw water and going to exhaust elbow and out to sea.
 
Brian, I am afraid it is an exchanger tube. I can get the end cap off, but don’t think the exchanger can be removed with the engine in the boat.

I’ll try my ir thermometer. Good idea.

There was no antifreeze in the block when I pulled the drain plug. That is below the heat exchanger????

A leak in the reverse cooler should not matter, the manual says it is salt water cooled, as is the air charge cooler,
 
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