18 hp Yanmar overheating after replacing domestic wate hoses

[steveebryant]

Anyone know anything at all about small diesel engines?
I had to replace a hose that ran from the engine to the domestic water heater on the boat. Of course a lot of coolant ran out. When I reconnected the hoses and filled that part of the water system, the engine started to overheat.
On this 18 hp Yanmar, there are two separate water systems. One for heating domestic water; this is a closed system which employs a heat exchanger of sorts and is the system that I was working on. The other water system is use for cooling the engine; this system takes water from the lake to cool the engine. To my knowledge, the two systems are not connected.
The engine has been run a total of 20 hours since I have owned it and it has never over heated. After I changed the domestic hot water hoses, the engine will get hot after running but a few minutes.
Anyone got a clue what might be going on?
Thanks,
Steve

 

[Ralph Johnstone]

Air ........................

Usually happens every time you even "think" about your engine coolant. :cussing:

Just make sure your coolant tank is as full as possible and look for any and all high points from which to vent air. Run your engine for a minute or so and feel around on the coolant outlet from the block to make sure it's warming up. If not, fill the tank again, vent the air again and again ad nauseum until you have circulation.

Once it does start, it's good until you remove coolant again.

 

[Steve Dion]

Steve: Have you tried removing the return hose from the water heater. You want to be sure that you have removed as much air as possible.

 

[jibes138]

closed loop system

I just did exactly what you describe. I replaced my hot water heater. Since the coolant system is a closed system with the radiator cap sealed tight there is no where for the air to go in the system. You need to fill the coolan tank, then run the engine until the thermostat opens an starts circulating the coolant. Now when this happens the coolant going throught the thermostat will no be cold and it will shut again so it takes a while to get the thermostat open and continuously circulating the coolant. Use a plastic cup with 50/50 antifreeze/water mix and keep filling the coolant tank as the level drops and air is released. watch the temp gage and if it overheats shut her down and let it cool off then repeat. Air will continue to bubble out until the heater ank is full of coolant. Once it is circulating continuously and the bubles have stopped with the engine in gear let her run under load for a while. If the temperature is about where it normally is and steady state you should be ok. The speed of the circulation helps get the air out so run your engine at a faster than idle RPM. This process worked well for me just last weekend.

 

[Stu Jackson]

Burping the coolant lines

is what you need to do. jibes is right. Another way to do it without dealing with engine overheats and loosening the petcock at the top of the thermostat housing is to simply assure yourself that BOTH of the hoses to the hot water heater are full. How? Although for my engine, should work for your, too: http://c34.org/bbs/index.php/topic,4518.msg26462.html#msg26462

 

[Prime Time]

Trouble shooting

If the previous posts don't help, go back to basics
1. Are you making water out of your exhaust?
2. Check the level of your coolant when engine is hot?
3. Is the thermostat opening?
4. Is the fresh water pump for the coolant working?

 

[Maine Sail]

Air Bound

As others have said your sealed system is air bound. You may have a pet cock that looks similar to the one below located somewhere near the top of the engine. If you loosen it it will bleed the air so long as it is the highest point in the system.

It will look like this:

Here's an easy way to bleed.

1) Remove radiator cap.
2) Start engine and let warm up.
3) If fluid is low add some coolant.
4) Crack the pet-cock and allow the air to be purged from the system and close it as it burps out.
5) Wear gloves and use a rag when cracking the pet cock as it will be hot.
6) With the engine circulating fluid, and the cap off, top up the radiator fluid and re-install the cap.
7) Depending upon how much fluid you lost it is sometimes quicker to remove the t-stat, put antifreeze right into the t-stat housing until full, re-install the stat with new gasket, and then circulate and purge as above..


Because I change my antifreeze on a regular basis I installed a set up with a 1/4 turn ball valve and a PVC hose that automatically becomes the highest point in the system.

it sure makes bleeding air, and topping up the system as easy as it gets. Dex-Cool antifreeze HATES air and the two can wreak havoc on the engine internals:

This is how I purge air now (one of the neatest and most handy little tricks I have come up with):

 

[Stu Jackson]

And the hose from the valve

goes where?

Nice illustration. The M25 series have the same petcock on the top of the thermostat housings, too. My link to the burping includes the suggestion to fill both lines from that housing. If you're changing your thermostat, too, at the same time, fill 'er up right from there, good idea.

 

[Maine Sail]

goes where?

It is just zip tied to the HX for my refrigeration and it is aimed at the engine sump when not in use. I purposely left it long enough to make it useful. When I need to use it I simply cut the zip tie and stick the end into Coke bottle or similar and crack the valve..

Nice illustration. The M25 series have the same petcock on the top of the thermostat housings, too. My link to the burping includes the suggestion to fill both lines from that housing. If you're changing your thermostat, too, at the same time, fill 'er up right from there, good idea.

Yeah, it just dawned on me one day that we use similar valve/vents on hydronic heating systems so why not just use a quarter turn valve with a hose connected to keep it neater, easier and cleaner than the .59 cent pet cock... The hose also extends and creates the "highest point" in the system too. Works amazingly well.. Cost about $6.25.. or about the same as the paper towels I'd use cleaning up spilled antifreeze..

 

[jibes138]

Chipped Paint

Hey Maine Sail I noticed a couple of spots on the bolt for your alternator adjustment has paint chipped off. What up with that homey? Perhaps you are slowing down a bit in your old age and not keeping up with your maintenance to perfection?

 

[Maine Sail]

Hey Maine Sail I noticed a couple of spots on the bolt for your alternator adjustment has paint chipped off. What up with that homey? Perhaps you are slowing down a bit in your old age and not keeping up with your maintenance to perfection?

Darn single part paints just aren't as tough as they used to be..