Yanmar 3GMF high temp alarm

[jwerkjr]

This past Sunday I had my high water temp alarm sound. This occurred on my way back to the marina after running 30-40 minutes at medium RPMs. (Wasn't monitoring to know exactly). I have checked all the obvious items and have received a few more ideas from various threads I've read on the topic that I will check but in the meantime I'd like to run these details past you guys. While out on the water I shut it down immediately when the alarm sounded. When it cooled enough to allow me to pull the HE cap I found no coolant in the top of the HE. I added about 32 oz of water which brought the level to the top. I was able to motor about 10 minutes under low rpm before the alarm sounded again. Again, no fluid showing in the HE. The next day after checking all the obvious areas in the raw and fresh systems, I ran her at the dock in forward gear at low rpms with and without the thermostat for 30-40 minutes each time. No issues. The heat exchanger got hot but not too hot to touch. The elbow remained cool. (I seem to recall reading that the elbow should warm a bit). I was able to remove the cap with a rag almost immediately after shutting the engine down and I still had fluid level in the HE. Curiosly, I left the boat to return about two hours later and found the engine still hot and the elbow hot where previously when I first shut it down it was cool. Additionally, I rechecked the fluid level in the HE and found it to be dry!! Would the normal heat from the engine transfer to the elbow once coolant is no longer flowing? I'm worried I may have a head gasket issue. I see no signs of fluid leaks but it's going somewhere. When I pulled the thermostat after returning to the dock and the engine completely cooled down, the fluid level was right to the top under the thermostat. Looks like I'm loosing coolant into the exhaust but I ran the engine without the thermostat to insure coolant was passing from the engine to the HE and the level in the engine remains ok. One other thing - when I checked the flow of fluid through the HE I observed a stream flowing through a hole approximately 1/16th inch in diameter. I will need to double check, but there didn't seem to be an observable flow from the main body of fluid, rather this almost jet like flow out of the tiny hole. I'm not sure what the flow should be under low rpm. I realize these thoughts are somewhat out of sequence but hope someone can shed some light on my situation base upon my comments. Thank you in advance!!

 

[Benny17441]

First you need to insure you have good flow of water in the raw water system. The best tell-tale is to observe the water coming out of the exhaust port. It should put out a healthy stream of water making a strong ripple behind the boat. If there is no ripple or if it is weak then you need to check the intake port, impeller, hoses, HE, mixing elbow, muffler for any obstructions. If there is a strong flow in the raw water system then your problem likely lies in the closed coolant system. From your explanation I could not ascertain that you are properly filling the coolant into the system. Pardon if I'm being overly thorough; if you pour coolant into the system with the engine not running you can get a false indication that the system is full when there might be pockets of air in different parts of the system. This could cause that as soon as you turn the engine on the coolant that you poured disappears into one of those pockets. Go ahead and remove the cap, turn the engine on and pour coolant into the system until all air is purged out. Once the engine has been running for a while and you can observe that the coolant level is constant then you put the cap back on. At this point if you open the cap at a later time and there is a significant loss of coolant level then you can ascertain that you have a leak. If the engine continues to overheat even though the level of coolant remains constant then you have a flow problem. The most likely causes for a flow problem is a faulty thermostat (actually running an engine with no thermostat can cause it to overheat), obstruction in the heat exchanger, plugged hoses or soft hoses that collapse under pressure. To check for flow with the engine running I will open up a hose at different points to determine how strong the flow is at that location. For example a common place to find an obstruction is the heat exchanger so I will open up the hose at the discharge point and check the flow. I would also open up the hose that exits the engine and observe flow. The idea is to try and identify which component may have an obstruction. If your engine only overheated once and you turned it off immediately chances are your head gasket is fine as the buzzer will sound well before a critical temperature is reached. Remember the two systems are independent of each other and only meet at the heat exchanger. Last, one of the functions of engine oil is to help maintain operating temperature so an inadequate level or poor oil condition could help an engine to overheat. The primary enemy of engine oil viscosity is heat so that it is why a change of oil is recommended after an engine overheats. So make sure the coolant system is totally full and purged of air and make sure there is adequate flow of raw water as well as coolant in the systems. Good luck.

 

[kloudie1]

Attached is the flow sschematic :
Sounds like you are losing coolant.. If there is no water in the engine oil, and the engine starts and runs ok, probably not a head gasket. If the exhaust ell is cool while the engine is running, you have some sea water flow.. There are a couple of places that coolant can go without being able to see a leak.. first might be the hoses (chafed or cracked) to/from the water heater.. under the floor, the leak would go directly to bilge without being seen.. The coolant can go into the water heater itself, but that would be rare.. If the heat exchanger tube bundle has a hole in it somewhere, or there is a leak between those systems, coolant will exit into the seawater and out the exhaust..
Running a GMF without the thermostat is not good because the thermostat on these engines closes a bypass passage while opening the main coolant flow path.. Make sure the belt tension is OK in the seawater pump drive and the coolant/alternator belts.

 

[jwerkjr]

Thank you for those quick replies. Here goes with some clarifying info. I am fairly certain the raw water side is good. I have what seems to be normal flow out of the exhaust port, at least while observed at the dock. The impeller is good (its new and I pulled the pump to check it). The HE is clear. I ran a stiff wire through each hole and found no obstructions. I disconnected the intake hose and got steady flow. The strainer is new and totally clear. I have not checked the elbow yet but doubt that's the issue since I have good flow out the exhaust. Will pull that just to see if it may be a contributing factor. All the hoses were replaced last season. As for the fresh side, I have one suspicion. I replace the two hoses going to the water heater during winterization. I seem to recall struggling to eliminate a tight bend. I will bypass the heater entirely and see if that solves the problem. The thermostat is good. I tested it in on the stove and it opened property at about 170 degrees. The engine oil is new as it was replaced at winterization. (This was my first time running the engine for an extended time this season. The only other time I've run it was when launched and moving the boat to my slip in the same marina - short distance at barely above idle speed). There is no water in the engine oil and the engine starts and runs as it should. The belt tensions are good. So moving forward, I will fill the coolant while running the engine which I did not do previously to insure no air pockets. I will bypass the hot water heater entirely and I will observe the flow through the HE. I assume there will be no flow until the stat opens, followed by an immediate observable flow when it opens. I suppose the possibility of an internal leak between the raw and fresh in the HE is possible, but if that were the case why would the level in the engine remain full? Only the level in the HE dissipates. The more I think about it, the more I suspect a crimped heater hose!
Anyway I'm still curious about a few of my initial questions: Should the elbow be cool upon normal operation or should it feel slightly warm? Would it be normal for the elbow which was cool during operation, to warm up significantly when the engine is shut down? Is that thin jet of water flowing across the mouth of the HE normal? Thanks again guys! And please don't worry about being TOO thorough! I really appreciate the time you've both taken to assist me.

 

[kloudie1]

Good clarifying info..
Elbow has a sea water passage that goes across the top down to almost where the hose is clamped on. That will stay cool when running, depending on your sea water temperature. The ell should be warmer on the under side away from the cooling passage. When you shut down, the heat from the engine will go to the exhaust ell and make it hotter because there is no internal water flow. That sounds normal.
IF you didn't burp the water heater hoses after installation, you probably have a bubble in there causing a problem.. Sounds like you are almost done burping with running with cap off and refilling .. that is a typical way to clear the bubbles.. you may have to run it with cap off until the thermostat closes, then run it up to 2000 or 2500 rpm to get the flow going.. don't bypass until you've tried the burp.. 'cause you'll have to burp it again..
The heat exchanger housing is the highest part of the cooling system so bubbles will accumulate there above the engine; the level in there is probably same as engine, but ya can't see it down half way on the tube bundle. You can see from the diagram that the bundle shroud (which is pulled back in the diagram; it normally touches the plate where the tubes are fastened) has a large hole in the side "looking" at the engine coolant outlet.. The coolant goes in the shroud there and works its way back.. The shroud also has a little bleed hole to help eliminate air pockets; that hole is looking up and would have flow out of it when the coolant is flowing well.

 

[jwerkjr]

Good call on the burping. My first action will be to run it again with the cap off to "burp" it and check for good flow at the 2500 rpm range as you suggest.

you may have to run it with cap off until the thermostat closes, then run it up to 2000 or 2500 rpm to get the flow going..

Do you mean " until the thermostat opens" ? Just want to make sure I'm understanding properly.

I'll also inspect the heater hoses by the heater to check for a kink. My next day off is next Thursday so may not get out this week. I'll let you know how things go. BTW - thx for the schematic!

 

[jibes138]

A crimped hose will restrict flow but will not change the volume of coolant in the system. If you are seeing a loss of coolant volume it is either going to fill air pockets in the system or escaping from the system.

 

[kloudie1]

Yeah.. opens.. uuuhhhh.. I might have been thinking "..closes the bypass.." but yup.. you are right..

 

[gdudik]

My training is as an auto mechanic. I work on Subarus that are notoriously difficult to bleed coolant on. My favorite tool for this is
https://www.amazon.com/Astro-78585-Universal-Radiator-Pressure/dp/B0042KOK28
This will pressure test the system for leaks and also let you pull a vacuum on the cooling system before you fill it so that air pockets are eliminated.

 

[jwerkjr]

So I was finally able to get out this weekend to test the engine heating issue, after having to change out my fuel control cable. That turned into pulling the pedestal and stripping and refinishing it. That turned into reinstalling my steering cables backwards. What fun pulling out of my slip to discover the steering was backwards. Getting back in required some interesting challenges! I must say I’m happy that’s done so all in all I can’t complain. One less thing on the “want to do” list! Anyway, after “burping” the water system my problem is solved! Ran a good 45 minutes with no rise in temp and no coolant loss! Thank you to all for saving me lots of money with your advice. I was a day away from dumping this problem onto my mechanic.