3GM30F problem

[tcbro]

I have a problem with my 3GM30F. I'm loosing the fresh water. I can't figure out where it's going. There is no evidence of a leak, no accumulation of water under the engine. To my thinking, it must be going out the exhaust through 1 of 2 ways;
1. through a leak in the heat exchanger that bleeds it in to the raw water then out through the mixing elbow.
2. through the cylinders (oh no!).

Anybody have any ideas?

Tom
s/v Orion's Child

 

[markwbird]

check the oil to see if there is water in it. It will be milky and bubbly.

 

[Rick]

Tom... need more info. When you say water, do you mean antifreeze? You mentioned fresh so I am assuming. Any antifreeze in the bildge? Do you have a hot water heater in your cooling circuit? Could be a leak in the lines or even corrosion at the heater itself. Blending antifreeze in the raw water circuit would probably show some evidence somewhere maybe even the color of your exhaust water.

Suppose the exchanger could have a crack or leak but pretty rare.

 

[tcbro]

OK, the oil is good, no white stuff. That was the first thing I checked.

My overheating alarm went off as I was exiting the marina. Luckily, I was able to get the jib up and kill the engine. I sailed out and away and set my hook. I then proceeded to check the raw water side starting with the thru-hull and ending with the pump impellor. Everything was fine. I opened the pressure cap on the heat exchanger and it was dry. My service manual actually suggests water with an anti-corrosive additive unless there is a possibility of freezing. I didn't have the additive or the antifreeze so I just put the water in figuring that it would get me through the last month or 2 of the season. Now, I check it before starting and have to add a few ozs every time I start up depending on how long the engine has been running.

There was no antifreeze under the engine or in the bilge. Right now there isn't even any antifreeze in the engine.

I would think that if it going through the cylinders (bad head gasket) I would see steam coming from the exhaust. I see a bit of white/grey smoke but nothing unusual or excessive. Of course, the little I'm loosing probably wouldn't make much steam.

Thanks for your interest,
Tom

 

[tcbro]

OOPS! Yes, there is a hot water heater in that circuit but we did not notice antifreeze or odd smells coming from the faucets.

Tom

 

[Rick]

Antifreeze is also anti "boil". Straight water will evaporate and does not have the cooling qualities of antifreeze. And if you leaking straight water in the heater lines or at heater, unless you have a dry bildge its gonna be hard to spot. Your not going to smell a leak at the faucets and the antrifreeze/water will not be in your fresh water tank. Antifreeze circulates around your heater to heat the water in its 6 gallon tank for your drinking, cooking, shower fresh water supply. Inspect the heater itself and fittings. The lines are tough because the are usually hidden beneath the sole. But if they are leaking you will see antifreeze in bilge.

Do some reading about antifreeze types and make the decision if you want to add it to your fresh water circuit. Me.. I would. The reason I say that is you CANT mix antifreeze types. Your either pink or green. Because it is colored it will be easier to spot.

Dont think this is anything major. It might just need to be filled up with coolant! And when you have a heater loop it is quite common to get and airlock so when you think its full, its not. Takes patience to burp the system sometimes. Its not going through your cylinders so dont worry there. It wont run on water! If you have a blown headgasket, the water will be in your engine oil. Dollars to dognuts thats not the problem.

 

[Calif. Ted]

My 3GM30F is VERY particular about the radiator cap, the $17 Yanmar cap has a larger diameter gasket at the top than a $5 cap from the auto parts store. I don't want to reveal how long it took me to figure out where and why I was losing a little coolant every time the engine warmed up.
There wasn't always visible coolant from the leak, and when there was it was difficult to track that it had come from the mouth of the filler. The most apparent symptom was that the overfill reservoir was not functioning correctly.

 

[Charles Erwin]

Obtain, rent, borrow a radiator pressure tester from the auto supply. Fill and pressurize the cooling system to 13 PSI or whatever your radiator cap value says. I usually pressurize about 3 psi higher than the cap value. Pressure should not drop during the next half hour or so.

If the pressure drops you might be able to hear or see the leak. Consider the hoses and clamp joints that that transport coolant to and from the motor block or possibly the thermostat housing gasket. Perhaps a heat exchanger gasket is leaking. If so coolant or air will pass into the seawater side of the heat exchanger and you might hear bubbles at the sea water discharge hose if you disconnect it and listen.

This is the cheapest and easiest diagnostic tool you can use - and while it takes a bit of imagination to get precise results there is no motor disassembly required. Anyway it is far better than guessing.

Speaking of guessing - based on your evident lack of coolant leaking inside the boat it is likely the heat exchanger is leaking coolant to the seawater side and so coolant is discharged to the exhaust and overboard.

Charles

 

[tcbro]

Losing coolant

Well, there WAS antifreeze in it. I just replaced it with water because that was all I had with me. I don't want to replace the antifreeze until I figure out where it's going. So, at the initial loss of coolant, there was no antifreeze in the oil, under the engine, in the bilge or coming from the hot water heater.

Rick, I thought maybe small amounts might be leaking into the cylinders, turning to steam and exiting through the exhaust valve.

I'll follow Charles idea about the pressure checker. I have a friend who probably has one (if he can find it) for automotive use. Ted, Ill check the gasket diameter on the tester before I use it. That's a good thing to know. I would have thought that an automotive cap of the same rating would work.

Thanks for all the input. I'll have some stuff to do/check on my next trip to the boat (2 weeks).

Tom

 

[Charles Erwin]

Kindly let us know your results - otherwise nobody will learn anything

 

[tcbro]

Roger,

Will do.

 

[Rick]

Good luck and they are spot on about the radiator cap. Very finicky. The pressure tester will probably yield a drop in pressure. Now you know that you have a leak. Where? Tough one. This is outside the box but what if you put a little food coloring in the water so it was other than clear. Might be worth a try.

Hang in there

 

[Rick D]

Second everyone's suggestion to check the water heater. I have had coolant loss before that didn't get into the fresh water system but rather was lost at the connection to the heat exchanger. The insulation in the heater was soaked when I pulled it.

 

[richk]

tcbro
I had a very similar problem with my 3GM30F on previous boat. Turns out the loop going to the water heater went through a stringer and the hole in the stringer wasn't big enough. Over time, vibration wore a hole in one of the hoses and all the coolant leaked into the liner. Made hole bigger, replaced hose. Solution found.

 

[kloudie1]

Yup.. check radiator cap and coolant catch-bottle system. If the cap is working correctly, the bottle should make up any leakage.. and you should be able to see the drop in water level there..A small leak around the cap gasket or around the spot where the "overflow tube is attached at the cap neck would allow leakage that would evaporate quickly and be hard to find.. Try to get some antifreeze in quickly because that is what is protecting the expensive heat exchanger from corrosion.

 

[Claude L.-Auger]

The idea of a pressure tester is great. I suggest you get yourself of short piece of hose same size and diameter as the ones going to your hot water tank. Disconnect the 2 hoses and install the short piece where there were clamped on the engine. You now have by-passed the hot water tank and can check the engine accurately. Follow the advice and fill with coolant. It is a lot cheaper and easier than replacing parts. Run engine and burp it. Add coolant as necessary. Put coolant in the small plastic reservoir. Now use the tester. If you have no loss of pressure your engine is in good shape and the leak (or air pocket) is either in the hoses or the hot water tank itself. Once your satisfied that the engine is OK, reconnect the hoses (connect one end and raise the the other as high as you can then fill with coolant before connecting the 2nd one). Run the engine and burp it again. Add coolant if necessary. Then use pressure tester again. If there is a leak in the hoses or the tank you'll notice it immediately. Good luck.

 

[mz4wheeler]

Antifreeze is also anti "boil". Straight water will evaporate and does not have the cooling qualities of antifreeze.

Antifreeze (only) provides the following:

1) Anti Freezing
2) Anti Boiling
3) Anti Corrosion

Pure antifreeze has TERRIBLE cooling qualities. What cools the engine is DISTILLED water (has a lower boiling point) that is mixed in with the antifreeze.

So, it's a trade off. We put in enough antifreeze to perform 1-3 but the actual cooling is performed by the water.

Always use "pre-mix".

 

[Rick]

Antifreeze (only) provides the following:

1) Anti Freezing
2) Anti Boiling
3) Anti Corrosion

Pure antifreeze has TERRIBLE cooling qualities. What cools the engine is DISTILLED water (has a lower boiling point) that is mixed in with the antifreeze.

So, it's a trade off. We put in enough antifreeze to perform 1-3 but the actual cooling is performed by the water.

Always use "pre-mix".

Nice catch MZ. Miss spoke myself but I meant premix like you said. Very subtle I might add.

Cheers