Lost antifreeze yesterday, but not today

[jalmberg]

We are on our way south through the Chesapeake. Yesterday we had a good wind, so only had our Mercedes OM616 Diesel engine on at the beginning and end of the day... maybe a half hour on each end,

When I did my daily engine checks this morning, I discovered that about 1.5 quarts of antifreeze had ended up in the bilge. Since I check every day, I know it wasn’t there the day before.

This morning, I topped off the antifreeze, ran the engine up to operating temp (185 F), with the engine in reverse at about 1400 rpm. After an hour of this, nothing had leaked. There are only two short hoses in the antifreeze circuit. Both seem sound and tight. No leaks there. The cap seem okay. Unfortunately, there is no evidence of the leak on the engine. I.e. nothing obviously wet from yesterday, other than the floor of the bilge.

I’m a bit at a loss. I expected to find a cracked hose or something fairly simple. What else can leak?

Any experience or thoughts much appreciated.

TIA,

John

[rslifkin]

Was the system (or overflow tank if it has one) too full? If it's overfilled and you work it hard and get things good and hot, it can end up puking antifreeze out of the overflow. Especially if the pressure cap is weak.

[jalmberg]

No, I always fill to the same level: about an inch headroom in the tank.

[Bill O]

When was the last time you changed your pressure cap?

[Tayana42]

Have a careful look at the connections to your water heater. I’ve had a small leak there that caused a loss of engine coolant. That was easy to miss.

[jalmberg]

Originally Posted by Bill O

When was the last time you changed your pressure cap?

Well, not since we’ve had the boat (3.5 years.) It could be quite old.

If it was the cap, how would the antifreeze come out? Not as a spray, I dint think, or everything in the engine compartment would be wet. There is a thin tube adjacent to the cap. I wonder if it could flow out of that some how. That would be neater and leave less trace.

[jalmberg]

No water heater. No connection to any other unit that I can see. It’s a very simple engine.

[rslifkin]

The thin tube next to the cap is the overflow tube. If the cap is releasing at too low a pressure or the inner cap seal is bad, the coolant would exit through that tube.

[jalmberg]

Originally Posted by rslifkin

The thin tube next to the cap is the overflow tube. If the cap is releasing at too low a pressure or the inner cap seal is bad, the coolant would exit through that tube.

Yes, I just inspected the cap and tube and can see how it works now. The stopper in the cap is a bit soft. I think you nailed it. I’ll have to keep a close eye on it until I can find a replacement. Thanks for pointing me in the right direction.

[Captain Puget]

I had a similar, periodic problem. It ended up being an air lock due to the height of the expansion tank from the cooling fluid connection on the engine being insufficient. I changed the engine connection plumbing to the bottom of the engine vs the top of the engine, adding about 2 feet of “head” … never had the issue again.

[EmeraldCoastSailor]

Originally Posted by rslifkin

The thin tube next to the cap is the overflow tube. If the cap is releasing at too low a pressure or the inner cap seal is bad, the coolant would exit through that tube.

But wouldn't it go to the overflow reservoir? It should not leak.

I just solved a coolant leak on my Yanmar that was the filler neck seal with the heat exchanger after replacing pressure cap. JB Weld to the rescue!

[rslifkin]

Originally Posted by EmeraldCoastSailor

But wouldn't it go to the overflow reservoir? It should not leak.

I just solved a coolant leak on my Yanmar that was the filler neck seal with the heat exchanger after replacing pressure cap. JB Weld to the rescue!

If there is an overflow reservoir, yes. But some engines don't have one and just rely on a little air space in the heat exchanger to avoid overflows. And a too-full overflow reservoir can also end up overflowing, especially with a bad pressure cap where it has to absorb more fluid than normal.

[jalmberg]

Yes, we don’t have an overflow reservoir. It just goes into the bilge. I might rig up a container to catch the overflow, just to keep the bilge dry.

Well, I cleaned up the cap a bit and was careful to screw it back on properly. We motored south on the Chesapeake for about 4 hours, checking the engine every 15 minutes. No problem again. One more day and we will be in Solomon Island where we should be able to track down a new cap. I think it’s a standard size: 68 mm. I will buy a spare for good measure.

There was a bit of grass (not much) in the raw water strainer. I wonder if that could have raised the temp just enough to cause a problem, though we didn’t see a change on the temp gauge.

Just wondering about the cap pressure rating. The current cap has a pressure release button. There doesn’t seem to be a lot of pressure at operating temp.

[jalmberg]

Your system sounds more complicated than mine, which is pretty self contained and compact. There are only two very short hoses in the antifreeze circuit, and it’s been working as is for about 35 years, other than needing periodic cleaning.

[billgewater]

When did you last do a coolant change?

Apparently it should be changed regularly dependent on manufacturer's recommendation. Generally the radiator repair folk can advise when and what type to use.

Be sure you are aware of what type A and B mean. Type B does not contain antifreeze. Some types have an altered boiling point.
Examine the removed coolant carefully via its engine block drain. If it has any black or other stuff in it, it may be a sign of head gasket problems. (e.g. exhaust gas leak into the coolant)
Generally the pressure cap is designed to open at fairly low pressures e.g. 7 psi, but make sure you check the engine manufacturers advice. These caps do fail.