Concerned with Closed System Coolant Leak

Hampton

Hampton

Air Defense Dept
TECHNICAL Contributor
Nov 26, 2006
7,628
Panama City, Fl
Boat Info
2008 44 Sedan Bridge
Engines
Cummins QSC-500's
Straight Drives
I found a few drops of engine coolant on the engine room floor on the port side of the port motor when viewing the motor from the back of the engine room (looking forward, engines mounted with serpentine belt facing aft). This was last week.

I traced it up to the port side of the heat exchanger. It seemed to originate from the fitting leading to the FW coolant hose on that end. I decided to replace the fluid (top off the reservoir) and keep an eye on it. I took the boat out for 30 minutes last week. Today, I opened the Engine Room hatch and found lots of coolant outboard (port) of the stringer which support that engine.

Soooooo, I started it and warmed it up today. I ran it at 1800 RPM at the dock. I found that the coolant was leaking out of the top of reservoir due to being over-filled (imagine that). The coolant looks pure - not mixing with any other fluids that I can tell. If it is just over-filled, why did it just begin to put out a few drops recently (I don't think I had filled it before I saw the drops in the bilge). Perhaps I have a small leak, then when I filled it up I caused the over-flowing to begin.

Questions:

How long would you expect the heat exchangers to last being slipped in salt water in Fl?
If it developed a leak, would it be likely to over-fill the coolant reservoir?
Is this something to keep an eye on or get to the shop ASAP?
How did the fluid get outboard of the stringer? Does it have a leak that sprays out?
We hare planning a 100-mile round trip on the ICW tomorrow. To go, or not to go?
 
John:

Don't you have overflow resevoirs? If so, then you really can't overfill the HE. You may just have a bad pressure cap. you could try switching caps from the other engine and see if still leaks.
 
Sounds to me that you probably have a faulty gasket or hole in your heat exchanger and you're "making water". This can cause raw water to be added to your coolant. Since you found "lots of coolant" in the bilge I'd solve the problem before cruising. I'm assuming the expansion tank is still full? Pull the cap and check. If it's full, and you're still dumping coolant it's got to be raw water mixing in. A pressure check of the cooling system should confirm the problem. Assuming it fails to hold pressure, pull the heat exchanger, have the core cleaned/pressure tested, then put it back together with new gaskets.
 
Yes. I'm talking about over-flowing from the reservoir after I (probably) over-filled it. I imagine it's supposed to leak once you over-fill it, right? It couldn't hurt to switch 'em out and see what happens, though.

I'm a little baffled that after running on a plane for about 10 minutes, then idling around at 1250 RPM for another 1/2 hour last week, that today at 1800RPM at the dock it spilled more out. I would think that any excess would be dumped out by now. Could I be making coolant via a leak in the heat exchanger? Like I said, it doesn't look like it's mixed with anything, but a little salt water would probably be imperceptible. Anyone know if the heat exchangers are covered under the extended warranty? It's a Merc Extended Warranty which is the same as the original warranty, but longer.
 
Put new caps on and keep extra coolant aboard, then watch. You may need to stop a few times to monitor, but clean it up and make sure that's where the fluid is coming from.
 
OK - Should they drain the fluid out when the fluid level reaches the bottom of the cap?
 
The fluid should be right at the top of the HE reservoir, not all the way up to the camp lip. The coolant overflow reservoir should have a "hot" and "cold" mark on it.
 
oops...I mis-read your post....you ARE leaking out of the top of the resevoir.

When the engine is cold....where is the level in resevoir? It should be at the mark "cold". If it is, and you are still overflowing from the top when hot, you could be leaking water into the coolant side from the Raw Water side.

Try a new cap...or switch caps and see if the problem follows the cap. In the mean time, you could also send a coolant sample out for analysis....from both engines. That should tell you if there is saltwater in the mix.
 
I'll try tasting it.

I haven't noticed a "Cold" or "Hot" level, like a car. Mine are pretty full and always have been. They are within a inch of the top when cold. I'm guessing now that that is too full.
 
I just found out that we're on for tomorrow. Anyone see any reason to not go?
 
John,

Have a good trip and stop overfilling the reservoir :) As a guideline, never fill the reservoir more than halfway. Heat expands most fluids and the heat exchanger pressure cap relieves that expansion by letting fluid into the reservoir and bringing it back in as the engine cools. The heat exchanger pressure cap can have seal and pressure problems. It is an inexpensive and easy replacement item.

-John
 
tobnpr said:
Sounds to me that you probably have a faulty gasket or hole in your heat exchanger and you're "making water". This can cause raw water to be added to your coolant. Since you found "lots of coolant" in the bilge I'd solve the problem before cruising. I'm assuming the expansion tank is still full? Pull the cap and check. If it's full, and you're still dumping coolant it's got to be raw water mixing in. A pressure check of the cooling system should confirm the problem. Assuming it fails to hold pressure, pull the heat exchanger, have the core cleaned/pressure tested, then put it back together with new gaskets.
Click to expand...


I missed this post 'til just now. I'm going to watch the level to be sure that it's not making water. I believe the first couple of drops may have been due to a leak at a hose fitting. Loose hose clamp? Corrosion? Then, I over-filled it and this other stuff started.
 
John,

My guess is that it was just a loose clamp that started the whole thing. Have a good trip.

-John
 
Thanks again, John.

I see you're a Master Mechanic.

How long do the heat exchangers generally last in salt water?

I have 253 hours and splashed in Aug '04.
 
John,

I always stay away from the "religious" questions on this forum :). Any question that begins with "How long should it last......" turns into everyone jumping in with their opinions. Mercruiser engineering will tell you that factory FWC is designed to last the length of the engine. That is a bit of doubletalk.

The first 1000 hours of a gas engine's life will determine if it will even make it to 2000. Saltwater versus fresh water makes a huge difference. In saltwater, I would have them removed and inspected every 3-5 years depending on use. It's a simple job and the gaskets are inexpensive. Some might want to do it sooner and others will say that they have 2000+ hours and have never had them pulled.

-John
 
Oh, and John, I want everyone's opinion!

Frank helped me out with this one. It turned out to be nothing. We ran it about 125 miles the last 3 days. All went well.
 
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