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Hot water expansion tank? something else? necessary?

WhiteNoise

Member III
I have removed the hot water heater from the system. There"s a square tank that seems to me to be an expansion tank in the water circuit on the motor, I would suspect as part of the hot water system in the circuit. I am thinking of removing it also and would like to see what you guys think. Here's my logic:

I had a marine mechanic previously look at the motor after I rebuilt it. I was having trouble bleeding the air out of the system, causing random overheating. He said the rebuild was done well and the air issue is common after a rebuild. He was able to remove all the air and resolved the overheating.
He recommended I remove the expansion tank as he saw it as a high point in the system and a possible place for air to be trapped.

What do you think?
 

Cory B

Sustaining Member
Our boat had a square expansion tank (different than the "fill" tank over the engine) for coolant in the lazarette when we bought it. When I replaced the WH I removed it from the system and added in-line valves at the hose high points (above both WH and engine) to bleed air from the system. We've had no problems since, and gained a little laz space in the process.

You could probably bleed the system from the expansion tank by cracking the cap while the engine is running - I think thats what Ericson intended. And if you no longer have a WH, I'd get rid of it.
 

newpbs

Member III
Stop

I would not remove the expansion tank. This compartment allows the heated water to travel into the tank as it expands. Your engine uses this reservoir to draw from when the coolant contracts.The tank also holds extra coolant in the event that you have a small leak in the system. The tank should be located in the highest point of the system and as such would not add to any issues regarding air in the coolant.

Look under the hood of your car. You will find an expansion tank there as well.

Paul
 

Gary Peterson

Marine Guy
Stop - Stop

Paul is absolutely correct.

This is why I have said before don't have mechanics reconfigure your application. Marine application engineers have done this work on pre-release models and the results have been validated to the approval of the engine manufacturer.
 

Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
I have a friend with an M-25 Universal in an '83 Ericson. Very similar tank was/is present, from the factory. That engine has a pressure cap on the manifold and on the metal tank.
My '88 M25XP has no such metal tank. My engine does have a plastic "overflow" bottle that is connected by hose to the nipple under the pressure cap and holds a cup or two of coolant.

Loren
 
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Greg Ross

Not the newest member
Overflo

Whatever you call it, an internal combustion engine needs the overflo resevoir. If you remove it you'll be topping up the coolant for the rest of you life. When the engine reaches operating temperature the coolant expands and has to go somewhere, either into the overflo tank or strtraight to the bilge.
 

mherrcat

Contributing Partner
You should have both an overflow tank with a connection to the fill cap on the engine and an "expansion" tank between the engine and the hot water heater. That's the configuration on my E30+ with Universal M18. Check the 30+ System Plan drawing in the downloads section. There is a note on the drawing next to the expansion tank that says "Universal only", so it may only be present on boats with that engine. (I think it is called an "accumulation tank" on the drawing.)

I removed my water heater to replace the fuel tank. Rather than removing the expansion tank I just removed the hose from the tank to the heater and looped the hose from the engine to the heater back to the tank. The WH has been out for several months and everything works fine; no overheating.

Just like a car, the overflow bottle should always have a couple of inches of coolant in it. Eliminates the need to remove the engine cap to replenish coolant; but the cap on the bottle is a little hard to reach through the port lazarette. I end up using a funnel and a short piece of hose, but have only had to do that after losing some coolant when replacing the thermostat.
 
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Cory B

Sustaining Member
I think as others have stated, there are 2 "extra" coolant tanks on some Ericsons. There is what I've been calling an "expansion" tank (probably "accumlation" is the better term) that sits inline with the coolant system in the lazarette, and the traditional overflow/fill tank that sits above the engine.

We've removed the "expansion"/"accumulation" tank with no problems (I believe it was put there simply to aid bleeding the air from the coolant due to the waterheater). I was NOT advocating removing the fill/overflow tank in case there was any confusion.
 

Gary Peterson

Marine Guy
The overflow bottle is unpressurized and connects by hose to the heat exchanger cap. The overflow bottle's hose connection has to be on the bottom and always has to be covered by coolant when the engine is cool. The correct heat exchanger cap has to be double sealing and double acting. It has to make a pressure seal when the engine is hot and a vacuum seal when the engine cools. One can tell the correct cap by the two seals inside. This fact allows the coolant overflow bottle to be mounted above or below the engine. It will work in either position.
 

WhiteNoise

Member III
All great input. Thanks so much.

To clarify, the mechanic I had on the boat was a "marine" mechanic but, by evidence of me posting here, I always validate important changes/modifications no matter how good the info may seem.

I must clarify, I am speaking of the metal tank, not the tank that feeds the manifold. I was thinking of configuring as Loren had described on his M25XP. I have the heat exchanger cap that is "double sealing and double acting" on the manifold. Below that cap is the connection for the overflow tank which I gather should be able to act as an expansion tank also?

I have seen the "2 extra" tanks on other boats but all had hot water heaters which I no longer have nor plan to put back in. The hot water heater necessitates more coolant and therefore causes more expansion. Maybe the hot water heater has nothing or everything to do with it.

Now I am a bit unsure.
 

Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
I sent this thread over to an expert marine mechanic, and got this reply:

"I've seen the metal expansion tanks or resevoirs on many of the older boats, especially with hot water heaters. Mine is stainless steel and mounted high and holds about 3 quarts, it has a pressure cap and that is where I check my coolant level. Many hot water tanks are located at level or higher than the engine therefore trying to top off the coolant level and bleed air out of the sustem would be a challenge without high mounted expansion or surge tank that is pressurized."


I should also point out that our boat has a hot water tank, and that the tank was mounted quite low in a lazaret. Perhaps that's why our particular installation never had the additional high-mounted expansion tank installed.

Loren
 
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WhiteNoise

Member III
Thanks Loren

So it would seem that because I removed the hot water heater the metal expansion is probably unnecessary.

I am looking to remove this for two reasons, lack of space and to simplify the system. Removing it would exclude some failure points for air leaks, two less hose fittings, etc.
 

WhiteNoise

Member III
Found the answer

This quote is from www.marinedieseldirect.com. I included the link down below. I thought this would be good info. Thanks much for everyone's input!:egrin:

"The manifold serves as the engine expansion tank to allow for expansion of coolant as it is heated. You also fill the system at this point. In some cases when hot water heaters are installed an expansion or surge tank may be required to prevent air from entering the system."

http://www.marinedieseldirect.com/universal/200157/universal-owners-manual-seawater-diagram.html
 

Gary Peterson

Marine Guy
Loren,
That is correct. It is easier to have an additional tank to add capacity above the highest point in the system but it has to be connected to the original H/E tank by a hose or pipe system with the engine H/E cap removed and plated over. There has to be a small coolant bypass hose from the thermostat housing to the additional hard piped tank. If not, then there is no coolant flow in the new tank and as a result it won't help in the cooling process. Then if an unpresserized expansion tank is used, it attaches to the new tank at the filler neck making sure a double acting cap is used.
 
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