I have a puzzling coolant mystery I am hoping somebody can diagnose. As a reward for rebuilding the Westerbeke 40, I bought new gauges. When preparing to install the new water temp sender, I pumped some coolant from the Bowman exhaust cooler/manifold that is side mounted on the W40 so the block would not drain as I was installing the new sender. On completion, I added the old coolant back in via the header tank that is located in the starboard locker above the engine. Noticing the header tank seemed low to empty after adding the old coolant, I added about a quart more of 50/50 antifreeze. When I started the motor and as it warmed up, it leaked a continuous stream of coolant from the Bowman exhaust cooler cap on the engine. In the past, I always ran with the header almost full.
The engine runs at 180 and does not change, but the header is dry or extremely low. The leaking from the Bowman cap has stopped.
Should the header have coolant at all times? I wonder if the header should only be filled after the thermostat has opened and the engine is at operating temp? Heading up to Maine in a couple of days for my annual cruise and would like to resolve this question before leaving. Anybody have a suggestion about the appropriate coolant level in the header tank? I do not have a water heater plumbed into the engine BTW.....
In my Universal 5444, the exhaust manifold is the expansion tank with the 7 psi radiator cap. If coolant expands past 7 psi, it pushes past the cap into a recovery tank (right now it's a juice bottle). As engine cools, fluid is sucked back from the recover tank into the expansion tank.
The expansion tank runs at the same high pressure as the rest of the coolant system. The recovery tank is vented to the atmosphere. The highest point of the coolant system is either the radiator cap or a petcock on the top of the thermostat. This is cracked during refilling to purge air.
If your engine's exhaust manifold is designed to be the expansion tank and the cap is the highest point in the cooling system or if you have some kind of valve at the highest point ( thermostat?), you don't need a header tank. You need a recover tank to capture coolant overflow; otherwise it will drain into the bilge.
If you have a water heater or any other device through which engine coolant is routed and that device is higher than the expansion tank cap (aka radiator cap on the exhaust manifold), you need a header tank plumbed between that device and the engine (on the return hose to the engine) so the air can be purged. With a header tank up high, it needs a radiator cap that meets the engine specs (mine is a 7 psi cap) and the radiator cap on the exhaust manifold needs to be replaced with a higher pressure cap (10 or 15 pounds so it does not release before the one on the header tank. You essentially move the over-pressure release mechanism (the 7 psi radiator cap) from the exhaust manifold to the header tank.
In your case, with no water heater an no other coolant route that is higher than the exhaust manifold radiator cap, you shouldn't need the header tank.
The header tank is exist so coolant can expand in it during high temps and so air can be purged. It should be big enough for the expanded volume without over flowing and without sucking air back into the pressurized system
Unless you know how much your coolant will expand, you cannot know how large the header tank needs to be or how full to make it.
Base on the numbers for my system, the coolant will expand by about 2 1/4 cups, so the header tank needs to hold about 3 - 4 cups and the total volume should be near 5 cups. This gives the expanded coolant (2.12 cups) a place to go and when those 2.12 cups return to the engine, I can have a cup or two still in the header tank to ensure that no air returns to the pressurized system.
Attached is a spreadsheet you can use to calculate expansion base on initial volume, coolant chemical, and temperature difference.
I also attached a diagram that shows the height relationships of the different components. The logic behind the heights is so air can travel upward and end up in the header tank, then get forced out of the 7psi cap into the recovery tank, where it is vented to the atmosphere.
Edit: I added another spreadsheet (CoolantTank.xlsx) that has another way to calculate expansion tank ( header tank) volume. This one is based on percentages of total coolant, rather than calculations based thermal expansion of the fluids. Source URL is in the spreadsheet.
I am so grateful for your methodical approach-as usual you have cleared it up for me. I used to have an engine connected water heater for domestic use, but removed it two years ago. It was plumbed a little below or level with the exhaust manifold/expansion tank. I ran that way uneventfully with the small tank above it that seems to function now as a recovery tank. I am going to check radiator caps to see if the caps are the same psi or perhaps are not and the lower pressure cap is now mounted in the wrong respective location. Will report back!
My my my... I learn something new everyday here. Nice write up!
Quote from: P69 on July 09, 2020, 12:11:20 AM
In my Universal 5444, the exhaust manifold is the expansion tank with the 7 psi radiator cap. If coolant expands past 7 psi, it pushes past the cap into a recovery tank (right now it's a juice bottle). As engine cools, fluid is sucked back from the recover tank into the expansion tank.
The expansion tank runs at the same high pressure as the rest of the coolant system. The recovery tank is vented to the atmosphere. The highest point of the coolant system is either the radiator cap or a petcock on the top of the thermostat. This is cracked during refilling to purge air.
If your engine's exhaust manifold is designed to be the expansion tank and the cap is the highest point in the cooling system or if you have some kind of valve at the highest point ( thermostat?), you don't need a header tank. You need a recover tank to capture coolant overflow; otherwise it will drain into the bilge.
If you have a water heater or any other device through which engine coolant is routed and that device is higher than the expansion tank cap (aka radiator cap on the exhaust manifold), you need a header tank plumbed between that device and the engine (on the return hose to the engine) so the air can be purged. With a header tank up high, it needs a radiator cap that meets the engine specs (mine is a 7 psi cap) and the radiator cap on the exhaust manifold needs to be replaced with a higher pressure cap (10 or 15 pounds so it does not release before the one on the header tank. You essentially move the over-pressure release mechanism (the 7 psi radiator cap) from the exhaust manifold to the header tank.
In your case, with no water heater an no other coolant route that is higher than the exhaust manifold radiator cap, you shouldn't need the header tank.
The header tank is exist so coolant can expand in it during high temps and so air can be purged. It should be big enough for the expanded volume without over flowing and without sucking air back into the pressurized system
Unless you know how much your coolant will expand, you cannot know how large the header tank needs to be or how full to make it.
Base on the numbers for my system, the coolant will expand by about 2 1/4 cups, so the header tank needs to hold about 3 - 4 cups and the total volume should be near 5 cups. This gives the expanded coolant (2.12 cups) a place to go and when those 2.12 cups return to the engine, I can have a cup or two still in the header tank to ensure that no air returns to the pressurized system.
Attached is a spreadsheet you can use to calculate expansion base on initial volume, coolant chemical, and temperature difference.
I also attached a diagram that shows the height relationships of the different components. The logic behind the heights is so air can travel upward and end up in the header tank, then get forced out of the 7psi cap into the recovery tank, where it is vented to the atmosphere.
Edit: I added another spreadsheet (CoolantTank.xlsx) that has another way to calculate expansion tank ( header tank) volume. This one is based on percentages of total coolant, rather than calculations based thermal expansion of the fluids. Source URL is in the spreadsheet.
As a follow up, I still noticed weeping from the exhaust manifold/coolant tank. Engine was cold. I noted the small tank above the exhaust manifold holds about 4 cups of fluid, but was almost empty-which I think is because the radiator cap on the exhaust manifold may be shot. So coolant that would normally remain in the uppermost little tank drains down and out of the manifold tank. That's my best explanation because I ran the identical config last year and that little tank above the manifold was always over half full and almost never varied. The radiator cap on the exhaust manifold is a 7lb cap and the cap on the upper little tank is a 4 lb cap. Also, the way my coolant exits the block is from the block directly into the little tank and then out the little tank and down to the manifold. From there it enters the oil cooler then into the sendure and the transmission cooler after that and then back into the block. I think it might be possible to eliminate the uppermost little tank because I don't have a water heater plumbed BUT it should run perfectly fine if I keep the current configuration in -as it ran that way for the past two or three years-never lost coolant and always stayed at 180 degrees or less.
Any holes in that logic?
Nope, totally sound as far as I can see.
Plus or minus depending on how you look at it: With the tank and the large sized hoses running to it, you have more coolant capacity.
Minus, with that config you still need to crack the cap on the manifold when you check oil to let any stored vapor out. (it is a high point and you can get a hot spot from lack of coolant circulation.
I got rid of my water heater and got an instant propane fired water heater. But kept the high tank and had no issues. Plus it was easier to check the coolant level in the stbd cockpit locker than it was to check/fill on the manifold in the engine compartment.
Mystery solved-added a quart of coolant, ran it up-no loss of fluid. New cap did the trick👍. Glad I had a spare. Onward to Maine! Thanks for batting around the ideas with me.
TOTALLY jealous of you or anyone getting to cruise this season i the age of covid.