Coolant Conundrum/Exhaust Riser Replacement [Master Thread]

[Kenneth K]

Yeah, Jeff, I agree with Pete.

Since you never had a separate, pressurized, accumulation/expansion tank as part of your system, I wouldn't add one now. And, if you did, then you'd still need to vent it to a non-pressurized coolant recovery tank (a 3rd tank).

Sounds like all you need to do is replace your old, vented, coolant recovery tank with a new, albeit better looking, one.

 

[Prairie Schooner]

Overflow Tank
I still felt like I was missing something. Digging around, my current understanding is as follows:


The introduction of overflow tanks, their pressurization, and increasing system complexity is for: reducing the amount of coolant sprayed into the environment, reducing the need to add coolant after any overflow, reducing the frequency with which we need to monitor coolant levels, adapting to higher performance engines, and greater system efficiency.

Pressure on the coolant raises its boiling point. Some formulae state every psi raises the boiling temp of a typical mix by three degrees, giving a wider protection band.

Normal operation involves the coolant expanding with heat to fill the OF tank. As it cools, it sucks fluid back in. This reduces the accumulation of air in the system.

Engine designers specify the correct pressure rating for the cap based on system components and configuration. Go by what the manual says.

OF tanks work by pressure differentials, not gravity. They don't need to be mounted above the manifold coolant tank. Ideally the tank should be mounted so the cold fluid level is roughly even with the manifold coolant cap. If much higher and vented (unpressurized), when the manifold tank is opened gravity could make the manifold tank overflow.

Accumulation tanks are a further sophistication of the system. I don't think there should be multiple pressure caps in a system. Steven's cap wired shut reinforces this notion. (post # 67) If there are, each pressure should take into account the stacking of caps. I'm not sure how, but we don't have multiples so I didn't research that.

Our systems are relatively simple compared to modern automobiles, but are perfectly adequate for our needs. I don't need to add extra complexity.

Much of this is a recap of what had already been discussed in this thread. If I'm wrong on any of it, please correct me. It's an unfolding mystery.

These references were especially helpful.

The Coolant Recovery Bottle: Unsung Hero of the Engine Room

Here's how to make sure your coolant recovery bottle is properly installed and in good working order.

passagemaker.com

Know Your Coolant Recovery Tank System | Cruising World

You may not fully comprehend their significance, but coolant recovery bottles are the unsung heroes of the engine compartment.

www.cruisingworld.com

Various opinions on mount location for OF tank:

Coolant overflow tank location

I will be adding a coolant overflow tank to a 5424 Universal diesel. Should the tank be mounted higher or lower than the coolant reservoir on the engine? Thanks

forums.sailboatowners.com

 

[peaman]

To add to your nearly comprehensive summary, an elevated accumulation tank as I seem to have, is also recommended if coolant circulates through anything, such as a water heater or cabin heater, above the engine manifold. My water heater coil is quite low, so I’m not sure of the rational for my remote tank. But it does facilitate maintenance of coolant level.

 

[peaman]

The picture below shows how my remote tank is connected to the engine, through a bronze elbow teed off from the inlet to the engine manifold. The radiator cap on the engine manifold is rated at 13 psi while the cap on the remote tank is 7 psi.

 

[Pete the Cat]

The picture below shows how my remote tank is connected to the engine, through a bronze elbow teed off from the inlet to the engine manifold. The radiator cap on the engine manifold is rated at 13 psi while the cap on the remote tank is 7 psi.

View attachment 52704

I am really curious about this arrangement. I don't get why anyone would do this. What is the purpose?

 

[Christian Williams]

The manifold cap seems wired closed, with multiple warnings do not open. So the fluid level is checked in the remote tank?

 

[Kenneth K]

I am really curious about this arrangement. I don't get why anyone would do this. What is the purpose?

It's because you can't fill water "uphill." If parts of the FW system rise above the engine manifold tank, you need to add a higher fill point so you can top off the system. Ultimately, the filler cap that you actually "use" needs to be a the high-point in the system.

 

[Pete the Cat]

It's because you can't fill water "uphill." If parts of the FW system rise above the engine manifold tank, you need to add a higher fill point so you can top off the system. Ultimately, the filler cap that you actually "use" needs to be a the high-point in the system.

I really do not see overflow tanks as being something that was designed to take 14 lbs of pressure--seems like a situation of induced potential for failure. I believe the idea was that overflow tanks were there to collect overflow if the pressure on the manifold expansion tank exceeded 14 (or whatever) lbs of pressure from the rated cap. I always thought the overflow tank should probably be higher than the manifold tank if the thought was that overflow would somehow siphon back into the expansion tank. But I have never been sure that occurs in any of the applications on the boats I have owned. I began to think the idea of them was adapted from the overflow tanks on car engines which I think have saved a few dogs' and rodents' lives. . I generally keep and regularly check the coolant in my 25XP about 1/2" below the top of the expansion tank and skip the overflow as it never seemed to work right anyway (filling and depleting with temperature fluctuations). I have never had a problem with overheating in many years.

 

[Kenneth K]

I really do not see overflow tanks as being something that was designed to take 14 lbs of pressure--seems like a situation of induced potential for failure.

Yeah, I think you're spot on about the overflow/recovery tank--it's not meant to be pressurized.

I think the device peaman is talking about is an accumulation / expansion tank. If the water heater sits much higher than the manifold on the engine, you can no longer open the engine cap, or fluid from higher up comes gushing out. So they add a second pressurized tank higher up, with a similar pressure cap, which then becomes the system's access and fill point. This second pressurized tank is then usually fitted with the unpressurized overflow/recovery tank that you're talking about.

 

[David Grimm]

So the expansion tank serves two purposes, one is obvious as it catches coolant from over flowing into the bilge, the other not so obvious as it keeps fresh air (oxygen) from entering the coolant system and corroding the internal metal components. So in all it is not just an EPA add on.

Over flow tanks are not pressurized. Yes coolant tanks are usually higher than the top of the radiator cap. However the coolant is not psyphend back into the engine, it is pulled back into the engine as the coolant cools and takes up less volume than when at operating temperature.

 

[Christian Williams]

peaman, if you don’t mind all the questions, what device using coolant is higher than the manifold cap on your 32-3? My water heater was much lower.

 

[peaman]

First, I have avoided terms like "expansion tank" and "accumulator tank" as those terms are not actually descriptive of their function, at least not in my opinion for my system. "Overflow tank" seems to be well understood as the unpressurized plastic tank in which the fluid level may rise as the engine warms, and as the engine cools, that fluid should be drawn back into the system.

The "remote tank" in my system is simply an extension of the engine coolant system since the coolant is entirely unrestricted between remote tank and engine circuit. It will be pressurized to the same pressure as the engine system, less the small (14"?) static head due to its higher elevation. If the engine pressure exceeds 7 psi, the cap on the remote tank will release fluid into the overflow tank. As long as that cap is functioning, the engine should never have enough pressure to open the 13 psi-rated manifold coolant cap.

No part of the coolant circuit is higher than the manifold cap. I believe that the elevated remote tank was installed to facilitate monitoring and maintenance of the coolant level. It is so much easier to simply open the cockpit hatch rather than to remove companionway ladder and engine cover just to check the coolant.

 

[Christian Williams]

Convenience. Aha!

 

[Kenneth K]

Convenience. Aha!

Convenient for the next guys that inherit/buy the boat. Not so much so for the guy that had to install the second tank, hose, and tee fitting.

 

[peaman]

Convenient for the next guys that inherit/buy the boat. Not so much so for the guy that had to install the second tank, hose, and tee fitting.

Certainly convenient for me, the guy who bought the boat. But not so much once I saw how the oversized remote tank made it difficult to remove trash bags from the very handy built-in bin. So I was the guy who sourced and installed a smaller tank to replace the previous one. But no complaints: it’s only time and money spent in the name of convenience and elegance.

 

[Prairie Schooner]

I'm getting confuseder and confuseder.

As I understand the Theory, there are two pressure valves in the cap and during cool-down atmospheric pressure will push coolant back in by way of the vacuum valve. Makes sense. Whether it works in practice is another matter. There are variables in installation, the cap might be defective or the wrong spec, hoses might be clogged, etc. Or, it's a bogus theory.


This video drags on, but is the best I could find for explaining how the cap works.
- Radiator Pressure Cap on YT by Vehicle Engineering

But if atmospheric pressure at sea level is around 14.5 psi, and the radiator cap is to release at 14-16 is it even making much of a difference? Does the vacuum valve release at a lower pressure? I'm guessing engineers have tested this.

-

This is how I'm planning to install the overflow tank. (Puke Jug is the colorful moniker used by some) I'm wondering if the up and over will create a siphon problem when I open the manifold pressure cap. I wasn't really sure how a siphon works so I looked that up. Shocker! It turns out 'they' don't even know how a siphon works!!
- https://en.wikipedia.org/wiki/Siphon

So, the progress is: I've increased the number of things I'm ignorant about. But I'm going to go ahead and install this as planned, which is pretty close to what was already in the boat.
J

 

[Loren Beach]

Thanks for the additional picture and thoughts. I am a bit confused also, but can report that the factory install of our engine overflow plastic container was about even with the cap on the heat exchanger (albeit inside an adjacent lazaret compartment). I read where this 'bottle' should be at cap level or a bit higher, and when I replaced that old icky looking plastic bottle with a new one, I put it in the engine compartment and the level seems about the same as the recommendations.
Here in this blog entry is a picture of it in place.

O34 - Wiring & Engine Detail, part 2

These photos show the Halon bottle in place, and also a much better look at the inside of the compartment where the meter and terminal strip are mounted. As an "extra" there is a shot of the new coolant overflow tank showing how the level in it...

ericsonyachts.org

 

[Kenneth K]

But if atmospheric pressure at sea level is around 14.5 psi, and the radiator cap is to release at 14-16 is it even making much of a difference? Does the vacuum valve release at a lower pressure?

Jeff, that's the difference between PSI and PSID (differential). When the manifold cap is open, both the manifold and the "outside" air are at 14.5psi. When the cap is sealed in place (and nothing else changes) both are still at 14.5psi and PSID is still zero. But since the manifold is now sealed off from the atmosphere, its pressure starts to change with temperature changes. When the PSID gets to 14 psi (outside air pr=14.5, manifold pr=28.5), the cap releases pressure.

I'm wondering if the up and over will create a siphon problem when I open the manifold pressure cap. I wasn't really sure how a siphon works so I looked that up.

If the height difference between the top of the loop and the manifold cap (H2)--probably greatly exaggerated in this photo--is greater than the height difference between the fluid level in the plastic tank and the top of the loop (H1), then the downward suction force from H2 overpowers that of H1, and a siphon will occur. It's not a big deal though. It's the same situation I have with my plastic tank mounted high up in the cockpit seat compartment. No siphon in my situation, just a downward flow of coolant. But I usually check coolant level just by inspecting the plastic tank. If I need to open the manifold cap, I have to remove the small overflow hose at the cap fitting and plug it with my thumb (or, drain the plastic tank first). No biggie, I mean when's the last time you removed the radiator cap in one of your cars?

Also, if you add a filter or 'catch' to your crankcase ventilation line, you have to be sure the filter doesn't clog from oil. Mine did once. When that happens, pressure builds up in the oil pan until oil starts pumping its way up through the dipstick handle tube. There's no real need for a filter element in the ventilation line.

 

[Prairie Schooner]

Also, if you add a filter or 'catch' to your crankcase ventilation line, you have to be sure the filter doesn't clog from oil. Mine did once. When that happens, pressure builds up in the oil pan until oil starts pumping its way up through the dipstick handle tube. There's no real need for a filter element in the ventilation line.

I've been thinking about this Ken. I'm going ahead with the filter, but will keep an eye on it. In that same area there will be also be the domestic water filter, raw water strainer, air filter, and overflow reservoir. I'll have good reason to check all those regularly. If it starts to get clogged, I can take the screen out. My concern is that routing right into the filter top bypasses the filtration fiber. I guess the odds are low that a particle would get through, but I think it would be bad if it did.

 

[Prairie Schooner]

. .

The muffler was in quite good condition except for the inlet nipple which was delaminating. I found an adhesive that will take up to 300ºF, Loctite HY 4090 GY. Since these were originally assembled with adhesive, I figured this is safe. Using cut up plastic bag as a release barrier, I inserted a tapered arbor and used hose clamps on the outside.


The adhesive was $30 while a new muffler was about $300. A pleasant byproduct of the clamps is ridges sort of like a barb.



I've given a lot of thought to installing a drain petcock, but decided against it. There is already a drain screw and I was worried a valve sticking out could snag something or get broken off. The only thing in the muffler will be dirty sea water so if some of that spills in the bilge while draining, it's not a big deal.