Help explain coolant expansion tank??

[catalinajack]

Your example of an expansion tank slowing the heating of an engine is flawed;

the thermostat controls that.

I think that adding one to older engines designed without a tank is not likely to

improve much.

Quite right. At most just a few ounces of coolant may find its way to the bottle. No way that those few ounces makes any difference.

 

[Ski in NC]

A big benefit of the recovery bottle is that it limits air intrusion (oxygen) into the coolant. Without the bottle, with every thermal cycle (start up, heat up, shut down, cool down) the coolant in the engine expands and contracts. With a recovery bottle the coolant is forced through the pressure cap and a pint/quart or so ends up in the bottle. On cool down, the little check valve on the bottom of pressure cap allows coolant in bottle to refill the engine.

But with no recovery bottle, the same expansion/contraction occurs, but now on cool down, it sucks in air. With oxygen. A primary purpose of the corrosion inhibitors in your coolant is to chemically scavenge oxygen, as most corrosion processes in the coolant path are driven by the dissolved O2 content. The more DO2 in the coolant, the shorter time the inhibitors last.

So setting up a recovery bottle and a proper recovery type cap (they are different) helps you coolant last longer and thus less corrosion in your engine.

Also easier to monitor coolant level. Cold engine bottle should be mostly empty (but not empty!!). After getting up to temp, just a glance at the bottle should show level increased a bit. On mine, it goes up about and inch or two. Then after engine cools back down, level should drop about the same amount.

If you consistently see that level change with thermal cycles, all is well with the system. No need to fool with the pressure cap.

The recovery type cap has a rubber gasket under the handle flange. Non-recovery types just a thin metal ring. Non-rec caps don't work with recovery bottles as they don't seal with the top flange of the cap neck.

And don't go cheap with the cap. Lots of garbage out there, especially auto parts stores. One of my local engine dealers sold very nice stainless caps in what ever pressure rating you want (DD's 7psi, FL 4 or 7, Cummins 10? or 15, etc). They were like 10-15bucks, not much more than the crap from the auto parts stores. I replaced all on my machines as prior the cheap caps were always leaking or otherwise being POS's.

 

[rolomart3]

To complete the excellent explanation given by DavidM, let me answer why coolant should be added to the expansion tank.

I will illustrate with an hypothetical scenario: let us say that the radiator engine is 3/4 full with coolant and the expansion tank is completely empty. Probably in a normal day the engine will operate just a bit hotter but within the normal range depending on the ambient temperature. Upon turning off the engine at the end a trip you notice
the empty expansion tank and you proceed to fill it up to the hot mark.
Now as the engine starts to cool, the coolant in the radiator contracts and begins to pull coolant from the expansion tank. Although it may not completely refill the radiator, it will improve its cooling capability compared to before. If there is coolant always kept in the expansion tank, over several heat-cool cycles the radiator is completely refilled.
Conclusions:
1) due to the expansion of hot liquids, it is NOT possible to check the coolant level of a hot engine through its refill cap. It will show to be full.
2) because of 1) above, the amoubt of coolant to be added to the radiator is best determined by the amount of cooling contraction of the hot coolant in the radiator. Therefore, the user responsibility is just to insure that there is enough coolant in the expansion tank. This is done by msking sure that the expansion tank always has more coolant than the mark indicating to the temperature conditions of the engine.

Why have a radiator cap then? Because if coolant becomes sufficiently low and the engine overheats due to an empty expansion tank (really due to an operator error or a leak) the only remedy is to wait until the engine cools and refill both the radiator and the expansion tank.

3)Avoid at all cost operating an overheating engine

 

[Marco Flamingo]

Although it may not completely refill the radiator, it will improve its cooling capability compared to before.

I think this is a misconception that increased coolant volume is increased cooling capacity. Let's say my expansion tank is 400 gallons! The engine heats up to 180 degrees, the thermostat opens and keeps it at 180 degrees. The excess 400 gallons sitting beside the engine does nothing towards improving cooling capacity. Even an extra quart in the regular FL fill tank (overfilled to the top) doesn't improve cooling. It is the effectiveness of the impeller, heat exchanger, and thermostat that determines cooling capacity. As long as the original tank doesn't run dry, the cooling capacity remains essentially unchanged whether full or half full. If the impeller stops, the heat exchanger is plugged, or the thermostat doesn't open, an extra quart in the coolant tank wouldn't make 10 seconds difference in overheating.

Keeping oxygen levels low in the coolant is the first possible advantage to installing an expansion tank that I've heard. Of course, routinely heating water to 180 degrees would drive the dissolved oxygen out and I'm not sure an appreciable amount could enter back in, but the theory is plausible. If the expansion tank kit is $10 and a 10 minute install I'm in. Otherwise, I'll just change my coolant regularly. Oh yeah, I get to change less of it which saves me $$$.

 

[mickand]

A good explanation recently published in PassageMaker

 

[ismar1]

Prospective,
I have the same Volvo engines as you except mine are the 430HP 74 LB. My set-up does not have the overflow bottles with any excess draining into the bilge. My owners manual is very specific regarding the fluid level in the expansion tank. The level should be at the second knuckle on your index finger, which I check on a regular basis. I wonder if your manual indicates something different. Thanks

Have same engines with set-up as JSK55 mentions . Thankfully no issues till now after 1600 hrs and trips of 800nm.

 

[rslifkin]

I think this is a misconception that increased coolant volume is increased cooling capacity. Let's say my expansion tank is 400 gallons! The engine heats up to 180 degrees, the thermostat opens and keeps it at 180 degrees. The excess 400 gallons sitting beside the engine does nothing towards improving cooling capacity. Even an extra quart in the regular FL fill tank (overfilled to the top) doesn't improve cooling. It is the effectiveness of the impeller, heat exchanger, and thermostat that determines cooling capacity. As long as the original tank doesn't run dry, the cooling capacity remains essentially unchanged whether full or half full. If the impeller stops, the heat exchanger is plugged, or the thermostat doesn't open, an extra quart in the coolant tank wouldn't make 10 seconds difference in overheating.

Keeping oxygen levels low in the coolant is the first possible advantage to installing an expansion tank that I've heard. Of course, routinely heating water to 180 degrees would drive the dissolved oxygen out and I'm not sure an appreciable amount could enter back in, but the theory is plausible. If the expansion tank kit is $10 and a 10 minute install I'm in. Otherwise, I'll just change my coolant regularly. Oh yeah, I get to change less of it which saves me $$$.

The extra capacity in the system isn't from the coolant in the expansion tank. It's from having the main system completely full with no air space.

 

[rolomart3]

Marco you misread my words when you say "I think this is a misconception that increased coolant volume is increased cooling capacity."

When the volume of coolant inside the radiator increases, the cooling capacity increases. Although the amount of cooling demanded of the radiator is determined by the flow restriction of the thermostat, a partially filled radiator may not be able to provide the demanded cooling and the engine overheats.

The statement stands.

 

[Marco Flamingo]

Marco you misread my words when you say "I think this is a misconception that increased coolant volume is increased cooling capacity."

When the volume of coolant inside the radiator increases, the cooling capacity increases. Although the amount of cooling demanded of the radiator is determined by the flow restriction of the thermostat, a partially filled radiator may not be able to provide the demanded cooling and the engine overheats.

The statement stands.

I've never been on a boat with a radiator. I agree if one exists, and the radiator were half full, that would effect cooling capacity just as it does in an automobile.

I said that the increased amount of coolant in a boat's expansion tank might increase the time of overheat by 10 seconds. Not in the case of a pump failure. Circulation stops and the coolant surrounding the engine overheats. It doesn't matter that there is more uncirculated coolant in the expansion tank (or an overflow tank). If a thermostat doesn't open, increased capacity in the expansion tank makes zero difference. Of course a hose failure makes no difference (other than maybe more coolant in the bilge). There might be the some scenario where an extra quart in a system that slowly overheats extends the time to overheat. I guesstimated that at 10 seconds.

I think my system holds about 2 gallons when properly filled. Adding a recovery tank would allow me to overfill by a quart, maybe two. As the engine heats, it would poop out this excess into the recovery tank, as do all recovery systems. I would still be using the same amount of coolant in the system. The increased capacity, now sitting beside the hot engine in the recovery tank, has no effect on cooling. My saying the increased amount of coolant used might provide and additional 10 seconds may have been too generous.

If you have a partially full radiator system, this analysis would not apply.

 

[oscar]

I've never been on a boat with a radiator.

Funny you should mention that. I saw one this weekend. 35 ish foot 60's or 70's heavy glass "center console" open work boat with a MASSIVE Cummins 500+ hp truck motor in it, complete with radiator and what probably once was a Kenworth grille. Open on the sides, just a hard top over the console and engine in front of it. Straight dry stack up (chrome of course). When the turbo spooled he sounded like a diesel electric locomotive revving up..... pretty cool actually. Forgot to take a picture......

 

[FF]

"The extra capacity in the system isn't from the coolant in the expansion tank. It's from having the main system completely full with no air space."


This is correct because air is an insulator .

 

[smitty477]

"The extra capacity in the system isn't from the coolant in the expansion tank. It's from having the main system completely full with no air space."


This is correct because air is an insulator .

When an engine is under load the coolant will have expanded and filled up all the available air space. When you need the cooling capacity the most there will be no extra coolant available with expansion tanks - even though I prefer them.

 

[FF]

"When an engine is under load the coolant will have expanded and filled up all the available air space."

Air is compressible so the entrapped air bubbles might be smaller , but there still there.

Folks needing better cooling that live in non freezing areas can use 1/3 antifreeze 2/3 water.

Antifreeze only has about 5/8 the heat carrying ability of plain water, so less is more , and it will still have enough additives to keep the cooling system happy.

 

[smitty477]

"When an engine is under load the coolant will have expanded and filled up all the available air space."

Air is compressible so the entrapped air bubbles might be smaller , but there still there.

Folks needing better cooling that live in non freezing areas can use 1/3 antifreeze 2/3 water.

Antifreeze only has about 5/8 the heat carrying ability of plain water, so less is more , and it will still have enough additives to keep the cooling system happy.

"Air is compressible so the entrapped air bubbles might be smaller , but there still there."
No sigificant entrapped air in a system whether or not it has an overflow tank.
Dropping coolant/water ratios may affect any engines with non ferrous parts and also lower the boiling point of the resultant mxture. Fresh coolant of the appropriate mix required by the engine manufacturer is the best approach.

 

[FF]

"No sigificant entrapped air in a system whether or not it has an overflow tank."

This is not what car, truck and other liquid cooled builders believe , which why they installed the refill tanks , and are delighted to save about 25% on every radiator installed.

Most antifreeze mfg have to plan on folks not changing out the old antifreeze on time as PM , so the usual chemicals are enough to be used up over a longer period of time.

Many older marine diesel engines have a 2 or 3 lb pressure cap, a higher temp boiling point coolant is not of any use.

 

[smitty477]

"No sigificant entrapped air in a system whether or not it has an overflow tank."

This is not what car, truck and other liquid cooled builders believe , which why they installed the refill tanks , and are delighted to save about 25% on every radiator installed.

Most antifreeze mfg have to plan on folks not changing out the old antifreeze on time as PM , so the usual chemicals are enough to be used up over a longer period of time.

Many older marine diesel engines have a 2 or 3 lb pressure cap, a higher temp boiling point coolant is not of any use.

"This is not what car, truck and other liquid cooled builders believe , which why they installed the refill tanks , and are delighted to save about 25% on every radiator installed."
Added for environmental reasons so that coolant is not expelled onto the ground - not for any added cooling capacity.


"Most antifreeze mfg have to plan on folks not changing out the old antifreeze on time as PM , so the usual chemicals are enough to be used up over a longer period of time.
Many older marine diesel engines have a 2 or 3 lb pressure cap, a higher temp boiling point coolant is not of any use"

As mentioned it is best to follow manufactuers specs -- not sure what 'older marine diesels' mean but boiling points are affected under any and all pressures and all of ours had higher pressure caps even from the 80's.
Refer to your manufacturer for your specified requirements.

 

[Marco Flamingo]

My stock Lehman has a 4psi radiator cap. At 4 psi, water boils at 225F. With 1:2 glycol/water, the boiling point is 230F. If the mixture boils, the entrained steam greatly reduces cooling and the boil-over shoots into the bilge with the stock system or into and expansion tank which then overflows into the bilge. A higher pressure cap increases the boiling point (with a 12 psi cap, the coolant would boil at 253F).

If the cause of the overheating was momentary (i.e., the plastic bag washes off of the raw water intake), then the 20 degree delta provided by the higher psi cap may save the day. If not temporary and ignored, the boil-over is 20 degrees hotter, more violent, and takes longer to cool.

The expansion tank can save cleanup in some cases, but if protecting against overheat is the goal, a warning light/buzzer set just above the thermostat rating would be the better improvement. I've seen the ohm chart for my Stewart Warner temp gauge, but I don't think I've ever seen a warning light that would work with the same sender (adjusted to activate at a certain resistance).

 

[catalinajack]

My stock Lehman has a 4psi radiator cap. At 4 psi, water boils at 225F. With 1:2 glycol/water, the boiling point is 230F. If the mixture boils, the entrained steam greatly reduces cooling and the boil-over shoots into the bilge with the stock system or into and expansion tank which then overflows into the bilge. A higher pressure cap increases the boiling point (with a 12 psi cap, the coolant would boil at 253F).

If the cause of the overheating was momentary (i.e., the plastic bag washes off of the raw water intake), then the 20 degree delta provided by the higher psi cap may save the day. If not temporary and ignored, the boil-over is 20 degrees hotter, more violent, and takes longer to cool.

The expansion tank can save cleanup in some cases, but if protecting against overheat is the goal, a warning light/buzzer set just above the thermostat rating would be the better improvement. I've seen the ohm chart for my Stewart Warner temp gauge, but I don't think I've ever seen a warning light that would work with the same sender (adjusted to activate at a certain resistance).

My Lehman 120s have 205 degree overtemp alarm senders. Don't they all, including FL 135s? Equipped as such, shouldn't these engines be shut down long before the water temp reaches 225 degrees with a 4psi cap?

 

[diver dave]

My Lehman 120s have 205 degree overtemp alarm senders. Don't they all, including FL 135s? Equipped as such, shouldn't these engines be shut down long before the water temp reaches 225 degrees with a 4psi cap?

Hmmm, the hottest coolant would be the exh man. Output side. But a lot of coolant alarms seemed to be placed on the eng block since the blocks were designed for radiator use. I dont know about Leyman set ups.

 

[FF]

" if protecting against overheat is the goal, a warning light/buzzer set just above the thermostat rating would be the better improvement."

The solution here would be to install a Murphy Gauge which is mechanical and has an adjustable alarm one can set at the desired over temp to alert.

A full set of Murphey Switchgauge would be my first choice for instrumentation if I often traveled offshore.

 

[rslifkin]

Warning buzzers are very useful. If you hear one, throttles to idle immediately and scan the gauges to figure out which engine to shut down. Don't just blindly kill them, as then you don't know which one is safe to restart.

 

[catalinajack]

Hmmm, the hottest coolant would be the exh man. Output side. But a lot of coolant alarms seemed to be placed on the eng block since the blocks were designed for radiator use. I dont know about Leyman set ups.

On a Lehman the overtemp sensor is quite close to the tank. So, the alarm will sound before the 4psi cap reacts. Do I have that wrong?

 

[HTurner]

https://www.passagemaker.com/technical/the-coolant-recovery-bottle-an-unsung-hero-of-the-engine-room

 

[Marco Flamingo]

My overheat buzzer is something that I came up with because a prior one (original?) was not working. It is on the exhaust manifold several inches below the raw water injection point. It is simply a circuit that has a 75C (167F) thermal switch, a 3A fuse, and a red 12V light/buzzer on the instrument panel. I thought that 167F might be too low, but I've had the engine at sustained 2K rpm without a problem.

If an overheat situation was caused by a raw water circulation problem (blown impeller), the exhaust manifold would heat up faster than the coolant. Without raw water injected into the manifold it would get to 167F in seconds, while the thermal mass of the engine and coolant would take a minute or two to overheat.

But there could be overheat situations in which the failure of the raw water circulation isn't the problem. If the engine coolant stopped circulating (air pocket or obstruction), the raw water would continue to cool the manifold while the engine overheated. My temperature gauge, which is only concerned with coolant temperature, would show the increasing temperature but there is no alarm. Was a coolant temperature alarm standard on Lehmans?

 

[Prospective]

https://www.passagemaker.com/technical/the-coolant-recovery-bottle-an-unsung-hero-of-the-engine-room

Excellent on-point article. Thank you.

 

[Roger L]

Overflow tank spewing coolant

I have twin Yanmar 4lha stp engines one is overfilling the overflow and blowing coolant out the lid. Even if I empty the tank it still happens. I assume I have some salt water intrusion? Is it only from the heat exchanger? There is no oil in the leaked fluid.

 

[mickand]

Blown head gasket?

 

[rgano]

Have you checked the transmission oil and the lube oil to ensure there are no problems there. Hopefully not but, a good thing to do at this point. Get an exhaust gas check kit to see if you have that problem with your coolant (busted head gasket).