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Once known as Hartley18
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Discussion Starter · #1 ·
After replacing the ancient cooling hose, topping up the coolant on my fresh-water cooled MD2040 and heading out for a sail last weekend I discovered a not-insignificant amount of coolant in the bilge. I instinctively blamed a loose hose-clamp, but on closer inspection it seems the coolant sprayed out of the side of the heat exchanger 'radiator cap' at the top of the engine through the fitting where an overflow tank would be if one were fitted.

With apologies for being somewhat mechanically inept, the coolant level is(was) correct and far below the cap and it's my understanding the engine will run quite happily without the radiator cap even on (it's not like the system is pressurised) - so how is it even possible for the coolant level to get high enough to come out of the cap? The clamps are tight - am I getting air in somewhere?? :confused:

Thanks,
Cameron
 

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Why do you say it's not pressurized? When the cap is on it should be. The actual pressure will be stamped on the cap - usually a miminum of 7 psi up to as much as 20psi. We have a 7 psi on our H/E.

The minute you cap a trapped reservoir of water and heat it up you'll get pressure because the water expands as heated. The cap is meant to maintain that pressure and will 'lift and relieve' to the overflow tank (or your bilge) if it goes above that. The added pressure reduces the risk of actually boiling if overheating.

Perhaps you have a weak or underrated cap for your system? From this manual:

http://www.bluemoment.com/manuals/Volvo_Penta_MD2010-20-30-40.pdf

... it appears you need a cap that relieves at 12.8 psig.
 

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Well worse case a blown head gasket will put more pressure on the system. But I would start looking elsewhere. First get a new cap. You may have just put in too much coolant when topping it up. If that does not solve it then it will be on to going over the whole system.

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...and while you're getting a radiator cap, be advised that the Volvo cap is frighteningly expensive @$87, and I was able to source from NAPA, who matched the example I brought, for $5. Be sure the pressure etc is the same/bring your old cap along.

My engine is MD2030 so it might not be the same, but the NAPA part number for my cap is NAPA Balkamp 703-1708


---wait, you DON'T have an overflow tank? You should fit one, or some facsimile. Mine would have drained to the bilge, but I put a milk jug in to catch it.
 

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Once known as Hartley18
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Discussion Starter · #5 · (Edited)
Thanks, guys - I'm learning stuff here.

My initial thoughts were that I'd overfilled it (quite possible) but once the engine is cool again the level certainly seems lower than usual. It seems an amazing coincidence that this occurred immediately after replacing the hose, but I've had amazing coincidences before..

I'll replace the cap and see how that goes. Surely that can't be too expensive.. it's a Volvo after all. ;)


EDIT: Just saw Multihullgirl's post. Thanks for the warning on the price of a new cap!!! It's never been an issue in the past, but perhaps it's time to fit an overflow tank also... :(
 

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Back in the day the over flow tank was a jug on a hose (bottom cut off) wired to the bulkhead up high.Probably could do better than that today but expanding liquid still needs a place to go.
 

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Discussion Starter · #7 ·
Ok then...

Dumb question alert: If I fit an overflow tank, do I actually need to put coolant in it like I do in the car - or is it ok to leave it empty?
 

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Ok then...

Dumb question alert: If I fit an overflow tank, do I actually need to put coolant in it like I do in the car - or is it ok to leave it empty?
Yes fill it halfway, then keep an eye on it. Think about how it works: liquid expands when it's hot, so the tank is there to collect the extra liquid and when it cools it goes back into the manifold.
 

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No, it's not a sealed tank like in a car whereat the liquid would come and go. Just give the expanding fluid somewhere other than your bilge to overflow to
I wonder why it is not, and that really it should be for 2-way flow.

The primary purpose of expansion tanks in vehicals is NOT to catch antifreeze, but rather because it prevents air from being drawn into the system as it cools. Less oxygen, less corrosion. In fact, I've seen serious corrosion issue in vehicles where the expansion tank design was incorrect.

I would like to hear why a full radiator/HE and a functional expansion tanks is not better.

Of course, the greatest risk to any marine cooling system is not air or choosing the wrong coolant, it is a minor seawater leak. A teaspoon of seawater is enough to condemn any glycol coolant. Chloride is a bugger.
 

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I wonder why it is not, and that really it should be for 2-way flow.

The primary purpose of expansion tanks in vehicals is NOT to catch antifreeze, but rather because it prevents air from being drawn into the system as it cools. Less oxygen, less corrosion. In fact, I've seen serious corrosion issue in vehicles where the expansion tank design was incorrect.

I would like to hear why a full radiator/HE and a functional expansion tanks is not better.

Of course, the greatest risk to any marine cooling system is not air or choosing the wrong coolant, it is a minor seawater leak. A teaspoon of seawater is enough to condemn any glycol coolant. Chloride is a bugger.
IIRC, the expansion tanks on most/all of the cars/trucks I have had are not sealed, but open to the atmosphere, with the radiator cap allowing coolant to flow back into the radiator as it cools, the tank holding more as the coolant warms & less as it cools.

I think the small hose that goes to the bottom of the tank & forms a "siphon" as long as there is enough coolant to cover the bottom of the hose. A tank, when cold, that keeps going down is an indicator that coolant is being lost.

IIRC, on an older Detroit diesel we had there was no expansion tank on the heat exchanger, just a radiator/HE pressure cap.

Paul T
 

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Once known as Hartley18
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Discussion Starter · #12 · (Edited)
See that's the bit that doesn't make sense to me:
  1. The engine doesn't come standard with an overflow tank,
  2. The manual says to fill the HE up to the bottom of the neck of the cap (ie. full, very full!) and
  3. The radiator cap acts as a one-way (safety) valve ie. it contains a valve seat held down by a spring.
If the argument was that the coolant expands when heated, there is no way any released coolant is going to get back in to the HE once it cools, hence the only function I can see the overflow tank having is to contain excess coolant... so I must be missing something. :(


BTW, I've bought a new 13psi cap (no, not a genuine) but didn't get a chance to try it out on the weekend. Racing was called off when the wind forecast exceeded 30 knots.
 

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See that's the bit that doesn't make sense to me:
  1. The engine doesn't come standard with an overflow tank,
  2. The manual says to fill the HE up to the bottom of the neck of the cap (ie. full, very full!) and
  3. The radiator cap acts as a one-way (safety) valve ie. it contains a valve seat held down by a spring.
If the argument was that the coolant expands when heated, there is no way any released coolant is going to get back in to the HE once it cools, hence the only function I can see the overflow tank having is to contain excess coolant... so I must be missing something. :(


BTW, I've bought a new 13psi cap (no, not a genuine) but didn't get a chance to try it out on the weekend. Racing was called off when the wind forecast exceeded 30 knots.
I think overflow tanks came to be as automotive radiators began getting smaller & thinner, at least it seems that way on the many cars I have worked on. I guess the theory is that if the engine gets hot the expanded coolant goes into the tank instead of on the ground, or in the bilge.

That way, the radiator/HE is always "full", having sucked the overflow back after the coolant has cooled. I think some/all? of the caps allow the coolant to be "sucked" back into the radiator, as the tank is open to the atmosphere. Not sure if a cap with more than 15 lbs of pressure would allow the coolant to be sucked back, unless it has some kind of 2 way directional valve? Kind of like magic?

On our Detroit diesel, which did not have an expansion tank, we only checked the coolant when it was stone cold. It was always about an inch or so "low".

Paul T
 

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Discussion Starter · #14 · (Edited)
A small update on this: When I got down to the boat yesterday and removed the old cap I found the HE rather overfull and worry that there may be seawater in it (it's not all bright green coolant and what has spilled out and dried is a bit crusty, like salt).

I replaced the 'radiator cap' anyway and gave it a good run - nothing leaked out from the new cap. :)

My service tech thinks I probably got an airlock in the system after replacing the cooling hose and that I should have given it a good run with the cap off instead to get all the air out (that'll teach me to call him first in future.. but I saw nothing in the manual about that). So, the saga continues.

Hopefully I haven't popped a tube.. :(
 

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A high spot in the hose can be a place the air accumulates. The fresh water pump may not be able to push it thru and that means a cooked engine. If a bubble can't rise own its own to the header cap, the installation needs looking at. Both air and excess fluid will push the cap open into the reservoir and coolant sucks back when engine cools. Air is to atmosphere. Better to leave cap off a while ,run her good and watch temp to insure things are copecetic before going back to ignoring stuff.
 

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so how is it even possible for the coolant level to get high enough to come out of the cap? The clamps are tight - am I getting air in somewhere?? :confused:

Thanks,
Cameron
What caused the water to rise and exit the HX is the change in the density of water due to temperature changes.

You changed/added water at ambient temperature (20°C) and then the engine heated the water to ~82°C/180°F. That change in temperature causes a density change of a nearly 4% increase in volume of the water .... and 4% of that water exits the 'container' through that nipple below the 'radiator cap'. ... You lost 4% of your water if the 'cap' did not do its job of containaing the water at about 7psi pressure.

 

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Discussion Starter · #17 ·
What caused the water to rise and exit the HX is the change in the density of water due to temperature changes.

You changed/added water at ambient temperature (20°C) and then the engine heated the water to ~82°C/180°F. That change in temperature causes a density change of a nearly 4% increase in volume of the water .... and 4% of that water exits the 'container' through that nipple below the 'radiator cap'. ... You lost 4% of your water if the 'cap' did not do its job of containaing the water at about 7psi pressure.
Thanks, Rich - that makes sense now. :)

As alluded to by Faster, this engine uses a 13psi cap and I'm 99.99% sure I didn't get all the air out when I refilled the system.

The crazy manual contains all kinds of warnings against running the engine without the fresh-water system topped up, but then (on the next page) goes on to say you should run at idle whilst filling it up! I know what they mean now (at least I think I do) but it was less clear before I started..
 

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A small update on this: When I got down to the boat yesterday and removed the old cap I found the HE rather overfull and worry that there may be seawater in it (it's not all bright green coolant and what has spilled out and dried is a bit crusty, like salt).
"Crusty"? not good. Maybe get the coolant tested by an oil analysis company or other sources. Salt/coolant heap big trouble.

I replaced the 'radiator cap' anyway and gave it a good run - nothing leaked out from the new cap. :)
There may be a small hole between the coolant side & the sea water side?
A pressure test of the coolant side of the heat exchanger could verify that?

My service tech thinks I probably got an airlock in the system after replacing the cooling hose and that I should have given it a good run with the cap off instead to get all the air out (that'll teach me to call him first in future.. but I saw nothing in the manual about that). So, the saga continues.

Hopefully I haven't popped a tube.. :(
When I used to change coolant I used to run it up to temperature with the cap off. Always had to add additional coolant once the thermostat opened. Some engines have a "vent" plug which should be opened while filling, then closed when coolant flows out.

Paul T
 

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Discussion Starter · #19 ·
When I used to change coolant I used to run it up to temperature with the cap off. Always had to add additional coolant once the thermostat opened. Some engines have a "vent" plug which should be opened while filling, then closed when coolant flows out.

Paul T
Thanks, Paul. I wish you'd told me that back when I started this thread.. :(
 

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Thanks, Paul. I wish you'd told me that back when I started this thread.. :(
IIRC, I used to add at least another quart. It was interesting to watch the coolant level suddenly drop as the engine warmed, kind of like a toilet flushing.

The "crust" you mentioned may very well be salt? If, after running it up to temp, you should get some coolant escaping after very slowly opening the cap, as it should be under pressure. If not, you may have a small leak from the coolant side into the sea water side. When the coolant cools it may be possible that the sea water side, at atmospheric pressure, may be passing sea water into the coolant side, which may be at a slight vacuum?, I think.

Pressure testers:

Radiator Pressure Tester Kit

Amazon.com: radiator pressure tester kit

Coolant testers:

https://www.google.com/?gws_rd=ssl#q=radiator+coolant+salt+tester+for+marine+heat+exchangers

Or, if you are brave, you could taste a drop, I think coolant is sweet? Maybe you could taste salt, if there is enough of it? Or, maybe send a sample to a lab?

As coolant runs over 160 degrees any salt in it may solidify? Maybe some of our chemist members can add?

Paul T
 
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