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Old 25-08-2014, 06:19   #1
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Cooling fluid reservoir problem

Hi,

I have a minor problem with my engine's cooling fluid reservoir: the hose-clamp only imperfectly seals the supply/return hose to the reservoir cap - the clamp is as tight as I can get it - and when fluid is returning to the reservoir a small amount leaks out at this connections (I lose about 1/2 a tank over a couple of months).

Engine is a Yanmar 4LH-HTE.

My guess is that there is sufficient back pressure generated by the returning fluid to cause this leakage.

I was thinking that maybe making a small vent hole in the cap might solve the problem but wondered if anyone could see any downside to this.

Any other suggestions gratefully received.

Regards,
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Old 25-08-2014, 07:21   #2
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Re: Cooling fluid reservoir problem

Your overflow tank is supposed to be vented to atmosphere. There is never supposed to be any significant pressure in that tank or line. I'm just going to guess if you have tried clamping the line on that tank you may have crushed the tank fitting as it's plastic. Replacing the tank and line with a snug fitting piece of vacuum line may be in order, or if the tank is not crushed maybe just replace the hose with a snug fitting vacuum hose.


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Old 25-08-2014, 07:37   #3
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Re: Cooling fluid reservoir problem

The hose looks to big for it. The clamp shouldn't have to crush the hose like that to get it to seal. Like a64pilot said, it should be snug fitting before the clamp is tightened. Is it?

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Old 25-08-2014, 08:43   #4
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Re: Cooling fluid reservoir problem

It is the hose that was there when I bought the boat and she was only 4 years old then. I have assumed it was an OEM part. Perhaps not.
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Old 25-08-2014, 09:01   #5
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Re: Cooling fluid reservoir problem

Yes, it is OEM. You can see the same setup in the interiors picture section of the Nauticat 515.

The tank should be vented. I believe that in most "overflow" tanks the cap fitting is where it is vented.
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Old 25-08-2014, 09:07   #6
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Re: Cooling fluid reservoir problem

Quote:
Originally Posted by a64pilot View Post
Replacing the tank and line with a snug fitting piece of vacuum line may be in order, or if the tank is not crushed maybe just replace the hose with a snug fitting vacuum hose.

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If you replace the hose, it must be with reinforced cooling hose or strong vacuum hose. Why? There is significant suction during the cool-down phase, drawing coolant back into the pressure cap.

I had Jaguar where that pipe would collapse, it worked as a one way valve - constantly losing coolant.

You can buy inexpensive coolant recovery kits from the auto store, so if your tank is damaged, that would be an economical way to replace it.

I'd strongly recommend keeping a recovery tank of some kind, it keeps air out of the cooling system, which is important if you are using any kind of modern coolant like Dexcool - they don't like air in the system.
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Old 25-08-2014, 09:48   #7
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Re: Cooling fluid reservoir problem

Overflow should be vented and only experience atmospheric pressure. You might have a distorted spigot on your plastic reservoir either when made or from overtightening.

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Old 25-08-2014, 11:54   #8
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Re: Cooling fluid reservoir problem

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Originally Posted by bobsadler View Post
It is the hose that was there when I bought the boat and she was only 4 years old then. I have assumed it was an OEM part. Perhaps not.
It may well be, it just looks too big in that photo. The end of the hose looks distorted to me, caused by the hose being larger than the fitting on the cap. I would check its fit on the cap without the clamp on it, it should be quite snug.




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Old 25-08-2014, 12:45   #9
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Re: Cooling fluid reservoir problem

I think we need more information before we go drilling vent holes. Cooling system design is a part of my day job.

Is this the location of the fill, or is it elsewhere? Is the fill designed to be pressurized? If you vent a part of the presurized system the coolant may boil on certain hot surfaces (head near injectors, sleeves). Cavitation both on the cylinder liners and the water pump are probable. You can ruin an engine this way.

The hose is certainly too big. That is interesting, the results of parts speced from different vendors. You won't see that on cars (designed as a system) but on buses and boats, yup, it's common. Yes, it is probably OEM. I'll bet the other end is a different size and and adapter is needed.

What is the function of the top line? It should NOT be the main coolant return; it is incredibly bad practice to return coolant through and expansion tank, as it is exposed to oxygen there and corrosion will be terrible. Is it from a heater? An air vent? There should not be regular flow though such a line. You need to understand the system. I've seen bungled cooling system designs on transit buses so bungled that initiating a recall campaign was the only answer (that did not make me popular).
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Old 26-08-2014, 02:16   #10
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Re: Cooling fluid reservoir problem

Hi,

Thanks for the inputs,

The vent/return hose connects the port below the pressure cap directly to the coolant reservoir.

I removed the cap for a close inspection and found on the underside that though there is a seal ring/gasket ("A") there is a very small diameter port ("B") that opens to what appears to be a gallery encircling the stem. On the cap's top surface there is another port ("C") that also appears to access the same gallery. The two ports are offset.

These ports are very fine (needed a magnifying glass to find them and couldn't get a paper clip in to probe them and had to use the tip of a small safety pin) and I'm not sure I didn't dislodge a bit of junk when inserting the pin tip.

If one or other of these ports was blocked it would certainly explain the generation of back pressure.

I've re-installed everything and will see what happens when the engine next cools down.

Apologies for the quality of the pics but my little camera doesn't really do clos-ups.

Regards,
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Old 26-08-2014, 03:20   #11
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Re: Cooling fluid reservoir problem

In the previous post it should have read "....when the engine next warms up"

Also I checked the fit of the hose. The cap nipple the hose pushes on to is "belled" at the end (i.e. a larger diameter) and the hose is quite a snug fit over that increased diameter. The engine's parts catalogue indicates that hose clamps should be used to secure the hose.

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Old 26-08-2014, 04:10   #12
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Re: Cooling fluid reservoir problem

Quote:
Originally Posted by bobsadler View Post
In the previous post it should have read "....when the engine next warms up"

Also I checked the fit of the hose. The cap nipple the hose pushes on to is "belled" at the end (i.e. a larger diameter) and the hose is quite a snug fit over that increased diameter. The engine's parts catalogue indicates that hose clamps should be used to secure the hose.

Regards,
Yes, the end of the hose looks much better in that last post. Must have been bad lighting in the first post.

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Old 26-08-2014, 05:37   #13
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Re: Cooling fluid reservoir problem

I can't tell, is the reservoir mounted to the engine or the boat? I ask because with engine vibration you want the tiny vents that are offset to prevent the vibration from sloshing out the coolant, but if its mounted to the boat there should be no harm in making the vent holes larger if they are clogging up
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Old 26-08-2014, 07:35   #14
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Re: Cooling fluid reservoir problem

Reservoir is mounted to the engine but given the holes 1) open into a gallery and 2) are offset I'm sure they could be opened up a little with sloshing being a problem.

They really are small - I would guesstimate less than 0.25mm (hardly visible without magnification).

I never keep the reservoir full as it's checked all the time.
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Old 26-08-2014, 07:43   #15
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Re: Cooling fluid reservoir problem

Like most cars, pressure regulation is through the cap on the engine. These no reason for the plastic tank to be under pressure. So, What A64pilot said, there is not reason the vents shouldn't be a bit larger. That may be the entire problem.
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