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Old 05-12-2011, 19:47   #1
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Losing Coolant - Need Some Advice

Hello all, I have an issue. I have a Perkins prima 50 that looses about a cup of radiator fluid an hour. I have tried dyeing the coolant a very dark color to see if it would come out my exhaust system, but as my exhaust pumps out raw water at a few gallons a minute I couldn't tell if there was any change in color. The engine runs great exept for this issue. There is a small amount of white smoke at the start up but none after a couple of minutes of running. I have a very dry bildge, and have found no sign of coolant in my engine pan. The oil looks to be in great shape and not cloudy at all. This has been going on for over a month now and I really want to get it fixed. Does anyone have any good ideas? Tomorrow I am going to try and rent a radiotor pressure tester, but I'm not sure what that will tell me other than that I am loosing radiator fluid which I already know. Any help would be appreciated.
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Old 05-12-2011, 19:57   #2
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Re: Loosing coolant need some advice

pressure test the heat exchanger. a leak there means coolant is joining cooling water and exiting through exhaust
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Old 05-12-2011, 20:03   #3
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Re: Loosing coolant need some advice

+1 for "coma" - Perkins usually have copper tube heat exchangers that rapidly dissolve if not kept properly "zinc'ed."
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Old 05-12-2011, 20:26   #4
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Re: Losing Coolant - Need Some Advice

+2 Pressurise the coolant system with the exhaust elbow off. I suspect the H E as well.
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Old 05-12-2011, 20:39   #5
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Re: Losing Coolant - Need Some Advice

When my hx went out raw water was getting into the coolant.marc
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Old 05-12-2011, 20:52   #6
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Re: Losing Coolant - Need Some Advice

Is there any issue starting the engine after its been running for awhile.

I'm not an expert on engines, certainly not boat engines, but I did have a coolant issue with a snowmobile we have and one of the rubber header gaskets was bad. Engine would run, but was awful starting up after being used - especially when it was only shut off for a short time. It was clear that it was burning coolant though due to the smell and smoke, but it was much less noticeable when the engine had been sitting.
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Old 05-12-2011, 21:24   #7
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Re: Losing Coolant - Need Some Advice

Thanks for all the suggestions. I will give the pressure tester a try while the exhaust elbow is off.
I do not believe there is any salt water getting into the coolant. An old timer recommend me tasting it ( no swollow) if it's sweet and not salty it's good. If it's salty at all bad news.
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Old 06-12-2011, 02:22   #8
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Re: Losing Coolant - Need Some Advice

If it's ethelyne glycol I wouldn't taste it. I'd get my kid to taste it...

+3 on the HE.
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Old 06-12-2011, 02:50   #9
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Re: Losing Coolant - Need Some Advice

The clue that I would encourage you to follow is the white smoke at startup. There may be a small hole developing at the cylinder headgasket that allows your coolant to enter a cylinder in smal lamounts. At startup this maybe evident by the smoke but once running and engine heated that smoke dissapears.The coolent evaporates with the heat and very little finds its way to the oil.
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Old 06-12-2011, 03:06   #10
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Re: Losing Coolant - Need Some Advice

A head gasket leak is a possibility but the HE is an easier check.

Head gasket leaks -
Coolant to cylinder - Presurizes coolant system, bubbles may be seen with coolant cap removed, low compression test
Coolant to oil pressure passage - oil in coolant sytem
Coolant to oil drain passage - Water in oil
Coolant to intake port - Maybe undetecable, possible rust build up in valve guide area.
Coolant to exhaust port - Probably undetectable

Rule of thumb for pressures -

Cylinder pressure - highest
Oil pressure - Second
Coolant pressure - third
Oil return - lowest

Leaks flow from high pressure to low pressure.

1 - It is very, very unlikely that coolant will flow across a headgasket failure into the cylinder.
2 - If enough water to cause white smoke leaked into the cylinder while "static" and did not flow past the rings into the oil sump, it would surely cause a hydraulic lock upon trying to start the engine.
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Old 06-12-2011, 05:19   #11
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Re: Losing Coolant - Need Some Advice

Check the rubber end caps connecting the heat exchanger to the manifold tank and separating the fresh and raw water systems. There are two hose clamps - the smaller one clamped to the heat exchanger tube bundle and the large clamped to the manifold tank. If they are not clamped properly, the raw and fresh sides will mix. These are a bit tricky to seat correctly, and are the most common cause of coolant loss in these engines.

The part I am describing is the two rubber caps on the top of this picture - one on each side of the tank.

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Old 06-12-2011, 05:56   #12
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Re: Losing Coolant - Need Some Advice

It could be the tube stack, but more likely the head gasket as your dye would color the exhaust outflow. Check your oil, taste for salt; if it's good make a salad.
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Old 06-12-2011, 06:12   #13
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Re: Losing Coolant - Need Some Advice

Check those rubber end caps before tearing anything apart. They are, by far, the most common cause of coolant loss in these engines. Make sure you have a good seal on both the tube stack and the manifold tank - particularly check the seal on the tube stack.

You will not see a change in exhaust color (without fluorescent dye and a UV light) if the leak is a cup of coolant per hour - that is a thimble full per minute.

The tube stack is not copper and the design does not have a zinc.

A pressure test will most likely lead you astray into tearing apart and replacing a heat exchanger. If the rubber boots are not set correctly, the pressure test will fail but you will assume the heat exchanger is bad and go about spending a lot of money and time fixing it for no reason.

Head gasket coolant leaks are the least likely cause of loss of coolant in most engines, and definitely this engine.

I'm not sure why everyone is jumping to a catastrophic failure conclusion when there is a known, simple issue with a coolant system component of these engines.

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Old 06-12-2011, 07:03   #14
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Re: Losing Coolant - Need Some Advice

You might obtain some water soluable UV dye and add a few drops to your cooling system and then check your raw-water output with a "Black Light". Odd's are, however, that either the rubber gaskets are bad or you dod have a leak in the HX tube bundle.

FWIW...

For an example of UV Dye Testing see:
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Old 06-12-2011, 19:39   #15
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Re: Losing Coolant - Need Some Advice

Thanks for all the hel everyone.
Mark I think you may have hit the nail on the head. I pulledthe Hx out and it looks in great shape (not saying it's not leaking though) but he end caps sure do looked cracked and fatigued. I'm looking onto getting them replaced. Once I get new ones I will rig something together to check the hx while it's out. I'll keep you updated.
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