Cleaning Heat Exchangers DIY

[Island Time 1,230]

see new article,here

I hope it helps some save some $$!!

[Battgirl 23]

Thanks IT for adding to my job list and hopefully reducing my expenses list.

[rigger 47]

Anyone have keel coolers?

[Island Time 1,230]

In my experience, keel coolers are pretty rare on NZ yachts.

 

For those who don't know what they are, they are basically a heat exchanger OUTSIDE the hull - the engine coolant flows through tubes (or a box arrangement) attached to the outside of the hull. They are pretty standard equipment on large commercial vessels I understand.

 

However, they do ad drag (although some are installed flush with the hull), and can have problems with fouling and filling with mud etc. As with, it seems, all things boating, there is no perfect solution!

[Steve Pope 243]

A lot of metal boats have an area of the hull below the waterline that is double skinned with around 25mm + - distance between them, the area of the "box" is calculated accordingly to the cooling needs of the motor and would have a horizontal baffle around 7/8ths of the width of the box 1/2 way down to stop the engine cooling water from making a direct link between the upper (inlet) and the lower (outlet) connections to the motor. This gives you a fresh water cooled engine with out any direct salt water interface. Generally either anti freeze / corrosion inhibiter is used or as in the old days they used a small amount of soluble oil to protect the system. The n...er in the wood pile is that you either have to have a dry exhaust or else fit a small separate saltwater pump to be able to run a conventional water cooled exhaust system. Usually the inner skin of the "box" is welded to the inside of the hull and therefore doesn't affect the smoothness of the hull plating. 

[Island Time 1,230]

Yep, absolutely right Steve. Steel boats can and do have this system. It was never my intention in the Article to cover all possible types of engine cooling system, but it's probably good that this is added.

 

The ability this "internal Keel cooler" to transfer the heat from the engine to the sea is directly related to the hull surface area they cover, and the temp of the seawater. As the hull is basically a flat surface, they are generally larger than a conventional heat exchanger, as the conventional heat exchanger has tubes and therefore more surface area in contact with the seawater. That being said, this is a good system for a steel boat - no seawater pump, nor blockages from sea life, no impellers to change etc.

 

The downside, unless you have, as Steve mentioned, a raw water pump for the wet exhaust, is you must have a dry exhaust. That can be good it it is designed in, can be noisey, hot, and smelly if not. If you then ad that wet exhaust pump, you are re-introducing the issues with pumps and seawater/sealife! Everything is a compomise...

 

One other advantage of this over the external keel cooler, is that in a muddy environment (like drying out in a creek etc) it does not clog up. Both are susceptible to loss off efficiency if the hull is allowed to foul too heavily - but we keep our boats clean, right?  

[Steve Pope 243]

If you get some phosphoric acid and dilute it by 4 or 5 to 1with water then either immerse the core in it or position the hoses leading into the HE so that you can pour and hold the acid in there within 15 minutes all scale and contamination etc. will flush out when you drain the acid, continue the flush with fresh water to neutralize any acid left, although once the motor is started it will self flush. Check your zinc anodes after doing this process as they will most likely need replacing if you had left them in place.

[Island Time 1,230]

Yep, as Steve says, many people use acid to dissolve the calcium. It wont dissolve any impeller fins that could be stuck in it, or other foreign objects. I've also seen long periods of acid bath cause leaks in the core, so by all means use it, just stick with the 15mins and the DILUTE solution.

Personally I prefer to take the ends off and inspect them. Dilute acid is fine if it's just calcium.

 

MB, that sure needed doing! It is not the hours running that (normally) causes an issue. The spawn/seeds/eggs are in the water, and will grow inside regardless of whether or not you fit a strainer. Strainers are a good idea though, they stop larger objects getting into the cooling system.  

[smithy09 50]

Nice article. Thanks Matt! We lost cooling on the Marshall in the RNI. I checked the strainer, a few bits of crap, but not much. Then opened the seacock with the strainer feed hose off. No flow. Removed the hose from the seacock. No flow. Pushed around with a bit of wire and the seacock itself was packed tightly with seawead and leaves.. Amazing.. Your article has prompted me to open up the heat exchanger though. Never been done in 4 years much to my shame!!

[Island Time 1,230]

Smithy, I expect that is the same on many boats!

 

As in most fault finding, the cooling system (as you found out) should start with the basics - is there any water to use? I've actually seen a fish jammed in the thru hull of one boat ! In the case of no water coming in thru the through hull, or a really blocked strainer (if fitted), I'd expect that that raw water impeller may also suffer, and need checking/replacement.

 

A hint to all this - if you run your engine at full revs and load for say 15-20 mins, it should NOT overheat. The temp gauge (if fitted) should stay in the "normal" zone, as the thermostat should control it. For the temp to rise past the range of the thermostat indicates the beginnings of a problem. This is regardless of whether or not your engine is raw (sea) water cooled, or has a heat exchanger. Oh, and all engines should have a thermostat! Not to have one (or to have one stuck open) will cause the engine, in most cases to run cool, and that causes excess wear. 

 

If you don't have a  temp gauge, I highly recommend getting a laser temp gun. Cheap on trademe. Then use that to check the temps of the engine, and record what is normal. Then when you suspect an issue, it's easy to see if something has changed. You can also use it to get fridge/freezer temps, seawater temp, anything.

[smithy09 50]

Yeah a temp guage is on the list of things to do for sure... I agree with everything you say in this post. Common sense, but easily forgotten. One blade off the raw water impellor was gone with that little mishap, so you were correct!