Raw Water Heat Exchanger replacement CD28?

[Balestrand]

Looks like I may have to replace my raw water heat exchanger for my CD28, which is currently in Boothbay Harbor, Maine. She was overheating in transit. The HX is at a radiator shop today, but I'm not hopeful.

Any suggestions for suppliers or manufacturers? This HX was strapped to the starboard side of my original Volvo MD2B.

Many thanks!

Robert Strong
"Spondee" CD28
Homeport Camden

[mgphl52]

Have you checked the exhaust elbow? You should be able to easily blow thru the hose from the HX to the mixing elbow. If not, that's most likely your over heat problem.

[Wayne Grenier]

The original manufacturer for the heat exchanger on my CD 28 volvo MD 11 was Sen Dure. They sent me an exact replacement a few years ago. They can be located on the Web and are currently still in business.They have many different exchangers for multiple applications. Mine boltes on the engine as most do. If the radiator shop cannot fix yours you can contact them or why not identify the manufacturer of your heat exchanger and if they are still in existence get an exact replacement? Mine lasted 40 years and cost $300 to replace, which is not bad considering its a boat.

You also need to be aware of the fact you have a thermostat as well.

Overheating can be caused by multiple issues. Water pump impellers broken or missing? Clogged intake? Thermostat? Loose water pump belt? clogged up rusted out exhaust riser? etc.

Good Luck

Wayne Grenier

[Balestrand]

Thanks for these replies. The exchanger was cleaned and a small exterior crack fixed. I have established that all hoses are clear and impeller good. The raw water is flowing well, and is not over hot leaving exchanger or leaving exhaust out the boat. In fact, it is suspiciously not very warm.

There is, though, a BIG difference in coolant hose temps: very hot entering from engine and cool leaving exchanger. I suppose this could mean exchanger is working great, but I'm suspicious that raw water does not seem to be taking much heat out AND that the exterior of the exchanger remains cool while the expansion tank where coolant enters from engine is very hot.

Could it be that the coolant circulation is the culprit? And what causes that circulation? Coolant from exchanger goes down to a sleeve around where the shaft enters the engine and the appears to exit into a metal pipe on the opposite side of the jacket. There could be a pump in there.

But it then also travels about 8 inches upward to a small circular housing, about 3 inches in diameter with a removable plate, which is on the back of the engine and looks like it could house an impeller? The metal pipe continues out the circular housing and into some darker region of the engine.

Any further thoughts would be very much appreciated. This Boothbay mooring is adding up fast! Though I feel lucky to be waylaid in a beautiful safe harbor.

[Wayne Grenier]

On a motor with a heat exchanger there are 2 pumps-one for the raw or seawater and one for the fresh water. Normally the heat exchanger and the 2nd water pump that feeds it are aftermarket add ons. It is possible your raw water pump needs and impeller but if that were the case you would not be pumping water copiously out of the exhaust. If you have a temperature gauge we need to kow what temp your engine is running at.

You have ruled out the heat exchanger as a source of problems. You can now move onto the water pumps.

[mgphl52]

You have ruled out the heat exchanger as a source of problems. You can now move onto the water pumps.

or maybe a bad/stuck thermostat?

[Stan W.]

But it then also travels about 8 inches upward to a small circular housing, about 3 inches in diameter with a removable plate, which is on the back of the engine and looks like it could house an impeller? The metal pipe continues out the circular housing and into some darker region of the engine.

On motors converted to fresh water cooling that is the fresh water pump. You need to remove the cover plate and inspect the impeller. From the symptoms you describe, it is very likely that is the problem. If you don't know when the impeller was last replaced, you should just replace it now to establish a base line. Then, inspect it once a year, or at least every other year. Most people carry a spare impeller for emergencies.

[Balestrand]

Found it!
Thanks so much, everyone. It's an interesting tale:
We started overheating...
Removed thermostat -- still overheating.
Exchange cleaned and small outer crack repaired -- still overheating.
Slight wear on raw water impeller, also some upstream blockage-- replaced and resolved-- still overheating.
Then the big one, which Stan W. pointed toward: total failure of coolant / fresh water impeller -- one flange left. Replaced-- running cool!

Just have to put the thermostat back in. (I tested it, and it is perfect.)

I am certainly inspired now to get to thoroughly know all the systems on this original 1975 Volvo MD2B.

Thanks for all the guidance,

Robert
CD28 Spondee
Camden, Maine

[Wayne Grenier]

If only you had started with the fresh water impeller first! I have the same motor, its actually an upgraded version called the MD11-it was rebuilt 20 years ago and still going strong. I have a decent amount of knowledge on these motors mostly gained by the same type of experiences you are having! hopefully we can walk you through any future problems.