MD-17c Convert Raw Water Cooling to Heat Exchanger

[Lou-In-NJ]

I bought a 1979 S2 last season from the original owner, with a the original Volvo MD-17c on it. It's always been in salt water, and if the general condition of the outward appearance of the engine and boat is any indication, this engine has been well taken care of.

However I'm put off by the wild temperature swings of this engine. The temperature reliably builds until the temp gauge hits a little past mid-way, and then falls dramatically when I guess the thermostat opens. My familiarity with engines is enough to make me think this is not good for several reasons, metallurgical, thermal efficiency, combustion efficiency, carbon build-up, etc. I did wind up having to replace the reinforced rubber exhaust coupling that goes between the exhaust manifold and the wet muffler; the old one was brittle and developed cracks. But I was also able to scrape nearly 1/4" of carbon build-up from that immediate area of the manifold.

I think operating the engine at a more even temperature will be better all-around, and if I do a heat-exchanger (H.E.), I'd be likely to raise the priority of de-carbonizing the heads and manifold.

I read a post on this model engine and an over-heating issue someone was having, but that's not what's going on here. I'm currently operating in Maine, and while the water temp barely breaks 60F in the dead of summer, I still don't think the temperature should be swinging as much as it does.

Here's what I'm think about doing, and please feel free to comment or add any practical advice.
1. De-scale engine & check thermostat
2. Re-plumb engine to run coolant through a coolant loop that includes a plate heat-exchanger (H.E.) and an expansion reservoir.
3. Use self-priming electric pump to continuously (or intermittently*) pump raw water to heat-exchanger. (pump switched by relay triggered by engine key position)
4. Split raw water output of heat exchanger to maintain some water flow to exhaust fitting pre-wet-muffler, and most of the water flow to the exhaust system, post wet-muffler.

*MAYBE install a temperature sensor on the coolant side of the H.E. to turn the raw water pump on and off, although the way I'd likely design the raw water plumbing from the H.E., I'd likely have the H.E. drain-off through gravity after the engine is turned off; in which case I'd likely not install a thermal switch for the raw water pump.

<<<COMMENTS>>>

[sailormed]

Salt water cooled engines have a thermostat opening temp set very low to prevent salt build up in the engine bloc. Something like 65°C if my memory is correct.
Going with a HE you can put in a thermostat that allows a normal operating temp.
I agree with your line of thought.

Edit Watch out for the use of an electric pump. It will turn at a set speed, not proportionate to engine rpm. At low engine rpm the possibility exists that there is to much water pumped, resulting in water in cylinders.
A simple engine driven impeller pump would avoid this.

[Lou-In-NJ]

Thanks Sailormed. You're point about electric pumping is a consideration and a concern for me. On one hand, I don't want to necessarily rely on an electric motor when the rest of the engine is entirely mechanically self-sufficient; on the other hand, I didn't want to have to build/modify a bracket and belt setup to add another mechanical pump. Also, the pump I'd likely use can be obtained in flow rates of 6L-12L per minute; my initial thought was too much cooling! But I realize that the HE is the buffer, and the relatively low coolant capacity (compared to the ocean filling the engine) of the HE would limit how much the temperature reduction could be, even if the HE efficiency was very high. But this is the other reason I'd likely have the pump operating continuously,and just let the engine's mechanical thermostat control coolant flow.

[Rucksta]

I drilled a 3/16" hole in the thermostat and blocked the external bypass between the middle and front cylinder. (MD17d)

Temp gauge comes up to just under half way in 15 min and sits there.

Watching the waterflow in the strainer indicates the thermostat is opening and closing.

Temp gradient between the cylinders (taken from the rocker cover) is reduced to 15C, previously 35C

[Lou-In-NJ]

I will consider doing that Rucksta.
I still like the idea of not running sea water through the engine, but I may not be in a position to do the HE conversion this season due to logistical considerations.

[cagney]

@Lou-In-NJ

A few ideas...

There is a conversion kit to freshwater cooling available from Martec, see https://www.martec.se/en/group-15929...-13621157.html

If you don't like an electrical pump there used to be an option with a Johnson pump F4B-9 10-24144-1 piggy backed on the original saltwater pump, which should be a Johnson F4B-9 10-35098-2. The snag here is that I don't think that the F4B-9 10-24144-1 is available any more.

Good Luck!

Thomas

[Lou-In-NJ]

Thanks Cagney,
That's interesting and helpful. I see they're using a counter-current heat exchanger. I've seen that piggyback pump somewhere when I first started thinking about doing this. I actually prefer an electric pump, they're cheap enough, I can carry a spare.

[Scubaseas]

The reason the salt cooled engines run at 60*C is that salt precipitates out of the cooling water above that temp. There is no question that the engine runs more efficiently and evaporates more crud from the oil at higher operating temps like 82*C.



I converted my MD2C to FWC and have done a couple other Volvos. Use an off engine HE to reduce chance of the HE cracking due to vibration plus it's easier to gain access to it. I did a couple of motors that I had a 3 groove pulley made up for the crank and could then run twin alternator belts, A/C compressor for fridge and a FWC mechanical pump. Electric coolant pumps work fine as long as you have enough flow. They certainly make the conversion a lot cheaper and easier too.



Sendure makes a good selection of heat exchangers.



There should be a vent hole in the thermostat regardless of Raw or FWC engines. If not drill a small hole.

[mark maulden]

Have you looked at the thermostat? The original ones were a bellows type and worked well. They went to a wax type and had issues with those as you describe. This happened several decades ago. You might just try another thermostat. BTW, I have some exhaust manifolds, heads, pumps I’d like to unload...

[Rdl]

I have also converted to FWC on a 50yr old Atomic4 10 years ago, still running with electric pump.
I'm currently converting my Volvo 2002 Diesel with the same kit.

I have been very happy with the following vendor Indigo Marine
Atomic 4 - Indigo Electronics, Inc.

[RexSnr]

I would like to warn about using a plate heat exchanger on a used engine, or any engine for that matter. Plate heat exchangers have lots of tiny little water passages in them. They are super efficient in size and are very cheap to buy. In a boating application the S/S construction is also an attraction. On paper-ideal.

However, they block up very easily with any form of contaminant and cannot be cleaned by any means. We were fully equipped with chemical cleaning plants of many different types and pressure of chemicals. Eventually we never wasted our time. They went in the bin and were simply replaced. We used to repair a huge qty of water cooled machinery and the plate heat exchangers became a no-no in nearly every application. They become very expensive when you have to REPLACE them regularly.

There are ones with the plates clamped together, not welded, but normally the viton seal between the plates comes with a new plate and cost more than a whole new exchanger. This type can be cleaned but the cost is enormous are more expensive than a new unit.

If your engine was brand new, you could TRY a plate heat exchanger if using distilled water with a GOOD coolant added. The distilled water has no minerals in it, to drop out and attach to the water jackets with heat, as a few have already stated.The coolant would want to be excellent (not Chinese) and you'd need to be sure it won't allow ANY rust AT ALL.


Me??? No way known. I would only use a copper nickel shell and tube exchanger designed for sea (salt) water. This type can be cleaned in minutes if the access is good. Again, if distilled water is ALWAYS used with coolant, and no leaks were permitted, (which traditionally are topped up with mineral laden tap water) you should never need to clean or touch the engine heat exchanger.



In saying this, your engine is decades old and the water jackets will be extremely rusty - too rusty to be confident any form of cleaning will get them fully clean.
It can be done with an acid solution (I'd have to search for the book with the correct acid and ratio but if the acid is not neutralised correctly after a set time cleaning, the acid will continue to burn through the cast iron forever until you spring holes in the block or cylinder walls. It is not something an inexperienced person should attempt.



Get a proper marine shell and tube exchanger. Clean the block as well as you can but know you will have to keep cleaning rust out of the front bonnet of the heat exchanger (hopefully eventually it will stop) so make the access easy and quick. Keep supplies of distilled water with the correct coolant always made up ready to go. Once you have the system up and running, then buy a 185 degree F thermostat to keep the engine running warm and at the correct temp. Your problem should be resolved and your maintenance should be minimal and predictable. If you have a problem at sea, you have a chance of getting yourself going again. Plate heat exchangers in your situation will cause many tears.


As for the water pump, I don't have any special knowledge on these, except to say every manufacture of marine engine I have ever seen uses rubber impeller bronze pumps for the raw water. I'd be asking for the reason why they ALL use these. I don't know what that reason is, But I'll bet there is a very good one!!