Engine Part 3a: Converting to Closed Cooling (the beginning)

Until last spring and for the first 31 years of her existence, Milou’s engine cooled itself by sucking up water from the outside, circulating it through the engine and spitting the now-warmer water out of the exhaust. Up until now, this has not really been much of a problem. Actually, even now, including the 31 years of calcium/mineral buildup clogging the cooling passages, direct cooling would probably work just fine for us as long as Milou remained in a body of freshwater. The problem with direct cooling is that once we make it to the Atlantic, the saltwater will eat our motor.

As an aside, I’d like to know if anyone has actually seen a marine survey worth the paper it was printed on? If so, I think it should be put in a museum. Before becoming a nurse, I spent ten years of my professional life working on boats. I did both mechanical and fiberglass work, ended up writing service and I managed a couple of shops. I am a little bit boat savvy, but the amount that I don’t know is still much larger than the amount that I know about boats (well, any subject really). When I flew down to Texas to check out the cheapest boat we could find that satisfied our list of basic requirements, I hired a marine surveyor to go through it with me. I did this because I wanted an objective observer and frankly I hadn’t spent much time on 40-foot cruising sailboats with inboard diesels. At the time, I assumed that the motor already had a heat exchanger; and when I asked the surveyor where the antifreeze was kept, he patted the exhaust manifold and said, “It’s in here, this is the heat exchanger”. I said ok and paid more attention to the batteries that were venting hydrogen sulfide gas.

Well, the spring after we took possession I went to run up the motor. I checked the oil level, and the transmission fluid, but I could not find a cap for adding or checking the coolant. After a little more research on the Perkins 4108 I realized that our motor was missing a circulating pump, and that it was set up for direct cooling.

Engine coolingWhat is this engine cooling he keeps yammering about? Lets go back to our friend the less-environmentally-friendly-then-advertised VW. Every combustion engine makes heat. The one in the VW has a radiator. The VW circulates antifreeze through the motor, where it picks up heat, and then through a radiator, where a fan blows cool outside air on the hot radiator and the heat is carried away on the wind (there are also air-cooled motors, but they all still need fresh air). A boat motor lives in a small confined space below deck–very little air movement. A radiator would just heat up the engine room until the engine overheated. Marine motors get around this by dumping the heat overboard in exhaust water. They can either do this directly by sucking the water right into the motor, or indirectly by sucking up seawater (or lake water) and passing it through a heat exchanger–basically a radiator, but it radiates heat into water instead of air. The advantage of indirect (or closed) cooling is that it keeps the motor separated from the corrosive effects of salt water. It also lets heat flow through the motor in more of a controlled manner, leading to a happier, longer-lasting engine.

Math and Trade-Offs – At this point I had already decided I wanted a big alternator; to do that I needed to upgrade to a serpentine belt. The $600 serpentine belt kit included a new, beefier water pump, which I also needed to convert the cooling system. The other thing I would need was a heat exchanger and some plumbing parts; that kit cost an additional $1800. A well-cared-for Perkins 4108 should last about 10,000 hours before needing to be rebuilt. Our hour meter reads 2929.6, and I’d wager that it has not been well cared for. Was it worth $2500 and who knows how many hours to convert the motor? Well, a new motor with closed cooling would be around $12,000. I could probably find a used rebuilt 4108 with closed cooling for $5000 – $7000. In the end I elected to spend $2500 to upgrade a motor that is probably worth about the same amount.

Parts to convert motor to closed cooling.

Obviously it is now time to start bolting on some new parts. Hey–they came as complete, expensive kits from an authorized dealer. I’m sure this will be as easy as removing some 30-year-old bolts!

Engine cooling 1
Ok, this is easy; take off the fan belt and remove the alternator…
Well, this cover has to go. It is where the new water pump is supposed to be. Wow that is gross behind there.
Well, this cover has to go. It’s where the new water pump is supposed to be. Wow, that is gross behind there.
Cooling 3
Uh huh, thermostat housing is off. I hope these studs are the right size for the new housing. Time to move over to the port side of the motor and remove the exhaust manifold.

Here is the first of many problems. The bracket that holds the throttle cable in place is bolted to the old manifold, and there is no way to attach it to the new Bowman combination manifold/heat-exchanger.

Throttle cable adapter
Where there is a will there is a way. I manufactured this bracket and was done for the day.

I realized that if I didn’t come up with a solution for the throttle cable now, it would be much more difficult once the new manifold/heat exchanger was in place. There was an unused 3/8 inch threaded hole machined into the side of the block. I had a bolt and a sleeve that fit to act as a stand off from the side of the motor. Then I took a walk around the boatyard looking for a piece of scrap. I found a nice little piece of galvanized bar stock. Using my hand drill, I machined it into a bracket to attach the cable clamp to the offset. The picture shows the first version; I didn’t like the alignment of the cable. I ended up taking the assembly home and tweaked it a little to get everything lined up well. Admittedly, the fix has a very “agricultural” feel to it, but hey it works.

Easy out
Starboard side of the motor. I need to get this bushing out.

Part of converting to closed cooling involves installing a pipe that transfers coolant from the heat exchanger to the engine block, upstream of the circulating pump. After hours of internet research, looking at pictures and YouTube videos of running 4108’s, I determined that this was where I had to attach the pipe. The coolant pipe is large diameter, 3/4 inch. After removing the 3/8-inch plug, I was concerned the restriction would cause problems with the cooling flow. One of the issues I had with this !*##@! piece of bronze is the I could not directly eyeball it; my head doesn’t fit between the motor and wall of the engine room. I had a quick phone consult with a good friend who has rebuilt a bunch of Land Rovers (English diesels). After telling me there are absolutely no guarantees, he thought the bronze thing was a bushing that I could maybe unscrew.

The above pictures show me destroying the plug thread with an EZ out and a large crescent wrench. I used a MAP gas torch to heat up the metal of the engine block around the plug and repeatedly doused the whole thing with penetrating oil. The bushing didn’t budge. I went back out to the boat yard to grab a piece of pipe I saw when scrounging for throttle cable assembly. With the pipe in place as a cheater I managed to move the whole engine block up, unweighting the pressure on the forward engine mounts, and I broke the big wrench in the process. The EZ out really dug into the bronze bushing, but the thing would not move. Another phone call to Gustaf (childhood friend of 42 years and Land Rover enthusiast); his advice:

“The bronze threads are probably corroded into the cast iron of the engine block. Well, you could take a hacksaw blade and cut through the softer bronze right up to the peaks of the cast iron threads. Don’t mess up the threads in the block. The cut may relieve enough tension to unscrew it, but you will probably need to cut out a pie piece and then pry out the bushing.” I swear I heard laughter as he hung up.


Remember I can not visualize this hole. (In nursing, when I come at you with a hose that is going to go somewhere uncomfortable, I always visualize the hole.) I have like 50 pictures of this, because I would run the hacksaw blade back and forth in two inch strokes until my forearm hurt too much or I got nervous about ruining the block. Then I stopped and took a picture, to see where I was–each picture a little more horrifying the the one before. I made the relief cut. Heat. Lube. EZ out. Nothing. I spent another six long hours hand cutting a second relief until I could knock out a small pie piece. Heat. Lube. EZ out. Nothing. Man, at that point I was done. Done.

It would have been easier to pull the motor out of the boat and be able to see what the heck I was doing. I was kicking myself, thinking that I was going to have to tell Deb I had spent three days away from my family creating a new, expensive problem. I went home thinking I was going to have to pull the motor to fix this horrible mess I had made. I was also thinking it was too bad I went at it blind with a hacksaw, when I could have simply drilled out the bushing a little and cut new larger threads in the thing.

...and after
Last shot. Leaving after three days of maybe making things worse. Feeling as glum as the rain.

3 Comments on “Engine Part 3a: Converting to Closed Cooling (the beginning)

  1. Ah, I feel your pain! Hopefully by now you’ve resolved the issue favorably – and I doubt you’ll regret the cooling conversion once it’s done.
    I’m assuming your question about marine surveys wasn’t rhetorical (though it could well have been!) in my experience the best of surveys is only 50% reliable, and the worst are worse than useless. My apologies to any marine surveyors out there, but darn it, you don’t have a good record in the industry!

    • Thanks for reading Keith. Yes, it works out alright. Details to follow. I do still have a slow coolant leak that I plan on attacking next month.
      I totally agree with your assessment of the marine survey. The more I ponder it, the more I think the surveyors are in a tough spot. We are asking a lot for the $350 we spend to get a 38-foot cruising boat surveyed in one day. There are so many things to look at and check over. After the fact we have the luxury of weeks aboard living with the systems, getting dripped on by the leaky hatches (how could the surveyor have missed those on a cloudless day!) to gripe about the rotten survey. I am not a dumb guy and if you asked me to do a survey in a day, I might put out a 50% reliable survey. Or, it might be totally worthless.

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