djmarchand
Captain
- Joined
- Jul 24, 2012
- Posts
- 664
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- 295
- Location
- Litchfield, CT / Punta Gorda, Fl
- Boat Make
- Atlas Pompano 23 outboard
The Cummins-Yanmar thread suddenly morphed into acid flushing, so I thought I would start a new thread specific to acid flushing and repost something I posted to boatdiesel last year:
This discussion is specific to the Yanmar 6LY but the general principles are applicable to any marine diesel.
Today I tackled acid flushing the raw water cooling side of my engine. I had disassembled, cleaned, greased and reassembled the air cooler about a year ago, but now it seemed time to do the entire system.
In the summer at a cruising rpm of 2,800, the engine temp runs about 190 and rapidly increases to 200 or so at wot. No real problem; the engine doesn´t overheat but the rapid temp increase at wot led me to believe that the raw water heat exchanger was marginal. And AFAIK, it had never been cleaned in ten years and 800 hours.
My first approach was to remove the main heat exchanger. But after partial disassembling it and looking at the half dozen or so hoses that needed to be detached to get it out, I decided to leave it in place and acid flush the whole system.
So I first pulled out the raw water pump. I used its rubber elbow as the supply attachment to the circulating loop I hooked up. I used a couple of PVC/nylon fittings and a hose to a spare bilge pump I had laying around. The return hose was simply the raw water hose that normally goes to the exhaust elbow.
I used one gallon of Barnacle Buster mixed with a gallon of fresh water. You can use Rydlime, CLR, etc. But I don't believe in HCl- swimming pool acid. Too corrosive.
The first picture shows the bucket and hoses to and from. The Barnacle Buster solution immediately turned black so I knew it was doing something, but you can´t see the bilge pump as a result. The second picture shows the attachment to the rubber elbow. The corrugated white thing in the back is a plate I made from an old pvc shingle to block where the raw water pump normally bolts to the block- keep oil in and trash out.
Before adding acid you have to remove all zincs. Zincs will quickly waste in acid and will deplete it unnecessarily. So remove the brass cap, unscrew the zinc and reinstall the brass cap.
Also pinch the prop shaft log cooling hose with a pair of vice grips or similar. This is shown in the third picture.
I did something a bit unusual. I used engine heat to heat up the system a bit. It was 40 degrees in the engine compartment when I started this morning. So I hooked up a water hose with duct tape to the water injection elbow to keep the exhaust hose from overheating. You can see this in the first picture. I then started the engine and let it warm up at idle in reverse gear. When the dash gauge showed 160, the circulating solution felt like 100 degrees so I stopped the engine at that point. I restarted the engine every hour for 2-3 hours. I only ran the circulating pump for 5 minutes every half hour or so.
The fourth picture shows the Barnacle Buster solution after 15 minutes. Something was getting dissolved by the BB!!!
After acid flushing, I dumped the acid and dropped a garden hose into the bucket and displaced the acid with fresh water. I then hooked up the exhaust elbow and flushed some more with the engine running.
I will post temperature results the next time I go out, but with water temps now down to 50 or below, I won´t really know how it worked until the middle of next summer.
David

This discussion is specific to the Yanmar 6LY but the general principles are applicable to any marine diesel.
Today I tackled acid flushing the raw water cooling side of my engine. I had disassembled, cleaned, greased and reassembled the air cooler about a year ago, but now it seemed time to do the entire system.
In the summer at a cruising rpm of 2,800, the engine temp runs about 190 and rapidly increases to 200 or so at wot. No real problem; the engine doesn´t overheat but the rapid temp increase at wot led me to believe that the raw water heat exchanger was marginal. And AFAIK, it had never been cleaned in ten years and 800 hours.
My first approach was to remove the main heat exchanger. But after partial disassembling it and looking at the half dozen or so hoses that needed to be detached to get it out, I decided to leave it in place and acid flush the whole system.
So I first pulled out the raw water pump. I used its rubber elbow as the supply attachment to the circulating loop I hooked up. I used a couple of PVC/nylon fittings and a hose to a spare bilge pump I had laying around. The return hose was simply the raw water hose that normally goes to the exhaust elbow.
I used one gallon of Barnacle Buster mixed with a gallon of fresh water. You can use Rydlime, CLR, etc. But I don't believe in HCl- swimming pool acid. Too corrosive.
The first picture shows the bucket and hoses to and from. The Barnacle Buster solution immediately turned black so I knew it was doing something, but you can´t see the bilge pump as a result. The second picture shows the attachment to the rubber elbow. The corrugated white thing in the back is a plate I made from an old pvc shingle to block where the raw water pump normally bolts to the block- keep oil in and trash out.
Before adding acid you have to remove all zincs. Zincs will quickly waste in acid and will deplete it unnecessarily. So remove the brass cap, unscrew the zinc and reinstall the brass cap.
Also pinch the prop shaft log cooling hose with a pair of vice grips or similar. This is shown in the third picture.
I did something a bit unusual. I used engine heat to heat up the system a bit. It was 40 degrees in the engine compartment when I started this morning. So I hooked up a water hose with duct tape to the water injection elbow to keep the exhaust hose from overheating. You can see this in the first picture. I then started the engine and let it warm up at idle in reverse gear. When the dash gauge showed 160, the circulating solution felt like 100 degrees so I stopped the engine at that point. I restarted the engine every hour for 2-3 hours. I only ran the circulating pump for 5 minutes every half hour or so.
The fourth picture shows the Barnacle Buster solution after 15 minutes. Something was getting dissolved by the BB!!!
After acid flushing, I dumped the acid and dropped a garden hose into the bucket and displaced the acid with fresh water. I then hooked up the exhaust elbow and flushed some more with the engine running.
I will post temperature results the next time I go out, but with water temps now down to 50 or below, I won´t really know how it worked until the middle of next summer.
David



