How to flush, clean or remove heat exchangers

In my experience, (8 years with MAN 900 CRMs) Rydlym can help keep the raw water side clean, and may allow you to increase the service intervals, but it does not address the fresh water side of the heat exchangers.

Skip, You're very on top of MAN's but just for context. I have 2006 MAN1550CR's. I cleaned them when I bought the boat 2/15. They had been done about 3 years prior and were 20% blocked. The boat had been on the Gulf side.

My boat runs 183 port and 185 Sboard at 1850RPMS. At 2000RPM I'm about 187. The same temps before and after cleaning. All measures are in summer water temps.

As I've learned, an issue with MAN's is that the heat exchanger on your 900 is the same as my 1550. My tosses off a lot more heat so I need to be more careful. That said, regardless of your temps if the cores corrode it's a use expensive problem.

Smaller engine, but on my Perkins I did the heat exchanger twice in 14 years.
Had a spare onboard, fully acid boiled and cleaned, zero downtime.
As reported above, found zink fragments in the heat exchanger each time.

Skip, I pulled my commissioning reports from April of last year. mid-load in April Gulf water I was 182P and 185sboard at 2150. Those are perfect conditions with an immaculate bottom, new impellers and so on.

Also, I believe on your motor there is a diverter valve on the after cooler that lets the motor warm faster in cold water. One it comes to temp the valve opens. They can be an obstruction if they aren't working well.

Isn't one of the issues with the HE service is to check for corrosion on the tanks where the end caps meet the tank? If the tank corrodes you are looking at a pricey repair.

Is that problem solved on the new CR's? Mine are 2003 vintage.

That's the issue. It's $10's of K's but now there are some processes where a machine shop can bore it out and insert a ring so the tank is saved. Mine was ringed.

Mine had to be done in FLorida by MAN. Supposedly

Mine were sent to Florida in the spring to MAN. They were able to insert the ring and save the tank.

Supposedly the new ring doesn't corrode like the factory surface of that era.

Anyone know if this is true? That's what my MAN wrench told me. He says I can go 3 years now.

Every two years is their current recommendation and that's what we follow.

Here's a picture of the ring. Mine were 3 yrs and had zero corrosion. Your mileage may vary.

I use Rydlyme for flushing the heat exchangers. A cycle of 4 hours per engine. An extremely efficient process and the cooling system is back to new condition. I have only performed the Rydlyme heat exchanger flush when engine coolant temperatures start to rise above normal levels at WOT. I believe MAN are exaggerating. I had twin MAN 1100 engines on my previous boat and I ran them for over 7 years without flushing or cleaning the heat exchangers and engine coolant temperatures were always within normal levels. The MAN 1100 engine coolant temperatures never exceeded 87 degc (188 Fahrenheit) at WOT during our summers which are very hot with sea water temperatures rising to over 86 Fahrenheit.