How to flush, clean or remove heat exchangers

My experiences have been opposite. I've noticed the Rydlime only cleans so so. The biggest issue I've seen with heat exchangers and a lack of cooling have been with broken off zincs stuck in them which the Rydlime and such don't remove, however Mans don't have any zincs so no need to worry about that.

While MAN does recommend cleaning all heat exchangers every 2 years. Most MAN owners I know and most Man mechanics recommend cleaning them every 1000 hours at the 1000 hour service and not on a years basis. I manage a 2007 yacht with 1100 common rails and they've never been done and it's at 980 hours. We're getting ready to do them all now. All numbers are still pretty much where they should be on temps.

192F at 80% load. Motors are a little underpropped 2360 rpms loaded......80% is anyhere from 2050-2150 depending on fuel load. EGT's around 1250-1280F The alarms will sound at 202 or 204F I think it is. Temp has been this way since I met the boat with 600 hours on it. The current owner is planning on doing the 1000 hour service and all heat exchangers, Full throttle they will slowly creep up to just below the alarms at 201F, so they're due. You shouldn't get any barnacle growth inside of the engine anywhere, however, silty water will pack the coolers a lot quicker.

Our boating is clean water, and almost all of it offshore. Ft. Lauderdale to either the keys or bahamas every single trip. This owner has a 47' Fountain also, so he runs the predator similar.....4 day weekends.....run 155NM to Key West on Friday, run back on Monday.....etc...every other weekend...or run to Nassau on Friday, Lucaya on Sunday, run home on Monday........good thing fuel is cheap and she cruises at 28 knots! The boat does 6-800 NM every single month and has for the past year and a half.

Unfortunately those conditions will scale up the heat exchangers a lot faster than usual. They'll also wear out impellors quicker. But it is what it is.

Surprisingly since the boat is fast, it's not a lot of hours. 6 hours to Nassau, 5 hours to Key West, 2 to Bimini (each way), just over 3 to Port Lucaya. But yeah, he's chewing through around 1200-1500 gallons per month.

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.

It depends on the motor, the sea water temp and the thermostats. I "think" the common rail 1100's I run have 192F thermostats in them, and yours might also. If that is the case, then 192F is the temperature they're designed to run at.

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.