Raw Water flow rate low....

[CTOlsen]

I've noticed my raw water discharge overboard flow rate has decreased over the last ~3 seasons. After the engine has heated up, the overboard flow is hot enough to show vapor (not just water) coming from the overboard line. Running temps are good, < 180 deg. I've inspected the suction screen, strainer, and the heat exchanger and don't see fouling. I replaced the impeller this spring and it had no effect.
I plan to disconnect the raw water hoses and have a look see inside, I have a small borescope I can use as well. Has any one seen this before? What are your thoughts on where the problem lies?

 

[Christian Williams]

Likely the heat exchanger needs boiling out, even if it looks OK. Standard maintenance every 5 years or so and the first place to start. Lots of threads on the subject.

Marine Diesel Cooling System Upgrade 2020

Symptoms: Apparent decrease in water volume at exhaust. Temperature RPM limitation at Wide Open Throttle. Steam from exhaust at idle. Solution: clean heat exchanger, optional general upgrade. When I took over Thelonious II four years ago, the boat would run at near seven knots all day at...

ericsonyachts.org

 

[Slick470]

Craig, Which engine do you have? On our Yanmar, if the raw water injection port to the mixing elbow gets clogged with bio goo, it can reduce flow out the exhaust. If the restriction is high enough, water will start coming out of a thru hull on the stern that is tied to a vented loop ahead of the elbow.

 

[footrope]

Yes, as Andy says, check your exhaust elbow for clogging, both the raw water port and the exhaust passage itself. A friend of ours with a Yanmar had to clean his injection port at the start of every season.

 

[Slick470]

I will warn however, that the smell of the mostly cooked and compacted remains of the little creatures that were clogging up ours gave replacing head hoses a run for the money. Also wear gloves, if you get any of that goo on your hands, your significant other might not let you any where near them until you get that smell to leave, and it was persistent.

 

[CTOlsen]

Craig, Which engine do you have? On our Yanmar, if the raw water injection port to the mixing elbow gets clogged with bio goo, it can reduce flow out the exhaust. If the restriction is high enough, water will start coming out of a thru hull on the stern that is tied to a vented loop ahead of the elbow.

I've got the original Universal 25XP. I replaced (had replaced) the mixing elbow 2 seasons ago, not because of fouling, but had developed a through-wall leaker.

 

[toddster]

Maybe strategic disconnection of hoses along the flow-path cold help pinpoint the source of the problem?

Another possible culprit that I've encountered is wear on the cover-plate of the pump. Even a tiny groove will let water go around the impeller blade instead of through the output - especially if there is any back pressure. Lapping the plate smooth again on a piece of fine sandpaper sometimes fixes the problem.

 

[CTOlsen]

Late follow up, but I found the problem
Noticing that the flow from the vacuum break line was low as well, I concluded that the problem is in the supply to the heat exchanger, not down stream of it. This winter, I pulled the raw water inlet screen and cleaned it. It had layers of bottom paint on it limiting the surface area of the inlet to the suction strainer.
I also found the suction strainer cap- the forespar clear plastic cover had a crack in it. Since this is on the suction side of the raw water pump, it was likely sucking air rather than drawing in raw water. I replaced it.
I acquired a small phone Borescope (eBay, $25.00) and inspected all of the accessible raw water lines. No fouling found.
After commissioning 3 weeks ago, my raw water flow is back to original. The vac break line is squirting normally, lots of raw water flow. I believe the biggest contributor were the painted raw water suction and even more so, the cracked raw water suction strainer.
Cheers!

 

[Grizz]

On the other hand...

Christian replied in #2 that the HE may be the culprit and recommended it be 'boiled out'. Without an awareness of this thread's existence, I pulled the HE from my Universal 25XP and took it to a local radiator shop to be cooked, boiled and cleaned out. Didn't need the HE last year anyway...

A pressure test of the unit proved that 1 of the end caps had an almost invisible crack, it mounted on the side not readily visible (of course). Ran (5?) new hoses (why not?) that are part of this HE, a couple being THE definition of PITA, especially when it came time to be a left-handed contortionist to press the ends onto the fitting. Ugh.

Bottom line? There is a noticeable increase of FW gushing from the stern AND the engine temperature on the gauge is down a bit, although the latter may be wishful thinking.

Sailing on a FW lake has some advantages, extending cycles between service intervals being one. I'll bet this is the 1st time this HE has ever pulled and boiled (from 1989).

Onto the evening! Take care.

 

[SurfingGuru]

I've got the original Universal 25XP. I replaced (had replaced) the mixing elbow 2 seasons ago, not because of fouling, but had developed a through-wall leaker.

Do you know if the threads on the 25XP mixing elbow were 1.25 or 1.5"?

 

[Kenneth K]

That likely depends on the riser/elbow configuration you have.

The exhaust flange off the back off the M-25 is 1.25" NPT. So the MFG supplied riser/elbows would likely be the same.

The Yanmar-type elbows are different.

They may be 1.25 or 1.5" BSPT which might require an adapter.

My replacement saga here:

E32-3 - Mariah Part II: Exhaust Riser/Elbow Replacement with Support Bracket

As I mentioned in the previous post, I was unable to remove the bottom flange nut that held the exhaust flange on to the exhaust manifold. It wasn’t simply a case of the nut being frozen on the stud; there just wasn’t enough physical clearance...

ericsonyachts.org

 

[CTOlsen]

Do you know if the threads on the 25XP mixing elbow were 1.25 or 1.5"?

I am not near the boat, just arrived at our winter residence in VA. Sorry, can't measure or get pix.

 

[CTOlsen]

That likely depends on the riser/elbow configuration you have.

The exhaust flange off the back off the M-25 is 1.25" NPT. So the MFG supplied riser/elbows would likely be the same.

The Yanmar-type elbows are different.
View attachment 45065
They may be 1.25 or 1.5" BSPT which might require an adapter.

My replacement saga here:

E32-3 - Mariah Part II: Exhaust Riser/Elbow Replacement with Support Bracket

As I mentioned in the previous post, I was unable to remove the bottom flange nut that held the exhaust flange on to the exhaust manifold. It wasn’t simply a case of the nut being frozen on the stud; there just wasn’t enough physical clearance...

ericsonyachts.org

My elbow doesn't look at all like this beautiful stainless piece of hardware.

 

[Kenneth K]

My elbow doesn't look at all like this beautiful stainless piece of hardware.

Yeah, the stainless ones are from HDI Marine. They sell through eBay. I only discovered them after I already purchased my stock Yanmar elbow.

 

[Kenneth K]

Apparently, the M25 (21hp) and M25XP (23hp) use the same 1.25" exhaust flange:


The note says this will not fit the M25XPB (26hp) which uses a 1.5" fitting.

Exhaust Flange Rectangular Universal Diesel 3 hole

Catalina Direct, publishers of the Catalina 22 and Catalina 25 Owner's Handbooks and the largest supplier of parts and Lewmar winches for Catalina Yachts in the country

www.catalinadirect.com

 

[light24bulbs]

What is the general thinking on running barnacle buster through the system? Might be easier than removing the exchanger and having it boiled.

 

[Nick J]

I just cleaned my heat exchanger since I had the engine removed and easily accesable. Barnacal buster helped loosen the deposits, but it still required scrubbing with a scowering pad. Inside the tubes was clean so it wasn't that difficult once I had everything apart. That being said, it can't hurt to give it a shot before pulling it apart. Worse case, you loosen everything up for when you have it apart.

 

[Christian Williams]

Definitely worth a try for maintenance (although I haven't tried it). For circulating the acid, some directions say remove the impellor and use a separate pump, others say close the raw water seacock, start the engine and use the existing raw water pump. Then after 4 hours or so with the product in the system, just open the seacock and start the engine to expel the acid and its glop. It does take some rigging of bucket and hoses.

One benefit of boiling out the whole system is that hoses often have salts buildup as well as the heat exchanger.



I believe in physically removing the heat exchanger periodically. They can host bits of rubber impeller, which acid won't remove. The end gaskets can be changed (they're only $3) and the unit spray-painted. On my boat the removal job isn't hard, and then you can just put the Hx in a bucket and let the phosphoric acid go to work.

Be good to hear from someone who has introduced Barnacle Buster into the system, and how that worked.

 

[Nick J]

Good reminder on the impeller bits. I forgot they made up the majority of the blockage when I removed mine. It's easy to keep track of them when you've replaced every impeller between heat exchanger clean outs. If others have done it, you never know what they might have left behind.