Flushing Heat Exchanger

You guessed it. Post your technical questions or solutions about your boat's engine here.

Moderator: KenKrawford

Post Reply
User avatar
TBOT422
Posts: 355
Joined: Sun Jun 26, 2011 5:36 pm
Location: Clearwater, FL

Flushing Heat Exchanger

Post by TBOT422 » Sun Oct 13, 2019 5:50 pm

Engine temperatures seem to be running a few degrees higher than normal at 2400 RPM. Nothing extreme, just below 180 degrees. Pretty normal (just over 160 degrees) at 2000 RPM. I am considering flushing the Heat Exchanger on the boat with Barnacle Buster. Has anyone done this? I am thinking about disconnecting the inlet and outlet hoses for the HE and connecting an in-line pump and recirculate the Barnacle Buster through the HE only (no raw water pump, hoses, etc.). If you've done this what kind of pump did you use? I've considered everything from a drill driven pump to a submersible fish pond pump to a 110V transfer pump. How long did you recirculate it? Did you recirculate continuously or let set for a period? I plan to remove and plug the zinc before starting and likely will need to replace the gaskets on both end plates when finished.

Any advice will be appreciated.
Gary & Janet
The Best of Times (Hull #422)

wolfe10
Posts: 368
Joined: Mon Dec 11, 2006 2:58 pm
Location: League City, Texas

Re: Flushing Heat Exchanger

Post by wolfe10 » Mon Oct 14, 2019 8:36 am

The way I have always done it (every couple of years):

Buy new end gaskets and O rings and ZN. Saw off end of ZN so it does not bottom out (actually top out) in the exchanger and break leaving the pencil ZN to block some of the lower cooling passages.

Remove the heat exchanger.

Remove ONE end cap.

Use a 50/50 pool acid (Hydrochloric acid) and water. Let in there only 10 seconds or so. Drain (I use a bucket so I can dispose of it properly). Flush with fresh water. Repeat until no bubbling (acid eating mineral deposits).

Reinstall end caps with new gaskets and O rings and reinstall.
Brett Wolfe
C350 #180
"Vindaloo"
League City, TX

User avatar
TBOT422
Posts: 355
Joined: Sun Jun 26, 2011 5:36 pm
Location: Clearwater, FL

Re: Flushing Heat Exchanger

Post by TBOT422 » Mon Oct 14, 2019 4:05 pm

I was hoping to do this in place. My plan is to disconnect the inlet and outlet hoses to the HE. Then connect an in-line pump to them with a bucket full of Barnacle Buster. The pump picks up the solution runs it into the HE and the discharge from the HE goes back into the bucket, thus recirculating the solution through the HE for a period of time. Using a pickup screen on the inlet hose in the bucket should keep most of the debris from recirculating. After cleaning, put fresh water in the bucket and rinse. Maybe several times until the discharge is mostly clear. Replace the end plate gaskets and re-connect the HE hoses. Seems to be simpler than removing the entire HE.

My only question at this point is whether to recirculate in the normal HE flow direction or to reverse the cleaning flow, and how long should I run the recirculation cycle.
Gary & Janet
The Best of Times (Hull #422)

wolfe10
Posts: 368
Joined: Mon Dec 11, 2006 2:58 pm
Location: League City, Texas

Re: Flushing Heat Exchanger

Post by wolfe10 » Mon Oct 14, 2019 5:18 pm

Never considered doing it in place. No idea what effect acid (irrespective of "brand", you will be using a strong acid to dissolve the mineral deposits) will have on the gasket material and ZN.

Pretty easy to drain off enough closed circuit coolant to allow heat exchanger removal. But, also a good time to change coolant! Two bolts and hoses to remove.
Brett Wolfe
C350 #180
"Vindaloo"
League City, TX

User avatar
TBOT422
Posts: 355
Joined: Sun Jun 26, 2011 5:36 pm
Location: Clearwater, FL

Re: Flushing Heat Exchanger

Post by TBOT422 » Mon Oct 14, 2019 8:22 pm

I plan to remove the zinc and plug the hole before starting the process. I don't need extra 'zinc' debris accumulating in the bucket.

I recently had a plugged AC system as well and wound up using Barnacle Buster to flush out that system. I suspect that was mostly marine growth and not so much scale as I suspect to be in the HE. There is no way to remove and boil out the entire AC system, so I figure if it was good for the AC it should be good for the HE. Also nice that even though an 'acid' I believe it must be relatively mild as it claims to be 'biodegradable'.
Gary & Janet
The Best of Times (Hull #422)

wolfe10
Posts: 368
Joined: Mon Dec 11, 2006 2:58 pm
Location: League City, Texas

Re: Flushing Heat Exchanger

Post by wolfe10 » Tue Oct 15, 2019 8:12 am

Gary,

And, if a "full length/standard ZN" has ever been installed, you may still have a broken pencil ZN lying in there. Not many marine yards know that the standard ZN is just long enough to contact the upper housing and break off.
Brett Wolfe
C350 #180
"Vindaloo"
League City, TX

JohnNorton
Posts: 35
Joined: Thu Oct 13, 2011 12:27 pm

Re: Flushing Heat Exchanger

Post by JohnNorton » Tue Oct 15, 2019 10:24 am

Not fond of acids for many reasons I prefer to simply ream out the tubes in the exchanger every so often. You can make a "tool" for this from a coat hanger. Unwind one, straighten out the big bends leaving the tight twisted end intact. Use a smaller wire hanger, I think you'll find it fits nicely in the tubes. Remove both ends of the exchanger (leave exchanger in place). Carefully pushing and twisting this thru each tube removes most deposits that may be causing poor heat exchange, or unplug a few. You need to be careful to not break a tube or a solder connection to the face plates. I expect you did this but- did you clean the sea strainer before doing anything else ?

User avatar
TBOT422
Posts: 355
Joined: Sun Jun 26, 2011 5:36 pm
Location: Clearwater, FL

Re: Flushing Heat Exchanger

Post by TBOT422 » Sat Nov 02, 2019 10:00 am

Just finished testing results of the HE flush process I completed last week. Engine temperature at cruising speed dropped by about 10 degrees from where it was. Previously engine was running around 165 at 2,000 RPM and climbed close to 180 at 2400 RPM. After flushing temperature remained the same around 165 even at RPM up to 2600 for about 15 minutes trying to make a bridge opening.

I wound up buying a 12V transfer pump from Harbor Freight for $45. The pump came with a pick up screen and inlet hose. I removed the raw water inlet and outlet hoses on the HE and connected a short piece of the standard 3/4" and 7/8" hoses to the HE. Then reduced those hose connections to a section of 1/2" garden hose connected to the pump.
HE Flush 1.JPG
HE Flush 1.JPG (51.75 KiB) Viewed 80 times
The pump intake hose was placed in a small bucket containing Barnacle Buster (I used plain water to test setup for leaks before flushing). The outlet from the pump was connected to the HE inlet, and the HE outlet discharged back into the bucket. I let the pump recirculate for a little more than an hour.
Flush Setup.JPG
Flush Setup.JPG (48.57 KiB) Viewed 80 times
This is the inside of the HE after flushing:
Flush Result 1.JPG
Flush Result 1.JPG (74 KiB) Viewed 80 times
The other end of the HE with a new zinc installed: Note that all HEs are not necessarily the same. Notice that the zinc location on my HE is off center allowing for a full length pencil zinc without any modifications.
Flush Result 2.JPG
Flush Result 2.JPG (46.79 KiB) Viewed 80 times
Now I also have a 12V emergency backup bilge pump in case I ever need it. It just clips on to the battery terminals and is rated at 290 GPH
Gary & Janet
The Best of Times (Hull #422)

Post Reply

Who is online

Users browsing this forum: KenKrawford and 29 guests