Heat Exchanger Maintenance

[Mike Vaccaro]

Just finished servicing the 3" heat exchanger on our 1988 C34, Hull 563 mounted on a Universal M-25XPA engine.  Don't know the previous maintenance history of this engine, but we've owned the boat for almost three years now and the engine has approximately 650 hours.  We've been meaning to service the heat exchanger, and a recent galley replacement required draining the coolant; so the time was ripe.  Lots of good info on the website that aided in the process.  Some things we noted:

1.  It's very easy to remove the heat exchanger.  Disconnect the four hoses (2 x 5/8" sea water, and 2 x 7/8" coolant).  Depending on the technique you use to drain/pump the fluid from the engine, you're likely to have some of the glycol mixture spill as you detach the lines.  Also, ensure the sea water intake (engine intake) is closed before you disconnect the sea water lines.  Loosen the two large hose clamps completely that hold the heat exchanger in the metal saddle above the transmission.  Remove the hose clamps and lift the heat exchanger off the saddle. 
2.  Have a container available to set the heat exchanger in, since it will drip fluid after it is removed.
3.  Examine the exchanger for evidence of leaks.  It is made of bronze, and any leaks will be apparent as a light green chalky stain.  Make a note so that when you re-assemble, you can properly seal.
4.  Remove the two end caps by loosening the two 3/8" bolts that hold them in place.
5.  Prepare a solution of "Lime Away," CLR or any commercial de-scaling/rust removal product in a container big enough to submerge the heat exchanger completely.  If it's been a while (or the first time ever!) the exchanger is cleaned, there is likely to be quite a bit of crud in it.  This initial bath is only designed to clean out the majority of the crud before it dries.  It will probably still be necessary to take the exchanger to a radiator shop for proper "boiling" to clean the hard deposits.
6.  Clean the bolts and endcaps.  Any radiator shop should be able to boil the heat exchanger itself.  Even after the Lime Away bath, they were able to remove quite a bit more material from ours. 
7.  Re-paint the exchanger after cleaning.  This will help with dissimilar metal corrosion.  We left the end caps bare bronze, however to assist in detecting leaks in the future.
8.  Re-install the pencil zinc.  If you do this on the bench without the end caps in place, it will show you exactly how the zinc fits into the exchanger as well as how it looks with the cap bolt properly torqued.  A standard zinc will fit in the 3" exchanger without trimming.  We did find some evidence of old, broken zincs in the exchanger.  The best way to avoid this is to frequently change the zinc (every six months in salt water).  Do not use teflon tape to seal the zink threads.  A metal to metal connection is required.  Use a non-hardening sealant instead.
9.  Obtain replacement gaskets and reassemble the exchanger.  This are large round rubber gaskets that have a small 3/8" diameter hole in the center.  It would be possible to make these, but they may be obtained from a Universal parts supply source (there is no Kubota equivalent since the heat exchanger is a maritime modification).  Buy an extra set for your next maintenance cycle or a repair.  Some folks have also purchased "heavy" end caps.  The stock caps make an adequate seal if they are properly installed with an O-ring around the base of the bolt and some Permatex 2B (or other type of non-hardening water/glycol tolerant sealant).  The caps are slightly concave around the center bolt hole to allow the bolt to draw down the cap when it is torqued.  There is also a ridge along the outer perimeter of the end cap to make a seal.  Be sure that you assemble all of the parts "dry" before you add any sealant to ensure that you understand the proper assembly sequence and have the caps installed correctly.  Although I can't specify a torque setting for these bolts--be careful not to over torque and crush the gasket during installation.  To apply sealant, make a thin bead around the outside diameter of the exchanger and the base of the bolt (right over the O-ring).  To properly install the O-ring, put the bolt through the plate and slide the O-rind down the bolt.  Then insert the bolt into the gasket.  Tighten the end cap bolt.
10.  Re-install in reverse order.  If you're hoses are older than five years, you might consider replacing them.  Aside from the one 7/8" line that attaches to the base of the water pump, there are no specially formed coolant or sea water lines on the M-25.  You can use stock replacement hose from an automotive or marine outlet.  Buy the expensive, solid all-stainless hose clamps of the proper diameter.  This is not the place to skimp.  These clamps have a propensity for breaking due to vibration induced fatigue.  Make sure you carry a spare on-board.  We had to cracked clamp two and a half years ago and switched to the heavy-duty clamps.  The heavy duty clamps had no evidence of fatique after approximately 200 hours of operation. 
11.  As Ron Hill and some other knowledgable folks on this board have suggested, consider removing the exchanger at regular intervals for cleaning.  If this is done frequently enough, it should only cost a set of gaskets as it is probably not necessary to have a radiator shop service the exchanger--a home-made bath of some type of radiator cleaner/descaler should do the trick.  A great time to do this would be during the annual transmission fluid change, since you can remove the saddle and access the transmission fill cap from directly over the engine (i.e., no working upside down in the aft bunk area!). 

Cheers,

Mike Vaccaro
"Spirit" 88 Hull 563

[Ron Hill]

Mike : What a great article on the HX.  Send a copy to Mark so he can put it in Projects.

Let me add a couple of notes to Mike's write up:
1.  When you remove the end caps go ahead and install a new rubber gasket.  Call Glenn Mar Marine (800)282-0123 for the SemDure @ $1.50 gasket (#0332). 
2.  When you replace the hoses make sure that if the hose is on the intake of a pump or if it makes an acute turn (greater than 45 degrees) that the hose should be wire reinforced.  If the hose is on the exhaust of a pump the hose can be nylon reinforced.   You don't want the suction of the pump to collapse the hose or the turn to crimp the hose and restrict it's flow. 
3.  There have been two different size zincs that I've encountered in the 3 inch HX.  A 3/8 and a 1/2 inch diameter.  My 1/2" Zn need to be cut as it's length is too long as purchased.  So check your HX as the insert threads may be oriented such that the full length will not fit.  If forced in, the Zn will break off at the ZN's threaded portion and then will offer NO protection. 

A few thoughts.   

[Kathy Knowles]

Thanks so much for the great advice and detailed instructions

Question:  What paint did you use to re-paint the heat exchanger?  Is there a recommended source for the original engine paint color?

Thanks again!

Kathy

[Mike Vaccaro]

Kathy,

Doesn't really matter.  Any enamel will work fine at the temperatures that these engines operate.  If you buy paint, I'd recommend a fast drying "engine" enamel for high temp applications.  This is readily available at automotive shops.  I tend to use what ever is on the shelf!  So our engine and it's components are a combination of Ford blue, Universal gold and plain old white (which works well to provide a contrasting color to any leaks).  Haven't used any red yet, but it's too early to rule that out as well!!!

Cheers,

Mike

[Ron Hill]

Kathy & Mike : In the Mainsheet article on changing injectors, Hank Recla listed  a bronze paint that matches.  Good stuff in the Mainsheet Tech notes!!
Go to any automotive store and get a bronze metallic paint or ask Universal and pay 5 X as much.   

[John Sheehan]

Mike's article got me inspired to work on my heat exchanger since I am not getting the cooling we had in the past.  However, on the MK II's the access to the heat exchanger is almost impossible without removing the wood cabinet in the aft cabin.  I have taken every screw I can find off but it still appears to be firmly mounted to the bulkhead.  As far as I can tell there are no screws going back into the cabinet from the engine room.  Does anyone know if the cabinet is also glued or where some hidden screws might be.  Once the cabinet is removed there is easy access.  The other day I looked at a friends 87 or 88 year model and I can see how the earlier models had much better access.  The strainer, hoses, and pumps are all either clean or new and I have a good flow of water so it looks like I need to clean the heat exchanger.

[Roc]

John,
I made a cut-out and installed a door for easier access to that location.  Makes checking the pencil zinc easier too. 

[sail4dale]

I was able to take the screws out and the whole wooden assembly came out.  The screws were in the molding around the panel (I think )

I wanted to get to the hump hose and finally figured it out

[Ron Hill]

Guys : To keep the heat exchanger clear of minerals, here's what I do.
Once year I remove the outlet line from the raw water pump.  I take "Lime-a-Way" and pour it into that hose until it stops filling.  I let it set inside the HX for an hour and then reconnect the hose.  It bubbles and get rid of at least most of the calcium deposits. 
Must be working as I've never had to remove the HX and have it boiled out in the past 19 seasons!! 

[John Sheehan]

As a follow up on removing the wood housing at the rear of the engine on the MKII's here is some additional information.  Today I finally got the time and inspiration to get serious and get it off.  There a small amount of glue on the upper brackets and also on the piece where the hinged top cover was mounted.  It took a bit of "careful" hammer work to get everything loose.  Now I know there are only 6 screws that need to be removed and they are fairly easy to get to and  remove the housing in one piece.  Catalina had told me there was no glue there but our dealer said he thought they may have put some glue there and he was right.

[Jeff_McKinney]

Ron,

Regarding the lime-away treatment: pardon the stupid questions, but I want to get it right.

1. Full strength or diluted?
2. About how much will I need (volume)?
3. What keeps the lime-away in the HX during this? I'd think it would all head down the outflow pipe to the exhaust
4. Clearing it-reconnect the hose, open the water intake & run the engine for a couple minutes?
5. End of the season or at the beginning?
6. Change the zincs before or after the flushout?

Thanks

[Ron Hill]

Jeff : Let me try to answer your questions:
I.  I use the full strength liquid Lime A Way(not the spray)
2.  I'll guess that you use about 1/4 of a bottle.  I take off the exhaust raw water hose (inlet hose to the HX) and use a small funnel.  If you hold the hose higher than the HX, pour it in until it fills.  Then I blow into the hose and make suer that air is out and refill with Lime A Way.
3.  If you look at the IN and OUT of the HX you'll see the IN on the bottom and the OUT at the top.  Then the OUT hose goes up higher than the HX to the nipple on the exhaust riser. 
4.  I do it at the beginning of the season, but you can do it anytime.
5.  I change my Zn at the end of the season and as I posted before leave it out of the HX during the winter.  Then reinstall it in the spring.  That way I know there's no liquid in the HX that can freeze ( after winterizing with antifreeze - belt&suspenders!!)

I think you need to take some time and examine your hoses and see where they come from and go to.   

[Jeff_McKinney]

Ron,

Thanks for all the good info. I'll give everything a good look so I am more familiar with the hose setup.