Hopefully you never find yourself in a position where you need to replace your heat exchanger (like I did!). But if you do, firstly, I’m sorry! And secondly, hopefully this article will help ease your pain.
On this page, “front” refers to the end of the engine with the crankshaft pulley and belt, while “rear” or “back” refers to the end with the exhaust elbow and transmission.
Critical note before you begin! The heat exchanger rests on two studs which screw into the engine block. If you want to preserve these studs, you’ll need at least 4 inches of clearance on the right (when facing the front) side of the engine to slide the heat exchanger off the studs. Otherwise, you’ll need to remove the studs, which may damage or destroy them. I did not have enough clearance, and had to use vise grips to remove the studs, which gouged the studs and removed a bunch of their delicate plating. So I had to replace the two studs as well when replacing the heat exchanger.
DISCLAIMER. I am not a professional mechanic. This is just a record of what I did. It could be entirely wrong. You work on your engine at your own risk. If in any doubt, engage a professional.
1. Close raw water seacock and disconnect or switch off engine/starter battery.
2. Drain both cooling sea water and fresh water from engine.
3. Remove alternator.
4. Remove exhaust elbow.
5. Remove two sea water hoses from rear heat exchanger end cap.
6. Remove the overflow hose from the coolant cap.
7. Remove thermostat cap (2x M8 bolts, 12 mm hex head). This aids in the removal of the upper fresh water hose (below).
8. Remove the two sensor leads from the thermostat housing. The one on the right is a Phillips head screw, the other is a nut with an 8 mm hex head. This is necessary so that removal of the heat exchanger isn’t hampered by these wires.
9. Remove upper fresh water hose from front of heat exchanger (5/16″ hex nut on hose clamp).
10. Remove bolt securing cooling fresh water pipe (1x M8 x 55 mm bolt, 12 mm hex head). This aids in the removal of the lower fresh water hose (next step).
11. Remove lower cooling fresh water hose from front of heat exchanger (5/16″ hex nut on hose clamp). Note, if you didn’t fully drain the heat exchanger in Step 2, coolant will gush out when this hose is removed.
12. Remove nut securing impeller pipe to bottom of heat exchanger (1x nut, 12 mm hex head).
13. Loosen three upper bolts on side of heat exchanger (3x M8 x 160 mm bolts, 12 mm hex head).
14. Remove two lower nuts on side of heat exchanger (2x nuts, 12 mm hex head).
15. Remove lower bolt on side of heat exchanger (1x M8 x 100 mm bolt, 12 mm hex head).
16. Remove three upper bolts on side of heat exchanger (3x M8 x 160 mm bolts, 12 mm hex head), taking care to not misplace the washers.
17. While prying down on the raw water pipe below the heat exchanger—to get the pipe clamp clear of the stud there—slide the heat exchanger over, taking care to not lose the spacer that sits between the heat exchanger body and the pipe clamp.
18. If you have a minimum of 4 inches clearance to the right, you’ll be able to slide the heat exchanger right off. Otherwise, you’ll need to unscrew the two studs (see the caution at the beginning of the article if you do this). If you unscrew the studs, pay attention to the thin metal cylinder head gasket, which may drop off once the studs are out. Note that the end with fewer threads is the end that goes into the engine block.
To install a new heat exchanger, see Yanmar 3JH2E Heat Exchanger Installation, Step-by-Step with Photos.
Good evening Chuck… I have to ask. What do you think caused your heat exchanger to “go bad” in the first place
Cheers, DK
I’m no expert in these things so I’m not positive. But the o-ring on that side was not in the best shape. Perhaps the o-ring allowed some minute amount of sea water through, which, over time, slowly ate away at the metal on both the housing and the cover plate. I don’t know if the o-ring was like that when it was installed, or if it deteriorated over time. If the latter, I don’t know what would cause the rubber to degrade. I’ve since learned that the heat exchanger should be opened and inspected (and o-rings replaced, I figure) every three years, which seems like a reasonable interval.
Replacing the entire heat exchanger might seem extreme. One of the bolts holding the cover plate had corroded so badly that the head snapped off when I tried to remove it. I was able to drill it out and tap a new hole. The surrounding surface on the housing, though, was badly corroded and rough. It wasn’t clear it could maintain a water-tight seal any longer with that texture. I did consider the possibility of silicone sealant. But the most prudent course of action seemed to be outright replacement. I try to lean towards prudent, even when it’s painful.
Whether or not replacing the heat exchanger on a 27 year old engine makes economic sense versus replacing the engine altogether, I won’t know for a while.
Lesson learned… open and inspect that heat exchanger on schedule!!
Chuck B, You are a godsend!! In early Spring, I discovered the SAME problem with My Heat Exchanger. A mechanic got it apart, and I was able to get one of the last three H-E’s from Yanmar in Japan. Anywho, I am having to replace it Myself ‘cuz the mechanic is “too busy” to schedule Me anytime soon. Discovering Your two, pictorial articles, hopefully will allow Me to put the puzzle back together. However, I have a cylindrical “spacer” (?) { Plated S-Steel/40mm/1-1/2in L; OD=15mm/5/8in; ID=10mm/3/8in } ; and a Plated Bolt a little thicker than the M8 bolts, and 120mm/4-3/4in L; Hex head, and threaded end ( 30 mm/ 1 in ), with or without (?) washer & M8 Nut. Both of which I do not know where they go??? Yanmar’s Manuals’ Diagrams do not show them anywhere ??? PLZ, can You, or anyone else help Me??
Hey there John, than you for stopping by and I do hope this ends up being helpful to you! What engine do you have? The only thing that comes to mind that might have a spacer that long is the lower mounting for the alternator. Could that be it? Failing that, do you perhaps have a photo?
Chuck B, I DO apologize for not Thanking You for responding to My query about the metal tube which, in fact, is a spacer for the underside mounting bolt for the Alternator. My engine is the Yanmar 3JH-2E. However, in replacing the Fresh Water Tube, stern End-cap, I get a small fresh water drip, at @ 15 secs. intervals. I’ve tried a peripheral seal with a) Permatex #2; and b) Permatex Blue Gasket Former. The latter worked better but I still get a drip. There is @ an 1 mm gap between the end cap and Heat Exchanger on the underside. Do You think a more copious amount of P-Blue, and/or Silicone Caulk would be sufficient to “stem the tide”/drip ?? Many Thanx, “MRF”
Hey there John, good to hear from you again. That is interesting. 1 mm is quite a substantial gap. There was no gap when I assembled my heat exchanger. You’re sure that you have an o-ring in there and that it is seated properly?
Chuck B, Thanx for the timely reply. I used a thin strip of silicone caulk to hold the ” O ” Ring in place, firmly seated in the groove created by Heat Exchanger lip and End of Sea Water Tubes Cylinder. I had precisely aligned the horizontal space between Sea Water Tubes with the Septum on the rear endcap. I had applied a layer of Permatex Blue Gasket Sealer on the lip surfaces to be joined. I tightened the endcap bolts as tight as I could. The side openings/ “windows” at both ends of the Raw Water Tube were “face up”, on the tube’s top, as they were when I removed the tube from the Heat Exchanger. However, the Yanmar Manual diagram shows the openings towards one side, and some videos show the openings to be on the tube’s underside when in place ??? Could the tubes on topside be causing a leak?? Would a copious amount of Permatex Blue Gasket, or Silicone Caulk on the lower gap between endcap and H-E Body stop the drip ?? Many Thanx to You and anyone who can help Me solve My dilemma.
Chuck B, DUH !! I forgot to mention that one of four ” O ” Rings that I got from Yanmar is very slightly thicker than the others. Would this be the better ” O ” Ring to use,….maybe seal better. OR, being thicker could it prevent the Endcap from being tightly sealed ?? Many Thanx, “MRF”
Hey John, the o-rings I used were part number 24321-000750, “O-RING 1A G-75.0”. At the moment I don’t have access to the spares I got, so unfortunately I’m not able to measure the thickness for comparison with yours. You’re right, it’s certainly possible that if the o-ring is too thick OR too thin, a good seal may not be achieved. I can say, though, that the two heat exchangers I have experience with so far did not require the use of any sealant. I don’t believe it should be necessary, unless your heat exchanger body and/or end caps are damaged. At most a small quantity of silicone o-ring lube on the o-rings. Even if you’re able to stop the leak by applying more sealant, I’d be concerned you might be masking an issue that could cause grief later (for instance a crushed o-ring, if it was too thick).
You also touch upon another good topic… There is indeed a particular orientation of the core assembly inside the HE body. See Yanmar 3JH2E Heat Exchanger Core Assembly Photos for some photos of mine. From your description it sounds like you got it. Good luck and keep us posted!