How To Install Yanmar 3JH2E Heat Exchanger, Step-by-Step with Photos

This is a follow-up to How To Remove Yanmar 3JH2E Heat Exchanger, Step-by-Step with Photos.

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.

Note 1: 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.

Note 2: These instructions assume the heat exchanger unit itself is already fully assembled.

Note 3: These instructions are appropriate if the mounting studs were removed during disassembly and will be reinstalled. If you left the studs in place by sliding the heat exchanger off of them during disassembly, your re-assembly will differ slightly from the steps below.

Note 4: If I had to do over, I’d consider ditching the two studs entirely and replace them with 100 mm bolts (same as lower middle). I’ve no idea why they’re using those studs.

Note 5: Where the heat exchanger attaches to the cooling raw water pipe bracket on the bottom, the old one had a stud protruding; the new one, just a threaded hole. Rather than another stud, I used an M8 bolt with a lock washer. This was much easier than dealing with the stud.

Part 1: Reassembly

1. Swap out the raw water impeller for a new one.

2. Remove the thermostat, gasket, and o-ring.

3. Clean off all remnants of the old gasket. Do not use metal tools for cleaning (i.e. plastic scrapers only).

4. Install new o-ring, thermostat, and gasket.

5. Clean the exhaust manifold gasket, or replace it with a new one if necessary.

6. Clean the mating surfaces of the exhaust manifold and heat exchanger. I used WD-40 sprayed onto a paper towel, but I don’t know if that’s correct or advisable. Wipe off any excess.

7. Take two of the 160 mm bolts (2x M8 x 160 mm bolts, 12 mm hex head), and insert them into the appropriate holes at the front and rear of the topmost row of holes on the heat exchanger. Leave the middle bolt out for the time being. Ensure the washers are in place between the bolt heads and the heat exchanger body.

8. Rest the exhaust manifold gasket in place on the two bolt protrusions.

9. Place the spacer onto the pipe bracket stud protruding from the bottom of the heat exchanger.

10. Carefully lower the heat exchanger into place, with the stud (if there is one) going into and resting on the pipe bracket. Ensure the two bolts and exhaust manifold gasket remain in place and don’t fall out.

11. By hand, thread the two bolts into place a couple turns.

12. Thread in the two studs into the front and rear holes in the lower row. The end of the stud with fewer threads goes into the engine body.

13. Tighten the studs. This can be a little tricky. I did it by temporarily putting two nuts on each, and tightening the two nuts against each other, effectively making a lock nut. Then the outer nut can be tightened to drive the stud. This works best if you have some extra M8 nuts that are relatively thin. I got down to about 14 mm protruding, but I think it could go down more. Some kind of M8 nut with a “cap” on the end, or a weld bead, would likely work better, if you have the means to acquire or create such a thing.

14. Remove the two upper bolts and slide the heat exchanger over a bit. Check to see that the studs are fully engaged; there should be no threads visible where they enter the engine block. Slide the heat exchanger back up against the engine.

15. Insert all upper bolts (3x M8 x 160 mm bolt, 12 mm hex head) and thread into place by hand. Ensure the washers are in place between the bolt heads and the heat exchanger body.

16. Insert the lower middle bolt (1x M8 x 100 mm bolt) and thread into place. This bolt has no separate washer.

17. Tighten all four bolts by hand so the heat exchanger is snug up against the engine.

18. Put the two nuts (2x nuts, 12 mm hex head) onto the studs and tighten by hand.

19. Now install and tighten down the nut (1x nut, 12 mm hex head) for the pipe bracket stud on the bottom of the heat exchanger. (Or bolt and lock washer, if applicable.)

20. Snug down all heat exchanger mounting bolts evenly, little by little, in the following repeating sequence:

a. bottom middle
b. top middle
c. bottom rear
d. bottom front
e. top rear
f. top front

21. Attach lower front cooling fresh water hose to the heat exchanger; tighten its hose clamp.

22. Attach and bolt down (1x M8 x 55 mm bolt, 12 mm hex head) the cooling fresh water pipe bracket to the right of the cooling fresh water pump pulley.

23. Attach the hose connected to the thermostat cover to the pipe at the top front of the heat exchanger. Don’t tighten the hose clamp yet.

24. Tighten down the thermostat cover.

25. Now tighten the hose clamp at the top front of the heat exchanger.

26. Attach raw water supply hose to the rear heat exchanger cover plate; tighten its hose clamp.

27. Attach raw water discard hose to the rear heat exchanger cover plate; tighten its hose clamp.

28. Attach gasket and exhaust elbow to exhaust manifold exit at rear of heat exchanger. The tab (with a “T”) of the gasket goes up; the side with the raised markings faces away from the engine. Note, this is an excellent opportunity to replace both the gasket and the exhaust elbow.

29. Attach the alternator and belt.

30. Attach the thermostat temperature sensor wires.

31. Connect the cooling fresh water reservoir tank hose to its connection point near the cap on top of the heat exchanger.

Part 2: Recommission

1. Fill the heat exchanger to the top with clean fresh water, preferably distilled.

  • I think any clean water is probably fine, as the water will be drained out in short order anyway. This is what I did. But if you want to err on the side of caution, use distilled.
  • Note that in some countries, water labeled “distilled” may not be as clean as what you’re used to. You’d need a meter that can measure total dissolved solids (TDS) to be sure.
  • The 3JH2 service manual indicates that the heat exchanger has a fresh water capacity of 6.7 liters, which would be about 226 fluid ounces. However, I was only able to get 152-156 fluid ounces in there.

2. Look for any leaks.

3. Screw cooling water pressure cap back into place.

4. Turn fuel supply OFF (engage engine stop cable).

5. OPEN raw water intake seacock.

6. Perform the usual engine pre-start checks (belt, oil, etc.).

7. Crank engine for 10 seconds—ensure engine does not start! This lubricates the engine and primes the raw water.

8. Turn fuel supply ON (disengage engine stop cable).

9. Start engine.

10. Check for discard raw water exiting with exhaust; stop engine immediately if water does not appear within 15 seconds.

11. Give engine a little throttle, perhaps 1,000-1,200 RPM.

12. Run engine for 10 minutes.

  • Stop engine immediately if anything unusual occurs
  • Carefully observe for any fresh or raw water leaks
  • Observe for exhaust and water leaks around exhaust elbow
  • Keep an eye on engine temperature; stop engine immediately if temperature exceeds nominal
  • Watch engine temp using laser thermometer

13. Stop engine.

14. Examine for any evidence of leaking water.

15. Allow engine to cool for at least 30 minutes. Wait for heat exchanger to be cool to the touch, then remove cooling water pressure cap.

16. Drain all cooling fresh water.

  • Drain cooling fresh water from valve on heat exchanger toward the front right until no more comes out; tighten valve.
  • Drain cooling fresh water from valve on engine toward rear left (near oil pressure sensor) until no more comes out; tighten valve.

17. Fill heat exchanger to the top with 50/50 antifreeze/coolant mix.

  • You can either mix it yourself or use pre-mixed. If mixing yourself, mix before putting into the engine, to ensure the correct mixing ratio.
  • Pre-mixed is an attractive option in countries where the quality of “distilled” water is uncertain.

18. Screw cooling water pressure cap back into place.

19. Start engine and run until temperature stabilizes, and continue running for an additional 5 minutes.

20. Stop engine.

21. Allow engine to cool for at least 30 minutes. Wait for heat exchanger to be cool to the touch, then remove cooling water pressure cap.

22. Top off with 50/50 antifreeze/coolant mix.

23. Screw cap back into place.

24. Fill reservoir tank half way with antifreeze/coolant mix.

Part 3: Follow-up

Please note, I made this part up entirely on my own. I don’t know if it’s correct, but it seems reasonable to me.

After 15 engine hours—including at least one continuous hour of operation with load:

  • Check the coolant level and top off if needed
  • Check all bolts involved here to ensure they’re still tight

Repeat the above again after 75 engine hours.

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