Help! Yanmar 3JH4E problem

[flightlead404]

Yanmar 3Jh4E. Recently cleaned impller bits from heat exchanger and descaled. New impeller. Raw water and fresh water pump both replaced 18 months ago. Loads of water exiting exhaust, engine running beautifully.

22 hours running at 2,600 from Hilton Head suddenly very slight change in engine tone odd rubber smell. As I’m scratching my head overheat alarm goes off. I’m in a busy seaway and have no option but to throttle way back but keep running for a few minutes (no wind). Next, smoke billowing from under companionway stairs. Shut off engine and use remaining steerage way to get to edge of channel and drop the hook.

Impeller was fine. Replaced anyway. Coolant reservoir cap blown off, coolant everywhere.

let the engine cool, restart, no water exiting exhaust.

Any pointers on the engine issue would be appreciated.

[Wolfe10]

Belt condition and tension?


Bearings on alternator or water pump seized?

[flightlead404]

Originally Posted by Wolfe10

Belt condition and tension?


Bearings on alternator or water pump seized?

On initial inspection belt appears to be fine. Fresh water pump appears to turn when cranking as does alternator. Raw water pump is gear driven.

My next steps are first, simple things. Make sure all hoses are clear and plenty of water comes in via through hull

After that maybe pull raw water pump.

[Jammer]

Originally Posted by flightlead404

no water exiting exhaust.

Raw water strainer clogged?
Thru-hull valve closed by evil spirits?
Heat exchanger clogged?

[flightlead404]

So far everything appears fine and no reason why no raw water flow
Through hull, sea strainer, hose to raw water pump all fine and flow water readily. Impeller fine, removed raw water pump it turns freely. Lines from pump to exchanger and from exchanger to elbow new and fine. Exchanger clear.

Belt is fine though I added a little more tension. Fresh water pump turns freely. Alternator does also.

One slight concern when I wiped out the bore the raw water pump sits in found some metal particles. They are ferrous not carbon. Very small amount. Teeth on gear that drives the pump have rough edges but no teeth missing or chunks missing.

[Jammer]

Probably a spun impeller. The splines in the impeller are shallow and are designed to fail if the impeller is blocked by a foreign object -- so that the shaft isn't damaged.


Take a very close look at the splines on the impeller and see if they're worn. With the impeller installed, see if you can turn it with a pliers or something. If you have the whole pump off the engine then see if you can hold the impeller in place and turn the gear instead. Either way, if you can turn it it's shot. Solution is to replace the impeller.


If that solves the problem for now but it happens again, either you're getting dodgy impellers and need to source better ones, or the shaft is shot and you'll have to replace the whole pump.

[GreenWave]

So those bits were found OUTSIDE the water pump? Maybe from the gears? That suggest some serious binding occurred on the pump and I would be looking at the bearings etc inside the pump. Might be time for a rebuild or new one?

[Madehn]

Possible spun impeller. Also possible a plastic bag or similar got sucked up against inlet. After stopping engine it dropped off. Best of luck

[flightlead404]

Pump itself is fine. Impellers are fine. Shaft is fine, splines are fine, pump bearings and seals are fine. Impeller not slipping on shaft. Impellers Johnson/yanmar branded. New impeller.

WTF?

[flightlead404]

Took cover plate off raw water pump and cranked engine.

Confirmed pump shaft is not turning with engine.

Is there some sort of shear pin perhaps in the accessory case?

[Ziggy]

Originally Posted by Madehn

Possible spun impeller.

This seems to be a common failure mode for Johnson impellers. Your rubber impeller may be bonded to a metal bushing (i.e., no splines!). The bond fails without any warning and the rubber impeller is free to rotate on the bushing. At first glance it looks fine, but when you inspect it carefully you may notice that the hole in the rubber impeller is no longer aligned with the pin through the bushing. Yanmar recommends replacing the impeller every 2 years. They are not expensive, so every year may be good insurance.

Originally Posted by Madehn

Also possible a plastic bag or similar got sucked up against inlet. After stopping engine it dropped off. Best of luck

This is also plausible.


I suggest installing a water flow alarm, in addition to engine overheating alarm.

[ScottRhodes13]

Possibly the drive gear is spinning on the raw water pump shaft. If it's like the 4jh2, it's just a press fit.

[flightlead404]

Originally Posted by ScottRhodes13

Possibly the drive gear is spinning on the raw water pump shaft. If it's like the 4jh2, it's just a press fit.

Thanks for not suggesting a spun impeller which, despite me posting numerous times it’s fine, folks can’t resist

Using my hands and hand tools, no bench vice, I cannot get that gear to turn in the shaft. I believe it’s fine. I think there is a woodruff key to prevent it spinning.

Now, the weird part. The pump is driven directly by the camshaft gear. If the camshaft gear was not turning the engine would not run.

There is no clearance adjustment for the pump and camshaft gears, so now I’m utterly at a loss

[Madehn]

Have you tried firing it back up to see if you had a temporary blockage of the raw water intake? Also is it possibly an issue at the mixing elbow being blocked?

[boatpoker]

Sherlock Holmes - “When you have eliminated all which is impossible, then whatever remains, however improbable, must be the truth.”