Coolant temperature at idle rpm on Yanmar 4JH5E

[noelex 77]

It would be worth checking the thermostat.

[jjorio]

Will do!

Any thought on my comments on the filler cap anyone ?

Last thing tonight :
I just managed to take off the coolant filler cap.
When I did so, the water level in the subtank dropped dramatically (lot of spill also).
I topped up the coolant through the filler cap, and I had to add half a gallon (again some spill but no so much ...), to fill until visible level through the filler cap.
Also topped up the sub tank.

The question is :
Can a faulty filler cap, prevent me from seeing the level in the sub tank go down, and thus have too little coolant in the engine ?

Can´t start the engine now, my wife would kill me.
More tomorrow
Thanks everyone

[Wotname]

Originally Posted by jjorio

The picture

Perfectly normal, one revolution (or less) of the impeller and the vanes will all be facing the right way.

When the engine stops, it can turn "backwards" for a few degrees and this causes the impeller to turn backwards by about the same amount (depending on pulley ratios if belt driven) thus causing the implore to look like the picture. As soon as you start it next, all is good.

[svlamorocha]

Originally Posted by jjorio

I'm in Hiva Oa, Marquesas Islands 1200 persons living in the island.
Very remote

I bet that in your anchorahe you can find someone with an IR thermometer. At least when I was there we had two on board

[svlamorocha]

Originally Posted by jjorio

Will do!

Any thought on my comments on the filler cap anyone ?

Last thing tonight :
I just managed to take off the coolant filler cap.
When I did so, the water level in the subtank dropped dramatically (lot of spill also).
I topped up the coolant through the filler cap, and I had to add half a gallon (again some spill but no so much ...), to fill until visible level through the filler cap.
Also topped up the sub tank.

The question is :
Can a faulty filler cap, prevent me from seeing the level in the sub tank go down, and thus have too little coolant in the engine ?

Can´t start the engine now, my wife would kill me.
More tomorrow
Thanks everyone

Your raw water circuit is fine; you have a blockage in your coolant circuit. Blockage may be stuck thermostat, rust/scale or just air. I have not see your install of expansion tank, etc. If it is not exactly as from factory then pretend you are a bubble of air in the circuit inside the engine block and your cousin bubble is in the coolant side of the heat exchanger. Both of you should be able to escape to the filler cup going uphill all the time. Otherwise there should be purge points installed. Use those purge points to get all the bubbles out after tstat opens but before it overheats, while adding coolant to conpensate.

While you are at that, learn to check coolant temperature in the two hoses that link block to heat exchanger and back. When you get your own IR gun take a baseline of those two temps and the differential both at low idle and high rpm in gear (ideally WOT). That will be helpful in the future.

If your coolant is not already diluted make sure you dilute it as specified (50/50?) with distilled water

[a64pilot]

Yes a bad cap can cause what you saw, however I’d be concerned about where the coolant went.
Have you serviced the coolant recently?
Finally you sure it’s a high temp alarm? On my Boat high temp and low oil pressure sound the same, same buzzer.

[Rough Magic]

Thermostat or air trapped in the system is my guess. Was the cooling system recently opened? I mean drained or parts replaced, hoses?

[boeing1]

800 rpm sounds low at idle, I could be wrong, most of the engines I have worked on Idle is about 1000. I would check your engine manual to see what they suggest it be set. I what you said your impeller is ok, you could run your engine at 1000 at idle and see if it makes a difference

[keith001]

Exhaust is getting into cooling loop.

[jjorio]

Hi everyone,
Thanks for your contributions.

I've been running the engine for 50 min now t idle, and the alarm doesn't sound (it fired before around 25 min).

I changed the filler cap a few month ago, and topped up the coolant at that time.
Since then, my checking of the coolant level procedure, was :
- Open the subtank for pressure relief
- Open the cap slightly and the coolant came off, AS IF the coolant in engine as full

As I said earlier, I couldn't remove the cap last night. I think it was du to succion, and later on I managed somehow.
I found then that there was much more air than coolant in the engine ... well I added half a gallon, and the tank capacity is 5L, says Yanmar.

What I think is that the cap is faulty, and let steam out (maybe), but didn't let the coolant from the subtank back in the engine when evaporated ...
And so on, since I changed the cap.

Conclusion, the alarm fired, because there was not enough coolant in the tank.
I got confused in my checks because of the faulty cap.

Cheers

[hellosailor]

Checking the thermostat, and checking the temperature alarm sensor.

Both can be done in a kitchen, and surely, there is someone on the island that has a simple kitchen thermometer, or someone who has a candy thermometer?

With a raw water cooled engine, you'd expect a 140F thermostat. With a closed water system, you'd expect 170F. You put the thermostat in a small pot on a stove, with the thermometer, and just observe to see it is functioning properly, open/close at the temp it is marked for.

Similarly you can test the alarm sensor. You'll need to find the specs for your engine, but the sensor typically is a variable resistor than changes from about 50 ohms to 250 ohms as it goes from "alarm" to cold. You test it with an ohm meter or multimeter, there should be one around someplace. It is also possible that the alarm sensor simply has a poor connection to ground, in which case the alarm 'sees' the wrong resistance and goes off at the wrong temperature.

Both thermostats and sensors have been known to be DOA when new, and they do break down as they age. If they're 20 years old, it might pay to just order new ones and replace them.

[a64pilot]

Likely you could not remove the cap because there is a safety to help keep you from being scalded, there is a catch just before the cap comes off, it’s on the filler neck.
To remove cap turn it until it stops, then push down on the cap to get it past the safety stop.
There are special caps with levers on them too, lift the lever to release pressure before you turn the cap and the lever has to be lifted to get the cap past the safety stop as well so it can’t be removed without lifting the lever.
I’ve never seen a Yanmar come with one of these lever caps, but they can be fitted for those that are nervous about opening the system.
Best to only open one cold of course.
Hopefully you had a bubble of air that finally worked it’s way out, this is common with water heater installations, to trap air.

However you could as has been noted either be getting exhaust gasses in thru a bad head gasket, losing coolant through a bad gasket or be losing coolant thru the heat exchanger.
I’d watch the level, checking it when the engine is cold before motoring, and if you keep having to add coolant, obviously you have a problem

[motretu]

have you checked the coolantpump/alt drive belt tension. if it is slipping, coolant pump at idle may not turn fast enough. any strange noises from coolant pump area?

none of the above seems likely, but worth a check..

[Armando95623]

As noted earlier, the symptoms you're describing sound like the issue is on the freshwater side of your cooling system. From the standpoint of working from the simplest solution to the more complicated solutions, you should first verify that the temperature sending unit is functioning correctly. The easiest way to do this is to replace it and verify that the problem continues with the new sending unit installed. You can also check the function of the sending unit by placing it in a pot of water and heating the water while measuring continuity across the sending unit terminals. If the sending unit is functioning correctly, the next place to look is the thermostat. Again, you can replace the thermostat or removing the existing thermostat and verify its function by placing in a pot of water and heating. If both sending unit and thermostat are verified to be functioning correctly, then it's time to open the heat exchanger and see if it's blocked.

A note of caution - be super careful about loosening the cooling system cap. As you've discovered, the cooling system pressurizes as the engine warms up. Opening the cap when the engine is hot risks doing some pretty severe personal damage. On the positive side, it does sound as though the cap is doing its job in enabling the cooling system to pressurize as it's supposed to.

[Armando95623]

Oh, and one other point, if the heat exchanger is not blocked, then the problem may be the coolant water pump. I'd check that only after working through the cap, sending unit, thermostat, and heat exchanger.