Yanmar 4jh2-hte questions

[dm567]

I'd like to tap on the knowledge of some more experienced sailors than me.

First, the engine runs just below the red on the temp gauge. (the red starts off real small and gradually gets larger) Seems to me like it used to be a little farther down. Is this OK or should I change the thermostat?

What is the cooling water temperature switch 120130-91370? Does my motor have one, where is it, and what does it do?

[Tim R.]

Probably not your thermostat. They do not fail very often and they are not cheap. Check your heat exchanger and water pump">raw water pump. Those are much more likely to cause an overheating situation. Could also be a bad sending unit or gauge. get a cheap infrared thermometer to ensure your temp gauge is working properly.

[Amnesia II]

Originally Posted by dm567

I'd like to tap on the knowledge of some more experienced sailors than me.

First, the engine runs just below the red on the temp gauge. (the red starts off real small and gradually gets larger) Seems to me like it used to be a little farther down. Is this OK or should I change the thermostat?

What is the cooling water temperature switch 120130-91370? Does my motor have one, where is it, and what does it do?

Temp switch is the "sender" to temp gauge. I don't understand...'the red starts off real small and gradually gets larger'? Are you saying it gradually gets hotter after start up? Thats normal!

Start at thr easy end...check you have no obstruction at water inlet, check water pump impellor for loss of blades, while you are in there change the impellor if its been in for years...broken off rubber blades can also block water pipes.

[rebel heart]

What kind of coolant are you running? Yanmar put out a service bulletin a few years back saying that everyone with the 4JH should switch to dexcool in order to preserve the aluminum inside. I had to have my heat exchanger cleaned and machined because of the corrosion in there. It wasn't manifesting any problems yet except for a small raw water leak at the rear coupling.

Not sure if this affects you, but maybe read up on it.

http://www.cruisersforum.com/forums/...tml#post256562

[Ambler]

My experience is with older models of Yanmar raw water cooled models.
Provided your engine is also raw water cooled (with sea water) this is a solution to your problems.
Rather than blame the sensors you need to do a flush of the cooling water system.
First of all, check the annodes in the system. Are they corroded away? Have they expanded with crumbly dross? Remove the annodes from their housings (bungs) and reinsert the bungs.
Next remove the thermostat and cover.
Next remove and check the water injection point into the exhaust elbow is clear of dross and blockages.
Also check the condition and replace the raw water impellor if necessary. Chances are it has been working hard.
Drain the cooling salt water in the engine.
Mix a solution of gellcoat restorer or rust converter (phosphoric acid) with fresh water, try a weeker solution at first. Pour it in to the thermostat hole. This should begin to froth up as it disolves the calcium deposits around the cooling galleries. Flush this out by removing the cooling water exhaust injection hose and attaching a fresh water hose. Do not use heeps of mains pressure or volume, just allow the hose to run. Remove the annode bungs again which should allow the dross to escape as well.
Now depending on how much crap comes out you should repeat the process a number of times until you are satisfied the galleries are clear. You may like to increase the concentration of acid but be warey.
Once satisfied you have removed the dross from the system, install new annodes, replace the hoses, thermostat and cover.
Run engine and monitor guages. You should see the engine restored to its normal operating temp.

The best way to prevent this happening again is to allow the engine to idle for a period of time to equalise the thermal tensions within the motor. I reccomend installing a fresh water flushing system which replaces the salt water while iddling down.
Add a hose from your water tank via a tap and T piece to the cooling water inlet between sea cock and engine raw water pump. Open the fresh, close the salt then time how long it takes before fresh water comes out at the exhaust. Friends of mine used the sink drain and a sink full of fresh water to insert fresh water into their yanmar after each run.