Trouble with my DT55!

[Dogma83]

Hi guys,


yesterday I could try my new (old) sports boat, equipped with a DT55 from 1985, on a river.
After first starting problems I was successful and my DT55 run smoothly.
With the first start-up,this acoustic noise came up and disappeared by itself after about 40-60 seconds.
In the begining I could also see that pilot water jet coming out form the motors side to make sure the cooling water supply is working. That contol jet disappears if the motor is on higher rpm. Why?
Now to my problem:

After I was running a vouple of minutes on full load,that acoustic alarm started to beep and I reduced the speed. Than I saw a lot of steam coming out of the motor.(Small hole in the back mixed with exhaust gases)
Is this normal?
I expect that this cooling water sensor is maybe damaged?
What about an impeller change?

What can I do?

Do anybody of you know this problem?

Thanks in advance

Marco

[Moonlighter]

Hi Marco

Most likely the water pump impeller, which is made from rubber, has become old and hard. In this condition it will pump some water at low speeds but fails as soon as rpm increases. This is likely why the alarm went off after some time at fast speed - the engine has overheated!

I would suggest a new water pump repair kit including impeller and housing, be installed before the motor is used again.

It would also be worth checking the thermostat to make sure it is working properly, replace if it is in poor condition.

Check that water passages are not totally clogged when you have the thermostat out.

If there is some build-up of salt or calcium in the water passages, once the water pump kit is installed and thermostat replaced, you can run the engine in a drum of water, with say 20% vinegar in it. Run until the water in the drum gets warm, then stop and allow it to cool. Repeat again when the drum of water mixed with vinegar has cooled. Repeat a few times. You should see salt and calcium residue in the bottom of the drum after completing this treatment. This will have helped to clean out the internal water passages.

When you are finished, flush well in a drum of clean water to remove all traces of the vinegar.