Help with Yamaha 4ac cooling system

[sudsy]

Hi,

I have a Yamaha 4ac outboard. I recently replaced the impeller (old one was partly broken). I reassembled and tested the motor and the water jet was flowing well. Fast forward a few months and the first time I take the boat out, the water flow is worse than it was before the impeller change.

I have since removed the bottom end and tested the water pump and it is working fine. I attached a garden hose to the bottom of the water tube and pushed water up the tube. The flow out the tell tale is dismal. I managed to hook up a strong jet of water to the telltale to flush the water system backwards and the water is flowing backwards very well however, the water is not coming out of the bottom of the tube, it is coming out somewhere further up the leg and flowing down. It makes me think perhaps I have a leaky water tube but I haven't been able to take the power head off the engine to inspect.

I'm wondering my thinking is correct. Should the back-flushed water be coming out the bottom of the water tube or is it normal for it to be coming out further up the leg. I'd like to confirm this before trying to remove the power head again. I'm wondering if there is any sense in removing the thermostat now given what I have found so far.

Thanks in advance!

 

[VicS]

If you connect a hose to the water tube you should get good flow from the tell tale. If not maybe the telltale is blocked. Try probing with a wire. If still no joy you will have to investigate

You may not get a flow through the engine while the thermostat is shut, I'm not sure about that with a Yamaha.