yamaha 30SG Cooling problem.

[duke-ray]

I have a 1988 30SG and I've been chasing a over temp/cooling problem.I hit the lower end and took off the skeg. I had a new one welded on and the next time I went out it suddenly stopped pumping water after about half an hour on the lake.Temp light came on and I shut down the engine.
When I ran it with muffs it just spit water so I started to troubleshoot.Blew out the water passages had airflow.Replaced water pump,gaskets,key and housing.Replaced thermostat even ran it without thermostat.Took exhaust gas cover off to visually look for blockages.The last thing I tried was replacing the head gaskets.Put it in the lake and it gives an intermittent stream(stream-stop-stream) of water until the overtemp light comes on.
I'm at a loss any ideas?????????

[Ken]

duke,
Pull the thermoswitch and test it - here is a link to a diagram for a 40SG - item #19:

http://www.boats.net/yamaha/partsyst...mponent=323362

You can test the thermo switch in a pan of heated water and thermometer and ohm meter - switch contacts should close at approx 180 degrees f.
and re-open at approx 160. I have personally seen one close at 130 and give me a false overheat alarm/rpm reduction.
Good luck [img]smile.gif[/img] ,
Ken K

[duke-ray]

Hey Ken, Tried the thermoswitch and it appears to be closing and opening as it should.I was thinking about running the engine with it disconnected. Good or bad idea?
Also I pulled the lower end off again and I found what looked like foamy gear oil in the exhaust section ,it was thick and coated one side extending straight up from the cavity forward of the pump/drive shaft into the exhaust section, but the pump housing and pump didn't have the stuff on it?The gear oil looks normal! Never seen this before any idea what it could be?
Would air getting into the cooling passages cause an intermittent spray pattern from the water indicator?
Any other ideas?
Thanks!

[Ken]

duke,
You definitely do not want to run your motor w/o the thermoswitch - it's there for a purpose - to tell you when there is an overheat condition.
I don't think your motor has a pressure relief valve, but if it does, check it to make sure it has not stuck open and allowing cooling water to dump.
It just sounds like the new water pump is not doing its job - maybe o-ring slipped out of place.
You might want to tear it back down and inspect.
As far as the "foamy oil" in the upper casing area, it has to be either lower unit oil, or oil from the injection pump (is your motor oil injected?). Check the oil injection pump for leak into the crankcase - maybe split diaphram in pump.
Good luck [img]smile.gif[/img] ,
Ken K

[duke-ray]

Hey Ken just thought I'ed let you know that I took apart the water pump again and replaced the two gaskets in there and this time it worked! Strange but true.
Thanks for the advice!