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Suzuki DF 90 cooling issues?

Z

zimm

New member
Started my little used DF 90 to get ready to winterize it. Engine lower unit is in water, not on muffs.

Ran it at a fast idle and it overheated after about 10 minutes. Checked the thermostat and it was open. Checked the poppit valve and it was closed, both of which are normal from what I know. The motor was peeing.

Impeller was replaced a while back, and has minimal hours on it.

Odd thing I noticed, was that the water outlet hose, when disconnected from the thermostat cover, had pressure in it. Not constant, like you would expect from a pump, but puffs of pressure and a bit of water coming out of it.

Is that normal? Not sure whats up here.
 
What’s the history on the water pump? Impeller might be ok but a slight warp in the base plate or the cup might be slightly out of round. Salt or fresh water engine? Year and operating hours?
One wouldn’t think a healthy water pump would “pulse” water but I’ve never checked.
 
At fast idle there may be lots of exhaust bubbles in the water.----The pump is not pumping just water.----Not meant to pump air !
 
I would suggest you change the entire water pump assembly then you know the water pump is 100%. While you have the lower unit off look up inside and gently wiggle the water tube, it should be tight and firmly seated in the engine. Have read where the rubber grommet at the top of the water tube has deteriorated so much that it no longer seals to the engine. Being a salt water engine you could have corrosion/mineral deposits throughout the engine. A vinegar/salt away flush might be in order. Do you have a set of muffs to try? Nobody ever recommends muffs over barrel or actually having the engine in the water but using muffs would prove/disprove racerone’s theory. Not all muffs are created equal. With my 2009 DF90A I bungee cord the muffs on the lower unit tight, they want to slide off. Try hooking a garden hose to the flush ports(I have 2) with the engine OFF and see what kind of flow you get.
Screenshots from a 2009 DF90A service manual IMG_6359.jpegIMG_6360.jpeg
 
Thanks. I found the diagram in the manual, but not the diagnostic page.

I did figure out the thermostat was bad. It was open at room temp, and should have been closed. Replaced that this morning. Ran the engine for a bit and it didn't overheat, but there is definite pressure in the return hose and it got hot quickly and the pulsing can be felt. That was noticed before the engine was hot enough for the thermostat to open. There was a small drip at the connection of the hose to the housing as well, I am guessing from the pressure. It peed just fine.

Is there some way exhaust is getting into it? Don't see how from the diagram, but that doesn't always tell the full story.

Guessing my next step is to pull off the lower unit to check things out?
 
The exhaust exits out the back of the lower unit while the water enters in the front. I have read that the exhaust pressure can mess with the incoming water if the exhaust has eaten away the aluminum that separates the two. Certainly would be worth researching or better yet another forum member with more experience than me offer their thoughts. @racerone
 
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