overheat or normal

[dunchumphrey]

99 Yamaha 60hp 2 stroke FETO 3cycl 850. <br /><br />Posted here recently re impeller failure with the rubber separating from the plastic hub and causing an overheat. I've since had it back from the mechanic (with new impeller) and taken it out. I noticed 2 differences which are a concern. <br /><br />1. The tell tale is much weaker and now changes significantly with engine RPM. Its more than a dribble but not by much at idle. Strangely though on the flushing cups its considerably better. Does mains water pressure make a big difference (we have 100 psi water pressure here). <br /><br />2. After running at 3-4000rpm and taking back to idle there is a little puff of steam coming from the 2 ports just under the power head on the mid section. (I think this exit opens up with the popet valve and lets water out). This only lasts for a few seconds but never happened before. <br /><br />The overheat buzzer doesn't go off and all cylinders are 125psi. The plugs are however splashed fouled and there is a thick buildup of shiny black baked on oil (I think) on the piston crowns. Hmmmm?

 

[rodbolt]

Re: overheat or normal

there is still a problem. did they do the kit or just the impeller and did they do the t-stat and pressure valve with the rest of the service ?

 

[31900]

Re: overheat or normal

With 100 PSI into the muffs it is no wonder that you are getting a better water flow that way. You still have a water problem. A dribble from the peehole at idle still suggests a water pump problem and probably illustrates that there is not enough water available further up the system. There should be a good stream both on the muffs and in the drink. How was the water pump housing when the impeller was replaced? As I remember it was replaced with the new 5 blade job not the original "spin on the shaft model". rodbolt, do you agree that there appears to be a lack of water supply rather than a thermostat poppet valve problem at this stage?

 

[rodbolt]

Re: overheat or normal

all I will agree to is there is a water pressure problem. could be the wrong pump, improper assy or almost anything but there is definatly a problem if its blowing out steam. I would also retest the alarm system and at a minimum retorque the head gasket

 

[dunchumphrey]

Re: overheat or normal

Hi chaps thanks for posting<br />Have the pump in bits,<br /><br />The impeller was replaced with what looks like exactly the same type (I have the old one and the part number and appearance matches)They are both 5 bladed. <br /><br />The plastic pump housing hasn't melted and looks ok, the steel cup that slots into the housing looks OK, there is a very small amount of corrosion towards the outer edge of the plate the impeller sits on (this is evident on the gasket aswell)<br /><br />The chamber under the impeller that the water passes up through and out into the water tube has a minor surface buildup of salt and corrosion but nothing large enough to restrict the flow (perhaps a little extra drag through the chambers). There is a pin hole in this same chamber just before the water exits up into the water tube which is odd because its perfectly round like its meant to be there. <br /><br />The gromets for the water tube appear OK (they feel snug, not tight on the water tube. <br />So nothing obvious so far.<br /><br />One thing sprung to mind, when the muffs are on and regardless of the engine running, there is a lot of water exiting from the oversize holes where the speedo cable and gear shift rod enter the gear case. The water pressure alone is not enough to spin the impeller (nothing from the tell tale until the engines running)so Should water be able to exit the pump through the top inbetween the drive shaft and the impeller somehow or at all for that matter, there doesn't appear to be an actual other than the impeller itself. I know I didn't damage anything with excessive water pressure cause the mechanic flushed it using a tank before I noticed the weak jet.<br />I am going to put a new pump kit on regardless, is it necesary to replace the impeller again if it came off without damage?

 

[dunchumphrey]

Re: overheat or normal

"oops <br />there doesn't appear to be an actual SEAL other than the impeller itself"

 

[dunchumphrey]

Re: overheat or normal

To keep you posted,<br />I put a complete Yami water pump kit on and took it for a spin with the same results. <br />I'm beginning to think the poppit valve is at fault, heres why. <br />The stream was OK at startup, maybe a bit weak. After a 20 min. high rpm run, the idle stream is much weaker but increases with RPM again. Its not overheating but is too hot to touch. Could this be the poppit opening at high RPM but not closing properly? <br />My Clymer makes no mention of the poppit valve at all, does anyone know how to check it or where it is? <br />I'm also keen to know where the cooling water outlets are as mine seem to be everywhere? I'm asking cause while on the flusher water exits from a little hole at the top of the leading edge of the gearcase without the engine on. Does this mean water is being forced out of the pump? If you just have the water on where does it go?<br />Finally what does the rubber dam do in the gearcase (seal the exhaust from the pump area?)