Overheating Issue 04' 150hp 4 stroke

[ThomasGrubb]

Hello,

My 04' Yammy 4 stoke has begun overheating at idle, id say after about 3-5min of idle the temp alarm will go off. The tell tail still has a water flow coming from it when the temp alarm comes on.

The outboard has only had a service 15hrs ago & the impellor & housing was replaced, straight after service it was fine & no alarm was coming up. But the outboard has always struggled to pump water when being flushed with just the muffs, so I now have a big bin I now place the leg into when flushing. There could have been some damage done somewhere trying to use muffs?

While I am travelling & underway the temp alarm doesn't come on, assuming its due to the greater pressure of water being pushed into the engine?

I am thinking I need to check the impellor & housing, and ill replace the thermostat. Any suggestions on what other things I should be checking & replacing?

Thanks
Tom

[pstephens46]

That would be a good place to start. Making sure the plastic housing has the rubber seal at top. Inspect the thermostat bore after removing thermostat. Look for excess corrosion. I use two water hoses. One for muffs and one attached to flush fitting. Never overheats doing this.... Oh....also look at the pressure relief valve at bottom of water jacket. Below the thermostat. Sometime they stick open. The newer part is designed to not stick as easily.

[fairdeal]

There could have been some damage done somewhere trying to use muffs?

While I am travelling & underway the temp alarm doesn't come on, assuming its due to the greater pressure of water being pushed into the engine?

Yes, the water pump supplies substantially more water, at higher rpms, than it does at idle.

And its "very easy" to melt the polymer water pump housing whilst attempting to run on muffs
(or with a bin, if the water level is not high enough)

A 'dry' impeller creates friction against the metal cup,
the cup gets hot enough to melt the housing,
the housing outlet becomes occluded with melted polymer.

By all means inspect the thermostat and its bore -
but if the overheat is at idle, not higher rpms - the problem is not the thermostat.


example of pump housing volute, blocked by being overheated:

[TownsendsFJR1300]

How many hours on the engine and is it used in salt water?

Lastly, do you flush the engine with fresh water after use?

While checking parts on the block, inspect for excess salt / corrosion inside and please report back.

[ThomasGrubb]

Thanks guys, I'll start at the impeller housing & go from there.

only 420hrs on the engine & its used in saltwater, flushed in freshwater.

[TownsendsFJR1300]

Thanks guys, I'll start at the impeller housing & go from there.

only 420hrs on the engine & its used in saltwater, flushed in freshwater.

There's O-rings with the housing, just make sure their there and in good shape. Same for the base plate, that it's nice and smooth. Doesn't take much leakage to cause issues. The SS cup has to be seated just right as well..




*Just an FYI, on my '06 F150 I flush on the muffs (and the attachment hose) but separately.

On the muffs, I've NEVER had an over heat and am on the original housing.

When doing the WP, I get the kit (doesn't include the housing) and replace everything. Just not worth the time doing it twice to save a couple of bucks. Worth noting, I guess my engine is one of the few (maybe good water pressure/volume) that doesn't overheat and I usually run up to 1,100RPM's W/O issue.

https://www.flickr.com/photos/147134...6/34909194323/