1997 Mercury 40 HP 2 stroke wont pump water

[bstuart]

Engine S/N 0G580809

I'm working on my Father inlaw's pontoon. He took it out for the first time this season and it overheated, stalled and he got towed back to the dock. Looked to see no water pumping out of the tell tale or whatever you call it.

Today I went over and changed the impeller. Old one was junk..some pieces missing. Put everything back together and there was still no water being pumped. Took everything back apart and installed a whole new water pump assembly. Put everything back together and still no water...boat overheated in a couple minutes. (He lives on a lake so I was standing in the water in my waders working on the engine and running it)

Now, I don't know where to check. I stuck some weed eater line back up the tell tale line and it's not blocked. Blew air from a compressor back up the line and can hear it in the engine. I can't find the thermostat to check, anyone know where that is?

I'm guessing some crud and probably pieces of the old impeller are stuck in the cooling system some where, but don't know where to check it. Is there some where else I can blow through the lines? Any problem area that gets clogged I can check?

 

[Texasmark]

Sounds like you are on the right track. If the pieces weren't small enough flow out with cooling water they are still in the water system somewhere.

T stats can stick shut with age, will surely get you an over temp problem, and are usually at the top rear area of the engine block meaning they could be mounted in the water jacket on the rear of the block, or in a small cavity on either side. The T stat is about the diameter of a US Nickel coin and about an inch and a half long. Cavity for mounting it, if off to the side would have to accommodate that sized element plus water porting into and out of.

The engine proper is controlled by the stat but the exhaust manifold is fed directly from the water pump. Pop the cowl and locating the Tell Tale hose at the cowling, follow it back to it's source. If it's coming from the flat plate on the left (Port) side of the engine (viewed from the rear), the stat has nothing to do with the pee stream.....the exhaust is hot and the cover over the exhaust has to remain cool...if the engine is running, water is circulating, regardless of what's happening in the block proper.and the pieces of impeller may be in the water tube connecting the water pump to the engine block.

To clean that out you would have to take the lower unit back off so that the bottom of the tube is open. Finding the Tstat and removing it, with the lower unit-water pump out of the way, and injecting water in the Tstat hole could force out any blockage.