1999 F4 4 stroke cooling problem

[Fishdeeper]

hi, new member here. Just picked up an F4, thermostat and impeller are shot. No water in the telltale or the exhaust port. Disassembled and flushed water up thru the bottom of the watertube using a pond pump. Got a bit of flow into the thermostat cavity, but it seemed to be leaking inside the leg housing. Also blew air thru to ensure no bits of impeller were lodged. Seemed clear. Installed the new thermostat and impeller, ran great, but still no water in the exhaust. Double checked that the watertube was seated in the waterpump grommet at the impeller housing. I think the rubber seal at the top of the water tube is shot. I think i can hear some air leaking up at the top of the leg when i run air up the water tube. Its possible the rubber seal may have melted when the previous owner ran it hot without knowing the impeller wasnt working. Does anyone have a method of getting at the water tube seal at the top of the leg without pulling the powerhead? Can the leg just come off the bottom without disassembling the shifter, the throttle, the pull start etc for powerhead removal? Thanks in advaance for any suggestions.

[99yam40]

I have never dealt with a little F4, but I do not think you will be able to get to that seal without pulling the power head.

Just what are you calling water in exhaust that you are looking for

[panasonic]

Is this the set up?

[panasonic]

To small of a picture...do not know what I am doing wrong..

[Fishdeeper]

I have never dealt with a little F4, but I do not think you will be able to get to that seal without pulling the power head.

Just what are you calling water in exhaust that you are looking for

The exhaust port that is located halfway down the leg normally spits some water, it was dry, or maybe a slight bit of steam.

The service manual says i need to take off the powerhead, i was just hoping for a shortcut.

[Fishdeeper]

Is this the set up?

I cant really see the image too clearly but yes, that is it.

[panasonic]

Sorry about the small picture...new forum. From parts and shop manual it looks like the water tube curves at the top and has a rubber grommet or seal up there to hold it in place. My guess you will have to take the power head off to change the seal...don't know for sure.

[panasonic]

At least it is small and should not be too much trouble to remove...

[99yam40]

The exhaust port that is located halfway down the leg normally spits some water, it was dry, or maybe a slight bit of steam.

The service manual says i need to take off the powerhead, i was just hoping for a shortcut.

My Yamaha C40 does not have water coming out of the idle relief ports like my old 35 Evnrude use to have, I worried about it for a while, but it has not caused a problem for 8 years or more now

[Fishdeeper]

On advice above i decided trying for shortcuts weren't going to solve it. I pulled the powerhead. Of course to do this means pulling lower unit, carry handles, lower covers front and back, fuel tank, control arm and recoil starter....basically everything. The seal at the top of the water tube was marginal but probably ok. I found 2 water inlet holes in the powerhead base that lead to the water jacket areound the cylinder. One was completely plugged with crud, no air would pass. Well i've gone this far so i pulled the cylinder head off. The water jacket around the cyl head was completely plugged w crud. Cylinder side had some crystals but was ok. The previous owner must have never flushed it. Given its obviously overheated, and how good it runs, this is one tough little motor. Now i need a couple gaskets.

[dray0151]

Good to hear your problem may be solved. You can get the gaskets from this site under the Yamaha Outboards Parts link above. Let us know how it goes after reinstall.

[cleddau1]

While it is apart might be worth replacing"O" rings in oil pump, checking valves for leakage, and checking head for warping........

[Fishdeeper]

While it is apart might be worth replacing"O" rings in oil pump, checking valves for leakage, and checking head for warping........

Compression was 130 after 3 pulls, with no oil squirrted into the sparkplug hole by me, before teardown, so thats a good sign.
i dont see an oil pump in any of the parts diagrams, so not sure which oring you are thinking of. Maybe its just a sump splash?
i dont have a way to measure head warpage, so im going to put a sheet of 320 grit wetpaper on a piece of glass and slide the head around it and see what it tells me, otherwise i think just torque it down good. The head gasket wasnt leaking before teardown.

[TownsendsFJR1300]

While it is apart might be worth replacing"O" rings in oil pump, checking valves for leakage, and checking head for warping........

It does appear to be a sump splash system, part/gear #26: http://www.boats.net/parts/search/Ya...202/parts.html

[Fishdeeper]

It does appear to be a sump splash system, part/gear #26: http://www.boats.net/parts/search/Ya...202/parts.html

It wasnt burning oil so i'm probably not gonna tear the crankcase apart. it was running fine, so i'm just gonna fix the cooling issue and see if i have a runner.