Cooling problems 6hp and similar

[Vic.S]

When I had cooling problems with my '84 6hp the cause was the grommet at the top of the water tube closing over it and cutting off the flow almost completely. I have recently been sent photos of exactly the same on a slightly older 7.5hp. This one had been to a dealer who had failed to rectify the problem!

I thought folks on here might be interested, especially anyone struggling with a cooling problem.

 

[Xcusme]

Re: Cooling problems 6hp and similar

What you're looking at is the RESULT of a common problem...overheat. Keeping the cooling system in good order is essential to longevity. Periodic water pump inspection and replacement can help to fix a problem before it becomes a disaster. Sadly, most folks wait too long and damage a vintage motor.

 

[Paul Moir]

Re: Cooling problems 6hp and similar

Is that evidence of a leaky bottom main crank seal I'm seeing?

 

[DJ]

Re: Cooling problems 6hp and similar

I have also seen a similar situation on 4 HP twins. You can't see it until you remove the powerhead. Which is not hard by the way.

 

[Vic.S]

Re: Cooling problems 6hp and similar

No doubt that the problem with mine was caused by corrosion of the alloy casting arond the grommet squeezing it over the top of the water tube. That lead to overheating. Certainly not "vintage" when it happened (the first time}

Is that evidence of a leaky bottom main crank seal I'm seeing?

what makes you ask that?

 

[Paul Moir]

Re: Cooling problems 6hp and similar

The whitish goo around where the driveshaft runs through. Looks like oil/water mix that you get when a blown seal spits out fuel/oil from the crankcase and sucks in water.

I'm no expert on the 6hp, but from here it looks like that can be the only source. It's worth looking at now with the powerhead off.

 

[Vic.S]

Re: Cooling problems 6hp and similar

Thanks I'll pass the comments on. I am assured that it starts easily and runs well. If it didn't then the owner probably would not be trying to cure the overheating. It has seriously overheated, the paintwork on the head is discoloured and I believe some plastic bits have suffered so it is quite likely that the seals have suffered as well. One of the pistons has been scuffed as well.

It has no thermostat or seal or retainer or spring at present and the seat for the themostat is badly corroded. What will be the complications if any of running without a thermostat?

Other pics are

The object of the exercise is to get the egine operating at minimal cost so that it can be used as an auxilliary on a small sailing boat on a lake

 

[Paul Moir]

Re: Cooling problems 6hp and similar

Yeah, there's nothing cheap about overheating an outboard. Big or small it makes no difference to the damage.

If you run without a thermostat, you risk cold seizure (piston heat expands until it jams in the bore) and lots of carbon, excellerated wear, etc. Do you go full throttle on your car before letting it warm up? It doesn't matter if the thermostat leaks a little. In fact it can help sometimes.

That engine's got some work ahead of it if it's going to run right. Obviously a new head gasket (surface that warped head!), water tube grommet, bottom main seal, water pump replacement and a new thermostat. Not so obvious is the collapsed piston skirts and perhaps the bottom main crankshaft bearing if that seal let go a while ago. I'd have a long hard look at that piston before choosing to put either back in service Really it will likely need a rebuild in order to get crankcase compression back to where it needs to be for it to idle well.

I know parts are pricey over there, you may be able to pick up the bearing and seal from a local bearing supply company though. In the interest of cutting corners to keep things cheap, if the compression is good you may be able to get away with it. But likely it'll never idle as well as before it was overheated.

 

[Vic.S]

Re: Cooling problems 6hp and similar

Thanks for the comments. Some of what you mentioned has alredy been done and the present efforts, following the failure of a mechanic to find the real case of the overheating, are prompted by the fact that it starts easily and runs well. A thermostat is to be fitted and it seems that the bottom crank shaft seal is OK.
I posted really just for the sake of interest and information as its not my problem. I do claim credit for pointing the finger of suspicion at the grommet in question though.