I have a Mariner 8hp which overheats after about 10 minutes. The tell-tale
stream turns to steam and the engine stops shortly after.

I started at he bottom and checked impeller and pipe up to powerhead all
working fine - good stream at idle and for about 5 minutes at high rpm so I
think the water flow is ample but engine gets hot and it can't cope.

I have taken off head and checked passages, ditched thermostat and removed
grit from water jacket around cylinders.
Some aluminium has chipped off around the sleeves exposing the actual
sleeves to the water. Could this be what heats the water up to such a high
temperature?

wrote in message
...
On Sun, 18 Mar 2007 08:55:47 GMT, "will_456"
wrote:

I have a Mariner 8hp which overheats after about 10 minutes. The tell-tale
stream turns to steam and the engine stops shortly after.

I started at he bottom and checked impeller and pipe up to powerhead all
working fine - good stream at idle and for about 5 minutes at high rpm so
I
think the water flow is ample but engine gets hot and it can't cope.

I have taken off head and checked passages, ditched thermostat and
removed
grit from water jacket around cylinders.
Some aluminium has chipped off around the sleeves exposing the actual
sleeves to the water. Could this be what heats the water up to such a high
temperature?


You may have a problem where the tube connects to the power head. Have
you checked the water pressure? "T" off the telltale hose. It should
be 15psi or so at WOT. If it drops to 3 or less you will overheat,
just not enough water to do the job.

May be a problem at the bottom of the tube, not the power head. There is a
rubber donut the tube goes into at the top of the waterpump. May be split.

"CalifBill" wrote in message
ink.net...

wrote in message
...
On Sun, 18 Mar 2007 08:55:47 GMT, "will_456"
wrote:

I have a Mariner 8hp which overheats after about 10 minutes. The
tell-tale
stream turns to steam and the engine stops shortly after.

I started at he bottom and checked impeller and pipe up to powerhead all
working fine - good stream at idle and for about 5 minutes at high rpm so
I
think the water flow is ample but engine gets hot and it can't cope.

I have taken off head and checked passages, ditched thermostat and
removed
grit from water jacket around cylinders.
Some aluminium has chipped off around the sleeves exposing the actual
sleeves to the water. Could this be what heats the water up to such a
high
temperature?


You may have a problem where the tube connects to the power head. Have
you checked the water pressure? "T" off the telltale hose. It should
be 15psi or so at WOT. If it drops to 3 or less you will overheat,
just not enough water to do the job.

May be a problem at the bottom of the tube, not the power head. There is
a rubber donut the tube goes into at the top of the waterpump. May be
split.

The rubber seal wasn't that good and someone had missed the centre with the
pipe when putting the leg on and the seal edge had folded in so I fixed that
up and smeared a bit of silastic sealant around it. I also took the motor
out and took off the side cover and head and removed heaps of dried up salt.
Most of the small passages were completely blocked. (The previous owner had
never flushed it after use - just layed it on it's side in the shed). I
don't know what you are supposed to use to clean it but electrical contact
cleaner works well to disolve all the deposits. Now it runs cool. Thanks for
your help.