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Enginetype: Outboardgas
> motormodel: Evinrude 88 spec
> Serialnumber: 199?
> Configured: single
> boatmodel: hewes
> Boatlocation: salt
> typeofneed: Tune-up
> Need_Other: overheating
> repairsdone:
> Replaced t-stats and poppet
valves 12-99 replaced water pump 8-97 periodic maintenance.
> Comments:
Running in 75 deg water at
4000 rpm with 20 psi water press, eng temp 120 deg. If you pull back
to idle 900rpm 8psi pres temp climbs until horn sounds. Pulled apart
t- stat housing and checked stats opening at 140 deg. Found what looks
to be crumpled up oak leaf in weep hole in housing. My guess is
running 4000rpm at 20psi 120 deg the stats are closed the poppets are
flowing water no problem. At 900rpm 8psi since the stats are closed
not enough pressure to open poppets, weep hole plugged up the temp
climbs because there is no flow across stats. What do you think.
Question: What problems would I get in to if I took stats out and ran
without them or enlarged the weep hole which is 1/16" dia to
3/16" which is larger than the intake screen on the lower unit
hence if it goes thru screen it will pass weep hole. What are the
poppet valves in there for any way. Thanks
Our answer
At idle only a small amount of water
is required to cool the cylinder heads so, the thermostat is designed
to handle that. The thermostat can only pass so much water and more
water volume is required at high RPM, to cool the engine. The poppets
open when pressure and volume exceed the preset amount. The
thermostats have to be in place and enlarging the weep holes is not
recommended.
Besides the chance that the overheat
sensor is tripping too early, the most likely cause is clogged cooling
passages in the head and/or collapsed rubber deflectors in the block.
(If so equipped.)
Note that the rubber is only
supposed to restrict water flow between the cylinders but when the
stopper goes flat or slips out of the intended location, it can block
water flow through the block.
Since you run in salt water, you may
find the heads are clogged with salt and corrosion. Removing the heads
and inspecting/cleaning the cooling passages and replacing the
deflectors, water cover gaskets, and the head gaskets should be done
periodically, depending on usage.
There are some other possibilities
but this is the best place to start.
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