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3.0 merc still over heating

S

sea rogue

New member
2000 bayliner capri 3.0 started over heating first time i put it in water after 5 months out of water ,with 2 seasons of no problems . dropped lower foot and replaced water impeller . (note found half of shutter valve aka flopper valve in lower foot.) job went well. replaced thermostat all so . put new 160.in (had 160 in) .put in water for test and still ran up to 175 and over to almost 200 degrees ,(normally always ran 175 all day.) ...next step .pulled lower and upper unit off .to look for other have of flopper valve .could not find it . Other videos showed it stuck behind shift rod in exhaust passage. but not mind ....then i removed the riser to see what the water passages look like .WAS NOT PLUGGED .ALSO removed piping to see where shutter valve sits (or did sit ,all gone .engine runs fine . .will be doing a water test on exhaust manifold (still on head ) .ill plug exhaust port so no water goes into engine ..if water flows out of manifold .what am i missing . it sucks to try things and nothing works and makes me keep digging deeper .What am i missing .and i no this is a common problem with 3.0 after a years in salt water. ..parts guy says replace manifold ...ps boat is in very good shape .garaged keeped all its life
 
1st verify the actual temp with a laser, dont rely on the gauge. Have a cust boat that has a 33 degree difference
a 2000 is probably the gen II and they will develop a air leak under the metal plate
 
Bt Doctur said:
1st verify the actual temp with a laser, dont rely on the gauge. Have a cust boat that has a 33 degree difference
a 2000 is probably the gen II and they will develop a air leak under the metal plate
Click to expand...
...Thanks for help ..one thing i did not mention ,when i pulled upper unit from drive housing , the water o-ring ,was anything but round . looked octagonal and not looking like it was sealing .Kind of strange to see it looking like that. ...waiting on shutter valve and new drive housing gaskets ,and riser gasket to re-try in water.....i am glad i pulled upper unit to look for other half of shutter valve ,to find bad o-ring , but still not sure if that's it...i will get back later in week after test no.3 ,,,thanks again for help .will use temp gun .
 
Bt Doctur said:
a deformed O ring on the water inlet could be the whole problem
Click to expand...
well just re-installed complete lower unit .with new gasket, water inlet o-ring seal and large o-ring in drive bell housing. also installed new shutter ,valve (aka flopper valve) .started engine , let warm up ,and just like before temp went to 175-and went to over 2000. ....stopped engine .let cool down a little removed stat , and i was wide open . pulled hose the come's from lower impeller to thermostat housing .started engine for a few sec.s and water flow was like a fire hydrant....so i pulled water pump for inspection .looks ok. so i pulled riser (again) and exhaust manifold ....now at this point i don't see anything but i don't understand how the manifold can be plugged by just looking at it. engine runs ok . but can the head gasket be gone ...i feel dumb as a car mechanic and can't seem to fix my own boat engine from overheating . 1- not impeller pump . 2 not thermostat 3 water pump is ok . .waterchecked hoses .used laser temp gun with reading showing water temp hottest at thermostat housing but not riser. ...so far it's been gaskets and small parts and my own labor . if i have to put a manifold and riser i will .Can't find smoking gun . I want to go boating
 
five things,

water in
water out
temp control (thermostat).
Temp gauge
sender



So...................

What is actual temp at sending unit? any idea?

If you are running and temp get to 160-170 and then in a matter of a couple minutes it shoots to 200 it could be a bad sending unit. How long before getting over 200?

It should take several minutes to get that hot.

1Serial number break:0L340999 and below. 143 degree thermostat, engine should run at ~ 160 all day long

2Serial number break:0L341000 and above. 160 degree thermostat, engine should run at ~ 180 all day long
 
Was engine actually running hot or was that what temp. gauge said ? Had mastercraft at shop today, replaced 1 1/4 water line to heat exchanger, closed coolant system. Turn key on 0 at temp. gauge after cranking then gauge shot to 175° then shot to 200°. Laser said. 110° cut off engine and gauge hung at 200°. Teleflex temp. gauge.
 
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