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Author Topic:   Mercury 225 Warm Up PROBLEM
IslandMan posted 05-16-2003 10:17 PM ET (US)   Profile for IslandMan   Send Email to IslandMan  
I have a 1997 Conquest with a 225-HP Mercury that has an PROBELM. It will not allow itself to warm up above 90-degrees F. The dealer has changed the spring that acts as a thermostat in an effort to allow the outboard to come up to temp. Negative effect. He has placed a call to the Mercury techs. I hope someone has a solution for me. He did let me know that this is a "known problem", and I am not alone. Can anyone help me with advice?
jimh posted 05-17-2003 12:51 AM ET (US)     Profile for jimh  Send Email to jimh     
[Changed all occurances of the word "issue" to "PROBLEM". Outboard motors do not have issues.--jimh]
TRAFFICLAWYER posted 05-17-2003 09:44 AM ET (US)     Profile for TRAFFICLAWYER    
JimH: You're right, only people do.
Clark Roberts posted 05-19-2003 06:37 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Island, the "spring" (and the associated valve) does not act as a thermostat but simply allows water to bypass the the thermostat when the water press exceeds the set point (usually at WOT) so as to allow unrestricted flow and max cooling. Some people take a turn out of the spring to make it weaker and thus allow it to open up at less press/lower rpm. Even with thermostat removed it seems like cyl head temp would exceed 90 degrees no matter how cold the ambient air and water temps...???? Clark... SCN
mustang7nh posted 05-19-2003 07:33 AM ET (US)     Profile for mustang7nh  Send Email to mustang7nh     
I have the same boat and engine (if yours is EFI). My guage doesn't spell out numbers but it never gets above about 1/3 from the coldest guage setting. I just assumed it was just the guage. Does anyone know what's the net temp effect on the engine?
Swellmonster posted 05-19-2003 05:09 PM ET (US)     Profile for Swellmonster  Send Email to Swellmonster     
My 225 efi never goes above 1/3 either..
pashopper posted 05-20-2003 05:13 PM ET (US)     Profile for pashopper  Send Email to pashopper     
I have the same 97 merc 225 EFI on my 97 conquest. I have the same issue of the engine not coming up to temp unless very slow troll. The temp needle hovers around the bottom tick mark on the temp guage.
IslandMan posted 05-23-2003 10:48 PM ET (US)     Profile for IslandMan  Send Email to IslandMan     
The whaler dealer has opened the "problem" (issue) with Mercury and I will post their responce. I thought it was a guage problem, and mine also moves only a hair off the pin.
Clark Roberts posted 05-24-2003 08:19 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Check your gauges/transducers! These things are never accurate and should be used only to detect a change from the norm (of course most will peg or increase reading dramatically if overheat actually occurs! To check the gauge/transducer: remove transducer but leave wired up, fashion a good ground to transducer; boil some water and drop the xdcr in the hot water; place an oven thermoter (or other) in the hot water and read the ACTUAL
Clark Roberts posted 05-24-2003 08:29 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
whoops! continued> ACTUAL water temp and compare to gauge reading! Using this technique you can calibrate the gauge and can make some sense of the readings. To bring a gauge up to scale and make it more readable you can try changing xdcrs. Also check cyl head temp (a more meaningful parameter IMO) by using a surface thermometer on highest cyl. But determine the actual temp FIRST so you'll have a baseline! Happy Whalin'... Clark ... SCN
mustang7nh posted 08-09-2004 09:05 PM ET (US)     Profile for mustang7nh  Send Email to mustang7nh     
Have solved the warm up and rough running problem with my family's 1997 Merc 225 EFI. Apparently the spring on the valve mentioned was getting stuck open by the fresh water flushing. The garden hose was putting out too much psi and forcing the spring to open and stay open. Engine had a tough time warming up evenly and I hypothesize was sending signals to the computer causing a rough ride and poor mpg. Now use hose at very little pressure and engine warms up in five minutes and runs smooth. Better mpg. Hopefully this will be the end of the issue as its purring like a kitten for now.
bsmotril posted 08-10-2004 08:37 AM ET (US)     Profile for bsmotril  Send Email to bsmotril     
The current issue of "Trailer Boats" magazine that is on Newstands now has an excellent article about the function, and rebuilding of poppet or "Pop Off" valves on Merc Motors. On the Merc V6s, that valve should open anywhere from 1800-3000 rpm. If your motor is never getting warm, I would suspect the valve is stuck open because of mineral buildup, or debris stuck inside. It is not as likley that both thermostats failed, but is possible. Both heads should be the same temperature to the touch. If one is not, then there could be a bad thermostat, maybe the one on the head where the temp sensor is located. BillS

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