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5.0 MIE 230 significant temp increase when coming off plane

J

jon_allen

Regular Contributor
Hi Guys,

This Inboard Merc normally runs about 130 on plane while underway. When slowing down to pick up a mooring the temp will climb to 190 and it takes along time for it to come back down. The motor is FWC. The coolant level and quality are ok. The belts are tight and the risers are touchable without to much discomfort. I suspect the thermostat may be weak. I would greatly appreciate any advice. This motor does not have an inline sea water strainer.


Thank You
Jon Allen
 
Hi Guy,

The motor is a 1986 model FWC straight inboard. I'm thinking maybe the increased coolant flow at cruise speed may be propping the thermostat open and once the engine slows down it starts to close to the point where it gets hot. If the seawater impeller were damaged would'nt it overheat at cruise where the cooling water is needed most?



Thanks, Jon
 
If the seawater impeller were damaged would'nt it overheat at cruise where the cooling water is needed most?
Click to expand...

Not if has just begun to fail. The exact opposite can occur; too low of water pressure at idle but sufficient at cruise speed.
 
To be safe, With the info you have givin here, For a starting point, you really should consider replacing both the thermostat and the rubber impeller/ Housing, Because it sounds like there is a chance that you may have two issues going on that could be related to each other.;)

You are running a bit to cold, and a little too hot.:eek:

Also you may want to get yourself a infrared temperature gun to compare the temperature of your gauge.

http://www.mercruiserparts.com/selectDocs.asp?doc_nbr=11905

Good luck with it.:)
 
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Hi Guys ,

Thank You all for your help. I was told it had a thermostat installed but it may be defective or for a RWC motor. I will verify temps with my I/R gun. One thing I don't quite understand is how a scored seawater pump housing or plate or a pump with a bad impeller can cause the cooling water to aerate.I mean how does a bad pump produce air ? Is cavitation the cause? I can understand the lack of flow but not air being produced. Also what would be the ideal running temp for this engine in salt water for the season in Massachusetts? I need to select a thermostat.



Thanks,
Jon Allen
 
jon_allen said:
Hi Guys ,

One thing I don't quite understand is how a scored seawater pump housing or plate or a pump with a bad impeller can cause the cooling water to aerate.I mean how does a bad pump produce air ? Is cavitation the cause?

Yes, If that housing is damaged in anyway, The cooling system to the engine is not going to get the correct water flow or water pressure that it needs.


Also what would be the ideal running temp for this engine in salt water for the season in Massachusetts? I need to select a thermostat.

Your engine calls for a 143 degree thermostat, And 143 is better for the saltwater then a 160.
http://www.mercruiserparts.com/Show...0&bdesc=THERMOSTAT+HOUSING+(STANDARD+COOLING)
Click to expand...
 
guyjg said:
Wouldn't it use a 160 F.
Click to expand...
No, Not according to the parts diagram for his style engine.

The parts diagram says both the standard and closed cooling system use a 143.

See closed cooling here, http://www.mercruiserparts.com/Show_Pictures3.asp?dnbr=%2011905&ivar=images/CRUISER/11905/25.png&inbr=906&bnbr=120&bdesc=CLOSED+COOLING+SYSTEM

And standard cooling here, http://www.mercruiserparts.com/Show...0&bdesc=THERMOSTAT+HOUSING+(STANDARD+COOLING)

On the older carbed engines, merc mostly used 140-143 degree thermostats, But now on most of the newer style carbed engines, merc now uses 160-163 degree thermostats, But certain style engines will vary between the two thermostats.

Also I double checked a service manual for you, and it also said 143 degrees.
 
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