overheat at idel speeds

[dhughes49]

i have a 1996 johnson 150 saltwater. i overheated at idel speeds but not at higher speeds. i pulled out thermostats to flush out motor because bogged it down in a bunch of mud. one tstat was wide open and one was dead shut. i dropped them in boiling water and the shut one opened a little but the open one did nothing. can anyone clue me in about thermostats. which is the bad one or r both bad?

 

[Daviet]

Re: overheat at idel speeds

They should be closed when cold and open when heated up.
How long has it been since the water pump was serviced, might be time to do it.

 

[dhughes49]

Re: overheat at idel speeds

just had water pump replaced 1 month ago.

 

[durban]

Re: overheat at idel speeds

i can understand why its over heating at idle speed , you are losing water pressure some where , as you throttle up the impeller turns faster pumping more water , or could be thermostats or deflectors

 

[emoney]

Re: overheat at idel speeds

Impeller changed before or after the mud? If before, I'd pull it and have a look at least. Might be simple, so forgive me if it is, but have you also checked water inlet to make sure it's not clogged with mud? The open t-stat would've still allowed water to flow at least. Tstats are cheap and they do wear out, so I'd replace them if it were me.

 

[WernerF]

Re: overheat at idel speeds

Opening "a little" in boiling water is not enough. In the engine boiling water would be an overheat situation. Some thermostats degrade when being overheated, so I would replace it in any case.

 

[kenmyfam]

Re: overheat at idel speeds

Agree. Start at the water inlet and work through. Blockage or restriction somewhere. Completely agree also that the water pump should be checked out again after sucking in all that mud and grit and stuff. Impeller could well be toast.

 

[Bob_VT]

Re: overheat at idel speeds

Replace the stats as a pair. I would hate to see one bank overheat and toast the motor.

I would probably also open the water jackets to insure they are clean from mud and debris.

I do t-stats, water jackets, head gaskets, water deflectors and all passages every 3-5 years and impeller at least every year or two depending on use. It's worth the investment.