engine temperature fluctuates?

[Shaun78]

I changed my thermostat and now my temp goes to 175ish then down to 150 and then back up and down and so on. Why is this? Is it ok? My other boat was the same way after changing the thermostat.

 

[mkast]

Re: engine temperature fluctuates?

Sounds like the thermostat is working.
Stays closed until temperature is reached, then opens until cooler water reaches the thermostat which then closes until the temperature is reached again.

 

[Shaun78]

Re: engine temperature fluctuates?

It is definately working but prior to changing it stayed at 170 degrees (no fluctuating)

 

[JCF350]

Re: engine temperature fluctuates?

What is temp rating on the thermostat you installed?
They will fluctuate some with RPM changes.

BTW!! fresh or raw water cooled???

 

[Shaun78]

Re: engine temperature fluctuates?

It's a 160 degree thermostat

 

[JCF350]

Re: engine temperature fluctuates?

Coolant flow is fluctuating. Could of had a bad run of thermostats (in which case there will be 1000's of them out there). Or it just plain wasn't designed right to begin with (opens to far and restricts to much).

You done something twice to change the water flow?

Thermostats are not designed to operate in constant motion (wears them out). You see this mainly in auto's that have they're radiator fans jumpered on all the time.

 

[Qubit]

Re: engine temperature fluctuates?

I had this fluctuation problem with my thermostat as well. I changed the thermostat, the upper and lower sensors, the impeller, flushed the engine and cleaned out the debris filter of residual debris in my cooling channels within the engine, also changed the water pump and water pump gasket. In my case after starting the engine cold, the fluctuation only starts after 8-10 min of running, basically after it warms up and usually I've been running at about 30 MPH during this period. At this point the temp gage starts to swing down to 100 then up to 180+ then down again. This just started happening about 10 hrs ago. When I reduce my speed to idling speed, in gear, the temp gage sits on 160 where it should be. I have never tested it on the lift with the internal flush kit assembly pushing fresh water through the engine block, nor have I confirmed that the internal flush assembly is or is not leaking. Also, I have not done the annual out drive maintenance inspection and clean by taking the out drive off for this purpose. Any further ideas with this additional information?

__________________
2000 Formula Thunderbird 260 Bowrider
7.4L MPI w/Bravo III drive