Thermostat maintenance

[jimgram]

How often should you test your thermostat and how frequently should you replace it? (Cummins 6BT 5.9 diesels or similar diesels)

Bonus question? What could cause a failure (specifically fail in closed position)?
And please venture an opinion (or experience): Can severe engine over-heating due to blocked cooling raw water (not engine coolant) cause a thermostat to fail in the closed position?

 

[rslifkin]

Overheating can cause a thermostat to fail (open or closed), but in my experience, thermostat failures are pretty rare in general. I've only ever seen one stick closed, not sure I've ever seen one stick open.

 

[Bacchus]

I haven't seen one fail but decided at coolant replacement (~12 yrs) it was time for a new Tstat.

 

[O C Diver]

I don't test thermostats, radiator caps, or antifreeze. Consider all of that stuff disposable for the effort to do the job.

I don't know what makes a thermostat fail, other than use. When you consider the cost of a head gasket job from over heating the engine, coolant parts are negligible in cost.

If you're doing the work yourself, I consider the freshwater cooling system a modest investment of time and a minimal investment in dollars compared to boating cost. My John Deere coolant system has about 6 gallons of coolant including the loop for the bus heaters and water heater. That's about $120 of their coolant. The two thermostats, gasket, radiator cap, and the 4 orings on the heat exchanger tube bundle may cost $150. So all in, I've got $270 invested in cleaning the cooling system. JD recommends flushing and changing the coolant every 2,000 hours and cleaning the heat exchanger every 500 hours. That may be excessive, but I normally do it every 2,500 hours which is about 3 years for me. Takes me a day and gives me peace of mind.

If you tested your thermostat a month ago and it failed next week over heating the engine, would you wished you had replaced it instead of tested it? As they say in the investment business, "Past performance is not a guarantee of future results".

Ted

 

[Sna]

My starboard motor was running cool last time out (~130 degrees F) so I changed the thermostats. The John Deere 6076 engines have 2 thermostats on each engine. I was thinking they were sticking open resulting in running below temp.

When I pulled them out they were both closed, but I put them in a pot of water and heated it up. They opened as expected at 180F but did not close as the water temperature cooled. I haven’t taken the boat out yet to fully test.

First picture: closed and heating up
2nd picture: Open at 180F
3rd picture: Still open even after water has cooled to 130F

Seems super curious to me that both have failed the exact same way. Unless they’re fine and I’m missing something.

 

[O C Diver]

My starboard motor was running cool last time out (~130 degrees F) so I changed the thermostats. The John Deere 6076 engines have 2 thermostats on each engine. I was thinking they were sticking open resulting in running below temp.

When I pulled them out they were both closed, but I put them in a pot of water and heated it up. They opened as expected at 180F but did not close as the water temperature cooled. I haven’t taken the boat out yet to fully test.

First picture: closed and heating up
2nd picture: Open at 180F
3rd picture: Still open even after water has cooled to 130F

Seems super curious to me that both have failed the exact same way. Unless they’re fine and I’m missing something.

I don't know about your engine, but my 4045 has double acting thermostats. They open on rise, but then when reaching full temperature, the thermostat blocks another passage, completely blocking the bypass so all fluid flows through the tube bundle.

As far as both failing, maybe it's your temperature sender or at the gauge?

Ted

 

[Portage_Bay]

Completely agree. They are inexpensive but their failure may be very expensive. If you have it open put a new t-stat in.

I don't test thermostats, radiator caps, or antifreeze. Consider all of that stuff disposable for the effort to do the job.