Cummins 6bt 5.9-m thermostat replacement?

[dsarazen]

Hello All. I have a year 2000 Cummins 6BT 5.9M in a 36' sundeck. It only has 420 hours on it. Runs great, but at 2000 RPM the temp is 190 pushing 200. I have boiled out the heat exchanger, replaced the raw water pump, cleaned out the intake strainer, and all the hoses are good. I don't know IF I have a problem, but a local marine mechanic suggested I look at the thermostat. I don't want to starting tearing down the engine, but it is 13 years old, and with the low hours, maybe the thermostat has deteriorated - don't know. Anyone ever replace theirs? Thanks

 

[rthomas]

Re: Cummins 6bt 5.9-m thermostat replacement?

That might be about right for that, Diesels like heat.

 

[kahuna123]

Re: Cummins 6bt 5.9-m thermostat replacement?

Have you had the heat exchanger cleaned after that many years?

 

[elkhunter338]

Re: Cummins 6bt 5.9-m thermostat replacement?

Most 190 thermostat open up at 195 to 200. Is your pressure cap holding pressure and do you have a good 50/50 antifreeze mixture.
Have you ever changed your antifreeze? I swapped the green stuff for the red long life Fleetrite.

 

[angus63]

Re: Cummins 6bt 5.9-m thermostat replacement?

Do not forget to verify the gauge is accurate before digging.

 

[170freedom]

Re: Cummins 6bt 5.9-m thermostat replacement?

My Hatt has 2x 6bts. port runs 170* and starboard 175* consistantly. Get a temp gun and verify gauge. When engines were shipped to me they both had 190*s in them. Gauge was reading 220 and 225, so I ckd with temp gun, found gauges were off. Actual temps were 195-200. I put in 160*s that I found online and never looked back since.

 

[Scott Danforth]

Re: Cummins 6bt 5.9-m thermostat replacement?

keep in mind the thermostat is a spring, a piece of metal stamping, and a hunk of wax in a small brass canister. they work when the wax expands.

so yes, they do wear out over time. I would replace the T-stat.

 

[magster65]

Re: Cummins 6bt 5.9-m thermostat replacement?

I'm pretty sure my 5.9 bta (270hp Diamond series) manual says the operating temp is from 160 to 205 degrees (to be checked at the engine outlet).
According to the gauges, mine both run at 192-ish at idle speed and about 195 at a 2200 rpm cruise... and don't seem to get any hotter if run up to the 2600 rpm max.
Assuming your strainers are clear and your rw impellers are in good shape... are you getting the correct max rpm?