903 cummins thermostat - Printable Version

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+--- Thread: 903 cummins thermostat (/showthread.php?tid=1316)

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903 cummins thermostat - wepaddle4 - 03-08-2014

When I brought the coach home last fall it was running cool on the interstate (140-160); seems like it needs a thermostat.
Now that the outside temperature is finally above freezing I'm able to do some work on it. I have a thermostat, but I can't seem to find where it goes.
Both upper radiator hoses and the lower have housings that don't seem to be the right size. Nothing else looks obvious either.
Can someone point me in the right direction?
We're leaving for spring break in 2 weeks, the pressure is on now.

Thanks

Scott

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RE: 903 cummins thermostat - encantotom - 03-08-2014

dean s. didnt you have a 903? can you help scott out?

tom

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RE: 903 cummins thermostat - HoosierDaddy - 03-08-2014

I had the 555 which is similar. Generally the thermostat will install between the upper radiator hose and the engine. Your 903 may have a thermostat in each hose. It will mount inside the housing that bolts to the head. An engine manual would show exactly where. Manuals are a good investment and can be bought on ebay. While you have the system apart you should drain and replace the coolant if you don't know when it was last changed. These engines have "wet" cylinder liners that are subject to coolant cavitation corrosion. A cavitation inhibitor MUST be added to the coolant. Cooling system failures are one of the most common causes of engine failure.

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RE: 903 cummins thermostat - wepaddle4 - 03-14-2014

I finally got both thermostats out last night, weird two piece housing design under the upper hoses.
I suspect the problem is leakage past the seals, the thermostats seemed to work when I tested them. Both new thermostats and seals will go in after I get the cast iron housings cleaned up and painted.
I bought several bottles of additive and test strips a few weeks ago. I tested it coming out, a little low in moly, the nitrates were good. Good to know what was in there recently was good, I hope it's been so for the previous 30 years.

Scott

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