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Just wanted to thank everyone who responded to my posting. And maybe help someone else with the same problem.
Harold suggested getting a heavy duty thermostat from Dodge. I opened up my system to see what thermostat the mechanic had installed. He said it was a 180 Stant and was the one the Stant book said was for the 1975 Dodge 440 truck. I found the thermostat in the engine was a 180, but the opening was only 7/8. The opening in the engine is 2 and the hoses are 2. I went to Pep Boys and checked the book, the thermostat was the one the book called for. I ordered the part from Dodge, the Dodge thermostat part #3418459 has an opening of 1 3/8, the only heavy duty thermostat for the 440 Dodge offers is a 195. After doing some testing with a candy thermometer and a pan of coolant on the stove I determined that the Dodge thermostat only begins to open at 195. The opening is only about the thickness of a dime at 200 and if the temperature is kept at 200 that is all it opens. As the heat is increased, the thermostat opens slowly until at 230 it finally opens fully. I checked two of the Dodge thermostats and both tested the same. I suppose the Dodge thinking is to insure the engine is kept at a good hot operating temperature. Especially with the smog stuff. That is fine for a truck with a lot of clearance and air flow around the engine compartment. But for a close cowled class A motor home, it isnt. I finally installed a Stant # 29108, 180. After testing on the stove I found the Stant starts to open at 180 and is fully opened at 190. It opens quite fast compared to the Dodge. The opening is 1 ½. After road testing it I found that it maintains a highway temperature of 200 and stopped in traffic it cools back to a comfortable 190. When pulling a moderate grade on a 90 degree day it went to 210. A far cry from the 250 260 with the Dodge. I also road tested the Dodge thermostat.
email Phil G.
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