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Ford Tractors Discussion Forum
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temp fluctuation

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Bob

10-31-2003 05:09:02




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Bought a pretty good ol 640 last spring. Went over the cooling system, which was in poor shape. Radiator to the radiator shop, replaced rusted out thermostat, new hoses, new belt,temp gauge and sender. Since then when I start it up it warms up quickly into the middle of the green, but you can tell the exact moment that the thermostat opens because the gauge drops quickly down into the yellow. It does this for several cycles before it reaches some sort of equilbrium and settles down. I'm worried that this fluctuation isn't good for the engine. I drained the radiator down so that the core is barely covered with coolant, thinking that the engine was getting to large of a sudden bolus of cold coolant from a too full radiator tank, but it still does the same thing. Is this anything to worry about?

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bill

10-31-2003 16:50:35




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 Re: temp fluctuation in reply to Bob, 10-31-2003 05:09:02  
there are two types of thermostats.. the cheaper one can only close or go to full open... this cuases the ocillations you see till the water is fully warmed up...

but you can pay slightly more for the deluxe thermostat.. it will vary its opening and do a better job of controlling the engine themerature... pep boys used to sell both types...

either way.. its normal and actually shows your thermostat is good, your water pump is good and your radiator is very good...

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Jerry/MT

10-31-2003 10:29:41




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 Re: temp fluctuation in reply to Bob, 10-31-2003 05:09:02  
Bob, Not to worry. Your thermostat is working properly. As it opens the "average temperature" drops and that cause the themostatic valve to close a bit , which causes a temperature swing upward followed by a valve response that opens up, etc. Your thermostat has a low time constant and your temperature guage has a large time constant (i.e.,increased sensitivity)so it the temperaure swings are picked up by the guage. That's a good thing. As long as the oscillations damps out to a steady state value of temperature everything is OK. Just get out there and enjoy your machine!

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ken in wisconsin

10-31-2003 06:38:02




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 Re: temp fluctuation in reply to Bob, 10-31-2003 05:09:02  
Bob,
What you describe is perfectly normal and absolutely nothing to worry about. That "blast" of coolant that is released by the thermostat instantly intermingles with rest of the coolant until all of the coolant in the system is at the same (optimum) temperature. It's not like you are throwing ice cubes on a superhot piece of cast iron. Relax.



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Gary

10-31-2003 05:41:10




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 Re: temp fluctuation in reply to Bob, 10-31-2003 05:09:02  
I have three Jubilee's, and they all do the same thing, I guess i wouldn't worry about it. I blame it on the foreign temp. guage.



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