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lilihow
New User
Dec 24, 2009, 10:23 AM
Post #1 of 5
(3571 views)
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Cooling Temp Fluctuation
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2005 Ford Freestar with 4.3L V6 -141,000Km.
Driving in the city at 50 or 60KM/hr the temperature gauge needle stays at about 1/4 of the total scale. When I drove on the highway however at 100 to 110KM/hr the gauge needle fluctuated constantly between the 1/4 and 7/8 mark over 1 minute cycles. In other words, it took 1 minute for the gauge to go from 1/4 to 7/8 and then back to 1/4. There was about a 5 second delay when it got back to the 1/4 mark and then the needle started to climb again. This happened during a 530km highway trip with an outdoor temp of -10C.
There is no coolant leaking as the level in the reservoir is at the full mark. The radiator cooling fan is working.
I'm thinking a defective thermostat, water pump or a vapour lock in the cooling system??
What do you think it is?
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Sidom
Veteran
/ Moderator
Dec 24, 2009, 11:01 AM
Post #2 of 5
(3558 views)
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Re: Cooling Temp Fluctuation
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With a problem like this I think I would want to 1st verify that the temp gauge reading is in fact accurate..... This would involve taking a reading by an alternative method, whether it was reading comp coolant temp sensor off the data stream or hooking up a secondary way to read the engine temp.....
It could be an electrical problem or in fact a cooling system problem but from what you posted about no coolant loss, no excessive pressure or heat loss, I don't see any signs of a head gasket issue, a restricted rad would cause that problem at high speeds, but then again it wouldn't cool down until you slowed way down or stopped....
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Dec 24, 2009, 2:36 PM
Post #3 of 5
(3551 views)
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Re: Cooling Temp Fluctuation
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Just curios - do you notice at -10C (you must have your heater on) that the output temp changes? Generally and vehicles can differ, the output air temp unless climate controlled will be about a 10 -15% less than thermostat's rating. If you notice changes when fully warmed up until wild extremes which IMO -10C is not,
T
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steve01832
Veteran
Dec 25, 2009, 5:52 AM
Post #4 of 5
(3541 views)
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Re: Cooling Temp Fluctuation
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Could simply be a lazy thermostat or low coolant level in radiator also.
Steve
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Dec 25, 2009, 6:35 AM
Post #5 of 5
(3535 views)
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Re: Cooling Temp Fluctuation
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I was leaning that way too. Just chance perhaps but not many thermostats have truly failed on me over the decades! If available for one that won't shut if this is now a regular wax pellet type the Robert Shaw type tends to allow any minor debris pass by if an OE fit. Doesn't take much of a crack held by debris to have colder temps that desired which over the years has been more common that stuck shut?? Chance??
They look like this. Now assorted companies sell them as Robert Shaw I think sold out or changed ownership??
T
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