400 operating temp.
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Posting Guru
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From: East Tn
400 operating temp.
How hot should my 400 run? It has a 4 core rad, 160 degree t-stat and an electric fan. It will run 220+ at idle. In normal driving, it runs 180-190ish. What can I do to bring the idle temp down so I can get the old girl out again.
MSEE
Joined: Apr 2004
Posts: 10,386
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From: Austin, TX
220 is way to hot for idle. And a 160 degree thermostat is too cool; I have no idea why they are even manufactured because continued operation below 185 is going to ruin your engine. Flush the cooling system, and check your fan belt. Sometimes the impeller breaks free inside the water pump. How is your coolant level? I'm glad to see you're reporting actual temperature numbers...that's the way to go!
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From: East Tn
Coolant is good I put it in a few years ago when I had the radiator leak repaired. It's either a 12 or 16 in electric fan. Why would I want to put a higher temp t stat in it when it runs to hot now? Alt is stock as far as I know.
Logistics Pro
Joined: Mar 2001
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I think it could 1 of two things baring your water pump being bad. 1) the electric fan is not of sufficient size and airflow to cool the radiator. 2) the alternator is not putting out enough amps to push the electric fan to its fullest capacity.
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From: East Tn
Could the pump be bad without leaking or having a bearing roar? This truck has been in my wife's family since the mid 80's and they say it has allways ran hot. I've had the truck for a few years and quit driving it because i'm afraid i'm going to blow a head gasket. Anyone make a higher volume water pump for a 400?
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Senior User
Joined: Apr 2005
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From: South Bend, IN
Thermostat sticking partway open? I'd change it first, since it's cheap and easy, and see if it improves. Note that the 351M/400 takes a different thermostat than the 300s and FEs -- even though I've seen a lot of parts catalogs that say they're the same. If that doesn't help I'd be thinking radiator restriction next, then water pump.
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Logistics Pro
Joined: Mar 2001
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Could the pump be bad without leaking or having a bearing roar? This truck has been in my wife's family since the mid 80's and they say it has allways ran hot. I've had the truck for a few years and quit driving it because i'm afraid i'm going to blow a head gasket. Anyone make a higher volume water pump for a 400?
I would also swap out the thermostat with a 192 or 195 degree unit and flush the radiator/engine. See what that does.
Fleet Mechanic
Joined: Feb 2007
Posts: 1,326
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From: Middle TN
As mentioned before, could be the radiator not flowing enough to cool, especially since the previous owner said it always ran hot. When you drive it at interstate speeds, does it build heat? This is a clear sign of a stopped-up radiator. Buy a good premium thermostat like a Robert Shaw, not the cheap ones. "400" is right, 160 is too cold.
Logistics Pro
Joined: Mar 2001
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Ok, well if it were me I would remove the electric fan, put a new thermostat in, flush the radiator. If that doesn't help replace the radiator-I assume it's the original-if that doesn't help replace the water pump. At that point I couldn't see it still being too hot.
What gauge are you using to test temps?
What gauge are you using to test temps?
Senior User
Joined: Feb 2009
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From: Southern NM
If the coolant temperature is 185/190 going down the road,that suggests that it is getting air thru the core.Your fan is not pulling enough(any)air at idle.A 12" or 16" fan does not sound like it is a large enough fan.Stock (belt driven) fans are at least 18.25 inches.Will you be running a shroud?All important for puller fans.When the radiator was repaired,do you have any idea how many tubes they closed to repair the leak?And yes,get a 192deg or 195deg thermostat.Overcooling will kill that engine.
Postmaster
Joined: Jul 2001
Posts: 4,956
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From: MD
Buy a Motorcraft RT139 - 192F thermostat.
ONLY buy the Motorcraft thermostat. They have another sleeve that changes the path upon reaching the opreating temperature. Other thermostats do not and can damage the rear two cylinders.
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Ditch the electrical fan unless you have upgraded its electrical system. Those fans will draw up to 300 amps! The clutch fan works the best. You also need the correct shroud.
ONLY buy the Motorcraft thermostat. They have another sleeve that changes the path upon reaching the opreating temperature. Other thermostats do not and can damage the rear two cylinders.
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Ditch the electrical fan unless you have upgraded its electrical system. Those fans will draw up to 300 amps! The clutch fan works the best. You also need the correct shroud.