Over heating at 70MPH
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Over heating at 70MPH
2005 XLT 4.6L V8 - Never had overheating issues until three weeks ago.
The check gauges indicators come on, looked at the temp. gauge and it was in the red. Pulled over and waited for it to cool, added coolant to get it home. Drained and replaced Coolant & thermostat. Got HOT again. Did a coolant flush and flushed the heater core as well. Replaced with 50/50 coolant. Drove for two days without no issues, then it would start to over heat at 70 mph. So I decided to replace the water pump and radiator along with upper & lower hoses. Drove for a couple of days with no issues. I can drive on the highway for over an hour at or below 70 mph with no issues.
If I increase my mph over 70, the temp. starts to rise. To get it to come back down I have to turn the A/C off and slow down. Once its back to normal temp. I can turn the A/C back on and drive at 65-70 with no issues.
Any advice on what is causing this or what to look for would be appreciated.
The check gauges indicators come on, looked at the temp. gauge and it was in the red. Pulled over and waited for it to cool, added coolant to get it home. Drained and replaced Coolant & thermostat. Got HOT again. Did a coolant flush and flushed the heater core as well. Replaced with 50/50 coolant. Drove for two days without no issues, then it would start to over heat at 70 mph. So I decided to replace the water pump and radiator along with upper & lower hoses. Drove for a couple of days with no issues. I can drive on the highway for over an hour at or below 70 mph with no issues.
If I increase my mph over 70, the temp. starts to rise. To get it to come back down I have to turn the A/C off and slow down. Once its back to normal temp. I can turn the A/C back on and drive at 65-70 with no issues.
Any advice on what is causing this or what to look for would be appreciated.
5 Year Member
Joined: Feb 2012
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Not sure, but does it have an electric fan vs an engine driven one? If electric, it may be a failing sensor for the fan. Seen it happen before, or the fan itself may have an issue. If engine driven, replace the fan clutch.
Senior Member
Joined: Mar 2016
Posts: 6,548
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From: South-central Ohio
Did you burp all the air out of the system?
Not sure where it is on 11 gen. trucks, but there should be a high point purge plug high on the intake/ water manifold area- may need to crack it and let trapped air out.
Not sure where it is on 11 gen. trucks, but there should be a high point purge plug high on the intake/ water manifold area- may need to crack it and let trapped air out.
5 Year Member
Joined: Feb 2012
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I'm thinking the higher engine RPM's at 70 is not spinning the fan fast enough, though it is just a guess without actually being there. As another poster said, it could also be air trapped in the system.
It is either poor circulation, or poor airflow through the radiator. The water pump might be sucking air and causing cavitation.
Senior Member
Joined: Jul 2009
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From: Lost Wages
I'm thinking the higher engine RPM's at 70 is not spinning the fan fast enough
It doesn't, it causes more load on the fan clutch, and more slippage.
FAN CLUTCH PROBLEMS
A slipping fan clutch is often overlooked as the cause of an engine overheating problem.
As a fan clutch ages, fluid deterioration gradually causes an increase in slippage (about 200 rpm per year). After a number of years of service, the clutch may slip so badly that the fan can't keep up with the cooling needs of the engine and the engine overheats. At this point, replacement is often necessary.
Other signs of fan clutch failure would include any looseness in the clutch (check for fan wobble), or oil streaks radiating outward from the clutch hub.
If the clutch is binding, the fan may not release causing excessive cooling and noise, especially at highway speeds
CHECKING THE FAN CLUTCH
A good clutch should offer a certain amount of resistance when spun by hand (engine off, of course!). But if the fan spins with little resistance (more than 1 to 1-1/2 turns), the fan clutch is slipping too much and needs to be replaced.
If the fan binds, does not turn or offers a lot of resistance, it has seized and also needs to be replaced.
Fan speed can also be checked with an optical tachometer, by marking one of the fan blades with chalk and using a timing light to observe speed changes, and/or listening for changes in fan noise as engine speed changes.
You should also try to wiggle the fan blades by hand. If there is any wobble in the fan, there is a bad bearing in the fan clutch, or a worn bearing on the water pump shaft.
A slipping fan clutch is often overlooked as the cause of an engine overheating problem.
As a fan clutch ages, fluid deterioration gradually causes an increase in slippage (about 200 rpm per year). After a number of years of service, the clutch may slip so badly that the fan can't keep up with the cooling needs of the engine and the engine overheats. At this point, replacement is often necessary.
Other signs of fan clutch failure would include any looseness in the clutch (check for fan wobble), or oil streaks radiating outward from the clutch hub.
If the clutch is binding, the fan may not release causing excessive cooling and noise, especially at highway speeds
CHECKING THE FAN CLUTCH
A good clutch should offer a certain amount of resistance when spun by hand (engine off, of course!). But if the fan spins with little resistance (more than 1 to 1-1/2 turns), the fan clutch is slipping too much and needs to be replaced.
If the fan binds, does not turn or offers a lot of resistance, it has seized and also needs to be replaced.
Fan speed can also be checked with an optical tachometer, by marking one of the fan blades with chalk and using a timing light to observe speed changes, and/or listening for changes in fan noise as engine speed changes.
You should also try to wiggle the fan blades by hand. If there is any wobble in the fan, there is a bad bearing in the fan clutch, or a worn bearing on the water pump shaft.
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Renaissance Honky
Joined: Jun 2016
Posts: 1,083
Likes: 156
From: Mound, MN
Dude, you're going 70mph, it's not the fan.
Have your Pressure Cap checked, I bet it says 0psi on the gauge. Drop $5 and get a good one (Stant or other aftermarket)
How many miles on your water pump?
How bad was the old coolant that came out?
did you flush the snot out of the radiator?
I'm betting it's a combo of pressure cap and water pump.
Have your Pressure Cap checked, I bet it says 0psi on the gauge. Drop $5 and get a good one (Stant or other aftermarket)
How many miles on your water pump?
How bad was the old coolant that came out?
did you flush the snot out of the radiator?
I'm betting it's a combo of pressure cap and water pump.
Senior Member
Joined: Jan 2013
Posts: 3,651
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From: KY.
The OP said the radiator, water pump, thermostat, and the hoses were all replaced so that should of taken care of any circulation problems. I would replace the cap and see if that helps, hopefully it's not a head gasket issue.