Running Hot - replaced all cooling components - Defender Source
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Old April 26th, 2013, 07:50 AM
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George
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Running Hot - replaced all cooling components

Had the typical run-hot issue on the 3.9. At idle or slow traffic, the temp gauge would creep towards the red zone. At speed it was fine. The water pump was replaced 3,000 miles ago. I recently noticed that the fins on the radiator were corroding away, so decided to go with a new radiator sourced from AB and set out to freshen the entire cooling system. All new hoses, new heater pipe, sensors, thermostat, and new expansion tank cap.

I'm aware that air locks are common in this system, so attempted to fill the coolant as best as possible. Turned it on the first time and it ran hot quickly, which it never did before Tried to bleed air by taking off the expansion tank cap and squeezing the top hose. Have done this a few times and seems to be getting somewhere.

This morning I topped up the system, turned the engine on and she seemingly ran cool for quite some time. I thought i finally had it figured. Turned it off for a bit to button things up, then restarted and the temp gauge ran up shortly thereafter. Touching the radiator and hoses, noticed that the lower radiator hose was warm, the very top and left of the radiator were Al's warm. However, the right hand side and bottom of the radiator were cold as was the top hose, except where it meets the thermostat housing.


I'm at a standstill. Any ideas? Thanks.
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  #2  
Old April 26th, 2013, 07:53 AM
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Steve Maietta
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Viscous fan coupling might be shot.. When hot, it should be locked up. When cold it should spin free(er) At highway speeds there is enough airflow to keep things cool, but at rest the system relies on the fan, which when not locking up isn't going to be pulling enough air.

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Old April 26th, 2013, 08:00 AM
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George
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I replaced that about a year ago, but may be worth looking into again. I have a hard time discerning a difference in its cold and hot operation, so could be an issue.

Still, what gives with the uneven temps at the radiator and hoses?
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Old April 26th, 2013, 08:02 AM
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Joshua
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Also not sure how you filled the coolant, but you should fill the system up while the truck is on a bit of an incline so that any air is at the very front of your system and more easily bled.
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Old April 26th, 2013, 10:18 AM
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Chris Davis
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Sounds like the thermostat is not opening.
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Old April 26th, 2013, 10:27 AM
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George
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Just might be the case. It's brand new, 82 degrees, installled with the float thing at the top with the spring (?) into the block. Does the sound right?

I don't like the thought of having to drain the system again and getting at those thermostat housing bolts, but it looks like the way to go.
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Old April 26th, 2013, 12:13 PM
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Head gaskets?
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Old April 26th, 2013, 12:32 PM
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George
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Has good pressure and holds coolant.
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Old April 26th, 2013, 02:56 PM
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Bill Campbell
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I had a bad thermostat out of the box from AB. Got another put it in and it cured my problems. You right though, changing that thing out sucks based on the pure mess factor.

Also when I filled my fluid up I ran the right side up on ramps so the filler was the highest thing on the truck.

B
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