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Junior Member
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83 Posts
Discussion Starter #1
I have a 2008 6.4 4x4 and while running down the interstate between 80-85 mph the coolant temp gauge pegs out and then it says reduce engine power. Slow down to 70 and it's fine. So I figured I wouldn't run that speed anymore but the other day pulling my airboat down the interstate it did it again and I was only going 70. The boat is light weight but it does hav some wind drag. Need to get tuis fixed before my next trip with my cattle trailer from Florida to west Virginia. I know it won't handle pulling thru the mountains. Looking for any advice.

Thanks
Ryan
 

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Let it all Ride
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1,316 Posts
Is the truck stock or tuned? Have you noticed any coolant under (puking) under the hood. The first place I would check is your degas botttle cap. If the system is not holding pressure, it will cause the coolant to boil before the fans turn on.
 

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Junior Member
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83 Posts
Discussion Starter #3
Yes the truck is tuned with a sct livewire. No custom tunes just canned tunes. It stays on max setting. I also have a aftermarket intake and I have deleted the burner. Just a straight pipe exhaust. I'm not losing any coolant anywhere and both egr coolers were replaced about 16,000 miles ago along with head gaskets all under warranty an while truck was still stock. As soon as the needle pegs out and it says reduce power you let off the pedal for about 15 seconds an it will drop right back to regular temp. I had my live wire plugged in to watch the temp and the hottest I seen was 200. It runs around 194 to 196
 

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Let it all Ride
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1,316 Posts
Try changing the degas bottle cap. It's a $5 part at any parts store. My truck was doing something similar and the cap fixed it.
 

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ADMIN/MAFIA
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4,834 Posts
I am not sure if the 6.4L has a similar Degas bottle but I know that some 6.0L Degas bottle cracked. You can rent a pressure tester from autozone I believe that have one that has the correct adapters. The other option is to do a hydro-carbo test on the coolant, it tells you if there are exhaust gasses in the coolant. O'Riely Auto Parts can order this kit you just have to specify diesel to get the correct fluid.
 

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Senior Member
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606 Posts
If your temp was only showing 200 and the message center says reduce engine power, sound like a bad sensor. 200 degrees will not boil the coolant.
 

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Junior Member
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83 Posts
Discussion Starter #7
thats what i was wondering if it could be a bad sencor. my degas cap was replace when i was having all my coolant issues before. Its just strange to me that it only pegs out when it has some what of a load on it.
 

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Senior Member
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606 Posts
Also, if the temp was high enough to have a CEl on, the fan should have been running. Was it?
 

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Junior Member
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23 Posts
If the temp gauge maxs out then goes back to normal right away that is telling you your oil is getting to hot compared to coolant temp. This happened to my brothers truck last winter and thats what ford told him. The oil cooler ended up getting changed out.
 

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Member
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278 Posts
I lost an oil cooler on my truck as well but my coolant temp was never high just my oil temp. Maybe check out what your oil temp is at when it does this. Anything over 230-240 and you have a problem oil cooler wise. 200 on engine temp is not bad so it could be a sensor sending it into limp mode.
 
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