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Old 05-27-2023, 09:27 PM   #1
Join Date: Apr 2022
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CAT C12 Overheating at Highway Speeds ONLY

Any idea what could cause this?

The rig will stay cool for 1000 miles at 55mph, but the moment it gets up to 60mph it gets warm, 65mph it gets dangerously hot. What gives? Allison 4060. Well under max weight
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Old 05-27-2023, 09:32 PM   #2
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That is classic bad radiator or fan not turning up to speed. Check the fan first of course. Then clean the radiator and other coolers in the stack. Plenty of threads on how to clean them.
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Old 05-31-2023, 08:18 PM   #3
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Could also be the water pump. A C12, or any CAT highway engine is getting up there in years. Water pump impellers tend to rot away if the coolant hasn't been conditioned perfectly over the last decade.
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Old 05-31-2023, 10:48 PM   #4
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You may be at the tipping point as you increase HP or the airflow around the radiator changes. My CAT C9 is a rear radiator so it is direct drive. Side radiators are notorious for these issues as the speed regulator fails.
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Old 06-04-2023, 09:15 AM   #5
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I had some over heating problems and here is what solved it.

I went to a Wax valve system and also changed out the thermostats to what CAT recommends.

I didn't buy a pre-made kit as IMO there is better way to do it and cheaper.

Engine never gets over 206* then drops back to 198* until it goes back to 206* then drops again..

Needle valve NVHH0375S1143 from With this you can adjust the rpm at idle of the fan. Infinite adjustment and takes 60 sec to adjust.

wax valve 553/1/09857/183 THERMO
HYDRAULIC VALVE from Legacy hydraulics

ORB weld bung..have welded on the water pipe.

5k hyd lines made locally.
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2004 Magna 42' 3 slide Chalet CC#6315M
C-15, 515HP 1650tq.
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cat, heat, heating, overheating

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