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Why does my C-15 Accert run cool

I have a 2005 475 Accert that will not run up to proper temperature since the cold weather has set it. Runs at 160° driving and will climb to 175° when parked until it starts to cool down at idle. Oil temp only runs up to 120°.

My fuel mileage has dropped significantly.

In warmer weather the temps run closer to where they should be.

I have installed 185° thermostats, replaced the fan hub and tried a winter front with no change.

Any ideas?

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Chosen Solution

Your fan might be stuck "On" when it should be turned "Off."

First, I would check to see if the fan is kicking on when you start the engine (the fan shouldn't) and then again while you are driving.

Make sure the in-cab switch- if you have one, it's usually labelled "Fan" or "Engine Fan" with settings of "Auto" and "Manual"- is set to "Auto"- Then start the engine.

Open the hood and see if the fan is spinning and listen for a whirring noise.

The fan should be spinning slow enough that you cannot hear it, if it is spinning at all.

If you hear the noise, can see the fan is spinning fast, and the engine is still cold, your fan is sticking on. Check your fuses and circuit breakers- make sure the 2 amp "Engine Fan" fuse or breaker (if your truck has either) has not blown or tripped. The location of the breaker or fuse varies, and it should be listed in your truck's Owner's Manual, Driver's Manual or Service Manual. Reset the breaker if it's tripped or replace the fuse if you find it's blown.

Then, shut the hood and drive the truck. Listen for the fan (a steady whining noise) to kick on while you are driving and note the temperature it kicks on at. On most CAT engines, It should kick on at 200, then shut off when the engine cools back down to 180 or 185.

If it's not the fuse or breaker, or if the fan kicks on and stays on while you are driving, then take the truck to your Caterpillar technician and have them take a look at the ECM settings, fan switch and sensor.

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Thanks for your input.

I suspected the fan in the beginning. It would function correctly in auto, but would stick if turned on manually. I would have to kill the key to stop the fan. The fan was spooling faster then normal at idle, so we rebuilt the hub, replaced the bearing which was going bad and replaced the solenoid on the firewall for good measure. The parameters in the ECM are correct and the fan is working properly now.

Going to try the coolant valve for the cooler next.


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Most Helpful Answer

Cat ACERT engines have a pre cooler that the air from the turbo's flows through before it goes to the after cooler in front of the radiator. The pre cooler uses engine coolant to drop the air temp down. There is a valve that regulates the flow of coolant through the cooler. If it is stuck open too much coolant flows through the cooler and the air from the turbo's will over cool the engine coolant. At light loads and idle the air from the turbo's is not that warm especially in the winter time. Have the valve inspected. I think it's called a coolant diverter valve. It looks like a solenoid and sits under the turbo's, inline with the small blue hoses that run to the pre-cooler.

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Thanks, will give it a try and let you know what we find.


If a stuck open diverter valve causes the engine to run cool, would a stuck closed diverter cause the engine to run hot?


Took the truck that had the stuck diverter solenoid out to haul canola yesterday. This is after we free'd up the plunger and got it to open. No more overheating, barely made 200 degrees. Just stupid power out of these engines when they work properly.


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The answer to ur problem is the thermostat ring in the housing if u take the thermostat housing off the truck remove the thermostat there's a metal ring that interference fits in the bottom of the housing with a black plastic ring inside it when i remove it replace it the same way plastic down put steel ring inside rubber gasket open thermostat and let rubber relax against thermostat base put it in the housing push til base seats on rubber gasket done.

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