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Cat Man
Cat Man, Caterpillar Engine Expert
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Experience:  23 Years Caterpillar Engine experience.
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C15: PEterbilt..oil cooler..a leaking water pump at the seap hole

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I have a 2007 PEterbilt 379 with a C15 Acert. I recently had my water pump replaced, thermostats replaced and oil cooler replaced by a Cat dealer. The problem started as a leaking water pump at the seap hole. The water pump was then replaced. My coolant/oil temps were running low, so it was diagnosed as thermostat seals. They changed the thermostats and we used Pittscugh Power's 180 degree thermostats. Then the oil temp was 240 degrees and the coolant temp was 210 at 80k pounds and pulling hills like in WV. Cat diagnosed the oil cooler was bad. They changed the oil cooler. Now, at 68k pounds, oil temp is 249, water temp 210 with the fan on. Ever since the water pump was replaced, there has been a chirp when you press the fuel petal. Any ideas?

Hi. Thanks for using JA! I will try and help you out.


Since the oil temp and coolant temp went up after replacing the thermostats, I would remove and inspect the thermostats. I would also inspect the thermostat seals.


If the coolant and oil temps are running hotter after the thermostats were replaced, it sounds to me like some of the coolant is most likely not going through the radiator and going through the bypass. When this happens, your temp will go up.


I have had customers complain of a chirp from their engine a few times and the problem was with the Turbo. I have not seen any chirping noises or problems after replacing a water pump.



Please let me know if you need more help or have more questions.

Customer: replied 6 years ago.

Thanks for the info. i don't think I explained the thermostat problem enough. The engine actually started getting hot after the water pump was installed. It dropped to 150 degrees at idle, that's why we changed the thermostats. It was still reaching collant 215 and oil temp 240 on a pull, but once the road leveled off, it would immediately cool back down.


When they replaced the thermostats, they said the thermostats were good, the seals were bad.


We have owned this truck since new. It has 475k miles and has never ran this hot, so we know there's a problem....just not sure what.



I see. Thanks for the information.


Your condition is called "Overheating at high loads. I find the radiator to be the leading part that causes overheating at high loads.


With 475k miles on the engine, and you have replaced most of the items that cause the engine to overheat, the next thing I would suspect to cause the overheating is the radiator.


Has it been removed and cleaned both inside and out?


If not, that is what I would recommend doing.

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Customer: replied 6 years ago.
One last you think it could be a bad water pump?
I do not think so. Everytime I have seen the water pump cause overheating, the engine would overheat at all times at any load. With yours just overheating at high loads, I don't thing it is the water pump.

Let me know if you need more help. Thanks for the accept and bonus!