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Cat Man
Cat Man, Caterpillar Engine Expert
Category: Heavy Equipment
Satisfied Customers: 8812
Experience:  23 Years Caterpillar Engine experience.
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C15: oil cooler and dripping..oil cooling system cleaner

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I have a C15 cat motor in an 05 Kenworth truck that is leaking water just below the oil cooler and dripping off the top of the oil filter. I had just replaced the thermostats and was flushing the system with cat cooling system cleaner when the leak occurred. It leaked about five gallons overnight. My view is obstructed by the frame rail, so I can't see what may be leaking. any ideas?

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


Your leak is coming from one of the outer O rings on the Oil cooler. I have seen this before. The coolant runs from the front to the rear of the cooler and then goes into the side of the block. The only place coolant can leak is at either the front or rear of the oil cooler. All you will need to do re replace the O rings on each end.


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

Customer: replied 5 years ago.
I have inspected closely around the ends of the cooler and there is no leaking from the o-rings. I could send you a picture of the leak if you if you want

I see. Thanks for the information.


If the O rings are clean and dry, the next thing I would suspect is Jacket water cooler or coolant diverter valve.

If you have a picture, that would be great. I would be happy to take a look at the leak.

The coolant diverter valve or Jacket water cooler could be leaking on the back side and running down to the cooler. The only other thing I can think of is a cracked oil cooler. But to be honest, I have only seen that once in 20 years.
Customer: replied 5 years ago.
can I e-mail you the picture? I can't figure out how to send you the picture on this site.
Unfortunately, JA does not allow emails to go between customers and experts sorry. You should be able to click on the paper clip icon to attach a picture.
Customer: replied 5 years ago.
I don't see a paper clip icon on my page

I'm Sorry. I do not get to see the customers side of this website. I figured you had one since I have one on mine.


No problem though. I think the coolant must be coming from the Coolant Diverter valve gasket or the Jacket Water Cooler that is beside of it. Other than the thermostat housing, those are the only items on that side of the engine that contain coolant.

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