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Cat Man
Cat Man, Caterpillar Engine Expert
Category: Heavy Equipment
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Experience:  23 Years Caterpillar Engine experience.
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I have a 2006 model CAT 625 hp C15. While the truck is running

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I have a 2006 model CAT 625 hp C15. While the truck is running down road, it sucks the reservoir dry on the radiator overflow tank and when the radiator cap is loosened it refills the reservoir. Also, it will sometimes just push water out of the overlfow tube, usually about a gallon in 4 hours or 250 miles. It only does it when the engine is under a load. We have changed the thermostats, water pump, cleaned radiator out and it has proper pound rating radiator cap. This truck is in the heavy haul application and it has an oversize radiator. It is running a little hotter than usual, staying around 200 degress most of the time. Any suggestions?

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


Could you get me your engine serial number? If not, that is OK. I just want to make sure you have an ACERT engine with 2 turbos.

Customer: replied 5 years ago.

yes it is a twin turbo

Thanks for the information.


I must say that I have not seen heard of a C15 that sucks the reservoir dry and when the cap is loosened, the tank refills.


However, I have seen several C15 ACERT engines with twin turbos push coolant out of the over flow under load. Many times when this happens most techs are quick to blame the head gasket for the engine pushing out coolant. But on twin turbo engines, there is another item that can push coolant out, and it will only do it under load.


It is a failed Jacket Water Pre cooler. JWPC. It is a cooler on the outlet of the turbos to cool the air before going into the air to air core. Basically what is happening is when the engine is under load and making alot of boost, there is a small hole or crack in the cooler and boost pressure goes into the cooling system and pushes out coolant from the over flow.


You should be able to remove the piping from the JWPC and see evidence of coolant in the piping.

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Customer: replied 5 years ago.
one of our mechanics removed the pipe and there was no water in the pipe
Thanks for te information. Sometimes you will see coolant and sometimes you will not.

Does the fins on the JWPC look like they have a white appearance? If so, that is a good indication that coolant is there and the JWPC has failed.
Customer: replied 5 years ago.
i have replaced the part it is still pushing water out under a load
Thanks for the information.

There are only a few other things that can cause coolant to be pushed out. One is the engine air compressor. Which I do not think it is the air compressor or else it would push coolant out under load or not.

Since your is only doing it under load, I would suspect the problem is a failed head gasket, a cracked liner flange, or cracked head. Of course the head would need to be removed and inspected.

Please let me know if you have more questions.
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