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Master Auto Tech.
Master Auto Tech., master tech.
Category: Transmissions
Satisfied Customers: 429
Experience:  A.S.E. Master technician. Over 20 years working on import & domestic. Owner/operator of an auto shop
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My name is Luis, I have a 2005 GMC 2500 HD 6.6l with the

Customer Question

Hi my name is***** have a 2005 GMC 2500 HD 6.6l with the Allison transmission. The problem is that the transmission is overheating all the way to 275*F. The transmission is working good no shifting issues or codes, the engine stays at 195*F. I noticed that the exterior trans cooler return side line is not hot, I did a test and I remove the cooler and installed a clear hose to see the flow of the transmission oil, the flow is minimal. From what I see the oil flows from the line that says (to cooler) to the bottom of the radiator it exit from the top then it goes to the external cooler and back to the transmission. If I am not wrong the radiator cooler is an open tank that hardly will get cloged, so my conclusion is that the transmission is not pumping enough oil pressure, do you know why?
Submitted: 6 months ago.
Category: Transmissions
Expert:  Master Auto Tech. replied 6 months ago.

Hi Luis, I'm sorry you are having problems with your vehicle. I will try to help.

I'm a full time mechanic and have been a mechanic for over 20 yrs and I work part-time here on JustAnswer to help you and others repair their own vehicles, and I get credited by your ratings.. So before leaving the site make sure and leave me a rating. You can still reply to me as many times as neeed, even after the rating.. I will need for you to be my hands and eyes since I'm not there.

So to answer your question, If the transmission wasn't pumping or the pressure was low it would slip as you tried to run down the road. I have to things you can do. First If you want, take the line off that goes to the radiator from the transmission and see if it pumps very fast. If it does then either the radiator cooler or the external cooler is clogged, or both. It is not unheard of for these to clog up. Also check the lines from the transmission to the radiator and make sure they aren't kinked or smashed thus restricting the flow as well. IF you have good flow, go by a transmission shop and ask for a can of flush for the cooler. It will come in an arasol can and will blow thru the coolers. you will have to back flush them. then use compressed air to blow the cleaner out. Let me know what happens so I can continue to assist. Thanks Sonny

Expert:  Master Auto Tech. replied 6 months ago.
Do you still need help with this problem? Was my reply helpful?
Thanks
Sonny

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