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roybelding, Master Tech/Trainer
Category: GMC
Satisfied Customers: 5431
Experience:  35 years of retail operations on all vehicles
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GMC Sierra 2500 HD SLT: I have a 2500 GMC Duramax, 2006 model

Customer Question

I have a 2500 GMC Duramax, 2006 model (diesel). It's my farm truck and we pull a lot of heavy things. Recently, we've replaced thermostats, water pump (it leaked recently), cleaned air intake filter/new, cleaned out radiator fins, put on a new A/C radiator (heavy duty). Radiator was flushed out a year ago. Aside from things obviously easy to repair (and we repair everything possible), an issue for a couple of years is this: When we pull a heavy trailer, the engine temp guage goes up (even on a cool day). Not pushing it much, I let off and temp cools to normal after a few minutes. After a few more minutes driving, when I need power up a hill (at normal temp), the engine cuts back and won't shift or gain speed. I suspect the temp/sensor kicks in the protection mode from getting up to 240+ deg. Mechanics (GMC and independent) say my trans is great shape (we had an oil seal last fall but it is good to go). However, it shifts somewhat rough when being aggressive acceleration. I have in the last 2 years/past replaced the gear shift (on the column) - which is the lever when you select Manual, D, N, R, P etc. Note that manual versus D (automatic shifting) does not affect anything, nor does trailer versus no trailer mode. One person suggested my radiator is restricting water so much that it overheats - we use Dex Cool all the time - so is that possible? Today we also checked radiator temps, and the output is 20 degrees cooler than input, we suspect thermostat, but they were just replaced. The sensor reads 10-15 deg. hotter than the water temp, so we think it could be sensor, but when not pulling, the pickup stays nearly constant on 200 degrees while driving (by the guage/sensor). When idling around and sitting it cools half way between 160 and 210 - is that correct or should it stay at 200/210? I thought the pickup always cooled back when idling on a cool day. In the hot summer, it stays at 210 idling/sitting. Oh, we tested the Dex-cool, and no exhaust in the coolant - so perhaps that rules out a gasket issues internally?
Submitted: 1 year ago.
Category: GMC
Expert:  roybelding replied 1 year ago.
good morning my name is ***** ***** I will assist how heavy of loads??? Roy
Customer: replied 1 year ago.
Typically 12-15,000 lbs. Although, I don't push the pickup much so we run 50 mph and about 1800 rpm in 6th gear (auto) I think. Up hills, it downshifts to 5th (if working correctly). Note that the issue seems to happen after the temp raises (delayed reaction of say 15-20 minutes). It never happens starting out, or short trips. That's why it is hard to show mechanic. I had two guys riding with me the other day (55 deg F), and 30 miles into the trip (against a 35 mph wind), it started gradually getting hotter by the guage. Another 5-8 miles, the engine cut out (as I described in my question).
Expert:  roybelding replied 1 year ago.
ok, thanks. it sounds like you are pulling a real heavy load. I suggest having a radiator shop build you a larger radiator. it sounds like the cooling system is being taxed too much with the load. I also worry about the trans. with it heating up like this, the trans is at risk with the fluid getting hot. Allisons do not last long with fluid getting real hot Roy
Customer: replied 1 year ago.
It never had any problem from 2006 through 2014, over 220,000 miles. Although, most miles are empty (not pulling). I think your advice not correct. Although, on hot days, I would say anything could / will get hot on heavy loads, but this pickup never ever did this in the past. I tell you what, I don't think I want to use your service or pay you for this advice. Can we just cancel my question, please?