i have a 2002 gmc serria 2500hd and just got 35 FT COUGAR FIFTH WHEEL AND NOTICED ON SOME HUGE HILLS THE TEMP GOT TO 221 IS THIS OK IT CAME RIGHT BACK DOWN AFTER HILL??
The temp your seeing is not uncommon for duramax's through about 2006. My 2004.5 will hit 230 on long steep grades and then hold, fan engages at about 210, and you KNOW it is on! Cools off quickly once you start downhill.
Trans temps stays in the 190 range.
By now you should have changed the coolant fluid several times, I change mine every 2 years.
Rule of thumb especially since I just had all my Differntial and transervice done on my 2002 Chevy 2500 HD yesterday... I bought it last year so I wanted everything gone through and fixed... Just wear and tear... The Trans guy told me the hotter your Transfluid gets the more often you need to get it changed....
What are you using to measure the temperature. I find it difficult to differentiate more than 10 degrees with the cluster gauge on my 05 Duramax. I use a Scan Gauge and find it will indicate 10 degrees or more different than the cluster gauge. But 221 for coolant when towing up a grade is no problem provided it does not continue to increase. Was your cooling fan engaged? What was the transmission temperature. Were you using the tow haul mode. Tow haul will lower both transmission and engine coolant temperatures.
221 is no big deal - most cooling fans won't come on until 226 or so. However, if it's just running warmer in general than it used to it may be time for some maint. on the cooling system.
I have a 2006 2500HD and see temps like that when going up a hill. I don't worry about it for a short time but on long grades I slow down a little to keep it from going higher. Brian