How hot does a P45 northbridge (MCH) get?

They tend to get hotter during heavy gaming, and blended stress-tests (cpu and ram).

If the temps are OK with the stock cooler, than you have nothing to worry about. NBs can handle quite a lot of heat, so anything under 80C should be fine.

I have OC'd a few chips now on this mobo and have not found a need to get any aftermarket cooling for the NB.

At full load touch the NB heatsink. If it's too hot to touch then you should opt for aftermarket cooling.

When I say too hot to touch I don't mean 'feeling unpleasant' or warm, I mean 'impossible to touch for more than a few secs without burning your finger'.

Cooler than any other I've ever owned. (NF4, P35, 750i, P45)

Don't sweat it.

They run cool until you start getting up there with the voltage. Mine started acting unstable around 75C, so i bought the HR-05 for it, and it hardly breaks 40C now.

In short, you don't need to worry about the temps unless you're doing some heavy overclocking. especially with a quad where you'll need more NB volts. Of course my DFI board had pretty minimal stock chipset cooling. Probably another reason that it ran hot.

I just got the UD3P and happen to touch the NB heatsink when running prime. It was hot to the touch. (almost made me worry, but it wasn't burning, just on the edge of too hot for skin after 15 seconds etc.) I initiall thought that this was too hot, but upon reflection, it wasn't too bad considering I was working a blend test.

Another thing to consider is that a warm heatsink is a good thing. I would be more worried if it was cold. (as in the heat is not making its way to the heatsink) From what I have read and experienced, there is no need for an aftermarket cooler on these unless you are really cranking the volts.

Definitely, cold heatsinks are badnews.

OK, sounds like I don't have anything to worry about. I haven't been able to get the RAM past 950MHz on this rig yet anyway.

it doesn't run hot at all

how much voltage have you added to the NB? How high would it be safe to go?

Right now I've got the MCH core and VTT undervolted, so I'm pretty sure it's all cool. Like I said, my OC isn't much anyway.

I have a thermal probe under the edge of my NB. given that I routinely run my quad at 4ghz 24/7, the temps peak in the high 40's celcius. Mind you I did pull the heatsink off and clean/re apply with AS5 which definitely helped.

That must be some much better stock cooling than my DFI board then. My board went into the 70C range with stock cooling at 1.36v on the NB.

No, the gigabyte UD3's big selling feature is double thickness of copper in the PCB which drops board temps by 23C. Strangely enough it actually works.