10C temp drop - and why

OK, I recently re-did my watercooling rig a little, and tidied things up, moving my radiator and pump. As my system is watercooled because of the noise aspect, I've purposely used as few fans as possible. That said, the side of my case is always off.
So, I power up my system, and I've gone from 3/8th barbs to 1/2 barbs on the pump - an eheim1250 - and stretched the 3/8ths tubing over them, taken out a foot of tubing and generally "tweaked" it. My temps before were sitting around the 45C mark on CPU0 and 43C on CPU1 with an ambient room temp of 20C. After the tweaks, and settling down, my temps were going up and up - to 51 and 47 at their peak. So I thought a little, and looked at it. Because the radiator had been moved, and was now not pointing into the case, there was less airflow over the northbridge - a passive aluminium heatsink. So, I found a 40mm fan from an old hdd cooler, and whacked it on. Then pointed an 80mm case fan at the northbridge area of the MB, tied to my rad with a cable tie or two. The result is my temps as monitored by MBM are sitting at 41 and 37 on my CPU's now. What made me twig exactly the cause was seeing the NB HS directly under the CPU that was getting much hotter than the second one.
I think the lesson from this is that even in a totally watercooled system, you need some sort of airflow - I know it's been said before, but it's quite an eye opener to see just how much of a temp drop you can achieve with some carefull planning. HOpe this helps someone anyway

The temp drop you're seeing here isn't actually a 10c drop in cpu temp. It's a drop in the thermister temp below the cpu. The fans blowing air on your NB is also circulating the air to a degree in the socket, hence the drop of temps & also why thermister readings suck in general. Take a can of compressed air & blow it at the base of your socket while the comp is running, the cpu temps will drop even more If you were using the cpu diode to measure the temps then there shouldn't be much of a difference with or without the fans.

Do you know for sure that my mainboard is taking temps from a thermistor? I didn't see one under the chip when I put them in. I'm running 2 MP2000's in an Asus A7m266-D. I haven't seen documentation either way, but know that the palominos have an on-die diode - I assumed (yes, I know assuming is bad) the 7M266-D read the diode, not a thermistor. The northbridge was baking hot, and is directly under the waterblock - the metal zif socket lever on the side of the CPU socket was very hot too where the northbridge was warming it, which is why I thought the northbridge was in effect adding to the heat load of the watercooling setup. Anyhoo..... They're lower...

Yeah i agree with banshee i have exactly the same problem, the thermister sits right in the middle of a dead spot of air and without a hs/fan no air flows off the heatsink and under the mobo because you dont have any fan on there anymore. What made it worse too is because i took off my nb fan for noise reasons. Now i just sit a 4v 80mm fan on my gfx card pointing at the nb and just under the waterblock. It also helps cool capacitors a lot!

Yes if your processor can read on die temps your mobo needs to be able to as well. Generally if your mobo has a thermister in the cpu socket its known not to be able read on die temps.

some boards do have both the insocket thermistor and the on-die sensor capability. you may be right that most can only do one or the other though, im not aware of that.

Hmm... There's certainly food for thought here. I still haven't found any documentation stating whether the A7M266-D reads temps off of the diode, or from a thermistor. From the temp drops, you'd think it would be a thermistor, but I know the A7M266-D has Asus COP - CPU Overheating Protection. Therefore, you'd think that for that to work, it would have to read temps from an on-die diode, rather than a thermistor, due to a thermistors temperature lag and innacuracy.

Edit:This review states that the A7M266-D reads temperatures from the on-die diode - and has pictures of the board clear enough to see that there isn't a thermistor in the middle of the CPU socket. So the point of this post would seem to remain valid - about a 10C drop in temps just by adding a fan in the right place... Strange.

Go onto the motherboard forum and then the asus sub forum then post a question in there, you'll get a reply very quickly.

sorry Seal - got the answer posted just before you ;-)