Repeated Kernel Panic with a dual 1.8 G5

Question

I have a dual 1.8 GHz G5 bought on the refurb Store in january.
It is the model with only two pairs of memory slots, 80 GB disk, and 2x128 MB of memory.
I have added 2x1GB of memory bought at macway.fr, and two SATA Maxtor 300 GB coming from my former Powermac.
The machine works well in basic conditions, but have Kernel Panic (or freezes, but mainly KP) when doing intensive task like h264 video encoding or everything CPU intensive.
Since the beginning, I have noticed that this machine fans never never accelerate when doing CPU intensive task.
(I use another G5 in my office, a dual G5 2 GHz, and its fans frequently accelerate when it works. And no Kernel Panic at all).
I have used Temperature Monitor. If I do a h264 video encoding, I see the CPU temperature raising, from basic 55°C to 71-73 °C, where the Kernel Panic arrives...
And fans never never accelerate during this time.
Temperature Monitor indicates a specified upper limit of 76 °C.
When I look through the pransparent panel, everything seems to be OK. Fans gently turn, no LED lighting.
Do you think, like me, that this machine could have a cooling problem ?
What could I our should I do ?
PowerMac G5 dual 1.8 Ghz   Mac OS X (10.4.7)   Fans never accelerate.

Answer 1

I think that you are right with the RAM.
I have removed the two 1 GB modules and made a test with only the original 256 MB.
Exporting a clip to h264 while playing another. 100 % of both CPU.
Temperature has risen up to 74 °C with no Kernel Panic.
The test is still going on with no problem.
I trusted the memory because I bought it in a Mac boutique. It seems I was wrong...
It is better for me, because it is easier to replace memory modules than to carry the G5 to an Apple Center and be without my computer