I've got a stock i5 760 with stock cooler which idles at around 30-40 Celsius as monitored by speedfan. After starting prime 95 I see the temps rocket to 70 c within 10-20 seconds activating the overheating alarm (set to 70c in bios).
The whole rig is new and assembled by the store I purchased it from and I was wondering whether this is normal (perhaps I'm confusing tcase temps with core temps ? or my speedfan is reporting erroneous temps) or whether I should take it back and get the cpu reinstalled/replaced.
Tcase is the temperature of the top surface of the processor, the part you put the thermal compound on. The principle behind Tcase vs Tcore is that the difference between the two should be as high as possible. This means that your heatsink is drawing heat away from the processor at a greater rate. So really Tcase is just a measuring point to determine rate of heat transfer. What you should be focusing on is Tcore.
Now to answer your issue. For a hot processor there are three common causes.
1) Your BIOS settings are in auto and the mobo is stepping up your Vcore
2) The heatsink is not seated right, most commonly too much thermal compound or one of your pushpins is not fully inserted causing the heatsink to not sit flush.
3) The CPU is overclocked beyond the capability of the cooling applied. Obviously not applicable here unless your BIOS is doing it automatically.
The rig has also crashed a few times
-once auto shutdown, no prompt on restart
-once auto shutdown, gave a prompt saying an error may have been caused by oc-ing though there I have not oc'd it (also ran a memory check which yielded no errors)
-once it just cut itself during boot up and restarted for no reason
Think this is grounds for a replacement of the cpu ??
If the heatsink was installed incorrectly (which seems to be the case given what I've read up on the topic so far) then the store should be liable for replacing the unit which could now be defective.
Is there something I can do to check whether the CPU is actually damaged ?? Either through a visual inspection or using some type of software ?
I wouldn't try to physically inspect the cpu you can damage them quite easily.
70 C is not a problem with an i5 760 you still have 25 degrees to go before you have serious problems, the problem is the how your cpu rises 35 c within 10 seconds. I would double check your cpu cooler to make sure all the pins are in as well as clean the top of your cpu, even a finger print can greatly reduce the power of thermal grease.
If this problem persists, i would try to do a warranty, as long as you didn't void it. Also getting an aftermarket cooler is always a good idea on an i5 or i7 because they are very cool at idle, and get hot under load. Rapid exchange of heat damages cpu's more than a slower increase in temperatures.