Ultra Fit USB 3.0: Excessive Heat

Hi There,

Just to let you know, I have found that this disk overheats, and found many threads about it like this one, that’s why I registered

My Cheap no-name USB 3.0 sustained 20MB/s with my test copying a movie file and a folder full of photos.

The SanDisk UltraFit starts at 90MB/s then all of a sudden drops to about 20MB/s for the rest of the transfer. I note if I pause the transfer for 10 seconds and then resume the speed ramps back up to 90MB/s and again drops off. I did this test many times, even trying different ports.

Really disappointed that my cheap USB stick is better overall than SanDisk. I was expecting that SanDisk was high quality but I am concerned that frequent use may end up doing some damage due to the heat problem. So after paying about 5 times the price of my cheapo USB I now have a dud product. Why should I have to wait for the SanDisk to cool down, I bought it for high speeds so I can get things done faster.

I’m sure many of you have seen this on their website:

So Small You Hardly Know It’s There. So Fast You Barely Have to Wait.

This ultra-small, low profile drive stays put for extra storage, or moves media super-fast between devices. Enjoy performance speeds up to ten times faster than USB 2.0 drives, transfer a full-length movie in less than 40 seconds.

ripped off

Do the excessive heat posters use the drive’s SecureAccess app on it?  I could see encrypting & decrypting large or many files on the drive being a load that could cause excessive heat.

I did not use any encryption appl. Only a plain disk, formatted normally and written with normal copy from either Windows Explorer and Linux.

Even worse, without copying anything, the flashdisk also becomes hot by itself.

formatted normally

So you are not using the USB drive with the factory format?  How did you reformat it and to what format?

Nope. I never trust the factory format as they do mass production and it is understandable that some may be formatted not perfectly. I always reformat on my own computer to let the flashdisk formatted structure matches the computer format.

Format normally = insert the flashdisk to USB port, wait until it is recognized by Windows Explorer (i.e. assigned a drive letter). Then right-click the drive letter and select Format.

The goal of the factory format is as a Super Floppy and is designed to maximize the efficiency of the drive.  Windows format does not support the Super Floppy format and may not even care if the drive is removable.  It’s just not a goal of Windows format function.

So did you format it as NTFS or exFAT?

It is very possible the overheating problem is a self inflected problem.

Doesn’t matter whether NTFS or exFAT, both runs extremely hot.

So what is the “factory format” standard and how can I do this?

@chin wrote:


So what is the “factory format” standard and how can I do this?


You can’t. You already burned that bridge when you re-formatted it because you didn’t trust the factory format.

So what is the “factory format” standard

For drives less than 64GB FAT32, for drives 64GB and larger exFAT., but all in superfloppy mode with the drive as a single partition. No partition table, no MBR.  And neither format has journaling which NTFS has that adds overhead to a drive.

@Tapeworm: if what you claimed is true, does Sandisk make this clear to the consumer? I do not see any notes neither guidance re. this factory format in the packaging.

@Ed_P: as I informed earlier, using exFAT does not help to reduce the heat either.

Is it anyone from Sandisk in this forum to help to explain this?

it’s a basic engineering problem. as you put more functional stuff into a smaller space, you get more excess heat. there are workarounds to deal with overheating, but the problem is always present (unless there’s a radical change in technology). this is why computers and game consoles have built-in fans, they would overheat and shut down otherwise.

I’ve had the same issue with my 128gb sandisk ultrafit. the metal gets burning hot when I transfer gigabytes, and even when I leave it in without doing anything, it’s hot right after ejecting. it makes sense actually, because they maximized efficiency - with as much speed and memory in as small a space as possible, there has to be a tradeoff: excess heat.

I’ll assume on good faith that sandisk is aware of this, and that QC determined that the excess heat is not enough to cause damage to hardware. But naturally it’s alarming to the end-user, and I wish they’d been more up-front about this.

In the meantime, I’ll still use it, but I’ll limit my usage to be on the safe side. It seems to especially heat up in my laptop. I’d think adding ventilation holes would’ve helped but there could be design reasons I’m not aware of.

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“I’ll assume on good faith that sandisk is aware of this, and that QC determined that the excess heat is not enough to cause damage to hardware.”

Have you seen the photos joeydee posted?


@xcalibur: you said “the metal gets burning hot when I transfer gigabytes, and even when I leave it in without doing anything, it’s hot right after ejecting” — I agree if it gets hot when there is data transfer, but when it is idle doing nothing, what makes it get hot?

In my logic, if it gets hot when idle, it will be no surprise if it overheat and fail when it is “in action” (i.e. huge data transfer). One thing to clarify, did you copy files into it straight away “out of the box” or did you reformat it before transferring anything into it?

My primary concern (which I guess others’ too) is whether this excessive heat will damage our laptop (i.e. USB port or burn/melt the palmrest area where the USB port is located)?

Sandisk does provide warranty but only on the stick (which makes sense), not our laptop neither USB port. Therefore I guess many would rather not to use, or at least use with high caution.

@Ed_P - those pics didn’t show up until I clicked the link. that is a serious malfunction for sure, but I haven’t had issues like that yet. you can’t rule out the possibility that it was defective and that the heat issue wasn’t at fault.

@Chin - it heats up while idle because it’s still running. there’s much more heat during data transfers.

I didn’t reformat.

it hasn’t caused any problems for my USB port yet, even though I did big transfers the other day. while I’m assuming the best, I’m still going to use it economically. for more routine data transfers I’ll probably use the 16gb flashdrives.

Thanks for the clarification xcalibur. This rules out the factor that the heat issue is caused by reformatting the stick (as explained earlier in this topic).

Just ordered the 128GB and probably should not have.

What was the Sandisk response to you?

I just RMA’d my SanDisk 128GB a month ago because it would drop-out after about 3 or 4 GB into a file transfer. It only did this when plugged into a USB 3.0, which led me to conclude that it was an overheating issue caused by the higher performance of the drive when plugged into a USB 3.0 port. I could copy over 60GB in one go over USB 2.0 however.

Anyway, got my RMA back the other day. Same issue unfortunately. I got a great deal on this drive though (only paid like $15), but if I paid any more I think I’d be asking for a subsitution from SanDisk, i.e. one of their other equal or greater performing 128GB drives.

Definately a lemon this series of Ultra Fits. My last 64GB version had all sorts of issues as well, which SanDisk replaced with 2x 32GB sticks. No technical issues with the 32GB stick, but the keychain holder did break on one of them; yet another design flaw of the Ultra Fit.

My 64GB FIT has run very hot from day 1 when copying files or formating. It is so hot I can’t touch the metal part for more than 2 sec while in use and I have to wait a few min to cool down after pulling it out. While at idle it is just slightly warm. I only use it in a 3.0 port on my  1 year old MSI gaming laptop. It obviously is not a hardware issue since there are so many reported heat problems even in new computers. A design flaw in the Fit has to be the problem . It’s too bad because the size and price per performance can’t be beat but I’d be a fool to trust my data on a drive that is too hot to touch. I will not buy another Ultra Fit at any price although mine is still working fine.

+1. I bought the SanDisk Ultra Fit 128GB USB 3.0 Flash Drive (SDCZ43-128G-G46) from Amazon, drive disconnects when file copied longer than 1 minutes and very hot even when idle.


So i just decided to make an account here to post my personal experience and thoughts. I just received the 128GB Ultra Fit from amazon, and am also experiencing some heat issues, although they are only mild so far compared to others. I am running the Fit in a 3.0 port on my macbook pro trying to get a time machine backup. 8GB transferred so far, touching it every minute or so to verify it isn’t about to “melt” and it seems that if you touch it like so, the heat will dissipate into your finger allowing it to stay somewhat normal in regards to temperature. So with that little technique, no issues so far, but will keep monitoring to make sure nothing happens.