Set the below mentioned parameters in config.txt (or in start.bat, depending on what you use for config your miner)

-tt 65
-ttli 80
-tstop 90
-fanmin 50

(Or you can choose other values, these are just recommendations.)

Did you overclock your 390X?

To all those asking about profitability of coins: go to http://whattomine.com/ GPU section, choose 6 of 480 6 of 380, select all protocols and click calculate. Compare.
Their numbers are good.

EDIT: I'd say if you have rx400 ETH is the best now, if you have older cards with UV maybe zec (depending on your power costs)

Dear Friends, Thank You very much for info and advice about ASUS R390x!

I just bought this Asus R390x. This is absolutely new video card. I didn't do any overclock. It has very good one(I beleive)  fabric cooler, hope there is good connection with radiator and chip...

I don't want to lose this card(about 500$) for 48$ in month and wondering: How long can live this card 24/7 doing minning with 85 degree C ?

If just one year : I will eat shit  for free In one year I will made 550$ minus electricity and will be that card still workable after this job...

Cheers

BTW card has almost all time in mining about 85-86 degree fans have from 45 till 55% may be if it will be critical temperature fans will have more %?
Or I have better to set up fans manual ?

If it is STRIX- 10 days before fan fail ( my expreience ) ... I RMA'd it twice, changed and after 10 days fan dies. 3 times.

Just downclock and under volt.  The card stays cool.

MY GOD!!! I'm exactly about that worring...!!!   it is STRIX....

Exactly could be lovely choice cause probably I will save this card and will make profit in second year )

Any idea what will be good choice for that card ? no more then 75 degree?

Cheers

Thank You! I made mistake when put this card for minning in close case!!! Bad ventilation!!!
I open it now and have 81 degree on 41% fans!!!

You gave me good advice! Beer from my side!

Cheers!

So what...? With the price a 1080 cost I could get 3-4 rx470 so 600 to 800 sols/s 

Buy one of this PCI-E Riser Card very good!