[Ford-ferguson] Thin out the hydraulic fluid in cold temps?

[jurors75973 at mypacks.net]

I have a 1957 Ford 860 with the piston-type hydraulic pump.

I've put the standard New Holland Multi G134 hydraulic fluid in.

In these cold winter temperatures (sometimes down to -5 or -10F), the 
hydraulic lift is very slow until it warms up, maybe 1/2 hour or 45 min. 
of operation.

Can I safely thin the hydraulic fluid, using kerosene or something 
similar, to quicken the warm up period a bit?

IS there a better fluid that will be good for cold temps as well as 
summer temps (summer is usually < 90F).

Thanks for any help.

--
Chan Webb