I think I'll change my brake fluid soon, and Dot 4 Super seems to be recommended for the X-Type, I'm assuming Dot 5.1 would work fine too, but is it recommended/better?
Or is Dot 4 Super preferred for some reason?
I know Dot 5 is different, silicon based and not compatible, and not "mixable" with the others fluids so I'll be avoiding that.

I went to my local car shop today and I was a bit surprised that they had nothing except plain old fashioned Dot 4, so I ran away, and I'll go shopping online now, but just wondering if I should pick up a litre of Dot 4 Super or Dot 5.1?
Or will I just go with whichever is the cheapest?

I was going to do it the lazy way, and just suck the fluid from the reservoir, but I think I'll probably just do it properly.

 

IF DOT 5.1 fluid is not compatible with anything else, then Super DOT 4 and only that then. I don't think you want to be picking sludge out of your brake system. Might make for a bad day.

 

I'm not sure that I understand you, are you saying that 5.1 is not compatible with the X-Type?

As far as I can gather 5.1 is generally compatible with other fluids, except for 5 (without the .1 at the end), but I don't know when 5.1 came out. Or if it was before 2011, when the workshop manual for the X-Type was released.
If that makes sense..?

 

 

Doesn't say anything about Super Dot 4 though..
Which is supposed to be what the X-Type needs.

Edit:
So it seems that Super Dot 4 has a higher spec than Dot 5.1, and is probably the way to go:

Boiling Point:

• DOT 3 - 205°C (dry) / 140°C (wet)
• DOT 4 - 230°C (dry) / 155°C (wet)
• DOT 5 (silicone) - 260°C (dry) / 185°C (wet)
• DOT 5.1 (PAG) - 260°C (dry) / 185°C (wet)
• Super Dot4 - 300°C (dry) / 195°C (wet) - Racing Brake Fluid

Now to find some..

 

Since you are in Ireland, look for Pentosin. Here in the U.S., I found Bel-Ray super dot 4 at Wal-Mart. Sometimes in stock but, usually ships to store or door.

 

I ended up going with DOT 4 LV from Mintex, from here: MX_ServiceInfo_BrakeFluid_ENG-1.pdf (mintex.com)
I went with the Dot 4 instead of the Dot 5 since it has a lower viscosity.
It seems to have all the same specs, low viscosity, and similar boiling points to the Shell ESL.
I can't seem to find Shell Super Dot 4 ESL anywhere, it kind of seems like maybe they just dropped the "super" from the name or something.

 

I concluded DOT 4 Low Viscosity is what Jaguar Intended. DOT 5.1 is very close. Here's my research on brake fluid when I flushed the X-Type.

From the manual: Jaguar Super DOT 4 (ESA-M6C25-A).
The brake hydraulic fluid in the master cylinder and brake operating system uses non-mineral polyglycol based brake fluid
with a minimum standard of JAGUAR SUPER DOT 4. ONLY FLUID OF THIS TYPE AND STANDARD MAY BE USED.

Specs are confusing:

• DOT 3,4,5 refer to fluid characteristics including boiling point
• Other characteristics include viscosity, which is covered by ISO 4925
• DOT 5 is silicon based and not compatible with X-Type
• DOT 3, DOT 4 and DOT 5.1 are glycol-ether based fluids and chemically compatible. (Traditional brake fluid & nasty for paint)
• Regarding "Super DOT 4":
  • Unfortunately "Super" can be a marketing word (i.e. not all Super DOT 4 are equal)
  • Sometimes "Super" refers to boiling point, sometimes viscosity. Jaguar intended the low viscosity version for the ABS to work well at low temps
  • ISO 4925 Class 6 viscosity is the viscosity requirement (i.e. max 750 mm2/s)
  • DOT 5.1 has higher boiling point than DOT 4
  • DOT 4 Level 6 has lower viscosity than DOT 5.1 at very low temps
  • DOT 5.1 has similar viscosity at normal temps and is OK to use and mixes with DOT 4

DOT 5 is Silicon based - DO NOT USE. DOT 5.1 has nothing to do with DOT 5


Looking further @ Viscosity:

Requirements @-40F
DOT 3 <1500
DOT 4 <1800
DOT 4, Class 6 <750
DOT 5.1 <900


Fluid Data Viscosity @-40F
Pentosin Super DOT 4 = 1500 (example of "Super" DOT 4 not having super low viscosity)
Pentosin DOT 4 LV = 700 (Meets ISO 4925 Class 6)
Shell Super DOT 4 = 675 (recommended - difficult to get in USA)
Bosch ESI6 = 685 (Best in USA? - very close to OEM recommended)
Motul 5.1 = 820 (Close to Level 6 and highest wet boiling point)

I used Bosch ESI6 - easily available in USA. Not sure what's available in Ireland, but any DOT 4 Level 6 (DOT 4 LV) should be almost identical to OEM.

Hope this helps!

 

Yea, I came to the same conclusion too, after far too much research!

Although I was going by the Workshop Manual which only mentions the Shell Super DOT 4, I didn't even think to check the Owner's Manual which says:

Hydraulic fluid
The brake hydraulic fluid in the master cylinder and brake operating system uses Shell DOT4 ESL or a low viscosity DOT 4 brake fluid that meets ISO 4925 class 6 requirements.
ONLY FLUID OF THIS TYPE AND STANDARD MAY BE USED.

I could have saved myself a bit of hassle by just reading this first, but I suppose doing the research and then having the knowledge is better than just blindly buying the correct fluid.