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I recently refreshed the clutch fluid, but could only get DOT 4 at the dealers I tried close to home (I wanted to get it done quickly). They are an Italian bike specialist, including Aprilia, and had done a full sevice on mine a year ago. They said they only use DOT 4 and that's what they would have put in mine at the service. It has been OK for the last year. However, Aprilia recommend DOT 5 or DOT 5.1 (DOT 4 compatible).

It seems to me that the DOT number is about operating temperature ranges and DOT 4 is fairly high. Any opinion as to whether DOT 4 is OK in the clutch?

I did go for a long run afterwards and it all seems OK, but I'm never sure about trusting dealers.

I've used DOT 4 in mine and it has always seemed OK.

iirc correctly dot 4 is the boy - and dot 5.1?? but not dot 5 for some reason?

I stand corrected Pete, whenever I have used Dot 4 it has been fresh new stuff, not sure what the difference is between the two, probably a revised standard with only minor differences.

DoT's 3,4 & 5.1 are all glycol based fluids. DoT 5 is silicone based. The DoT number refers to the fluids boiling point, both when new and after water absorbsion, and the higher the number the higher the boiling point. What you can't ever do is mix 5 with any of the others - it turns to emulsion, even with tiny amounts of contaminant.
The other thing to consider is that some seals and brake components may not react well to silicone fluid if they weren't designed for it. If the handbook says DoT 5 is OK then your fine, if not stick with the glycol based fluids. Also, apparently, DoT5 fluid, whilst resisting moisture absorbtion, is very prone to aeration so needs changing more regularly and can lead to a softer feel to the brakes - so 'They' say!

Think I'll go change me anorak now......

Thanks all, especially Teaker's very full answer. I found the remnants from my previous fluid change a few years ago and it was 5.1. So at some stage it's gone from 5.1 to 4. But it's been fine and your answers have convinced me I did the right thing.

Tweaker even!

DOT 4 is the stuff to use.

Tweaker wrote:If the handbook says DoT 5 is OK then your fine, if not stick with the glycol based fluids.

The handbook is badly phrased.
It says DOT 4 or DOT 5 (DOT 4 compatible) ... or words to that effect.

As you point out DOT 5 is certainly not DOT 4 compatible.
I think what they are trying to say is you can use a fluid that fits within DOT 5 numbering but is compatible with DOT 4 .... in other words DOT 5.1

Dangerously confusing cos if you put DOT 5 in you contaminate the system

D-Rider wrote:The handbook is badly phrased.
It says DOT 4 or DOT 5 (DOT 4 compatible) ... or words to that effect.

Could have been worse Andy - could have been translated from Japanese instead of Italian!

Tweaker wrote:

D-Rider wrote:The handbook is badly phrased.
It says DOT 4 or DOT 5 (DOT 4 compatible) ... or words to that effect.

Could have been worse Andy - could have been translated from Japanese instead of Italian!

You're so right there Dave !

Spend half my life trying to figure out what people mean from the nonsensical words they've written.

(guess the rest of the world has to do that with the stuff I write!)

D-Rider wrote:

Tweaker wrote:

D-Rider wrote:The handbook is badly phrased.
It says DOT 4 or DOT 5 (DOT 4 compatible) ... or words to that effect.

Could have been worse Andy - could have been translated from Japanese instead of Italian!

You're so right there Dave !

Spend half my life trying to figure out what people mean from the nonsensical words they've written.

(guess the rest of the world has to do that with the stuff I write!)

In your case Andy there is no problem in understanding it, it just takes time to read it
It's usually well worth the effort though.