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DHart 08-24-2014 05:37 AM

Dot 4 flush?
Hi folks, I have seen several posts where someone talks about flushing out the factory spec dot 3 fluid with dot 4, however, I've read somewhere that dot 4 fluid is not compatable with a dot 3 designed sytem. What i recall is that the seals are not the same material and that dot 4 will cause a dot 3 designed system to start leaking. So I want to ask the folks who are running dot 4 if they have changed seals, or am I just misinformed on this topic? Thanks in advance for any info!

Frango100 08-24-2014 06:15 AM

Re: Dot 4 flush?
Both DOT 3 and DOT 4 (and DOT 5.1) are polyglycol ether-based fluids. The difference between the two is the boiling point of the fluid, where it is higher for DOT 4 fluids. So when your car needs DOT 3, you can use DOT 4 instead. If your car needs DOT 4, you better not use DOT 3, because the fluid can start boiling on hot days and long braking (hill descend)
DOT 5.0 can not be used, because it is an other type of fluid, based on silicones.

DHart 08-25-2014 03:57 AM

Re: Dot 4 flush?
So, no leaks then? And thank you for the response!

Frango100 08-25-2014 05:38 AM

Re: Dot 4 flush?
I myself am not using DOT 4 in my jeep, but i know that some others do. The base material of both fluids is the same, DOT4 only has some additives to raise the boiling point.

lstowell 08-25-2014 02:30 PM

Re: Dot 4 flush?
Why would the OP want to change from DOT3 to DOT4?
Doing some heavy duty desert offroading in Death Valley or similar?

I cut an older ZJ over to DOT4 after an mild overheat on a very very hot day going down the east of the sierras, and that seemed to do the trick. No leaks detected in over 100K afterwards.

GCUK 08-31-2014 12:41 AM

Re: Dot 4 flush?
Apologies to the op, don't mean to hijack the thread.

I have just changed my fluid this weekend and used DOT 4. My reasons were it was compatible and allowed in the owners book, plus what I had read here. Secondly availability of DOT 3 is smaller in the UK, DOT 4 can be bought everywhere and most vehicles seem to run DOT 4.
Which means I can use the one tin to keep all my 3 cars and one Ducati topped up !

Two questions if I may ask, changing the fluid at home, me at the calliper the wife pushing the pedal ! , we can't/don't flush the ABS part, Only the device centre guys can do that ?
Should I be concerned, can air be trapped here, is it only a small qty of fluid ?

Secondly, I did the change as it looked a little dirty and I've had her 3 years now, with no record of the last change. After doing the change, hardy any air bubbles were noticed and the brakes felt sorta the same. Not super firm/hard like my old Porsche 944 did, but not supper soft either. I guess somewhere in the middle, a bit of pedal travel with progressive braking feel. But if you stamp on it hard the brakes will bite !

Does that sound about right ?

Cheers guys :-)

Frango100 08-31-2014 02:12 AM

Re: Dot 4 flush?
You could just let the ABS do its job and brake hard, so that any air trapped in the unit will go out. You maybe will have to bleed the brakes again after this. Ofcourse you will have to do this on an empty street, to avoid accidents.
The brake fluid should be changed every 2 years.
The WJ brakes are indeed not that firm.

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