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Discussion Starter #1
I want to top off my brake fluid before placing the Boxster in storage.
the brake fluid is just above the "min" line right now (and has been since getting the car).

The only product I can find locally is Valvoline DOT 3 & 4. Nothing that specifically says DOT 4.
is this DOT 4 that is backwards compatible or is it some kind of blend?
Since I am only adding an ounce or two I am not seeking a performance fluid but I am looking to add only DOT 4 per specifications. Can I trust using this product in my car?
 

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DOT is backward compatible with DOT 3. If you are street only, Id have no problem with some Valvoline fluid.
Since your typo could be misleading... I'll chime in to say specifically that DOT 4 is compatible with DOT 3.

DOT 5 IS NOT AND SHOULD NEVER BE USED. I mean... if you're building a race car and now how to convert it properly then fine... but then you don't need to ask this in the first place. :D
 

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Since your typo could be misleading... I'll chime in to say specifically that DOT 4 is compatible with DOT 3.

DOT 5 IS NOT AND SHOULD NEVER BE USED. I mean... if you're building a race car and now how to convert it properly then fine... but then you don't need to ask this in the first place. :D
i think he is saying that the DOT 4 fluid can be used in the DOT3 systems car.

BUT you must drain all DOT3 fluids in the system before you can fill it with DOT 4..

Lemon
 

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I've never heard that before. Obviously for best performance you'd want to drain out the DOT 3 but mixing the two shouldn't be an issue. You don't usually drain the brake fluid when changing it. That would be a pain. You just bleed in the new stuff until it runs clean. This obviously involves a bit of mixing and shouldn't be an issue.

I know you're an expert and know more than I do. Am I missing something?
 

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i was always been taught not to mix the two..

the fluid level for me also acts as a wear indicator of the pads. usually when you put new pads in the fluid level also goes up..

lemon
 

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i was always been taught not to mix the two..

the fluid level for me also acts as a wear indicator of the pads. usually when you put new pads in the fluid level also goes up..

lemon
Yeah... I've mentioned here before that you should never need to add fluid unless there's a problem and it's leaking out somewhere. People argued about it, suggesting it gives a margin of safety in case you develop a leak. Meh. To each his own. :)
 

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Discussion Starter #8
The car was delivered to me with 12 miles on it and came with just a bit over the min line at that time,
It has not dropped so I am not concerned about a leak. I just figured I would top it off since I was checking all the fluids for storage. Seems strange that the car did not come filled right to the max line when delivered.

So just to confirm, the valvoline fluid marked "DOT 3 & 4" is actually DOT 4 but backwards compatible? I think it may just be their label makes it misleading.
 

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I wouldn't worry about it. Its not like its going to evaporate while in storage.

I'm also not surprised about the level. Its a known that stealers will do as little as possible for delivery - checking fluid levels and alignments come to mind easily.
 

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The car was delivered to me with 12 miles on it and came with just a bit over the min line at that time,
It has not dropped so I am not concerned about a leak. I just figured I would top it off since I was checking all the fluids for storage. Seems strange that the car did not come filled right to the max line when delivered.

So just to confirm, the valvoline fluid marked "DOT 3 & 4" is actually DOT 4 but backwards compatible? I think it may just be their label makes it misleading.
Yes. It is DOT4, so it also meets the requirements of DOT3. That's why it states both DOT3 and DOT4. DOT3 and DOT4 are compatible and can be mixed without damage to the hydraulic system.

The only concern with mixing a DOT3 (only) fluid with a DOT4 fluid is if the brake system requires DOT4, the DOT3 fluid in the mix will not meet the required spec/performance of the system, although it is still mix compatible.

DOT5 is Silicone and is not compatible with DOT3 and DOT4. My 1998 Harley uses this.

Then there is DOT5.1. This is compatible with DOT3 and DOT4, but not DOT5.
 

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I would not add fluid just yet.

Wait until the car is fully warmed up. The brake fluid will be warmer and its volume may increase. If you top the fluid cold the system could have too much fluid next time you drive the car around some.
 

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I would not add fluid just yet.

Wait until the car is fully warmed up. The brake fluid will be warmer and its volume may increase. If you top the fluid cold the system could have too much fluid next time you drive the car around some.
That's not a problem. Fluid expansion from street driving is inconsequential and even for racing is far, far less than the air space above the "max" mark.

I keep my brake fluid topped up which means I add fluid as the brake pads wear (lowering the level). If that extra bit gets me 1 more stop or a second more of brakes should there be a leak, I want it. YMMV
 
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