Here is the puzzle:

I did not drive my 740 for 5 days. I drive it about 20 miles and look under the hood and see brake fluid all over the reservior and the level is about a 1/4 inch low. It has not happened since then.

I have not done any pad replacement or other brake work recently that would explain the overflow. Does anyone have any theories?

Thanks.

A dollop of water in your brake fluid made its way to one of your front calipers and flashed to steam blowing a little bit of fluid out.

(Well, you SAID to come up with a theory!)
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3 8s & 2 7s 740,000 miles total

Well, hmm, I said I not done any brake work, but a couple of weeks ago I wanted to change out my brake fluid the easy way, so I used a turkey baseter to suck out most of the fluid in the reservior and replaced it with silicone fluid.

Maybe this is another bit of relevant information (?)

NOT A GOOD IDEA - the two are NOT compatible!!

I'm not saying silicone brake fluid will ruin all your seals, etc but a mix is NOT good. Flush and refill twice with DOT 4, repeat.

Curious as to why you thought Silicone brake fluid was "the juice to use"?
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www.fidalgo.net/~brook4

HORRIBLE IDEA: Immediately power flush ALL fluid out of your brakes. The silicone will ruin your seals and render the brakes inoperable. It is completely immiscible with glycol fluid. Your brakes ARE NOT compatible with DOT 5 silicone. You will probably have to remove the calipers and clean these separately.

But it said DOT 4 and compatible on the label.

Silicone fluid is NOT compatible with glycol nor with any rubber components in your brake system. DOT specs describe temperature specs (wet/fry boiling points), not materials. Who made the product?

Again: get this out of your brake system ASAP.

It is "Valvoline SynPower", which seems to be "synthetic" but not silicone.

All brake fluid is synthetic. Synpower is marketinghype/ a name.

That fluid should be compatible with what you have in there....but me thinks you should find out if you have a dieing master cylinder...or water in the old fluid or some other wrongness.

No maliciousness intended, but you don't quite sound up to brake work just yet....

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www.fidalgo.net/~brook4

Wow, you had me going out for an underwear change a while back. Synpower is superb quality glycol-based fluid and is fully compatible, in fact it is one of the best mass-market brake fluids.

Your problem is likely water in one of the calipers that expanded and pushed the reservoir fluid out. To flush your system, do the baster replacement again at the reservoir. Then bleed each caliper, but gently push your pedal down about fifteen times for each bleed screw. Remember to keep the reservoir filled and DO NOT push the brake pedal more than about 1-1/2 inches down on each stroke. This will push the new fluid down, through the caliper, and out the bleed screw, and will remove most of the old fluid.

This is required every two years in your car. See the FAQ for more info.

Sorry about the misinformation gentleman. I have always used Castrol brake fluid in the past. I guess I just read the label that said it was compatible and got the "synthetic" confused with "silicone".

I know how to bleed the brakes, I just don't like to do it. Usually only when the pedal gets spongy. I know, I know. It's just like when my doctor says I should get more exercise.