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Brake Fluid contamination from Penetrating Oil on bleeder screw? #5389435 03/30/20 01:02 PM
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DIY4quality Offline OP
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Advance preparation for brake bleeding often includes the application of penetrating oil of some type (e.g., Kroil, PB) around the bleeder screw to assist in removal. In some cases, it's applied daily for several days in advance of the bleed operation to allow it to soak in and do its thing.

If penetrating oil really penetrates the screw threads as intended, won't it make its way into the caliper and contaminate the brake fluid? I read somewhere to avoid penetrating oil around brake fittings for this very reason. But I also read many forum posts and watched some videos describing this technique to deal with difficult bleeder screws. Is there any penetrating fluid that will not contaminate brake fluid?

Re: Brake Fluid contamination from Penetrating Oil on bleeder screw? [Re: DIY4quality] #5389445 03/30/20 01:12 PM
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The bleeder screws in tight to the base of the drilled and tapped hole of the caliper assembly, the tapered seat of the bleeder screw mates with the same taper on the drilled hole. It's metal on metal contact with design for no leakage. Penetrating oils are not endowed with super powers, they go path of least resistance and are chemically attracted to metal, but there is a limit to how far they can go.

The risk of contamination of the brake system from use of penetrating fluids is only possible if the bleeder was either not tight, or had significant damage to the taper in either the caliper or bleed screw. Basically, it would show signs of BF leakage before you even applied penetrating fluid to the exterior of this junction.

Last edited by KGMtech; 03/30/20 01:14 PM.

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Re: Brake Fluid contamination from Penetrating Oil on bleeder screw? [Re: DIY4quality] #5389464 03/30/20 01:44 PM
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Imp4 Offline
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Agreed with KGMtech.
The penetrating oil will work through gaps in the mating male and female threads but will stop at the metal-to-metal interface between the caliper and the bleeder screw tip.

Re: Brake Fluid contamination from Penetrating Oil on bleeder screw? [Re: DIY4quality] #5389537 03/30/20 03:22 PM
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racin4ds Offline
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Even IF a minute amount of Penetrant would creep through it would be so minuscule that it wouldn't hurt a thing. There is much more to worry about than this, I can assure you!


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Re: Brake Fluid contamination from Penetrating Oil on bleeder screw? [Re: DIY4quality] #5389581 03/30/20 04:34 PM
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MasterSolenoid Offline
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welcome

I agree with the others.
And any flushing of the old fluid would remove any penetrating oil.

When you get done, smear some Silicone Grease around the threads of bleeder screws
and install the Rubber Caps to keep them clean.


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Re: Brake Fluid contamination from Penetrating Oil on bleeder screw? [Re: DIY4quality] #5389583 03/30/20 04:38 PM
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Railrust Offline
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I wouldn’t worry about it one single little bit. Not a smidge.

This is not going to do anything, even if it could penetrate all the way past the bleeder screw, which it won’t. Think about it - you’re spraying penetration oil on it because it’s rusted - it won’t even get through the rust, never mind through the threads and into the brake fluid.


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Re: Brake Fluid contamination from Penetrating Oil on bleeder screw? [Re: DIY4quality] #5389610 03/30/20 05:25 PM
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Thanks for the welcome and responses! My concern is that I will follow the application of penetrating oil with backing out the screw to perform the bleed. As stated above, I guess it will be okay as long as I maintain one-way suction/pressure on the brake fluid so there is no backflow into the caliper. I'll stop worrying. smile

Re: Brake Fluid contamination from Penetrating Oil on bleeder screw? [Re: DIY4quality] #5389730 03/30/20 08:55 PM
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buck91 Offline
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Stop looking for new problems! ALWAYS try to spray your bleeders days in advance. Its simple, easy and helps a little.


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Re: Brake Fluid contamination from Penetrating Oil on bleeder screw? [Re: buck91] #5389769 03/30/20 09:58 PM
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Driz Offline
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Originally Posted by buck91
Stop looking for new problems! ALWAYS try to spray your bleeders days in advance. Its simple, easy and helps a little.


Yup, that’s the answer right there.....

Re: Brake Fluid contamination from Penetrating Oil on bleeder screw? [Re: Driz] #5389808 03/30/20 11:15 PM
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JHZR2 Offline
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Originally Posted by Driz
Originally Posted by buck91
Stop looking for new problems! ALWAYS try to spray your bleeders days in advance. Its simple, easy and helps a little.


Yup, that’s the answer right there.....


Actually, if you anticipate it’s going to be an issue, apply a few drops of penetrant. That limits the amount, and avoids getting it everywhere in a big mess...

Re: Brake Fluid contamination from Penetrating Oil on bleeder screw? [Re: JHZR2] #5390883 04/01/20 11:44 AM
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Originally Posted by JHZR2


Actually, if you anticipate it’s going to be an issue, apply a few drops of penetrant. That limits the amount, and avoids getting it everywhere in a big mess...


Good suggestion, which also favors applying the penetrant using a few drops from an oil can, instead of an aerosol spray which tends to backsplash.

Re: Brake Fluid contamination from Penetrating Oil on bleeder screw? [Re: DIY4quality] #5390962 04/01/20 01:19 PM
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It's miniscule amounts, plus you are going to bleed it.

Re: Brake Fluid contamination from Penetrating Oil on bleeder screw? [Re: DIY4quality] #5391205 04/01/20 07:03 PM
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motor_oil_madman Online Content
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I had this same question about my boat. I used penetrating oil on the fuel tank pickup tube and it was orange/yellow. Coincidently the fuel that drained out had that same orange color. Lol.

Last edited by motor_oil_madman; 04/01/20 07:03 PM.

2007.5 dodge cummins 6.7 liter. Chevron Delo400 15w40. 7000 mile or 250-300hr intervals.

Re: Brake Fluid contamination from Penetrating Oil on bleeder screw? [Re: DIY4quality] #5391210 04/01/20 07:05 PM
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The gas was pretty old so I attribute it to that more than the penetrating oil.


2007.5 dodge cummins 6.7 liter. Chevron Delo400 15w40. 7000 mile or 250-300hr intervals.

Re: Brake Fluid contamination from Penetrating Oil on bleeder screw? [Re: DIY4quality] #5391538 04/02/20 05:50 AM
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I doubt there will be any capillary action down the bleeder threads anyway. Your going to bleed the brakes anyway and that will flush anything present out to the bottle. Your best prep is to work a wire brush around the bleeder screw, give it a few gentle hammer taps and use a six point socket to loosen.

Last edited by Lubener; 04/02/20 05:53 AM.

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