lastdayx52

2006 Lexus IS250, RWD

About a year ago, while doing a brake job, my car's DOT3 brake fluid was flushed and replaced with ATE Super Blue DOT4.

About two weeks ago, my brake light came on. I checked my brake fluid and noticed that it was low. I didn't think much of it, and just topped it off.

Yesterday, my brake light came on again. My brake fluid was below its minimum, yet again.

Suspecting a leak, I went to a mechanic (Firestone) who informed me that there is no leak, and that all brake components are thick and in good condition.

He told me that what I'm experiencing may be because the car wasn't designed for DOT4, therefore the DOT4 fluid is making the rubber connections swell. He told me eventually, the rubber components in my brake system will need to be replaced, as this will one day explode.

Until then, just keep refilling it up with DOT4.

Is this an accurate assessment?

firelikeiy

I'm not an expert but AFAIK Dot 3, 4 and 5.1 are all compatible. Dot 5 is a synthetic and is not compatible.

lastdayx52

That's what I thought too.

I mean if all my braking components are fine, and there's no leak, I'm not sure why my brake feels spongy...

ThreeFive0

iTrader: (6)

You've got a leak. No other way around it. Check you connections and brake lines for any fluid built up on the outside of the parts. Check you brake lines for cracks. Check your brake cylinder seals for dry rotting and cracking.

ICU2

When I got my IS serviced at my mechanic he asked if the brake fluid I brought along with me was the Genuine Toyota stuff or DOT3. Apparently if you use anything else in a Toyota/Lexus it deteriorates the plastics?

An2ny

LOL no…I have always used DOT4 in many many cars for years, actually the exact same ATE Super Blue and the Amber one.

Assuming that you don’t have air in the system; you should have a leak.
I would just flush the system and make sure that there is no air in it, the pedal should feel hard and NOT spongy.
If you want to check for leaks you can park/ lift/ remove the wheels/ start the car and have someone pump and release the brakes, look at the calipers and lines at each corner and follow the lines back to the master cylinder.

RangerJoe

iTrader: (1)

Wasn't there a recall or TSB a while back for a seal on the master cylinder? Some about non lexus brake fluid causing problems? That being said, these guys are right. You either have air in the system and need to bleed the brakes, or a leak.

An2ny

Another thing; I can tell you with confidence that the car is definitely NOT going to explode. Maybe if you use nitroglycerin instead of brake fluid.

If this is the same guy that checked the brake system, just go somewhere else or check it yourself if possible.

NYKnick101

you may not have a leak in any of the lines but you may have a slow leak on one of the bleeders.. have you checked that?

lastdayx52

By "explode", I mean the rubber seals will explode apparently.

I don't have the tools necessary to personally check for a leak by raising the car up. On dry road, parked overnight, I didn't see any signs of puddles on the ground.

Firestone assured me it wasn't a leak in the system (though I don't know what they do to test it).

I've never had this issue for almost a year after the full flush... not sure why it's popping up now. Should I take it to another mechanic and ask if the system is leaking?

UniSlayEX

In my experience it sounds like air in the lines, if not a leak.

You can use DOT 4 Brake Fluid BTW. I think the synthetic blend (5 or something like that can be used but not recommended).

You may want to look at another mechanic that has experience with the vehicle.

Gville350

iTrader: (10)

The brake fluid just doesn't disappear; it has to be going somewhere. Now, if it was spongey and the fluid level remained the same...it would be something totally different. If you can 100% confirm that the leaks are not from the brake lines or calipers, I'd next look at the master cylinder. Looks for discoloration below the booster; ALSO look inside the cabin at the firewall behind the master cylinder/booster.

GL!

lastdayx52

I'm guessing it's from the master cylinder, as there is a recall for this.

An2ny

I know, nevertheless the “explode” was just too funny.

Yes, take it somewhere else. Any competent mechanic should know what to do, no need to take it to the dealer and pay more.

You may not see any puddles on the ground unless you have a huge leak, small leaks will only occur while pressing the brake pedal hard creating pressure in the system.
Just pump the brakes several times and move the car and see if there are any small drops on the ground. If it is leaking from the MC you may not see any puddles/ drops since the plastic under tray might catch them, so inspect under the hood and inside the car under the steering column.

smokyis350

iTrader: (21)

I'm pretty sure there is a small leak. I have been using ATE super blue brake fluid also and have no problems.

You should consider going to another mechanic.