Confusion over brake fluids: Which is right for your car?

  • Article by: PAUL BRAND
  • Updated: January 20, 2012 - 3:50 PM

How do synthetic DOT 3 or DOT 4 fluids differ from the conventional DOT 3 or DOT 4 ones?

Q I see many brake fluids on the market are now synthetic DOT 3 or DOT 4. How does that differ from the conventional DOT 3 or DOT 4 fluid? How does that differ from silicone brake fluid? And my main question: Does synthetic brake fluid "eat the paint" if spilled on the car?

A I think much of the confusion over brake fluids is whether "synthetic" is the same as "silicone" -- and it's not. All DOT 3, DOT 4 and DOT 5.1 fluids (the numbers refer to U.S. Department of Transportation specifications) are conventional glycol/ester-based hydraulic fluids, meaning they can and will damage paint if spilled on automotive bodywork. All are synthetic in the sense that they are blends, but the "synthetic" label on some indicates they are more resistant to absorbing moisture -- a characteristic of all conventional brake fluids and the reason many carmakers recommend periodic flushing, bleeding and replacement.

Silicone brake fluid -- DOT 5 -- is silicone-based with a high boiling point suitable for motorsports, isn't sensitive to absorbing moisture and doesn't damage paint. But it is not compatible with conventional fluids.

Q I had to replace the blend door motor in the climate control system of my '97 Town Car. Everything worked well, but when warm weather arrived in the spring I started having a problem. When the car sits in the sun and you start it up, you can hear the familiar clicking sound of the blend door motor trying to seek a position -- similar to what I heard when the gears in the motor were bad. If I quickly raise the temperature setting on the control to a high value, the motor will stop doing this. As the car cools down, I can slowly lower this setting, but if it's 80 or higher outside, I can never lower it to below 70 or so. I think it's because the temperature sensor for the climate control is at fault. The air conditioning in the car works great otherwise.

A Start by using the self-diagnosing capabilities built into the climate control system. With the car's interior stabilized near room temperature, enter the self-test mode by pressing the "Off" and "Floor" buttons simultaneously, then release and within two seconds push the "Auto" button to read fault codes. Hitting the "Defrost" button cancels the diagnostic mode and deletes any codes. Codes 024/025, along with the clicking noise, indicate a bad blend door actuator. Codes 030/031 indicate an in-car temperature sensor problem, and codes 040/041/042/043 point toward the ambient temperature sensor. Codes 050/052 indicate a sunload sensor problem.

Keeping in mind the car's age, I can't help but wonder about using an aluminized dashboard sun shield in place while the car is parked in the sun. I know it would be cheap!

Q I own a 2004 PT Cruiser. Lately there has been a noise coming from the front left driver's side wheel. I replaced two tires and had all the tires rotated and balanced. As speed is increased, the "we-we-we" sound increases and can be heard to 30 miles an hour and above. I have had the vehicle to the garage twice and was assured that everything is OK. Yet, the sound still persists.

A If you and the dealer can eliminate the wheels and tires as the origin of the noise, I would focus on the left front disc brake/rotor assembly. As you are cruising along and hearing the "we-we-we" sound, maintain that speed while lightly pushing the brake pedal with your left foot. If this lessens or eliminates the noise, it's coming from the brakes. Possible causes include rust and debris buildup, a slight warping of the rotor, worn brake pads or the audible brake wear indicator tab rubbing on the rotor.

The sealed front hub and bearing assembly or the drive axle and constant velocity (CV) joint are also suspects, but focus on the brakes first.

  • get related content delivered to your inbox

  • manage my email subscriptions


San Francisco - WP: M. Bumgarner 8 FINAL
Pittsburgh - LP: E. Volquez 0
Minnesota 7:25 PM
Green Bay
Buffalo 10/5/14 12:00 PM
Chicago 10/5/14 12:00 PM
Cleveland 10/5/14 12:00 PM
St. Louis 10/5/14 12:00 PM
Atlanta 10/5/14 12:00 PM
NY Giants
Tampa Bay 10/5/14 12:00 PM
New Orleans
Houston 10/5/14 12:00 PM
Baltimore 10/5/14 12:00 PM
Pittsburgh 10/5/14 12:00 PM
Arizona 10/5/14 3:05 PM
Kansas City 10/5/14 3:25 PM
San Francisco
NY Jets 10/5/14 3:25 PM
San Diego
Cincinnati 10/5/14 7:30 PM
New England
Seattle 10/6/14 7:30 PM
Washington 1 FINAL
Buffalo 6
Carolina 3 FINAL
Columbus 6
Pittsburgh 2 FINAL
Detroit 0
Montreal 3 FINAL
Chicago 1
Arizona 2 FINAL
Edmonton 3
Fla Atlantic 6:00 PM
UCF 6:00 PM
Arizona 9:30 PM
(2) Oregon
Louisville 10/3/14 6:00 PM
San Diego St 10/3/14 9:00 PM
Fresno State
Utah State 10/3/14 9:15 PM
(18) BYU
(6) Texas A&M 10/4/14 11:00 AM
(12) Miss State
Ball State 10/4/14 11:00 AM
Iowa State 10/4/14 11:00 AM
(21) Oklahoma State
Marshall 10/4/14 11:00 AM
Old Dominion
Southern Miss 10/4/14 11:00 AM
Middle Tennessee
(20) Ohio State 10/4/14 11:00 AM
Purdue 10/4/14 11:00 AM
Florida 10/4/14 11:00 AM
SMU 10/4/14 11:00 AM
(22) East Carolina
Virginia Tech 10/4/14 11:30 AM
North Carolina
Eastern Mich 10/4/14 1:00 PM
North Texas 10/4/14 1:30 PM
Massachusetts 10/4/14 1:30 PM
Tulsa 10/4/14 2:00 PM
Colorado State
New Mexico 10/4/14 2:30 PM
TX-San Antonio
(3) Alabama 10/4/14 2:30 PM
(11) Ole Miss
(14) Stanford 10/4/14 2:30 PM
(9) Notre Dame
(17) Wisconsin 10/4/14 2:30 PM
Navy 10/4/14 2:30 PM
Air Force
(7) Baylor 10/4/14 2:30 PM
(4) Oklahoma 10/4/14 2:30 PM
(25) TCU
Wake Forest 10/4/14 2:30 PM
(1) Florida State
NC State 10/4/14 2:30 PM
Buffalo 10/4/14 2:30 PM
Bowling Green
Ohio U 10/4/14 2:30 PM
Central Mich
Oregon State 10/4/14 3:00 PM
Vanderbilt 10/4/14 3:00 PM
(13) Georgia
Kansas 10/4/14 3:00 PM
West Virginia
Kent State 10/4/14 4:00 PM
Northern Ill
South Alabama 10/4/14 5:00 PM
Appalachian St
Texas-El Paso 10/4/14 6:00 PM
Louisiana Tech
(15) LSU 10/4/14 6:00 PM
(5) Auburn
UAB 10/4/14 6:00 PM
Western Ky
Texas Tech 10/4/14 6:00 PM
(23) Kansas State
Michigan 10/4/14 6:00 PM
Hawaii 10/4/14 6:00 PM
Toledo 10/4/14 6:00 PM
Western Mich
ULM 10/4/14 6:00 PM
Arkansas State
Georgia State 10/4/14 6:00 PM
Idaho 10/4/14 6:00 PM
Texas State
Memphis 10/4/14 6:00 PM
Arizona State 10/4/14 6:30 PM
(16) USC
So Carolina 10/4/14 6:30 PM
Pittsburgh 10/4/14 6:30 PM
Miami-Florida 10/4/14 6:30 PM
Georgia Tech
(19) Nebraska 10/4/14 7:00 PM
(10) Michigan State
UNLV 10/4/14 7:00 PM
San Jose St
Ga Southern 10/4/14 7:00 PM
New Mexico St
California 10/4/14 9:30 PM
Washington St
Utah 10/4/14 9:30 PM
(8) UCLA
Boise State 10/4/14 9:30 PM
Winnipeg 10/3/14 6:00 PM
Calgary 10/3/14 9:00 PM
Edmonton 10/4/14 3:00 PM
Brt Columbia 10/4/14 6:00 PM
Hamilton 10/10/14 6:00 PM
Ottawa 10/11/14 9:00 PM
Brt Columbia
Connect with twitterConnect with facebookConnect with Google+Connect with PinterestConnect with PinterestConnect with RssfeedConnect with email newsletters