I Put DOT4, Is That Ok?

#1
I just had a brake fluid flush yesterday and I told them to put DOT4 brake fluid when the cap of the fluid resevoir in the engine compartment says to put DOT3 only. My car is at 105,000miles I bought it used a 1.5 years ago at 98,000 miles. It is a 4 speed transmission automatic. I think it has ABS and antilock breaks. It has never been in any serious accident other than me T-boning someone going 15 or less miles per hour in the front-right part of my bumper. When I bought it, I got ripped-off because it needed new struts, bulbs, transmission flush, tires, and rear drum brakes. I got OES spectrum struts put on when i got it. I have new Yokohama Avid Touring-S tires on all three except 2 older Michelins Destiny's, 1 spare and 1 right-rear. The brakes were at 80% a week ago, so they are still good. I live in a desert climate in the southwestern United States. Elevation 2400 feet above sea level. Roads are usually flat since we are in a valley but some parts are hilly. Temperatures go up to 115 degrees farenheight in the summer and 30 degrees farenheight in the winter. We're in monsoon season right now so it will rain some more. Humidity during summer half is 15-70%. It's usually sunny clear blue skys.

It was not until after they did the service that I read a little online and realized I should have listened to the label. Some say it is okay because there is not much difference between DOT3 and DOT4. Others say to follow manufacturers recommendation and that DOT4 will damage the seals or something and absorb less water.

I told them to put DOT4 because I tend to drive rough but not race track and because I thought i would get better performance. The mechanic will not change it to DOT3 for free. How long will I last using DOT4? What can I do without spending more money? What are my options? They put Pyroil DOT4.
 

Zohan

New Member
#2
You may find that the DOT4 fluid will be slightly thicker (more viscous) than DOT3. DOT4 fluid can also handle higher heat levels as its boiling temperature is higher than DOT3.

Things to be concerened about:
1. The increased viscosity can be an issue in extremely cold climates but 30*F in winter should probably not pose any problems.
2. Brake fluid, in general, abosorbs moisture present in the system it is being used or when exposed to the atmospher such as when you open the top of the master cylinder. Over time brake fluid becomes less effective due to this. While DOT3 fluid tends have a higher susceptibility of absorbing moisture than DOT4...DOT4 tends be more affected by moisture absorbtion as its boiling temperature drops much more than DOT3 for the same quantity of water absorbed.

IN THEORY #2 basically means that DOT4 fluid SHOULD perform better than DOT3 up until DOT4 has absorbed enough moisture to affect performance...then the performance drop would be worse than if DOT3 was in the system...but one should expect problems with DOT3 to arrise earlier due to the higher rate of moisture absorption.

The reality is your brake system should be fine as long as the service was correctly and all air was properly bled from the system.

-Z
 
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