Recently, my brake fluid was low, so the sensor lights kept turning on. In response, I filled up to max line using Prestone DOT 3 Synthetic brake fluid. The manual said not to use synthetic, but I filled it by accident. Is it safe to use synthetic brake fluid?

 

Any Dot 3 should mix with DOT4 ok, but where the hell did you buy Dot 3? 1989?

I'd flush it regardless.

 

Well, the manual said to use DOT 3, and that's what I did. But is it safe to use synthetic brake fluid?

 

You will not get the same wet/dry boiling point advantages of the synthetic if it is mixed, but yes, as long as you keep it dot3/4 you're good.

I haven't seen dot 3 for sale in forever. Strange how Infiniti would recommend it.

 

Would they sell it if it was dangerous? This is brake fluid, they have got to know that peoples life is on the line with this product.

I would flush before putting it in, but yea you'll be fine.

 

Where does it say not to use synthetic brake fluid? I'm pretty sure ALL modern brake fluid is synthetic...

 

synthetic is refered to DOT 5.

DOT 3 and 4 can mix but DOT 5 will not mix with 3/4 systems and cause the brake lines to swell up. Its complete made out of different stuff.

 

NO! Synthetic dot 3 or 4 is compatible with dot 3 or 4. Synthetic does NOT mean DOT 5. That is SILICONE brake fluid which is a BIG NO NO if you are already using dot 3 or 4. DOT 5 is NOT compatible with dot 3 or 4. DOT 5 shouldn't even be considered since DOT 5.1 glycol based brake fluid is out now.

 

well i had the general understanding.

I learned this back then prior to synthetic brake fluid became mainstream. I just knew dot 3/4 were one and the same just 4 normally had a higher boiling point. But DOT 5 would make the brake lines swell up, since it would eat the rubber.

 

+1


I used Valvoline's brake fluid in all my cars.

 

[QUOTE=2slickg35;4700470]Recently, my brake fluid was low, so the sensor lights kept turning on. In response, I filled up to max line using Prestone DOT 3 Synthetic brake fluid. QUOTE]


If your brake fluid is that low, you shouldn't really top it off. Instead, you should inspect your brakes. Either 1 of two things is happening. Either your caliper pistons are extended to the max meaning your brake pads are basically worn out, or you have a leak somewhere in the the system.

If it's due to the pads being low, you will need to remove some fluid before pressing the caliper pistons back in. I've seen pushing them back in shoot brake fluid all over a nicely painted engine bay. Brake fluid eats paint, so if you miss a spot, you'll see a nice bare spot in the bay in about a day.

 

I think it is ok to top it off after you check the condition. The reason I say this is because I flush the lines with every change anyway.

 

The owner's manual for a 2003 G35 sedan in the DIY section said not to use synthetic.

 

It's all synthetic. There is no "natural" brake fluid, it's glycol ethers. Synthetic may mean that the glycol was manufacured synthetically as opposed to glycerine-derived, for example.

I beleive what the manual should say is do not use SILICONE (DOT 5) brake fluid

 

FSM recommends "Genuine Nissan Super Heavy Duty Brake Fluid or equivalent DOT 3 (US FMVSS No. 116)". I believe the DOT 3 recommendation is mainly because DOT 3 fluids, while starting off with a lower boiling point than DOT 4 or 5, tend to retain their boiling point longer than DOT 4 or 5 fluids. DOT 4 fluids tend to have more rapid dropoff in boiling point after they've been in the system for a bit, so you have to change it more frequently than you do DOT 3, hence the recommendation from the factory to stick with DOT 3.

Here's some more from the Stoptech site:

"As a trailing note on the DOT ratings, if your car was designed for a particular type of fluid (especially prior to the development of DOT 4 fluids), you should make every attempt to stick with that fluid! For example, if your car was delivered with DOT 3 fluid, the internal components of the system (seals, brake hoses, and fittings for example) were specifically designed and tested for compatibility with DOT 3. Because DOT 4 fluids contain a different chemical composition, the system may not necessarily react in a positive fashion to the borate esters floating around in the mix.

In other cases, just the difference in viscosity of the two different fluids may cause the seals to wear at different rates. What starts as an annoying squeak might eventually become a torn seal or worse. The examples could go on and on, but the message here is this: it’s fine to upgrade from DOT 3 fluid A to DOT 3 fluid B, but you should think twice (maybe even three times) before switching from DOT 3 fluid A to DOT 4 fluid of any sort.

That said, when dealing with modern hydraulic braking systems a numerically higher DOT rating is typically considered to be compatible with a lower DOT rating (except for DOT 5, of course). Unfortunately, this same generality just isn’t true for most older hydraulic system materials."

http://www.stoptech.com/tech_info/wp...fluid_1a.shtml

That being said, I think you would still be Ok going to a DOT 4 fluid like Ate' Super Blue, for example. But DOT 5 silicone-based sounds like a no-no.