Motors5

I did a search but could not find this question answered fully.

All my European family cars have had DOT 4 oil standard. My motorcycle as well. So why do Chevy put DOT 3 oil in a "track spec" Z51 2017 car?

You are asked to put DOT 4 in for track days but then switch back to DOT 3!!!.

Why can't you have the DOT 4 in all the time? It works on all other cars.

Is it too aggressive for some of the seals?

Best Regards

Henrik

dbaker

If I'm not mistaken,and correct me if I'm wrong,Pentosin makes the GM Super Dot 4 fluid.

It does seem odd than the brakes call for Dot 3 and the clutch Super Dot 4.

I suspect diff engineers did the specs.

Since Dot 4 is backward compatable with Dot 3 ,I see no reason not to use 4 in both applications.

\db2

BEZ06

Take a look at the Stoptech White Paper on brake fluid:

http://www.stoptech.com/technical-su...rs/brake-fluid


In there you can read:

Which still isn't a real big deal, because a lot of DOT 4 brake fluids have a wet boiling point that is still higher than some DOT 3's dry boiling points.

However, there are also some very good DOT 3 fluids with nice high dry boiling points that would even be good track fluids - if you flush in new fluid regularly due to the fact that they will degrade rapidly with track use.

Bottom line - have you ever heard of a street-driven Vette (or any other vehicle) have a brake failure due to boiling the stock DOT 3 fluid??

The DOT 3 GM uses is probably cheaper than DOT 4, and it's without question satisfactory for driving a vehicle on the street.

Here's a link to the Stoptech site with a bunch of other excellent bulletins about all aspects of our brakes:

http://www.stoptech.com/technical-su...l-white-papers


BTW - I run DOT 4 on the track and street - no problem.

.

Motors5

Thanks for the input!

The reason is that I don't want to change back to DOT 3 after changing to DOT 4 for a track day but it seem that it is no issue to keep it in!

2017 Z51 3LT Coupe

JerryU

Yep, read that doc. Thanks. The last statement was the reason I thought for the difference and one reason why one was probably selected over the other by the GM engineers, quoting:

"The real differentiating factor is that DOT 4 fluid should be changed more often than a DOT 3 fluid, because of the effects and rates of water absorption."

Dot 3 and Dot 4 are both hygroscopic, i.e. they pick up water like a sponge! Properties and performance change with water content. Apparently Dot 4 is worse.

Of interest, just changed the brake fliud in the Street Rod, which I do about every year. Have to take out the driver's seat to check the level so why not drain and refill. Used one labeled Dot3/Dot4! It meets both specs! Cost was $0.50 more!

mpuzach

This is great info, guys.

dbaker

I use the Ranger method ( baster) on the brake & clutch fluid at every OCI on all my cars....5k.


Amazon has the Pentosin.

\db2

JerryU

^^^
I use the Ranger method for my clutch but wonder if it does any good for the brakes. Unlike the clutch where the fluid does mix with the fluid in the slave cylinder, the brake slave cylinders are too far away to have any effect on them, IMO.

In my Street Rod I just empty the reservoir in the master cylinder and fill with new brake fluid. That would be of some help in the Vette but would not think pumping 30 times and repeating would do much good.

The percent fluid volume in the brake reservoir compared to that in the ABS valves and plumbing and the 16 pistons in my Grand Sport calipers is probably not very high.

BEZ06

Part#'s from the Owner's Manual, prices are MSRP from a GM parts site:
The DOT 4 fluid GM uses in the clutch system is about 2-1/2 times more expensive than the DOT 3 in the brake system.

So...I'm quite sure that because DOT 3 is perfectly satisfactory for use in the brake system in a street-driven car, GM uses the less expensive fluid.

Why they feel the need for DOT 4 in the clutch system, I dunno!?!?

However, the clutch slave cylinder is down close to the exhaust manifold, headers, Cats - and it gets very hot down there, so they decided to use DOT 4 in the clutch for the higher boiling point.

Also, the clutch system uses MUCH less fluid than the brake system does. So the savings to GM by using DOT 3 in the brake system is significant, and will work perfectly well for street driving.

.

Bill Dearborn

This is what the Owner's Manual says about brake fluid for track events:
Brake Fluid
Replace existing brake fluid with a
qualified high performance brake
fluid from a sealed container. Brake
fluid with a dry boiling point >279°C
(534°F) is qualified. If high
performance brake fluid is used,
replace it with GM approved brake
fluid before driving on public roads.
If high performance brake fluid is in
the vehicle and the age of the brake
fluid is over a month old or
unknown, replace the brake fluid
before track events and competitive
driving. Do not use silicone or
DOT-5 brake fluids.

Nowhere in that statement does it say anything about DOT 4 fluids. I know there are some racing brake fluids on the market that do not have a DOT listing. I don't think GM gives a crap about what brake fluid you actually use on the street but they can't make any recommendation that would lead polypublic with its low level of intelligence to use anything on the street that doesn't meet state and federal regulations.

Just imagine all of the BS that would happen if they didn't say to put in GM recommended street driving fluids and Mr. DIMBULB goes out and has an accident that gets blamed on him not having the proper brake fluid in the car. Who are they going to sue? Mr DIMBULB doesn't have enough money to make a big issue over it but GM does. Then throw in the regulators punishing them for encouraging people to violate regulations.

There are no known issues with using DOT3 fluid on the street so why should they recommend DOT4 when that would be over specifying. Think of all the DIMBULBs that would complain because they required DOT4 fluids. These guys don't change their brake fluid for years and when they take the car to a shop for service the shop charges them extra $$ for DOT4 and they will wail over it.

Bill

juanvaldez

My guess is that the vast majority of Americans cars never have the brake fluid changed. I have always used DOT 4 in everything (Valvoline) but recently starting using the ATE 200 in the Corvette brakes.

JerryU

FWIW here are the specs from the inexpensive Valvoline brake fluid I just put in my Street Rod labeled DOT3&4

"High dry boiling point up to 480 F"
Note does not meet the GM suggestion of meeting 534 F, but close.
"Minimum Wet Boiling Point is 311 F"
"Meets SAE J1703, SAE J1704

Comparable with all braking systems requiring DOT 3 or DOT 4

Have used straight DOT 4 for clutch flushing and all that container says is "Minimum Wet Boiling point is 311 F." Assume that is in the SAE spec for DOT4.

From the GM statements it does sound like the high performance brake fluids are more hygroscopic and therefore they want it replaced if over a month old!

07MontyRed

Just for reference:

Minimal boiling points for these specifications are (wet boiling point defined as 3.7% water by volume; dry point is zero water):

Dry boiling point Wet boiling point
DOT 3 205 °C (401 °F) 140 °C (284 °F)
DOT 4 230 °C (446 °F) 155 °C (311 °F)
DOT 5 260 °C (500 °F) 180 °C (356 °F)

DOT 3 is glycol ether based
DOT 4 is glycol ether / borate ester
DOT 5 is silicone based

Gearhead Jim

We used GM DOT4 in our 2001 (5 yrs/66k miles), 2006 (3 yrs/44k miles) and 2009 (8 yrs/102k miles), never had any fade problems during hard use nor any corrosion problems in the system.
But I had it completely flushed every year, including the scan tool to cycle the ABS to get all the old stuff out.

juanvaldez

When you get brake fluid boil your brakes don't fade . . . they go away, very exciting!

Cliff8928

Anyone who's seriously tracking their car is likely to be using Castrol SRF brake fluid (Which is Dot4 I believe). Recently on the store shelves is DOT 5.1 with an even higher spec boiling point, completely different than DOT 5 which is silicone based.

juanvaldez

I only use DOT 5.1 in my bicycle.

Michigan Racer

Any truth to DOT 4 gumming up in colder weather? I was told by a tech at Spring Mountain Corvette driving school if I change to DOT 4 I need to get it out of the car before I store it for the winter.

JerryU

Yep, vapor compresses instead of moving brake pad calipers! DOT 4 picks up water faster than DOT 3, which reduces temp where it boils. Racer cars use product with higher boiling point but even more hygrospocic! They change for each race.

BEZ06

DOT 4 won't "gum up" in cold weather!!

Take a look at the dry and wet boiling temps of a list of brake fluids on the site linked below.

I use Castrol SRF not because of the high DRY boiling point (well - that's one of the main reasons), but especially because of the WET boiling point!! In that list you can see that the SRF dry/wet temps are 608°/518°. There are 15 or so fluids with higher DRY boiling points, but only several that have a WET boiling point within 100° of the SRF wet boiling temp.

The Torque fluid has a very high dry point, but the wet is still 79° less than the SRF. The Endless is a great fluid but the wet point is still 94° less than SRF's wet point

Castrol SRF's WET boiling point is higher than many of the DRY boiling temps on that list!!!!! That's why I like the Castrol SRF - it's more expensive, but I can leave it in all track season (only flush in fresh once/year with minor bleeds when I put in fresh pads) instead of flushing in fresh fluid 3 or 4 times per season

https://www.lelandwest.com/brake-flu...ison-chart.cfm