AAA Tow Truck Added Dot 3 Brake Fluid...

36chambers

2006 T1N High Roof
Hi all,

We had a rusted out break line bust open on us while on the road two days ago. I called for a tow, but when the truck got there I was away finding service research shops to tow it to. When I got back to the car, my friend was standing by the engine with the AAA tow truck driver who was pouring dot3 brake fluid into my brake reservoir, despite the cap saying dot 4+ only.

I imagine most of it drained out of the hole after siting for the night because by morning my reservoir was empty. Will this cause any damage long term though?

Thanks!
 

lindenengineering

Well-known member
Hi all,

We had a rusted out break line bust open on us while on the road two days ago. I called for a tow, but when the truck got there I was away finding service research shops to tow it to. When I got back to the car, my friend was standing by the engine with the AAA tow truck driver who was pouring dot3 brake fluid into my brake reservoir, despite the cap saying dot 4+ only.

I imagine most of it drained out of the hole after siting for the night because by morning my reservoir was empty. Will this cause any damage long term though?

Thanks!
In short NO!
Dennis
 

220629

Well-known member
What Dennis said.

The DOT 3 and DOT 4 fluid is completely compatible. The DOT 4 fluid has some different additives to achieve a higher wet and dry boiling point, but the base chemistry is the same. There is absolutely no problem in using DOT 3 fluid in an emergency for the short term. If DOT 3 fluid is used the brake system should be completely flushed and purged with DOT4 or DOT4+ fluid at the earliest convenience. That will restore your T1N to proper specs.

NEVER use DOT 5 fluid under any circumstances. It is silicon based and is not at all compatible.

Added:
DOT 5.1 is compatible with DOT 3 and 4. Why they decided to use a 5.1 designation when it isn't compatible with DOT 5 silicon based fluid is beyond me. DOT 5.1 isn't very common on the shelves in N. America anyway.

:2cents: vic
 
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Nautamaran

2004 140” HRC 2500 (Crewed)
Finding a DOT4+ with the higher wet boiling point specified can be a challenge, and expensive.
MB 331.0 brake fluid is very cost competitive, especially compared to European brake fluids.
A full flush uses less than a quart bottle.

-dave
 

nutterbutter

2004 LTV Free Spirit T1N
I'd bet if we tested the boiling point of the brake fluid in most of our old T1n's today, it would be closer (if not below) to new DOT 3 than DOT 4. Age and moisture does that.

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.)

When you fix the brake lines, you'll do a full flush of the system with DOT 4.

In the meantime, CLEAN everything and everywhere you even suspect came in contact with DOT 3/4. Used brake fluid is very good at stripping paint. In my experience it can also increase corrosion of some metals, but it may just be because it is stripping paints or finishes. Old bike and motorcycle stuff shows it for sure.
 

Nautamaran

2004 140” HRC 2500 (Crewed)
MB 331.0 has a dry boil of 500’F and wet of 356’F

I agree many vehicles on the road have ancient (original?) brake fluid. I’m guilty of waiting, and have flushed more brown fluid than I’d like to admit...

The litre bottle of 331.0 from MB was around cad$35 - MUCH cheaper than the DOT4+ fluids I was researching specs of, none of which met the boil points and ISO spec listed in my owners manual. Do we actually NEED 500’F low viscosity fluid? Perhaps not, but I’m not interested in running trials.

:cheers:

-dave
 

220629

Well-known member
MB 331.0 has a dry boil of 500’F and wet of 356’F

I agree many vehicles on the road have ancient (original?) brake fluid. I’m guilty of waiting, and have flushed more brown fluid than I’d like to admit...

The litre bottle of 331.0 from MB was around cad$35 - MUCH cheaper than the DOT4+ fluids I was researching specs of, none of which met the boil points and ISO spec listed in my owners manual. Do we actually NEED 500’F low viscosity fluid? Perhaps not, but I’m not interested in running trials.

:cheers:

-dave
From everything I have gleaned about brake fluids, the chemistry of the various DOT4+ formulas is (chemistry) are (formulas) [I'm not an English major] such that it starts higher than DOT4 (and DOT3 for that matter), but it is less robust so those better numbers can degrade more quickly. DOT5.1 can even be worse for degrading more quickly. You don't get something for nothing.

My interpretation.
When using DOT4+ fluid it is more critical to follow the recommended service intervals. It ain't like your Grandfather's Chevy.

:cheers: vic

P.S. - Viscosity aside, fresh DOT3 fluid Dry Boiling Point is higher than DOT4+ wet boiling point. DOT3 fluid is fine for emergency use. It will not harm anything.
 
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nutterbutter

2004 LTV Free Spirit T1N
In the bike world, which commonly uses DOT4 and DOT5.1, I've also come to expect that some of the fancy higher priced DOT5.1 fluids definitely get worse FASTER than DOT4.
 

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