Where do fluids Go and Yellow ! Caution

My Nissan Leaf Forum

Help Support My Nissan Leaf Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

gmcjetpilot

Well-known member
Joined
Oct 30, 2017
Messages
130
Two questions..
1) Where goes coolant and brake fluid go? Is it normal to lose some?

2) Have intermittent yellow caution with [ CAR + ! ] symbol. The list of possible issues is long from low reservoir fluids to controller and other issues. Common issue to cause this waning?

My coolant and brake fluids were low (near MIN). Both have topped off. Caution is gone now. However before filling fluids it went away but came back. Just filled it so can't say if it will come back...

Just curious if others had same experience...
 
1. Yes brake fluid lowers as the brake pads wear out, by the time it gets to MIN you probably will need your pads replaced. I'd suggest NOT periodically adding brake fluid unless it gets below MIN and the pads aren't worn out. If you add to the top when the pads are worn out, when you put new pads in the brake fluid will overflow the reservoir and get all over the floor.
2. Radiator reservoirs often get low if the vehicle gets hot then contract as the radiator gets cool, the Leaf doesn't really have a radiator to cool the engine and I've never had to add to mine.
 
LeftieBiker said:
2. Radiator reservoirs often get low if the vehicle gets hot then contract as the radiator gets cool,


I'm pretty sure it's the other way around.

:lol: Yep, heat expands, cool contracts.......got a little mixed up and started rewriting physics :eek:
 
Brake fluid: I've not added brake fluid to ANY car I've owned in the past 25 years: Audis, VWs, Honda Odyssey, Toyota Tundra, Avalon. I've also followed a 3 year fluid replacement regimen with all cars, regardless of make.
 
gncndad said:
Brake fluid: I've not added brake fluid to ANY car I've owned in the past 25 years: Audis, VWs, Honda Odyssey, Toyota Tundra, Avalon. I've also followed a 3 year fluid replacement regimen with all cars, regardless of make.

You are replacing the fluid before there's enough pad wear to require a top-off. When I replaced the fluid on LEAF, the level was only about 1mm below the full mark.
 
jjeff said:
:lol: Yep, heat expands, cool contracts.......got a little mixed up and started rewriting physics :eek:

That's normally the case but there are some substances that are reversed, at least in some temperature ranges. And specifically to this case, it depends on the relative coefficients of expansion. Eg, does an aluminum engine block expand faster or slower than the coolant itself? I'm not sure of the answer but I know there is often a line to measure the coolant level when cold and another when hot. I'm not sure which is usually higher off the top of my head.
 
goldbrick said:
jjeff said:
:lol: Yep, heat expands, cool contracts.......got a little mixed up and started rewriting physics :eek:

That's normally the case but there are some substances that are reversed, at least in some temperature ranges. And specifically to this case, it depends on the relative coefficients of expansion. Eg, does an aluminum engine block expand faster or slower than the coolant itself? I'm not sure of the answer but I know there is often a line to measure the coolant level when cold and another when hot. I'm not sure which is usually higher off the top of my head.

For older cars with non-pressurized reservoir tanks the "hot" line was always higher, iirc. For LEAF, the pressurized reservoir has only min/max lines and is meant to be read "cold" (50C or less).
 
For older cars with non-pressurized reservoir tanks the "hot" line was always higher, iirc. For LEAF, the pressurized reservoir has only min/max lines and is meant to be read "cold" (50C or less).

That's because the coolant expands when hot.
 
Fluid is not compressible or expandable, the pressure in the fixed volume of the ICE engine passages goes up as the temperature goes up (remember the ideal gas law PV=nRT from 8th grade physics), when the pressure exceeds the release rating of the cap, then fluid gets pushed out to the reservoir.
 
nlspace said:
Fluid is not compressible or expandable, the pressure in the fixed volume of the ICE engine passages goes up as the temperature goes up (remember the ideal gas law PV=nRT from 8th grade physics), when the pressure exceeds the release rating of the cap, then fluid gets pushed out to the reservoir.


Looks like this topic is where we go to make mistakes! - the above post excepted of course. Funny: I knew that fluids are not compressible, but not (stupidly) that they don't expand. Yikes! I guess the term "expansion tank" had me fooled from such an early age that I never questioned it. Now that I think about it, though, here's what happens: steam forms from part of the fluid, or it out-gasses other vapor(s), and that steam or vapor behaves in part like adding additional fluid - or like making the existing fluid expand. It behaves as if it expands in this case.
 
This is a good thread to review how the coolant fluid works in an ICE car. It probably applies to an EV also.

Hopefully you will never have your coolant boil (unless you use water and it froze on a cold day creating a blockage and you started the engine anyway).

Automakers take countermeasures to ensure that the coolant never boils--boiling is a Bad Thing™ in an engine because the gas phase has little or no cooling ability and something mechanical is gonna seize up due to the expansion of metal creating an interference fit condition (e.g. piston in cylinder, or balls and races in a bearing).

The cooling system is closed and runs at a higher-than-ambient pressure due to the thermostat and pressure relief valve in the cap. The thermostat ensures that coolant by-passes the radiator until the engine comes up to operating temperature, then it opens to provide a path thru the radiator for heat to be transferred to the outside air and drop the temperature of the coolant.

The coolant has a higher boiling point than water due to the glycol or di-bromo-vomit or whatever organic compound it's made of. Think about cooking--if you add salt to a pot of water it increases the boiling point.

In addition the system pressure elevates the boiling point even higher than it would be at ambient. Think about cooking again--using a pressure cooker will cook food faster due to the higher boiling point of the water inside, e.g 15 psi raises the boiling pt to ~250F or 120C, versus using an open pot.

So the pressure and the dirty water both elevate the boiling point temperature, hopefully higher that any temperature that the system will ever see in normal operation if the radiator is not clogged.

When the engine is off and cools back down to ambient, then the internal pressure also drops, but there is less liquid in the fixed volume due to any that went to the reservoir. So the pressure drops below ambient and the reservoir liquid is pushed back into the system thru the return valve in the cap.
 
I recently had to do something involving this. Our 2013 Prius PHEV has developed a rough start/idle issue, and I had to check for exhaust gases in the coolant, using a chemical test kit. The instructions with the kit tell you to remove the radiator cap and test the air above the coolant - NOT the coolant. You guessed it: no radiator cap in at least later Priuses. So I mulled it over and decided that the expan...er, coolant reservoir should work, after carefully relieving the pressure. Hopefully it did, because the results of the two tests I did were both negative, indicating either no head gasket leak, or at worst a very tiny one. We still have to get the issue diagnosed, but I think I've got it down to either the EGR system or the intake manifold and/or its gasket...
 
nlspace said:
Fluid is not compressible or expandable, the pressure in the fixed volume of the ICE engine passages goes up as the temperature goes up (remember the ideal gas law PV=nRT from 8th grade physics), when the pressure exceeds the release rating of the cap, then fluid gets pushed out to the reservoir.

You can't compress liquid water with a piston, but it does experience density change (and thus expansion/contraction) with temperature.
Temp-Density-Water-300x263.jpg
.

With LEAF and many modern cars, the coolant reservoir serves also as a "degassing tank". It's part of the pressurized coolant system and the coolant inside is contiguous with the rest of the system. The pressure cap does not release during normal operation.
 
LeftieBiker said:
I recently had to do something involving this. Our 2013 Prius PHEV has developed a rough start/idle issue, and I had to check for exhaust gases in the coolant, using a chemical test kit. The instructions with the kit tell you to remove the radiator cap and test the air above the coolant - NOT the coolant. You guessed it: no radiator cap in at least later Priuses. So I mulled it over and decided that the pressuring exp...er, coolant reservoir should work, after carefully relieving the pressure. Hopefully it did, because the results of the two tests I did were both negative, indicating either no head gasket leak, or at worst a very tiny one. We still have to get the issue diagnosed, but I think I've got it down to either the EGR system or the intake manifold and/or its gasket...

You did the right thing. If the reservoir has the only pressure cap, then that's the pressure cap for the whole system. If you look at cars like this, you'll notice that the reservoir is made of much heavier plastic than traditional "overflow reservoirs". Having a pressurized reservoir like this allows the tank to serve the purpose of "degassing", so that gasses do not accumulate elsewhere in the cooling system and block flow. I had a Renault Alliance that I discovered empirically needed to have air "burped" out of the cooling system regularly. Most owners never discovered this and when I eventually had to take the vehicle to a shop for emissions testing, the mechanic remarked that he'd never seen one with that many miles on it. Seems they mostly died young from "overheating" problems ;)
 
I wondered why the Alliance died out so thoroughly. When my Sister was shopping for a new car in '86 I tried to guide her to a decent one. We drove an Escort that literally couldn't accelerate in overdrive with passengers in the car, drove a nice Civic, and drove two Alliances. I wasn't impressed with the hard plastic interior, or with the acceleration of the smaller base engine, but the ride - oh the ride was amazing for a small car. I suggested the Civic first (I'd just bought a then-new Civic Si) and the Alliance with larger motor second. She bought a just-renamed Plymouth TC-3 of course, because the interest rate was lower. It lasted about 6 years before getting junked. I guess the Alliance wasn't a good suggestion, either...

Damn, I digress. Wrong anecdote. I'll try again: we had a 90's era Mazda 323 hatchback for years, and for several Winters I drove Mercury Tracers, which at that time were re-bodied 323s that were actually nicer than the Mazdas, feature-wise. We thought that our 323's bad hydraulic lifters were a fluke, or a botched job by a mechanic. But no, it was a design flaw: Mazda made the oil passages in the head too small, and as most 323-engined cars approached or passed 100k miles (including my Winter cars), the lifters started to fail. By the mid Aughts we stopped seeing any on the road. I gather that those run on synthetic oil from early on kept running, but at least in the Snow Belt the '90's 323 is pretty much just a memory...
 
nlspace said:
Fluid is not compressible or expandable, the pressure in the fixed volume of the ICE engine passages goes up as the temperature goes up (remember the ideal gas law PV=nRT from 8th grade physics), when the pressure exceeds the release rating of the cap, then fluid gets pushed out to the reservoir.
The term 'fluid' in physics includes both liquids and gases. Gases are certainly compressible, as the PV= part of the ideal gas law testifies. Outside of physics, fluid may be used to mean only liquids, as in "fluid ounce".
 
Back
Top