Today I just thought of checking the coolant levels on my 91 Lexus LS400 w/ 130k miles. The engine was warm (drove for 45min on 90deg weather). Coolant is below the 2nd line



Got me thinking if I should add coolant. The car is operating normally with no issues/lights.

Can someone explain the coolant levels for 90-94 LS400? And the process of adding coolant (how much, etc).

Thanks

 

In a nutshell...
The reservoir is nothing more than an expansion tank. A place for surplus fluid to go as it expands from the heat. If you fill the reservoir when the car is cool it will overflow when the car heats up and fluid in the radiator needs a place to go.
If the car is cool and the reservoir is EMPTY then add a little. Otherwise, there's no need to worry about it and don't overthink the position of the lines...

 

The level on that looks good to me. What doesn't look good is the color of that coolant. It should be red, or some people use the green. But definitely not black. Also, the sensor on top of the expansion tank has a leak in it, not enough to really worry about it now but in the near future.

 

I often wondered that, so mine being under low when cold is not a bad thing?

 

Check the levels cold and hot. The pictured reservoir is a couple ounces low which isn't significant. Mine when cold ticks the cold level marker.

 

If it were me, I would fill to the upper line when cold. If you don't have the proper coolant handy, it should be fine to add distilled water. The amount added will not significantly affect the 50/50 mix.

I'd also check the condition of the fluid, as mentioned above. Maybe it needs to be changed. Whenever I do my scheduled coolant changes, the coolant coming out looks pretty much new. And that's at 30k+ miles.

Lexus spec's the red stuff, but also says the green stuff is OK. I use the green on as many of my cars as I can, for convenience and saving shelf space in my garage. In general I think there are a zillion different types of original fluids, and almost all of them are special only in the sense that they satisfy environmental laws of the country of the manufacturer. However, you do need to worry about mixing different types, since they can react chemically. So thoroughly flush if changing. And if you can't tell what's in there now, you should do that as well.

 

ideally it should be just at the top line when hot but no worries if it's a bit low

 

Do not put green coolant in this car, its a glycol mix which will mix with the proper oem stuff and become gel and destroy your entire cooling system. Either way, toyota red coolant is CHEAP and easy to find. And that fluid looks properly dark, please change it.
On top of all of that, the coolant fill on these cars is a bolt on top of the thermostat housing. Putting coolant into the expansion tank will do absolutely nothing for the coolant system, it will not flow in your engine and radiator, it will simply get pushed out of the expansion tank and out onto the grounf. Hop on lexls.com and view the tutorial for changing coolant and how to properly bleed the system of air bubbles.

 

Really? If that's true then why is there an expansion tank to begin with? When the system gets hot the coolant expands and goes in the tank. When it cools there is less pressure and the coolant gets sucked back into the radiator. That's why there's a hose from tank to radiator. (bottom of tank) When there's too much coolant and gets pressurized, then it will drain to the ground through the overflow hose when it expands. (top of tank)

 

Your understanding of the pressure going into the expansion tank is largely correct. BUT if the coolant system contains say 2 gallons of coolant, and it has pushed .25 gallons into the expansion tank, and thus likely poured some out on the ground, the space that the coolant once took up is now air. There should be absolutely zero air space in the radiator, engine block, coolant passages, etc. As the coolant get hot and pressurized, some get pushed into the expansion tank. And then pulled back into the system when it cools. Pouring coolant into the expansion tank wont get rid of the air space in the system, itll just force coolant out of the expansion tank. Ive changed my coolant enough times and bled the system enough times, on 2 of my LS's now, to know that pouring anything into the expansion tank is a waste of fluid. Read the lexls tutorial, it explains excellently the proper method

 

Not gonna start an argument here but, if by any chance the system overheats and builds up enough pressure to push any coolant out the overflow that's no problem. It's meant to do that. When it cools it will suck back the coolant, not the air, into the radiator. That's why the return hose is on the bottom of the tank. I highly doubt it would push out a quart of coolant, but if it does then you have more problems then a little air in the system. It wont suck any air unless you let the tank run dry. That is why you add coolant occasionally. (In the expansion tank) That is what the OP is asking about the amount of coolant in his tank.
Now, if you drain the system then there will be air in there and the way lexls.com explains it is the correct way to fill and bleed it.

 

I've added coolant into the expansion tank and it worked well. If it happened that I found coolant level too low a little later, I would fill up the expansion tank again, and during the day, all the coolant would get suck in by the cooling system. Then I'd add more, and again, few times in a row, within a day or two, and finally, when the coolant stops going low from the tank, I know I have enough in the system. So it is possible to fill it up that way. I have also tried to fill it up via that bolt at the middle, front of the engine, and it fills up right away but there is still air in the system. When I filled up via the expansion tank, it worked better. Just my experience, make of it what you will.

 

 

Direct cut and paste from the 2000 LS service manual:
"COOLANT INSPECTION
1. CHECK ENGINE COOLANT LEVEL AT RADIATOR RESERVOIR
The engine coolant level should be between the ”LOW” and ”FULL” lines at normal temperature (20°C (68°F)).
If low, check for leaks and add ”Toyota Long Life Coolant” or equivalent up to the ”FULL” line."

So when cool, the level should be between the lines. Since I think it is more likely that some coolant might leave the system than mysteriously enter it, I figure it's best to fill to the upper line when cold.

Thermal expansion of the coolant will mean that when hot, if I filled to the top line when cold, coolant level will be above the top line. That's OK. By design, the air gap above the coolant in the expansion tank should allow expansion without overflow unless something is wrong.

 

I disagree with both of these.

As I mentioned in a previous post, either red or green (pink, purple, etc. too) will work. We agree that the danger is in mixing two types that may react to form a gel. I've been running with green for over 10 years now - changed the fluid soon after I got it, following advice from my Lexus dealer on this. No problems.

I once had a problem with the fill bolt at the thermostat housing leaking. After finally tuning up the surfaces and getting a new washer I was able to stop that. Since then, I have not touched that bolt, despite refilling the cooling system a couple of times or more. You absolutely yes can fill the cooling system through the expansion tank. I believe ideally, you would then crack open the fill bolt to let air escape, but I have never had an issue with air in the coolant system, so I'm convinced that any air will work its way to the expansion tank and touching that bolt is unnecessary.