Hi All - My '94 LS400 is losing coolant, just noticed today. I check under the hood fairly frequently, so believe this is a new/recent development. The coolant level is about 1 inch below the minimum marking on the reservoir. Definitely has lost fluid just in the past few days. I noticed excess fluid around the plastic cap of the reservoir yesterday (on the outside, surrounding the cap). When I lifted the cap's rubber lid, I can see a whiteish plastic disc, with two wires coming out of it. Some of the fluid has a gum=like consistency in places. So I wiped it all off, and removed the gummy residue. Today, when I checked again, the gumminess and the fluid are back. Same as yesterday. I am only driving short distances (to the store and back) because I know it is not wise to drive with coolant fluids low. Do you think the coolant is disappearing from the reservoir (since there is dampness outside/around the coolant reservoir cap? If so, is it possible to just replace a cap, and not the entire reservoir (assuming that is the problem)? I pray it is not something else. What are the other possible causes of coolant leaks? This could not happen at a worst time.

 

that sludge could be engine oil. If your headgasket is leaking, oil could be entering the cooling system. Check your oil dipstick. After your car is warmed up, see if you get any smoke from the exhaust. If you get white smoke, then its most likely your headgasket.

 

i will bet money it isnt a headgasket, i have never seen one blow on a 1uz nor heard of it in my years of owning/working on LS/GS 1UZs.

most likely you have a simple leak in the cooliing system, check the hoses and cap for leakages, what kind of coolant are you using?

 

don't worry about a head gasket, a slight bit of sludge in a cooling system is normal if the system hasn't been maintained properly over the years.
have you ever done a water pump or did the PO do it? i bet it's leaking.
you can always buy a cheap pressure tester and test the system. if it's a leaking hose or fitting, you'll find it. the water pump won't show up on a pressur test though. look underneath after removing the belly pan. yo ushould find coolant dripping from somewhere. follow it up; theres' your leak. if it's dripping from the crank pulley area, you need a water pump.

 

What type of coolant? Toyota red or yellow/green after-market stuff?

 

toyota red....guys i think hes talking about the sensor that is located on the overfill tank.

the rubber cap thats next to the coolant cap..


OP mine leaks too, but i just keep an eye on it. ill replace it soon enough.

 

You guys never seen a headgasket go bad on a 1uz-fe? My uncle use to own a mechanic shop and once in a while, and LS would roll in with smokey exhaust :P The likelyhood of one having it is low, but trust me, it does exist!

 

$5 says that the smokey exhaust was from the power steering idle up pump spewing PS fluid into the intake rather than a blow headgasket. very easily mistaken. basic rule of thumb is that unless the oil has the consistency of a milkshake it's NOT a BHG.

 

Not that the coolant type/color would matter in this case...

It could be the sensor's O-ring causing the leak, or the tank is cracked:

Coolant Tank Leak

In post 7:

 

Ok, here's the latest...not great news. Yesterday the coolant was at about 1 inch below the minimum marker on the reservoir. Still plenty in there. I drove it a short distance, maybe 2.5 miles round trip on store run (low speed). Parked it and it sat overnight. This morning, no puddles of any sort under the car, but also almost NO coolant is visible now...maybe 1/2 inch in the bottom of the reservoir. I do have a gallon container in the trunk of Red Toyota Antifreeze Coolant (not sure if that is the exact title). I kept that from May 2007, when I had a disappearing coolant problem. I took it in to the dealer and spent a small fortune on replacing the water pump, timing belt and related components (it was due for replacement anyway, and they recommended that I deal with it as long as they were going in there), upper and lower radiator hoses and radiator cap. In September of '07, I had to replace the radiator,which was leaking. The antifreeze was switched out at that time. I looked all around the coolant reservoir, and see dampness around the rubber cap that is next to the coolant cap. There's not a lot of it, but definitely visible. The hoses that I can see related to the coolant tank do not appear to have fluid around them. There is no fluid splashed on other nearby parts. I will add some coolant to the reservoir and start it up to see if there is white smoke and will report back. Lexus warranty on any work only last a year, I believe...but this really sucks if I am back to the same issue with water pump, etc.

 

Pull the oil dipstick...is it clear brown?

An obvious coolant leak is easy to smell on a warm engine and most instances of that, there will be puddles/drips. Barring those it's going elsewhere and yours doesn't sound good.

 

...check the thermostat, if it's stuck it could be causing the tank to surge as it's cooling pushing hot/warm fluid up into the tank.

 

I was going to suggest this as well. Does the car warm up slower and run warmer than what you are used to?

 

Ok, I called Lexus and was told it was OK to add water to the remaining coolant in that gallon (red/antifreeze coolant). The mix is probably about 75% water and the rest coolant. I topped off the coolant reservoir. It took less than I thought -- only a cup or so to bring it up to the upper level marker. I decided to add up to the higher level on the theory that I would be losing some as I drove.

The car runs normally, the temp gauge starts out cold (normal) and moved up to midpoint normally (it stabilized a little past the second white marker...so near the middle between cold and hot). I got out to look at the exhaust pipes and the exhaust was whitish for about 30 seconds, after which it cleared up. Car was sitting out overnight, so I think that was condensation. At least that is what a dealership told me when I asked them about that ages ago. I drove about a quarter mile (slow 'in traffic' speed), then got out to look at the exhaust. There was too much white in the exhaust, but again, that cleared up later (I checked several times throughout the drive).

I looked all over under the hood and under the car. I don't see any big splashes of anything, though there is fluid around the reservoir cap (not the coolant cap, the rubber cap next to it). It seems limited to the top, though, and is not dripping down the sides. I've looked at the hoses (as much as I can figure out where they are, and do not see any leaks. I am not a mechanic so have no idea how to loosen it to check the entire reservoir for cracks or how to check the sensor's o-ring.

Read the manual and checked the engine oil accordingly. The oil looks fine; it's brown, not clear, but also not milky at all. It's just dirty. It's a reminder that it is time for an oil change.

The only other thing I saw was across from the reservoir, on what I think is the transmission, I saw seepage (not leaking) along a seam. It's best described as dampness of about 1/3 inch width running along the seam. Probably not a good sign, but isn't gushing by an means. Minor seepage best describes it.

I haven't been able to locate the receipt just yet, but I did have head gasket seals (?? I think that is what it was) replaced about four years ago at the dealership. Cost around $500 if memory serves.

I ran the A/C and it worked normally. Cranked it down to 69 degrees and it got really cold. I did not use the heater (hot here today).

So I will check the level again tomorrow. If it's low again, I will get it in someplace ASAP for diagnosis. Glad it appears to be driveable right now.

The only thing I can think of that I did differently (recently) was drive the car with the A/C off. I almost always have that on, for better air quality. Would that have had anything to do with the shift in coolant levels?

Thanks for everyone's comments. Very helpful. I hope it is something simple like that sensor's o'ring. I'll post back here to let you know what happens.

 

How would I get to the sensor to check the ring? Looks to me like the only access I have is the two caps on top -- the rubber cap and the coolant cap. Is the sensor inside? Where? If it is something simple, and with detailed instructions, I would try to look for that tomorrow.