myf16

The coolant level in my 1990 LS400 keeps dropping. I top it off with 4 to 8 ounces of water in the morning approximately weekly, every 50 to 100 miles. I don't drive very much or very far, but over the past year or two I must have added 3 to 4 gallons. This is a pretty rapid loss, yet I have never seen any leaks or puddles or drips and the car runs perfectly. The car has less than 150k miles. The water pump was replaced at 120k. I am baffled.

After searching forum threads I have checked the HVC valve on the firewall, I have peered into the valley area under the intake manifold. I have revved the engine. I have looked and felt all around the coolant reservoir. I can't see a drop of water anywhere. The oil looks normal with less than 1/3 quart consumed per 5000 miles.

I love this car and I want to keep driving it many more years. Help!

MedicalDoc

Fill it with Toyota super long life==pink==..
It will evaporate where it leaks, leaving a pink residue.
You can also try a fluorescent leak dye detector, with a UV light.
To test for a leaky head gasket you will need a kit.

spuds

Radiator cap? Just guessing.....

billydpowe

iTrader: (1)

definitely pressure test system... it should show up... is it running hotter than normal??

myf16

It's not running hot as far as I can tell by touching the valve covers. (The temp gauge doesn't work properly and stays near the low end of the range.)

If it's the head gasket I would part out the car. It has super-rare cloth seating in perfect condition, but the body is a mess and the AC is not repairable. The value of the car does not warrant $1500 worth of repair effort. I can get $1000 for the car even after selling off lots of parts including seats.

If it's the radiator I would replace that. Can a radiator leak this fast without dropping any water at all? I drive it 20 minutes at a time and I have to add at least 4 ounces after 2 hours of driving time.

RA40

iTrader: (6)

One thought is to check the radiator pet ****. When the O-ring deteriorates coolant will drain out the tube onto the road under pressure. I didn't find that leak until I left the car idling in the garage for a couple minutes to find a small drop there. I change the pet **** and O-ring at about 70K intervals now, ~$8. You can get the O-rings at any hardware store, I forget the size.

myf16

When I removed the reservoir cap 40 minutes after stopping the car it still had some pressure. Is that definitive or could there still be a substantial leak? Another 8 ounces added after 50 miles.

Does this car have a second pressure cap or only the one on the reservoir?

Yamae

There isn't any second pressure cap.

Your type of problem tends to happen if the leak only happens at the radiator while running after fully warmed up. Very small amount of leak at the radiator can't be seen by eyes because it quickly evaporates. Also if the leak is at the A/C condenser side it's difficult to see too. The airflow by the cooling fan also makes it difficult to find out the leaking point.

You need to apply the pressure at least 0.103 Mpa or 15 lbf/in2,psi to test the leak.
This needs to be done while the radiator is still hot. Because the copper alloy expands with the ratio of 19 X 10−6/K.

myf16

I tested it hot. The cap is 13 psi so in theory that's as high as the pressure can get by itself. I didn't want to cause damage so I pumped to 12.5 psi and waited 20 minutes. It dropped to 11.5 psi. For all I know, the pressure tester leaks that much. I can't see coolant anywhere including on the ground.

This is weird. Is it worth trying again at 15 psi after warming up? Is there any risk of creating a leak that was not there already?

myf16

The latter would be head gasket?

How would I detect and repair the former?

billydpowe

iTrader: (1)

A LITTLE WARNING:
RADIATOR:
I had to replace mine at 220k, this year, would not circulate coolant properly and ran HOT.. but I was on top of it and done no damage except to my childrens $$$.. water pump failed(from running so hot) so I redone TB/WP (actually thought I had bought a "cheap" kit) the heat overcame the pump, and after replacing IT, could not get it to run with out getting VERY hot in only two blocks,,, took us four days to find it was the radiator NOT circulating properly... it never leaked.. in fact we just replaced the radiator because there was nothing else to replace... and it was it... ran like a champ, still does... be careful.. guys.. (& gals)
SO: if yours is running over normal... well a hint to the wise is sufficient..

Losiracer2

I would double check your clamps, especially if you used the aftermarket worm type ones. I have those on mine due to the previous owner replacing the radiator and when I went to replace the hoses, I tightened it down and a small amount would leak out after a certain amount of time since they lose clamping force and need to be periodically tightened.

It would leak from the top inlet on the radiator hose, and leave a white residue as some had said so it was easy to spot where I needed to tighten.

myf16

Pressure testing was pretty good, and I can't see the water coming out, so I figure it must be a small or intermittent internal leak. Again, there is no oil at all in the water and the engine does not overheat.

Given that this car needs to pass smog in 4 months or be junked I am thinking of trying a head gasket stop leak product. I will read up on them, but I'd appreciate any advice you can give me.

YODAONE

Here...just prior to smog test deadline, transfer the title to a relative, corporation or trust you control...and thereby reset the certification time cycle (dispatch a certified letter to emissions people that vehicle has been sold) OR you can pay a Lexus dealer $100 to sort out your problem.

dicer

And hopefully its not going into the transmission.