dtewing

Driving a 1999 LS400 with 141k on it. The issue I am having is that I am loosing coolant "mysteriously". I have tried troubleshooting the issue, replaced the O2 sensor, the thermostat, updated the upper and lower hose, checked the radiator integrity and none of these appear to be the cause.

I am stumped. Here is my question is it possible that the water pump is the culprit (their are NO symptom of weeping or discharge coming from the pump).

The car continues to lose coolant, just not visibly and overheat as a result. It is NOT an air bubble in the system as I have run the air bubble fix several (read a dozen times) and that is not my issue I believe.

Please let me know what additional details I should provide as well.

Thank you Forum as always for excellent advice/support.

Cheers, Darren

billydpowe

iTrader: (1)

Thinking out loud since I drive a 99 LS with 203k on it, wondering how many days it takes to overheat.... how much coolant has to be replaced each time? and was the WP replaced when the TB was replaced? thinking that the 400 engine is not likely to have a leaking/seeping head gasket, I thing I would replace the Temp sensor/switch, if it has not been done.....

djamps

Is there any funky residue on the underside of oil cap or radiator cap?

RA40

iTrader: (6)

Change the O-ring on the drain ****. When that leaks it goes right out the drain tube. The one way you'll spot it is if you leave the car running on the driveway and see the drops-puddle. Otherwise the usual checks for the radiator cap, hose junctions, etc.

jaaa

An outside chance it is leaking behind the water pump and into the valley of the engine. As your car is running it evaporates. If the leak back there is bad enough it will start leaking through the back side of the engine and into the bell housing where there is a weep hole. Get a flashlight and try and look at the valley of the motor towards the front. If it's dry there, it's not your problem.

dtewing

Thanks for the feedback.

No residue on the oil or radiator caps. Fluids are correct consistency and viscosity. Replaced the radiator cap with OE during this whole troubleshooting and their was NOTHING out of the ordinary with the fluid.

I did replace the starter in the winter and that is when this all this started after that. When I removed the TB (using the tutorials posted in the forum) I replaced the o-rings on the front and rear coolant pipes.

I haven't tracked the amount of coolant loss as she red-lines and I turn the radiator cap to release the pressure and loose coolant at that point, so no chance to measure loss.

Interestingly when I remove the (new) temp sensor switch and fill the block through the hole (using a series of smaller hoses to fit in the hole) it takes quiet a bit of coolant, but she drives normal - long toughen to run errands. The filler bolt on the TB does not fill the loss I am experiencing sufficiently in the block. I did notice a faint coolant burning odor, but I do not see any coolant loss ANYWHERE (including the valley of the engine) not sure if the odor is just burning off any residue or if the coolant have evaporated overnight before I drove her.

This morning I opened the filler bolt on the TB and their is ZERO coolant observed in that area. So definitely coolant loss yesterday during running errands. Just not enough to trigger relining and air pockets in the system.

Thanks again for your posts and help !!!

djamps

Maybe it's only leaking at higher RPM's when your going down the road? Maybe rev it to 2k for a few minutes in your driveway and look for drips or steam. Also check the exhaust for coolant smell. Spark plugs would probably show signs of a headgasket issue, the water would steam off deposits making one plug look alot cleaner than the rest.

YODAONE

Check water control valve mounted on firewall for leaks... Stuff a wad of paper towels underneath it and see if coolant leakage over time. (color of coolant on paper towel)

dicer

If you changed the starter then you fooled with the rear coolant cross over manifold, that is a good place for a leak.

dtewing

I cracked the valve and had to replace it when I did the starter swap. (My only snafu of the project). I will definitely check the fittings again and try the wad of paper towels trick.

My linkage on the valve was off the original valve . It had criticized me out of the clip. When I replaced it I checked the linkage doesn't move the switch at all - any correlation or another issue?

dtewing

I made sure to use new o-rings and verified was seated correctly.

I hope to hell that ain't it- that job was a PIA to do...

brybo86

I second the exhaust check for coolant smell.
When it's cold does it ALWAYS seem to have moisture in the exhaust?
Even after a long drive?
I bet if you check the spark plugs they will show coolant usage.
My guess is head gasket slightly allowing coolant into combustion chamber in one or more cylinders.

Ask me how I know... I might have the same problem. My car "uses" about 1/2 cup every month

YODAONE

Did you purchase all new (Lexus) water valve hoses and clamps depicted?(very durable but nothing lasts forever)

No mention on how you cracked the water control valve...possibly you damaged fittings at firewall and, or, engine to water control valve resulting from tugging on preformed rubber hoses?

While replacing valve how did you stabilize those hoses while removing them?

Any sweet smell or visual evidence of coolant inside car?

dtewing

I did NOT replace the water valve hoses or clamps... They passed my visual inspection and were pliable with zero cracking or dry rot. The clamps all performed as well clamps should too, so they were re-used.

No coolant inside car.

Took her for a drive today : I put dry paper towels behind the valve and ran an errand and the paper towels were dry at the need of my 10 mile drive.

I am leaning toward the coolant inlet either front or rear. Dreading the thought of having to basically do a starter replacement again...

dtewing

I will do this. Check plugs and ehxhaust. Thanks.

My plugs were replaced when I did the starter a few months back and they had no signs of coolant. Some of the plugs were gummed up but with oil not coolant.

If I pull the dipstick - oil itself looks fine, light brown and normal viscosity...