Loosing Coolant & Intermittent Heat

[LA1]

Hello,

I have a 92 LS400 with 275K on the clock. The car recently began consuming antifreeze and I can't find a leak anywhere. I put cardboard under it and it shows no signs of leakage. I have to keep topping off the antifreeze to make the heater work but it goes back to being intermittent after a day of driving. Sometimes romping on it will make it blow hot but it goes back to cool at normal RPMs; I assume this is from low coolant as it is less noticable right after I top it off. When topped off it runs at a normal temp so it appears the T-stat is working. It makes me think headgasket but I don't have any classic headgasket symptoms; it has plenty of power, no smoking exhaust as I've seen with headgaskets in the past, no oil/coolant mixing signs in coolant or oil, etc. In addition, I've read from several people on Lexus boards that they have never seen the 1UFZ loose a headgasket. Every once in a while it will smoke on startup if I haven't driven it in a while but I'm sure this is the power steering fluid vacuum issue that is so common.

I should mention that it did get a little hot on a recent trip when it was warmer (about 3/4 way up the gauge) but I turned the heater on and it cooled right off and never got into the red (for what the gauge is worth anyway). I stopped as soon as I could get off the interstate and added some coolant and then it ran at a normal temperature, took almost an entire gallon though. I've been keeping it topped off since then but the next day there is never coolant in the reservoir which isn't showing any signs of leaking but was previously (a couple years ago) before I added that black hack job patch garbage. I'm adding enough coolant that I should see it leaking.

I change my coolant every 2 years in my vehicles but the last time I did this car (it is due now) I used Dexcool as shown in the LS400.com website as I couldn't get my hands on any Toyota red at the time. Could this have anything to do with a headgasket issue? I know Dexcool is a no no in the Lucas and GEMS Land Rover world and is partially blamed for the high headgasket failure rate of the later Rover V8 with the Bosch engine management system as some very rover-knowledgable people claim it becomes acidic and eats the gasket material.

Any suggestions before I end up having to take it in for a pressure check? I really hate to take it in as I do all my own repairs and the car isn't worth much anymore but I don't have the tools to do a coolant pressure check. I forgot about squeezing the upper coolant hose after a cold startup to check for a cracked block until writing this so I will do that in the morning when it is cold again.

I also forgot to mention that I've put at least 1,000 miles on it since I first noticed the low coolant level and nothing seems to be getting worse.

Any help would be appreciated.

Thanks!

[curiousB]

Yikes. It sounds like a head gasket to me. If it were a leak you'd see signs of it in the engine compartment and on the ground. Since you are not it sounds like coolant is leaking into the combustion chamber and getting vaporized in the exhaust.

A compression test or cylinder leak down test will give you the confirmation one way or the other.

If its a leak, the water pump is a prime candidate. You can tell if a water pump is leaking as you usually see caked up coolant near the leak where the water boil out of the coolant and caked residue is left behind. Might we worth pulling a cover to peek at the water pump. At 275k miles a water pump may still make sense to fix. A head gasket is probably not economic.

[LA1]

curiousB,

Thanks for your input, I've been afraid it is a headgasket as well but thought I should ask about it as I haven't had to do anything beyond normal maintenance to this car and therefore don't know the ins and outs of the LS.

I will have to check the water pump as it was last done at 135K but with the amount of coolant I'm adding I'm afraid it's not the pump. Sure can't be upset with this car as it has given me soooooooo many trouble-free miles and as it sits I only have $800 in her (other than an alternator and rotors) after a hailstorm but it may be time to trade her off.

I will post back if I find it to be something other than a headgasket.

Thanks again,

Levi

[landar]

It sounds like a fairly significant amount of leakage and you should see some on the floor if it were an external leak. Therefore, I would suspect a head gasket as well. If I were you, I would pull the spark plugs and carefully examine them one-by-one. If you have a gasket leak, you should be able to easily identify the leaking cylinder via the condition of the spark plug(s). If they all look similar, it might not be a head gasket after all.

I have attached a picture of the spark plugs in my 6 cylinder ES300 that had a blown head gasket. You can see that the plug on the far left is stained with coolant, still wet with coolant(even the threads) and electrodes a little 'cleaner' than the others. Burning steam in a cylinder will really clean the piston and plug. A dead giveaway.

[Daniel091]

Somthing else to think about is the cap for the overflow tank. If it isnt allowing the coolant to pressurise it could boil off.

[LA1]

I was going to pull the plugs yesterday but it is now blowing some white smoke so I decided to save a few hours work and call it a day.

Thanks for the help.

Levi

[Tony B]

I have a 92 and have had since 94. I was told that it was a defect. J never got it fixed to this day. Just keep topping off. But I never experience the heat problem. Goof Lu k.