dashan

1996 LS400 230K miles
The leak was observed behind the crank shaft pulley, close to the sink hole.
The water pump and timing belt were replaced 20K miles, two and a half years ago., using the aisin part kit from that reputable ebay seller.
https://www.clublexus.com/forums/ls4...-progress.html
The leak is small. Need to add coolant to the overflow bottle once a month. (about one inch). There is more leak when the weather is colder.
Do I have to do water pump replacement again? Nooooooooooooo

dashan

Water pump leak

dashan

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PureDrifter

iTrader: (10)

make sure the upper radiator hose is properly sealed at the thermostat housing, it work loose and you'll see about this much coolant loss. The way it drips down makes it seem like a water pump issue.

dashan

Upper hose checked dry.
Leak at 20K miles made me wonder the quality of the ebay Aisin water pump. The ebay seller had been in the business selling Japanese auto parts for a long time and had very good reviews.

billydpowe

iTrader: (1)

I went back and looked at your photos, and I think/guess your little o-ring may be the culprit. I also used aisin on 2 of our jobs without trouble, and used NAPA on the others with no issues. I just worried about that o-ring on all of ours, but it held up.. anyway good luck..

dashan

Thanks Billy for the advice, and for your time to go through my thread.
I have a question: How can I positively identify where the problem is when I tear the engine apart again? Gasket, O-ring, or the water pump itself? I am wondering whether I will need to buy a new water pump.
Is it possible to drive the car (say a 1K mile one way trip) while I closely monitor the leak?

LScowboyLS

I can think of many more likely sources than a relatively new water pump.

coolant migrates down following gravity, and there are a lot of places coolant travels higher up around the front of the engine that could be the leak source besides the water pump!

it's like for every 100 LS400's I see with a steering rack wet with power steering fluid, you know how many are actually the rack itself leaking? - maybe 1 or zero!

LScowboyLS

you are going to have to take off all timing covers and dry everything off good and drive around the neighborhood with covers off to find the leak - you may even need to remove the fan from the fan pulley bracket to make sure it doesn't blow away your evidence!

dashan

Actually I did have a Q in my mind yesterday: Why didn't the water drip from the sink hole? If it is a water pump leak, isn't it supposed to drip from the sink hole?

LScowboyLS

call it a "weep hole" for clarity, and yes, that is the most likely place you would see a water pump leak, but not 100% of the time

PureDrifter

iTrader: (10)

How exactly did you "verify" that the upper hose was dry?

When it leaks from the bottom you can't tell without pulling it off.

dashan

Touch。10cccccc

dashan

Thanks PD. I found that the thermostat housing is wet. I will replace the gasket and watch.

dashan

Remove the Thermostat gasket. there is a leak on the driver side of the gasket.