Hello Lexus people
First post. My 2nd GS showed it's 1st weakness.
I am loosing coolant drip by drip every 5-7 seconds
from right under coolant bypass pipe #1 right where it meets the Water Pump (ugly

orange arrow)



I obviously suspect bypass pipe gaskets. My question is whether I can replace them by simply unbolting the pipe. WP and Tbelt were done less than 20k miles ago so no necessity for that repair. Car doesn't overheat, lost half expansion tank of coolant over last 300 miles , and coolant is clearly visible...

 

I did not fin much info on replacing these gaskets. They are only mentioned in TB / WP DIYs and people remove this pipe after removing T belt

 

I removed my bypass pipe and replaced the gasket when I did my timing belt/water pump service.

 

Yes you can just remove the pipe itself without removing the waterpump.

The round tube with the two orings is the likely culprit. Being aluminum they usually will have a good amount of oxidation/buildup on them as every one I've ever pulled out has had. They need to be cleaned up really good, with some 320grit sandpaper or similar and the two grooves scraped out/cleaned back to perfection, then install your new orings. (Be sure to also clean the female sides that receive the tube on the neck and on the pump body as well.)

The orings can tear upon sliding them into the neck so be careful, I usually put a dab of dishsoap on my finger and just lightly coat the orings to help it slide right in and then the dishsoap will dryout and not effect the seal.

 

You always want to change those when you do the timing belt/water pump repair. What I found surprising is that none of the "kits" you find on eBay ever include them.

 

You can get assorted gaskets from any autoparts store.

 

Where can I get a new No. 1 water bypass hose hose (2002 Lexus is300)

 

here you can find the part number.
Link to ebay url

 

or you can buy set of Orings. I bought set of I think 417 Orings ranging from 3mm to 50mm for like 5$

 

Just did this repair today on my son’s 99 SC300

The leak appeared right below this bypass pipe exactly like the photo a few posts above. It’s not necessarily a typical place to look for minor coolant leaks and when I saw it I was thinking leak was from back of water pump. It looks almost like condensation but if you dry it you realize how quickly it returns.

The diagram from the repair manual in above post is helpful to see how the bypass pipe has 3 o-rings and how the bottom pipe piece separates. It takes a little work to twist and pull the bottom piece out. There are three o-rings to replace, Toyota part number 96761-24022 water by-pass pipe o-ring (need 2 of these) and 96761-24028 (1 pc.) water outlet by-pass o-ring (need 1 of these). When I did my water pump and timing belt on my 93 SC300 I ordered these Toyota rings at about $5 per o-ring. This time, I used some from a big box of metric-sized o-rings sold by harbor freight. Go with the smallest option that just fits the diameter of the pipe since the Toyota ones are a bit thinner and flatter.

Expect a lot of coolant to pour out of engine block when pipe is loosened and removed. Have towels handy and cover alternator with plastic to protect it. Clean off spilled coolant from any delicate engine components, electrical connections, etc.

Once the pipe is removed, I could see how flattened and brittle the old rings were. Remove em and clean the pipes well. I used a brass detail brush to loosen debris plus some brake parts cleaner and rinsed out the pipe well with water. My upper o-ring was stuck to engine block pipe connection.

The 2 bolts that hold this pipe in place are 10 mm and torque to 15 foot pounds.

Be sure to purge air from coolant system after this job. You’ll need to add some extra coolant to offset what you lost from engine block. I purged air using funnel method connected to radiator, which gets air out and adds coolant back as well. Take for test drive to check that leak repaired and that no overheating from air in system. Keep eye on coolant level in expansion tank over next few days.

Access to pipe is pretty good but it’s always easy to put pressure on other pieces. I cracked a brittle vacuum line going between my intake and pcv. Fortunately I had spare line in this size laying around.