Strange coolant leak

[Gary6]

Considering removing the intake manifold on my 1994 LS 400 to replace the by-pass O ring on the back of the water pump.  Not positive this is the source of the coolant leak...but as coolant leaks from the rear of the engine-front of transmission only when the engine is cold and the ambient temperature drops below 40 degrees.  I can see also see coolant puddled in the valley under the intake manifold.  So far it's my best guess?   What am I missing??  THANKS!

[Exhaustgases]

There are a lot of could be's. Also the rear coolant cross over manifold could be leaking, or any hoses that carry the stuff as well.

If you end up removing the intake manifold, I would do a starter if it needs it or not.

[Gary6]

All these hoses were all replaced around 20,000 miles ago...No sign, that I can find, of any of them leaking.  

Good suggestion on replacing the starter.  I read somewhere that these starter motors never really fail...but that the solenoid contacts do and should be replaced?

 

[Exhaustgases]

There are a lot of could be's. Also the rear coolant cross over manifold could be leaking, or any hoses that carry the stuff as well.

 

You read wrong, they do fail often. Its a motor with bushings and with brushes that run on the commutator, all are wear items, along with the bendix or one way clutch for the drive gear that engages with the ring gear, and yes the contactor in the solenoid needs attention as well.

It is just not smart to not deal with it while all the stuff is apart.

[Gary6]

All these hoses were all replaced around 20,000 miles ago...No sign, that I can find, of any of them leaking.  

Good suggestion on replacing the starter.  I read somewhere that these starter motors never really fail...but that the solenoid contacts do and should be replaced?

 

>>"It is just not smart to not deal with it while all the stuff is apart."<<

I agree.  I've noticed that "new" starter motors go for as little as $80 on ebay right next to "re-manufactured" starters for $140+? I'm guessing the "new" starters are NOT of the same quality as the OEM "re manufactured" starters.  What would you recommend? Do you have any brand preference? THANKS.

 

[Exhaustgases]

I just did an Oreillys one years ago on a 90. Its still holding in there. Though what I would rather do is have a spare ie keep my original and do it myself rebuild. I really don't know what is best new at dealer is too costly. In a pinch if I needed one right now I'd likely just do the oreillys thing again or napa, maybe denso at rock auto but that's a wait of a week or so.

[Gary6]

Where does a heater core leak drain or usually show it self on these cars ('94 LS 400).  I'm guessing it's not inside the car.  

It was obvious soon after I started disassembly that the bypass pipe O ring is not the coolant leak source.  Remember it only leaks when the engine is cold and the ambient temperature is below 45.  I believe the coolant in the starter valley came from the rear of water inlet housing and has been fixed.  Some of the coolant dripping from the rear of engine/front of transmission was coming from a lose clamp on one of the heater hoses.  I'm still getting a slight drip from the rear of engine/front of transmission...less than 1/16 of a cup along with a 3 psi drop (15-12 psi) over night on the coolant system pressure check gauge.  Drip appears to be coming from behind the black plate in the center of the front of the transmission housing?  It has only been 24 hours since I "repaired?" the leaks but it seems this drip should have stopped by now if the source has been repaired.  What am I missing?

Incidentally we've put about 145,000 of the 187,000 miles on this VERY nice car.  I've done all the required service/maintenance myself.  My daily driver is a 43 year old Dodge Van with 400,000+ miles...no one has put a wrench on that but me since I bought it 40+ years ago.

[sha4000]

Wow you have a 2018 LS 400. What do those look like lol. Just kidding but the only thing back there that I can think of are the heater hoses and the rear coolant bride.

[billydpowell]

On 3/25/2017 at 8:39 PM, sha4000 said:

Wow you have a 2018 LS 400. What do those look like lol. Just kidding but the only thing back there that I can think of are the heater hoses and the rear coolant bride.

North Carolina must be ahead of the rest of us...

 

[Lexus_DK]

Pressure test the cooling system (don't exceed 15lbs psi). Usually you can see where the coolant is spraying or trickling down when under pressure. If anything bring it back to the shop/dealership that last worked on it and complain to have them repair for it free. It's not fun pulling the intake manifold off yourself, trust me...

[Gary6]

Slow coolant leak (1/8 cup over night) from behind the black plate on the front of the transmission continued.  

Seeing no other possibility I replaced the by pass O ring on the back of the water pump...along with the starter while I was there.  O ring did appear a bit hard and flat...especially for only being 2 years old.  Every thing appears dry more than a week later with NO coolant loss.  However the ambient temperature has not dropped below 50 degrees since reassembly.  Remember cold engine & ambient temperature below 40 degrees were required for coolant leak to occur. 

Took about 40 hours.  Biggest problems were replacing the 1/4' x 3" by-pass hose on the rear passenger side of the engine (that eventually, after  8" of metal pipe and another 1/4" X 3" hose, connects to the throttle body) and finding replacements for the fuel injector plugs that crumbled in my hands during disassembly.  I wasn't being rough or careless...injector plugs seem to be made of incredibly fragile "crap" plastic.  

Now that I've figured out how to reach it I believe the by pass hose would only take me an hour (still a PIA) the second time around.  The injector plugs turned out to be a bit more complicated.  Plastic plugs I found fit the injectors perfectly and appear far more robust.  Sadly they had to be modified (VERY CAREFUL drilling) to accept the metal contacts which took a bit of time to work out.

In may be a while, this time of the year, before we see temps below 40 in my neck of the woods again.  I'll keep you posted should this strange coolant leak reappear.