Did a water pump and timing belt. Flushed the coolant and filled. I didn't have any leaks when filling the system and bleeding the air. Car sat for two days and now it has a coolant leak that looks like it's coming from behind the AC compressor on the drivers side. Where could this be originating from?

 

From ChatGPT:

1. Water pump gasket / O-ring (top suspect)

• The pump sits right in that area, partially behind/near the A/C compressor.
  
• If the gasket didn’t seat perfectly, or the surface wasn’t fully clean, it can:
  
  • Hold pressure initially (no leak while bleeding)
    
  • Then start leaking after heat cycles or sitting
    
• Coolant can run down and appear to come from behind the compressor.
  

Check: Look for coolant trails above the compressor or crusty residue around the pump housing.

2. Bypass pipe / water inlet pipe O-ring

• There’s a coolant transfer pipe that runs into/behind the pump.
  
• That pipe uses an O-ring that often gets:
  
  • Pinched
    
  • Reused (bad idea)
    
  • Slightly misaligned during reassembly
    

Symptom: Slow leak that shows up after sitting, often dripping from lower front engine area.

3. Thermostat housing or gasket

• Depending on engine (likely 3GR-FSE), the thermostat housing is nearby.
  
• If it was disturbed or loosened during the job:
  
  • Gasket may not reseal properly
    

4. Heater hose or small coolant hoses (disturbed during job)

• Hoses routed near the front/side of the engine can get:
  
  • Slightly cracked
    
  • Loosened clamps
    
• These often leak only after pressure drops or temperature changes.
  

5. Cracked plastic connector or flange

• Older Lexus/Toyota plastics can get brittle.
  
• Moving components during the job can cause a hairline crack that only leaks later.
  

6. Residual coolant (least likely if it’s still leaking)

• Sometimes coolant trapped in the valley or covers drains out later.
  
• BUT if it’s still actively dripping, this isn’t it.
  

What I’d do next (quick diagnosis)

1. Look from above with a flashlight
   
   • Check directly around the water pump and pipe connection
     
2. Pressure test the cooling system
   
   • This is the fastest way to pinpoint it
     
3. Check for a trail
   
   • Coolant always leaves a path (white/pink crust)
     

Key insight

If it was completely dry during bleeding and only leaked after sitting, that strongly points to:

• A marginal seal (O-ring/gasket)
  
• Not a major installation failure
  

If you want, tell me the exact engine (3GR-FSE vs 2GR-FSE) or send a picture of where it’s dripping—I can narrow it down to the exact bolt/connection that’s most likely leaking.

 

Ok, this is all great. It is a 2JZ-GE. Leak does not appear to have a trail above the AC compressor. There was a loose bolt in the AC compressor (bolt to block) it wasn't even threaded in, it was just hanging out in the hole.

This car sat for 10 years and we have been trouble shooting it back to life.

 

It's either going to be a radiator hose connection at the radiator or the radiator itself. Raise the front end and remove the undercover to inspect with a flashlight. If necessary pressure test the system. You can run the engine to build pressure if you don't want to get a pressure tester. Just takes longer and you have to wait for it to cool before you can begin repairs.

 

I checked around the radiator hose ( they are both new) it's dry. Water is not dripping below the radiator itself. Where ever the leak is originating it's created a path to drop off the oil pan lip just in front of the motor mount. Is there any information suggesting that the AC compressor bolt that goes into the block comes through a water path of some kind. Gemini is determined to convince me of this because of the loose bolt. I really feel like it's coming from between the AC compressor and the block.

I will be grabbing a pressure tester tonight.

 

Oh I mistakenly read "condenser" not compressor. My fault. That would seem to me that there was a problem with the water pump installation then.

 

Ok, so most likely it is leaking from the sealing surface of the new water pump behind the timing covers. Then rolling to the driver side of the block and dripping off? Which means i will need to get the covers off before i pressure test the system.

 

Ok, update to the coolant leak. I grabbed a pressure tester and discovered that it was coming from the coolant outlet housing and running down the block. I have the gasket, pulled and cleaned the housing and ready to install. The new concern is the bypass hose off of this housing, it looks like hell. It's swollen and possibly a cause for a leak after I seal the housing. Does anyone know what this hose is technically called or and what the part numbers would be? I feel like I should not try to reuse this.