GX470 Coolant leak - head or ?

Joined
Jan 12, 2020
Messages
3
Location
california
2003 GX470 with 150k miles. Pump and belts done by PO at ~120k, and I just replace the thermostat inlet housing o-ring which I though was causing the leak due to visible seepage.

After filling the reservoir to the full line, the next day it's back to half full. Coolant is visible on the front passenger side of the engine where the head mates to the block. I removed the PS bracket and the belt cover but can't really tell if the leak originates further up. I can also see wetness on the block under the manifold on the same side so assume it's related.

This has been going on for a while but the leak is getting more prominent. Any thoughts on the source? Hoping it's the water pump and not a head gasket.

Don't know if the engine ever overheated but it runs great and temp is always at mid-point on the temp gauge.

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Joined
Dec 25, 2018
Messages
258
Location
Ohio
There are two small coolant lines that go through the throttle body and back toward the passenger valve cover. Have a look at those, the hoses are rubber and the fittings plastic so perhaps you have some age-related dry rot or whatnot.
 
Joined
Dec 30, 2017
Messages
59
Location
Montana
I would also check the coolant line that runs into the back of the thermostat housing. Mine had an O-ring that was crushed due to poor installation and was leaking.

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Joined
Jan 12, 2020
Messages
3
Location
california
There are two small coolant lines that go through the throttle body and back toward the passenger valve cover. Have a look at those, the hoses are rubber and the fittings plastic so perhaps you have some age-related dry rot or whatnot.
I see two water bypass hoses going into the throttle body from the passenger side - those are dry. I don't see where they come out.



I would also check the coolant line that runs into the back of the thermostat housing. Mine had an O-ring that was crushed due to poor installation and was leaking.
The coolant line into the thermostat housing appears to be metal and I don't see any sort of clamp/connection. It's also clean. The only place I saw pink dry coolant was around the inlet pipe o-ring which I replaced and resealed the unit.

I placed a balloon over the radiator fill hole and started the engine cold - the balloon didn't fill up and I didn't see any bubbles in the reservoir. I'll rent a combustion leak detector / block tester tomorrow and try that next.

Visually, I don't see any leaking hoses, but also see a wet trail down the center of the oil pan and up in the plastic belt cover (weep hole?) when looking up at the crank pulley from underneath. That may be water from yesterday's work, or it could be the source of the leak, which seems odd if the WP only has 30k mi on it. if it's the WP, does it make sense that coolant is running along the head gasket and down the block behind the PS bracket, but the Driver's side of the block in dry?
 
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Joined
Jan 12, 2020
Messages
3
Location
california
I had the system pressure tested the other day and no leaks according to the shop I took it to. They had it pressurized for 30 min. Visually all leaks were dry, but again this morning there's coolant running down the side of the block and the vin area under the throttle body looks partially wet. Since I don't see leaking from the two water bypass hoses, and I just replace the thermostat housing inlet o-ring and resealed the port mating surface (no visible leaks there), it's possible the leak is coming from the back of the water pump inlet o-ring.

Any suggestions on how to confirm this is the leak?

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