Hoping to get some ideas on the issue I'm having trouble with regarding my daughter'* 2008 Pontiac Grand Prix V6 3.8, 128,000 miles. - In regard to the cooling system: replaced temperature sensor and thermostat, plastic coolant elbows, and coolant reservoir hose last year. Replaced water pump yesterday as It was cheap and looks to be close to where the engine shows sign of a leak.

Some history: Two years ago, the heater was not getting the cabin hot and I could hear the coolant flowing, especially when accelerating or turning corners, so I disconnected the heater hoses and used compressed air to blow out the heater core. Water was not an easy option as it was winter, but that blew out some junk and afterwards the heat worked well.

Next, about a year later, I started troubleshooting coolant disappearing. After some research I tested the pressure, I think up to 13 psi was recommended, so I borrowed a kit that threaded into the radiator coolant filler. At that time, the test held the pressure for a couple of hours, and no notice of white smoke from the exhaust. As a good measure, I replaced the plastic elbows with the metal ones and yet still had to fill up the system after a couple of months. I finally found that the hose leading from the radiator to the reservoir was cracked, so I replace it. In spite of that fix, I had to remove the air from the system multiple times fill up the coolant after about 3 to 4 months. No leak was found underneath the car until this week. I parked it on a hill with the radiator being the lowest point and filled coolant while using the coolant bleeder to remove air. There was an excessive amount this time as it took two heating cycles to get the air out. After that time, I noticed the car was now leaking coolant onto the driveway. The engine was dry around the thermostat, and air intake area, but was wet below the water pump, next to the A/C condenser. I replace the water pump with a steel Fel-Pro gasket. After refilling, there is still a significant amount of leak under the engine to the passenger side of the oil pan, since I do not see anything leaking out, it may possibly be leaking at the lower intake area around where the lower radiator hose connects. Is there any way to detect the leak'* source? Would I see the source if it were leaking at the lower intake? – The car is not worth much, so a mechanic’* diagnosis, if at all, would lead to me doing any more work.

To get the air out you want the front end high. We lift them 30 inches minimum.
Steam clean the engine and use dye to fine the leak.

Thanks for the reply, the air was pretty much out now. Any ideas why it would leak below the lower intake? (See description below)

Filling it with coolant, while I was pouring it in, it was leaking from the bottom of the car with excessive drips along the metal frame without the car running and engine cold. Also while squeezing the lower radiator hose you can see and hear the coolant leaking below the lower intake gasket. It is somewhat wet where the silicone bead is at the corner of lower intake and head as seen in the picture. Also, pictured below the lower intake gasket, beneath the lower hose, I have confirmed the leak. It is not from the underside of the hose, but it is leaking (running down the engine from below the intake gasket (right side of water pump). I would think the car would be running rough and possibly white smoke coming from the exhaust if the lower intake or head was leaking, but the engine sounds normal.


below lower radiator hose

below the lower intake

Check your oil level and the bottom of your oil cap for a milky residue.

Now is the time to change out both intake gaskets, coolant elbows etc.

Reddish area below lower radiator supply on the block is wet

Leak found and heard in block weld underneath the engine/radiator supply chamber. As you squeeze the lower radiator hose the sound of bubbles near the water pump grabbed my attention. Probably why I have been seeing the area next to the water pump wet for some time. I guess it finally started to leak enough to cause spraying and slight overheating. Since it is visible with a flashlight and mirror, any chance anyone has valuable experience with an external weld fix like J-B Weld?
Very likely could be from overheating. Anyway, thought I'd share this post with a short video showing the leak. The previous post did not show up, so hopefully, this one will work.

Thank you "carfixer007" and Mike for your suggestions. I appreciate all those with valuable experience and knowledge on this site.
-Eric

If its leaking externally, then there is a chance its leaking internally.

Did you inspect the oil level and under the oil cap like I asked?

Mike. thanks for the reply.
Yes, I checked the oil cap and it was dry. The oil level is a little low and smells like burnt worn-out oil as it was due for a change, so I did not notice any milky brown in the oil dipstick. I will be dumping the oil after I test drive it tomorrow or on Tuesday, so I can have a look at that too. I'll post back here when I can do some more testing.

At what point, do you think it would be worthwhile doing a DIY cylinder compression test? At this point, the engine sounds good still, just sipping coolant which isn't good as my daughter is not home with the car enough for me to check on it! Also, I Looked into replacing the gaskets, and with patience, I could do it. I'm somewhat undecided if I want to spend $150+ on new gaskets if the block is leaking externally.

I've never seen a 3800 block leak here. More than likely, its either the water pump gaskets if you see it coming from behind the pump. Now would be a good time to just to the upper plenum gasket, lower intake manifold gasket, the water pump gasket, the coolant elbows and be done with it. And you might as well reach in behind the engine and change out the oil pressure sensor. They are know to start leaking and cause OP concerns.

Thanks Mike. I will post back when I have an update.