My 1996 Monte Carlo with 3.1 engine is leaking coolant onto the ground. I replaced the intake gaskets FEB 2012. Checked intake mounting to block and no leakage. Radiator is not leaking, heater hoses checked, both engine to radiator hoses not source of of leak. Water pump is not the source.

The leak is coming from the passenger side to the ground and only evidence of coolant is suspended drops on the oval bottom of what I believe is a automatic transmission bottom. Drops were also on the tubes in this area.

I did a test run not driving the car running the engine well past normal heat up range after topping of the radiator and filling the coolant recovery plastic tank to the cold level.

The test run was long enough for the engine to send coolant from the radiator to the hot level on the coolant recovery tank.

No leakage during and after the test run could be found anywhere around the engine and no leakage on the ground.

Inspecting from actually be under the engine could not find any source of a leak from the engine.

Took a test drive last night and upon return home used bright light to search for any leakage. Could not find any leakage.

If the leak does not come from the above checked sources, where could it be coming from?

Checked the heater core drain connection, pulled off the dry rubber thing that was dry and nothing in the tube it connects to.

 

Get a radiator pressure tester (free loan a tool at most parts stores), bump the pressure up some and look/listen for a leak. That's the best way to go at it.

On the engine part, there is not much on the passenger side to leak. You have:
- Radiator
- Radiator hose
- Water pump
- LIM Gaskets

Water pump can be tricky to spot. Check the hood insulation. If it's wet in a line that follows the belt, chances are high, it's the pump (it leaks water on the belt and flings it in a line that matches the belt on the hood liner).

I'm not sure if that generation has a condensation drain on the passenger side of the firewall (my 2004 does). If it does, and coolant is coming out of that condensation drain, it's a heater core.

 

I would highly recommend going to your local auto parts and get a pressure tester for your cooling system that should tell/show you where the leak is comeing from...

I suspect..Its the coolant elbows... Our Montes are notorious for having them chemically break down and be the source of the leak...besides the UIM and LIM...

 

I did a run test with the radiator full, ran the Monte long enough to see pressured coolant leave the radiator and fill the coolant recovery tank to the HOT level. Later after cool down the coolant from the recovery tank was pulled back into the radiator.
The coolant has to get hot and build up enough pressure push up the radiator cap seal to pass coolant into recovery tank.
My heater core drain is about in the middle of the firewall. The rubber fixture on the drain was dry and I removed it to look at the tube it is connected to and it was dry.
Does a 1996 3.1 have the elbows that have been mentioned? I alone did all the labor/work in removing/installing the UIM/LIM in 2012 and do not know of any elbows.
My intake was leaking coolant into the oil in 2012. First thing I checked was to confirm no coolant was in my oil.
There is no evidence of coolant on the water pump, serpentine belt, or the hood insulation.
I have inspected the engine every where I could with good lighting, even last night after a short drive to see if it would leak. No leak found.

 

Run test is useless unless the leak is just POURING coolant out. AND the engine is WAY too hot to touch things and get a good look.

Get the radiator pressure tester. It's also good because a hot car cooling makes some sound, hard to find a "hiss". The pressure tester allows you to listen not just look and feel.

3100 and 3400 engines don't have coolant elbows. That's not a factor in this case.

 

i recently had a crack on the plastic side part of the radiator check the low side of the rad for a crack

 

No problem with my radiator, there has never been any evidence of any leakage from the radiator or the hoses connecting to the radiator. The frame at the bottom of the radiator has never shown any coolant. Only evidence of any coolant was posted above at the bottom end of the engine assembly on the passenger side and the evidence was just drops of coolant that had not fell to the driveway.

 

Good chance it could be a water pump, as there is not much on the passenger side of the engine. Get the radiator pressure tester, it will help a lot with finding what's going on.

If it is the pump, that is a pretty easy change out.

 

The water pump is very easy to inspect on my 3.1 1996 Monte. The water pump is easy to inspect for leakage since it is mounted high on the engine and I can see so much of it and have completely ruled it out as a leaking. Wish it was the leak source, extremely easy water pump to change since nothing is in the way.
Do not know about later model Monte Carlo's but my 1996 Monte and my 1996 Corvette's owner manuals specify with a coolant change to use GM Engine Coolant (sealer) (GM Part No, 3634621) with any complete coolant change.

How many owners do this? I have always done what the my owners manuals specify with the complete coolant change in adding the specified engine coolant sealer.

Drove my Monte to work yesterday and after returning home waited until the engine had time to cool and the coolant level in the recovery tank was just below the "Cold Level" line which indicated a very small amount of coolant loss. I made sure it was at the "Cold Line" before I drove to work.

I looked under the front of the Monte and could see droplets of coolant still attached in the previous posted location. No leakage was seen on the driveway. I will drive it again today after refilling the coolant in the recovery tank back the cold line.

Evidently no Monte Carlo Forum poster who has read my posts has ever encountered a leak of coolant like the one mine has.

 

I'm going to say this again: GET THE PRESSURER TESTER!
This will allow you to look and LISTEN for your leak. Plus, it will report back a pressure drop.
Typically you can find a coolant leak quickly and safely with this tool. Most auto part stores will rent it free of charger (under there loan-a-tool program).

The only other leak source I can think of on the passenger side of the engine is the timing chain cover (this is not a super common spot to leak, but it has happened to some of these engines). And that is a difficult one to eye ball.

There are not many common things to leak on that side of the motor. Pump, hose, radiator are you most frequent items.