I just got an 02 Monte 3.4L. It's got 85k miles and the lower intake manifold gasket was replaced at around 40k-50k.

I flushed the coolant, put on new hoses, new Stant Superstat 195* thermostat, and new Stant radiator cap. While flushing the system, I noticed I could take the radiator cap off while the car was at operating temp and there was no pressure. Also, I could remove the radiator cap on a cold engine. And let the engine get up to temp and no coolant gushes out. On other GM cars I've had, coolant would gush out if you try and remove the radiator cap while at operating temp.

I believe I've bled it pretty good as I've opened and closed the bleeders at least 10 different times.

The car doesn't overheat as the coolant gauge needle stays right in the middle. The heater gets real hot. And both upper and lower radiator hoses get real hot.

I got a coolant pressure tester to make sure the radiator cap was good. I then put the pressure tester on the radiator neck and ran the engine. I noticed on the gauge it build pressure. And I ended up having to shut the engine off as the pressure went to 20 lbs.

I don't know why it overpressurized with the pressure tester on it. As if it was building up too much pressure, I think coolant would be gushing out with the radiator cap off and the engine running to operating temp.

I also did a coolant block leak test with the blue dye to check for head gasket leak. And that passed as the dye stayed blue.

 

As far as I know your suppose to pump the pressure up with the tester while the engines off, maybe that'll change the reading?

 

You're supposed to be able to put a pressure tester on the radiator and run the car to see what pressure the car runs at. But for some reason mine started over pressurizing. Which doesn't make sense as it runs like it is underpressurized. And I can let it idle from cold to hot with the radiator cap off, and no coolant will gush out the radiator like what happens on my other older GM cars. Though it doesn't overheat, and it passed the block leak check.

 

Ive never had this happen but I would check the hoses running to the overflow they could be plugging up?

 

It doesn't have anything to do with that. If you remove the radiator cap, start the car with it cold and let it warm up. Eventually coolant should start gushing out, but that doesn't happen on my Monte. But has happened on every other car I've had. If it is at operating temp, I shouldn't be able to remove the radiator cap without coolant gushing out. But I can remove the radiator cap at anytime with no problem.

Though, at least it doesn't overheat and it passed the block leak check. I'll just keep an eye on the coolant level to make sure it isn't droping.

 

If the car is not overheating why worry?? just keep an eye on the coolant level

 

come to think of it.... Sounds like the water pumps gonna take a crap. Wich to me would make sense why its not gushing out at operating temp.

 

Reason why I was looking into it is because it's not supposed to do that. Plus a shop recently said they think either the LIM is leaking, or the prior shop who replaced the LIM gasket years ago didn't clean up the old mess. I cleaned up a sludge mess at the front of the engine inbetween the heads behind the power steering pump. So, I'll keep an eye there to see if something is leaking. It might have been from the power steering reservoir.

I did think it could be the water pump, but hard to imagine it being the water pump unless the fins rusted off reducing flow. Though I just changed the coolant. So, I'll probably change the pump next summer unless I have problems. But I guess the main thing is it doesn't overheat and doesn't lose coolant.

Nice thing is the pumps are cheap and look easy to replace compared to other cars.

 

I have an '03 w/3800 but I think the radiators are the same. I checked my coolant level over the weekend and with the engine at operating temp with the radiator cap removed I didn't get any flow out the filler neck either. However, I could see the coolant flowing about an inch below the filler neck using a flashlight. I think this is normal for these cars due to the design of the cooling system. With the radiator cap removed it won't build pressure, but coolant will flow once the thermostat opens. Since the system did build pressure with the tester it is safe to say that it is also building pressure with the radiator cap installed. The reason it went to 20lbs with the tester is because it doesn't have an automatic relief valve (or at least the ones I've used don't) like a radiator cap. The pressure would continue to build until you shut the engine off or open the manual relief valve. With the radiator cap installed if the pressure becomes greater than 15lbs it will overcome the spring pressure and allow coolant/pressure to flow into the overflow tank. From what you've posted I'd say your system is operating normal, but as others mentioned keep an eye on the coolant level for a few days to make sure all air has been bled from the system and top it off if needed.

 

Okay thanks. Just thought it was strange it didn't build up pressure as my other older GM cars would build pressure and the upper hose would get real hard compared to the Monte.

But if it's normal, then I won't mess with it other than watching the temps and keeping an eye on the coolant level.

The air should be out of the system since there are 2 bleeders. None of my other cars had bleeders on them. But I might could try idling it with it jacked up as that helps any air get to the radiator then out the radiator neck.