I am having a problem with the coolant building excessive pressure and while driving and giving moderate throttle it blows coolant past the cap. I am having no antifreeze in the oil and do not have any burning out of the exhaust. I am fearing that I have a head gasket that is allowing compression by but not allowing coolant into the emgine. I an not sure if it matters to anyone but the cr is 12.2:1. The engine just got completely rebuilt and the heads went on fine torqued in sequence and all. I guess my question is is it possible I am overlooking anything could a thermostat cause excessive pressure like that. I have bled the cooling system time and time again and then obviously when it pukes then I have to start all over. I have not done the head gasket chemical test yet I am just seeing if anyone has run into this. I have also read in some cases people re torque the heads but that wont be the easiest to do but still easier than pulling it all the way.
Thanks in advance
Bryan

 

Bad cap?

 

Before you suspect anything else, make sure you have not swapped the steam pipe and remote reservoir hoses on the radiator. They are right next to each other. Do the exhaust gas test next.

 

I had a brand new cap on it and then got another one to rule that out. The resivior hose connects right there at the cap correct. I will go double check that but I am pretty sure its correct. The thing I dont understand is they are a 18 lb cap which means if it hits 19 lbs it should push the seal and then into the resivoir but in this case i dont even think its going to the resivior its blowing right out of the top seal

 

Sure sounds like you have the hoses for the overflow and the steam pipe reversed.

 

Is the reservoir grossly overflowing? If those hoses are reversed, I've seen it fill that thing slam up.

Are you sure there is no small crack in the neck of the radiator? Is the cap new(a GM one)?

 

What the level on your overflow tank when the engine is cold? Could it be that there is too much fluid in the overflow tank and no room for the coolant to go when the engine is hot.

 

I have made sure it is not the steam pipe that is going to the outlet on the neck of the radiator. I still have not done the chemical test...it does not go out the overflow it blows right out of the cap. It is not a gm cap I bought both the caps I tried from o rileys. The cooling system will build pressure cold or warm and when I get on it all the coolant makes it past the top seal on the radiator, I dont even think its making it to the resivoir. I will try to mess with it a little bit tomorrow maybe I will see if the dealer is open and get a gm cap. I will probably do the chemical test. I am dreading the thought of gasket issue but it still doesnt make sense that the gasket is failing to where compression is making it through but coolant is not. Thanks for all suggestions
Bryan

 

Did you check the hose/pipe from the radiator neck to the reservoir for a kink or blockage?

 

Do you have a pressure tester? If you don't you can probably rent one from a parts store. You can test the caps with that instead of buying a bunch of new ones. I would also pressure test the cooling system. If there is a loose hose or cracked radiator it can be sucking in air.

 

To that point, you can attach the pressure tester to the radiator and fire the engine. If the engine is pressurizing the cooling system, you should be able to see the needle pulse or the pressure spike really high.

Be careful though....it really bothers me that the pressure is getting high enough to blow out the cap without first going to the overflow tank.

To Injuneer's point....are you sure there is no overflow blockage of some type?

Is there any way to video what is happening to it? At the very least, can you take some pictures of the engine and post them?

 

Ahh yes, I was going to say that too, just be careful doing it like ACE said.

 

I have a pressure tester at work I will run by and grab it and see what kind of pressure the system is seeing. I havent had too much time to mess with it lately but I have some time today. I will probably grab the chemical test also. I will check the resivior hose for kink or blockage. If I can I will take some pictures maybe a video if I can find my camera. Thanks for all your guys help I will have a update later today. Thanks
Bryan

 

Are u bleeding the system by just taking off the radiator cap or are u using the bleeder valve?

 

I had a little time to mess with it. It is building pressure with rpm. I have a video I will see it if works for you all to see. Now I never get to see it puke while I am standing there it is when I am driving and get on it then low coolant light comes on I get out and see it all around the cap. I tried to show the locations of the hoses and that there was no white smoke out of exhaust. Hope its good enought video. Thanks
Bryan