Thread: Pressure test cooling system

Is there a way to verify/test that there is no leak on the HG causing the cooling system to be pressurised?


I'm having a possible issue on my new build where the radiator resevoir bottle gets a lot of coolant pushed into it whenever I drive the car a bit hard. Now, I know someone's going to say it's normal for the level in the overflow bottle to rise due to water expanding when hot, but I want to be sure thgere is no problem.


Quick history that might be applicable.

• Motor was broken in and coolant NEVER altered from the "max" line on the resevoir.
• Motor was dyno'd and again, coolant level never changed.
• A few hundred miles later I got a big water leak, which turned out to be one of the coolant hoses behind the block that was rupturing where the hose clamp presses it. I fixed that and refilled the coolant system. Did not bleed it extensively, but figured I got rid of most air pockets.
• Took car for a 50mile drive with some hard revs etc. Got home and coolant bottle was about 80% full.
• Bled system completely using the FSM method. This morning did another 30 mile drive but not going over 5k rpm. Coolant level only rose about half and inch.

What makes me uneasy is that the coolant level didnt' fluctuate before. And now it does. I guess it is possible taht the leak at the hose clamp allowed the system to depressurise slowly which caused the coolant never to push up into the resevoir. And the leak then progressed to the point where I noticed the water leak.


I'm yet to see how it reacts under hard driving. What is an acceptable level for the coolant to rise in the resevoir? AND, if it didn't suck back into the system once it cools down, what does that indicate?

You can pressure test the cooling system with a rad cap/cooling system tester. You can also go the the auto parts store and buy a kit with a tube and dye that will test for combustion gasses in the coolant.

No such kit available locally it seems.

Anyways, I'm pretty sure the HG is on it's fcuken way out again. CAr doesn't get hot, but water pushes into overflow but doesn't suck back. Hoses gets rock hard after driving.


Fcuken sick of this build constantly failing on me.

Lisle 75500 combustion leak checker. I used to work at an oreillys and they all have it but it's in the back and no one that works there knows what it is.

I'm having the same issue, I just pray from what you guys are sayin the HG doesn't go because ill be fucked for real

Ok drove her home from work today. About 30 miles. Went extra gentle. Stopped half way to check and overflow was nearly full, and bubbling!! FFS!

Babied her home. Coolant was actually pushed out the overflow by the time I got home. No overheating though but aftermarket temp gauge did show temp was picking up a bit, even though I was driving gently.

Did a compression test. 167, 163,167,160 psi.

No water in cylinders.

All plugs are slight reddish brown.

Think I may have dropped a sleeve.

Refilled the radiator and started her with the cap off. Water just keeps pushing up and bubbling out of the radiator. Guess it's time for a new motor.

mine does this also....but only under boost......i got 90psi in #3 so i KNOW my HG is toast.....you have pretty even compression so i wonder if yours is a bubble in the coolant......it only has to make a little hot spot to make it push coolant into the overflow.....i've never had luck using the fsm method to bleed the coolant system.....i park on a steep hill...front end up....while engine is cold start the car.....open the bleeder on the the thermostat housing.....turn car off....air will push out the bleeder....close once water comes out......repeat untill no air comes out....hope you figure it out soon

my build is n/a. But my low lobe cams are massive, so the compression numbers are a tad low and to be expected. But at least fairly equal.

yeah, headgasket problem for sure. If you actually had the ability to pressurize the system you would probably see coolant pour into the cylinders. Time to take it apart and check. Could just be a headgasket issue/head lifting issue or could be something else.