Can a Bad Radiator Cap make you lose Coolant? - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

Propaganda · 11-26-2008, 06:59 PM

I've searched around and have been getting mixed answers about whether or not a faulty radiator cap can make you lose coolant.

I don't overheat when driving and it doesn't seem to be a head gasket because there's no white smoke, no bubbles coming out of my radiator, and doesn't seem to have coolant in oil or vice-versa. That and I changed out my head gasket for an OEM SR20DET one. I'm doing a combustion leak test tomorrow to be sure anyways to be sure.

IIRC, the stock radiator cap is 0.9 bar (~13.1 psi), but when I pressure tested the one on my car it came up to be about 0.76 bar (11 psi) and settled down at 0.55 bar (8psi).

I bought a new Z32 radiator cap rated at 1.1 bar (16 psi), but it reads 15 psi strong, and am going to test it out tomorrow.

Also, I can't pressure test my cooling system because the pressure tester I got from AutoZone is too big for the neck.. what should I do?

Bigsyke · 11-26-2008, 07:42 PM

It depends if its leaking. If its allowing coolant to flow into the resivour then no. The pressure will just suck it back into the radiator.

However if you ever pull the cap off the radiator, and coolant is low, then you have a leak somewhere in the system, which could be the radiator kneck itself.

The pressure is supposed to be vented into the reserve tank.

Does the cap hold pressure? or does it slowly decrease to 0.

If your system is bled, check the fluid level of the radiator 15 minutes after shutdown a few times (5 cycles) and if the level of the fluid remains the same (full) then the cap is working and you have no leaks.

georgesal · 11-26-2008, 07:49 PM

yes it cause you to lose coolant. one way you can see it drip out or the other way is it ill steam ouyt over time. the job of a rad cap is to hold pressure in thus raising the boiling point of water(coolant) but if there is no pressure or low pressure the water boils at a lower temp

*ManoNegra* · 11-26-2008, 08:44 PM

yes, replace it if you think it's going bad.

wow-thats-a-cool-car · 11-26-2008, 08:59 PM

Yes the same thing happened to me. Once the car gets hot the water will turn to steam and escape from the leaking radiator cap.

Bigsyke · 11-26-2008, 09:02 PM

pure water boils @ 212 degrees farenheit.

Add antifreeze i dont think he is going to worry about steam, unless he is over heating.

At 213*f the OEM fan kicks on high.

He wont loose coolant from the cap, it will just force it back into the reserve tank.

Try running a 0.0 bar greddy dummy cap, you wont loose a thing, in fact its good for bleeding the system.

11-26-2008, 06:59 PM	#1
Propaganda Zilvia Junkie Join Date: May 2005 Location: Charleston, SC Age: 37 Posts: 451 Trader Rating: (10) Feedback Score: 10 reviews	Can a Bad Radiator Cap make you lose Coolant? I've searched around and have been getting mixed answers about whether or not a faulty radiator cap can make you lose coolant. I don't overheat when driving and it doesn't seem to be a head gasket because there's no white smoke, no bubbles coming out of my radiator, and doesn't seem to have coolant in oil or vice-versa. That and I changed out my head gasket for an OEM SR20DET one. I'm doing a combustion leak test tomorrow to be sure anyways to be sure. IIRC, the stock radiator cap is 0.9 bar (~13.1 psi), but when I pressure tested the one on my car it came up to be about 0.76 bar (11 psi) and settled down at 0.55 bar (8psi). I bought a new Z32 radiator cap rated at 1.1 bar (16 psi), but it reads 15 psi strong, and am going to test it out tomorrow. Also, I can't pressure test my cooling system because the pressure tester I got from AutoZone is too big for the neck.. what should I do?

11-26-2008, 08:59 PM	#5
wow-thats-a-cool-car Post Whore! Join Date: Mar 2008 Location: California Posts: 2,663 Trader Rating: (6) Feedback Score: 6 reviews	Yes the same thing happened to me. Once the car gets hot the water will turn to steam and escape from the leaking radiator cap. __________________

11-26-2008, 07:42 PM	#2
Bigsyke Zilvia FREAK! Join Date: Jun 2008 Location: NA Age: 39 Posts: 1,342 Trader Rating: (0) Feedback Score: 0 reviews	It depends if its leaking. If its allowing coolant to flow into the resivour then no. The pressure will just suck it back into the radiator. However if you ever pull the cap off the radiator, and coolant is low, then you have a leak somewhere in the system, which could be the radiator kneck itself. The pressure is supposed to be vented into the reserve tank. Does the cap hold pressure? or does it slowly decrease to 0. If your system is bled, check the fluid level of the radiator 15 minutes after shutdown a few times (5 cycles) and if the level of the fluid remains the same (full) then the cap is working and you have no leaks.

11-26-2008, 07:49 PM	#3
georgesal BANNED Join Date: Oct 2006 Location: Los Angeles Age: 39 Posts: 842 Trader Rating: (2) Feedback Score: 2 reviews	yes it cause you to lose coolant. one way you can see it drip out or the other way is it ill steam ouyt over time. the job of a rad cap is to hold pressure in thus raising the boiling point of water(coolant) but if there is no pressure or low pressure the water boils at a lower temp

11-26-2008, 08:44 PM	#4
ManoNegra Guild of Skullduggerous Intent Join Date: Jan 2004 Location: Socal Posts: 7,841 Trader Rating: (48) Feedback Score: 48 reviews	yes, replace it if you think it's going bad.

11-26-2008, 09:02 PM	#6
Bigsyke Zilvia FREAK! Join Date: Jun 2008 Location: NA Age: 39 Posts: 1,342 Trader Rating: (0) Feedback Score: 0 reviews	pure water boils @ 212 degrees farenheit. Add antifreeze i dont think he is going to worry about steam, unless he is over heating. At 213*f the OEM fan kicks on high. He wont loose coolant from the cap, it will just force it back into the reserve tank. Try running a 0.0 bar greddy dummy cap, you wont loose a thing, in fact its good for bleeding the system.