rad cap

JimMet · Post by **JimMet** » Sat Mar 10, 2007 6:37 pm

I have a hilux with a 3.5 rv8 in. Once it heats up the rad pipes seem to be under a lot of pressure, to the extent that recently one of them split open. The radiator is from a shogun which has it's original cap that says 0.9 on the top of it. I'm guessing this means 0.9 bar (13 psi)??? Is it possible that the cap i have is unsuitable and thats what caused the split???

mikeinatruck · Post by **mikeinatruck** » Sat Mar 10, 2007 11:57 pm

Thats about the normal operating pressure for most vehicles, have you changed the cap? it might have jammed. but that aside are you sure you dont have any other problems?

has it been ok before? does the cap vent to anything? I think the shogun usually vents to a bottle depending on what engine it came from.

JimMet · Post by **JimMet** » Sun Mar 11, 2007 1:37 pm

I've recently done the head gasket so i don't think it's that. What else could be causing this pressure?? I checked and the cap isn't jammed.

The cap doesn't have a vent, the side of the part that recieves the cap has the vent, although it doesnt have a bottle or anything. Which shouldn't matter.

Is it usual for the pipes to get under a fair bit of pressure??

ian.stewart · Post by **ian.stewart** » Sun Mar 11, 2007 3:37 pm

Could be worth getting a Water/Co2 check carried out

JSF55 · Post by **JSF55** » Sun Mar 11, 2007 8:30 pm

Has the thermostat got a hole drilled in it to help remove air from the system, or one with a jiggle pin fitted? the other thing u can try doing is starting it up from cold with the rad cap off and see if it gives a big burp ! it could just be an airlock?

Post by **katanaman** » Sun Mar 11, 2007 9:05 pm

I would say if the cap is working properly then it doesn't matter if there is a problem or not, the cap should blow before anything else happens. Because of that I would say your hose splitting was a bad hose. Get your cap tested or just replace it then you know your system can't go past the set pressure its safe at. If the cap then blows then you can start worrying about something else being wrong.

sidecar · Post by **sidecar** » Sun Mar 11, 2007 10:40 pm

JimMet wrote:I've recently done the head gasket so i don't think it's that. What else could be causing this pressure?? I checked and the cap isn't jammed.

The cap doesn't have a vent, the side of the part that recieves the cap has the vent, although it doesnt have a bottle or anything. Which shouldn't matter.

Is it usual for the pipes to get under a fair bit of pressure??

If the cap is fitted to an expansion tank then you can get away without having a tube fitted to the vent at the side of the filler neck.

The tank should be about half full when the system is cold. As the water in the system heats up it will expand and fill the expansion tank, the air in the tank will be vented out passed the cap once the blow off presure is reached.

If you have slightly overfilled the tank the excess water will be lost out the system...this is OK.

If the cap is fitted to the radiator then you need a tube from the filler neck that goes in another tank via the bottom of this extra tank. The top of this tank should have a cap that has no blow off system fitted and the neck of this tank should have side pipe that is open to the atmosphere (The cap just stops the water spilling all over the place). If you dont have this tank you will lose water everytime the engine heats up. (As the system cools the small flap valve in the centre of the rad cap will open and let the displaced water back in to rad. (Or air back into the expansion tank).

Check that nobody has done something daft like blocking the vent in the filler neck with epoxy!

The coolant tubes should not be under anymore pressure than the rad cap blow off pressure. (Although I did read somewhere that the pressure in the head could be as much as 30 psi due to the pump forcing the coolant into the head and the outlet being restricted...I don't know which pipes will be at this much pressure. In any case you could probably put 100 psi into a pipe before it blows so I recon the yours must have been damaged or the system is not "wired" up correctly.

(If it spilt near where its pushed over a metal union or near where a jublie clip clamps on it then it was possibly just knackered!).

Regards,

Pete

JimMet · Post by **JimMet** » Mon Mar 12, 2007 7:21 pm

The split was quite near to one of the clips, so maybe it's just the hoses that are knackered. From what i remember the thermostat has a hole in it. I'll try starting it without the cap on and see if it 'burps'. cheers