High Pressure Radiator Caps - Opinions?

[oldcorollas]

have a close look at your radiator cap

one part is the pressure valve.. the other part is a vacuum valve (sealed by pressure, but open under vacuum...)

[mrshin]

The return valve is the little bit in the middle of the underside of the cap - you can easily pull it back with your fingernail.

[TA-022]

hrrrr u got the 2ov bottle in there -GT- ?

size diff between 16v and 20v perhaps???

[Enchanter]

im kinda confused about how the cap works, i get the part where it builds pressure, compresses the spring, and opens the seal and sends the water to the overflow, however, im not really sure on how it sucks it back in, surely after its sealed, the vaccuum locks the cap more tightly...?

can someone please explain this to me, if you dont mind..?

Eldar.O.

Same here...

one part is the pressure valve.. the other part is a vacuum valve (sealed by pressure, but open under vacuum...)

So there are two valves in the cap then ?
Cool, Ive learnt something today then. rep for you

[oldcorollas]

[EldarO]

Pressure build up, the cap opens, the liquid pours into overflow.
Pressure lowers, the liquid is sucked back in, the cap closes

So, the liquid gets hot, expands, opens the cap, flows into the overflow, and the cap stays open until the fluid cools down and gets sucked back in, all the while the cap is open...? thats what it sounds like...?

Thanks oldcorollas!

Eldar.O.

[CrUZida]

Nah, I had my understanding mixed up.

The cap closes pretty soon after venting some fluid, and fluid is sucked back in via the 'syphon back seal' in that pretty pic OldCorolla's posted.

[EldarO]

Coolies, all sorted then my curiousity is solvered

Eldar.O.

[oldcorollas]

the cap only opens when the liquid forces it's way out against the spring pressure, so the cap doesn't open as such.. it just leaks at a set pressure. in the pic,m that whole thing attached to the pressure relief seal (the metal behind it also) is pushed against the spring that you should be familiar with.

for cooling down, there is not much restriction at all, since the rubber bit just allows the liquid to be drawn back, with little resistance (ie no spring.) that little centre bit does have a weak spring pulling it up, but only enough to seat it when there is no pressure differential. on suction it is easily pulled down...

[-GT-]

So, if my pressure relief seal is deteriorated it would be venting pressure lower than its designed to, but maybe higher than it gets in normal driving, so its only done it on a hot track day?

There was no water left in the overflow, so it wasn't that there was air (/gas) in the radiator and the overflow was full, and my coolant still looks fine, so i'm not too worried BHG-wise, but i'll still get it tested when i replace the fluid.

[RobertoX]

It could be that you had air pockets in the system (heater maybe) which when released caused more coolant than was in the system already to be sucked back in thus emptying the overflow and sucking in a bit of air. When I change coolant I usually park on an incline and let the engine run with the cap off until the thermostat is open. Not too sure if this is what you are supposed to do but I do anyway.

[oldcorollas]

So, if my pressure relief seal is deteriorated it would be venting pressure lower than its designed to, but maybe higher than it gets in normal driving, so its only done it on a hot track day?

There was no water left in the overflow, so it wasn't that there was air (/gas) in the radiator and the overflow was full, and my coolant still looks fine, so i'm not too worried BHG-wise, but i'll still get it tested when i replace the fluid.

hmm.... when you stopped (before it cooled down) was there water in the overflow? surely it couldn't suck back an entire botle of fluid? in that case maybe a larger volume bottle will solve your probs?

[gianttomato]

I suspect you don't have a recovery style radiator cap on your car at all.

[Starfire]

Another point that was raised but not addressed was the lower temp thermostat. By lowering the temp a bit (about 10 degrees) you get a slight increase in power. The reason that the factory has a higher temperature is that while you drop a bit of power you gain fuel economy.

Most people are more concerned by economy than power.

[n0rto]

the only reason you would put a high pressure cap on your car is if you where boiling it while you we where giving it a hard time on the track. if your gauge dosen't go past bout 107'c or the big H at the top of the factory gauge you shouldn't be boiling it(rule of thumb 2psi = 1degree higher boilng point).You would know if boiled water pisses out everywhere.
so if dosen't get hot just wack the standard 90kpa on there.
And the hotter you run your cooling system the more efficient your engine is due to less heat is lost to the cooling system so the air in the cylinder expands more better fuel efficientcy equals more power that why a late model car runs a 92'c thermostate and instead of an 82'c.