expansion cap orientation-important!

[Paul Woods]

thought id throw a sticky in here regarding this as it seems to be cropping up a bit.When i completed my 1.5 years ago i fitted the expansion cap wrongly,i didnt even know it had a right and a wrong way! after all its just a cap right?

Well its plumbing is vital to how the cooling system works,it has two pipes going to it,one is the feed from the pressure cap and the other is the overflow pipe.The Overflow pipe is nothing more than a hole in the underside of the cap,so if the bottle gets full it exits the hole and out,simple.Now the feed from the pressure cap goes into the expansion cap and feeds into the tube that hangs in the coolant in the bottle....this is important.When you shut the engine off the pressure rises in the cooling system and the pressure cap opens up.This allows coolant to flow to the expansion cap,down the tube and into the bottle,then when the engine starts to cool it creates a vacuum in the cooling system that pulls the coolant back out of the bottle and into the engine....its a bit like the tides as it ebbs and flows to and from the bottle.

Now its very easy to fit the cap 180* out so that the overflow side is connected to the pressure cap and vice versa.What this means is that on shutdown the coolant still reaches the bottle,it runs into it via the overflow hole,but on cooldown the coolant has no way of returning to the engine and air gets sucked back in....so everytime you switch off coolant gets pumped out and air drawn back in,doesnt take long for overheating and head gasket like symptoms occur.

So its orientation is very important,i made the mistake all those years ago,and im seeing others do the same now,its a little detail that goes unnoticed.

In general the lift tab on the cap points at 6 o'clock,the overflow points to 3 o'clock and the pressure cap feed at 9 o'clock.If you look at a mk1 expansion bottle the lift tab on the cap points rearwards with the pipes in the above orientation.Ive yet to see a toyota cap that has the pipes the other way around so hopefully this sticky will save a few anxious moments!

[mart1975]

thanks paul, doh!

[colingo]

Any ideas as to where i can get a new one, as mine is cracked and looking abit fragile. at a push ill have to try toyota, any guesses to the price. cheers colin

[randomfactor]

Proper useful info Paul. EVen though I've got a sore head after the game.
Colingo, I noticed that Toyota use the same filler cap on many cars, instead of paying 15 quid on ebay fo r a mk1 cap, I paid one quid frmo a scrappy

Happy hangovers!:shades:

[colingo]

Nice one thanks

[mart1975]

got mine from a celica