Is250 Coolant Cap And Hoses

[bobbyc]

Good Morning All,

This is maybe a completely stupid question and I apologise in advance if it is, however I would appreciate confirmation.

I was checking the coolant level in the Is250 at the weekend and removed the cap. I noticed that at the top of the cap there are two hoses. One going into the engine (quite straightforward), however there is a thinner one which comes of the cap and does not seem to attach to anywhere. I had a look around the area and did not see anywhere this was meant to attach too. Is this similarly some form of overflow pipe, or does it attach to something and I have just not seen it.

If you could let me know that would be appreciated.

Cheers

Bobby

[johnatg]

The cooling system layout on the IS250 is actually rather unusual. On many cars, there is a pressure cap on the radiator, then a hose takes the expansion (as the engine warms up, and in the reverse direction as it cools) from that to the coolant reservoir and the coolant reservoir itself has an overflow hose.

On the IS250 the pressure cap is on the thermostat housing and the hose from there ('engine' in your post) is an 'overflow' (expansion) from the main cooling system to the reservoir (and it's also the route by which coolant flows back into the engine when it cools). The hose which is not connected is the overflow from the reservoir. (So don't worry!)

There is no pressure cap on the radiator itself. The reservoir is not under pressure even when the engine is hot.

Some cars do have pressurised reservoirs. There is a modern trend to not have a pressure cap on the radiator, but to put it somewhere else - further back. Not having a pressure cap on the radiator allows a lower front bonnet line.

[bobbyc]

Hi Thanks very much for the reply, therefore I should not concern myself with the small hose which does not appear to connect to anything?

I am not very mechinical minded, however I was also rather surprised that the coolant was not under pressure like in other cars.

[johnatg]

The coolant is pressurised in the engine itself (and in the radiator). It's not pressurised in the reservoir.

My wife's Seat Mii does have a pressurised reservoir - maybe that;s a VAG or German thing?

The unconnected hose is fine - meant to be like that!

[bobbyc]

Thanks again for your replies John and you have put my mind at rest.

Bobby

[toffee_pie]

what does this high pressure system warning come from thats on the engine bonnet? i thought this would be for diesels?

[ChumpusRex]

The warning is to do with the high pressure common rail direct injection fuel system. This operates at about 1800 psi, so the spray can cause serious injury, so you need to depressurise the fuel system (unplug the fuel pump fuse and run the engine till it stops) before servicing the injectors or removing a fuel rail.

You'll need to take off the fuel rails if you want to service things like rocker cover gaskets, cams, etc.

Thankfully routine jobs like spark plugs can be accessed without disturbing the fuel system, but you can't get the valve covers off without disassembling the high pressure fuel system.