Rad Expansion Tank Question

[zippee]

Evening,
Coming back from Cambridge today after a fairly long drive I had a spary of fluid (I think coolant) out of my drivers side bonnet vent, no increase in engine temp etc and it only lasted a few seconds.
On getting home I popped the bonnet but couldn't see any obvious signs of leak etc, so carefully I touched the side of the expansion tank (Serp engine) to find it cold. Thought this was odd after 2 hours driving. I then unscrewed the cap expecting the high pressure spray of hot coolant etc only to get nothing. The coolant level in there is fine but it shouldn't this be in with the coolant flow around the engine and therefore be hot and under pressure, especially after such a long drive?

[chimburt]

may be the cap just venting, but yes, normally i would expect the coolant to be hot in there, after a run.
mmm.
i would try bleeding the system, to make sure everything operates as you expect then, see the level drop when the rad comes in, and that the fans come on and go off in the appropriate way. get a new cap too.
worth checking that all that stuff operates as it should do, then, if it does, with the new cap as well, then i'd just keep an eye on it.
nothing that can't be fixed

[wolosp]

zippee said:

.....shouldn't this be in with the coolant flow around the engine and therefore be hot and under pressure, especially after such a long drive?

Not necessarily, the expansion tank is not actually part of the coolant flow. It is only a 'buffer' for the expanding coolant. So although you'll find that the swirl pot will be very hot, as will all hoses and the rad, the expansion tank may not be.
As long as the level is correct (I keep mine half-full...it seems happy with that level) you should be ok. I believe the handbook states it should be about 2" from the top, but that may explain the venting.
You could bleed the system if you want.

[shpub]

Please don't open any of the cooling system caps when it is under pressure and hot. You are asking to be scolded/blinded or worse.

[zippee]

shpub said:

Please don't open any of the cooling system caps when it is under pressure and hot. You are asking to be scolded/blinded or worse.

I know it was daft, the only reason I opened it was because on touching it was stone cold, despite the fact the rest of the engine was like an oven. Is this normal as I would have expected it to be hot along with the rest of the system?
Point taken though..

[mongoose]

zippee said:

I know it was daft, the only reason I opened it was because on touching it was stone cold, despite the fact the rest of the engine was like an oven. Is this normal as I would have expected it to be hot along with the rest of the system? Point taken though..

i dont think this is normal as it certainly wouldnt happen with any of the three that ive owned.remove the expansion tank,disconnect the rubber hose from the bottom,at which point your coolant shoud drain from it of course,then remove the brass slotted srew cap from the top of the swirl pot.now blow through the end of the rubber pipe to see if theres any blockage.fill swirl pot to top and replace everything.all the above to be done when cold of course

[steve1c]

The expansion tank I can make sense of, but what's the swirl pot do?

[mongoose]

steve1c said:

The expansion tank I can make sense of, but what's the swirl pot do?

its there to de-airate the coolant.