When should rad cap release pressure?

Angus · Post by **Angus** » Sun Apr 14, 2013 7:02 pm

OK, new cap (rated 1.2 bar, from Import Car Parts - note Honda have it on back order not due til the start of May) and 78 degree stat installed, system bled.

Certainly not overheating now (nice thorough spanking this afternoon, prompted by nerk in Astra VXR who, as usual, couldn't go round corners). Coolant pipes get as hard as ... erm ... well, um, they get pretty stiff. Pressure goes down after being parked up for 10 minutes or so, so I'm not overly concerned. No hissing, steam or evident coolant stains anywhere.

However, I've used a couple of cm of coolant from the overflow tank. This bit confuses me, cos I still can't fathom where it's going. Surely it can't be evaporating at that rate (approx 60 miles, 15 or so of which were exuberant). Not doubting you, wurly, but it seems strange.

Post by **vanzep** » Sun Apr 14, 2013 10:07 pm

it should all settle down - you may need to rebleed it at some point - just keep an eye on it

89 UKDM BA4 4WS (resto job!) · Post by **wurlycorner** » Mon Apr 15, 2013 1:58 pm

Angus wrote: However, I've used a couple of cm of coolant from the overflow tank. This bit confuses me, cos I still can't fathom where it's going. Surely it can't be evaporating at that rate (approx 60 miles, 15 or so of which were exuberant). Not doubting you, wurly, but it seems strange.

No, I agree - it wouldn't evaporate that quickly.

As vanzep says, just keep monitoring it over the next few days/week or so to see if it settles down.
I'd suggest don't top the expansion tank up each time, so you can see if it finds a 'level' or if it does keeps using it down to the min/bottom (check/top up the rad level each time though to make sure that isn't running low, obviously).

Have you checked all round the expansion tank and rad etc to see there are no splits in it, or in the hose that runs from the tank to the top of the rad?