Thread: Losing water through the resrvoir

Bad cap and/or bad reservoir ... I needed to replace both to get the cooling system to hold pressure

Steve

Vernon

Maybe try swapping the cap and or tank from your spare p38?

Gary

Originally Posted by TheTree

Bad cap and/or bad reservoir ... I needed to replace both to get the cooling system to hold pressure

Steve

Got to agree this is a high probability
My new car had been fitted with a new water pump, rad, expansion tank and cap before I rescued it. I could not get the cooling system right, I changed the thermostat and another new after-market cap. The car would behave perfectly but once out on a run after an hour or so it would boil over although the temp gauge never moved above normal. My low coolant sensor went off instantly so no dramas. After pressure testing over a full weekend all good. I then stumbled on the fact that the system was not holding pressure, coolant boils at a lower temp when not pressurised. New genuine cap and Tank fitted and now as it should be. System pressurises quite quickly and holds pressure for many hours after the car has stopped. I am now happy with it.

Can you see coolant on the bodywork under the reservoir?

I extended the overflow pipe from the expansion tank and fed it into a small (250ml) plastic drink bottle which just sits on the ledge below the expansion tank. If there's any coolant in the bottle after a drive, then there's an issue with the system...
* the tank might be too full
* problem with the cap

The section of the cap which protrudes into the tank should have two O-rings a few mm apart. I recently discovered the bottom section of the cap had neatly broken off and was wondering why I could smell coolant, but nothing was obvious... until I properly examined the cap...

There was a tendency for the expansion tank to split around the welded seam where the top and bottom halves join... not a lot you can do about this except buy a new tank.

If the tank is over pressurising... you may have a small head gasket leak which is getting into the water jacket but not necessarily into the oil gallery.

To check this: fill the coolant tank to 3/4 full, leave the cap off, get the engine on a fast idle up to operating temp then slowly top up the tank to about 10mm below the opening and look for tell-tale bubbles. With the engine at normal idle rev it a couple of times to around 1800 rpm...the coolant level will drop and then rise when the idle slows...watch for a continuous stream of bubbles at this point...

As has been said. I found a genuine cap is a must...no elcheapos!

At the moment on mine if I lift the bonnet when I get home, I can hear the air leaking out around the cap

Waiting for a new tank to arrive

Steve

Have a look at my previous thread here: http://www.aulro.com/afvb/p38a-range...eck-yours.html
If you look at the photo on the first post, this is what I found on mine, comparing a new cap to an old damaged one.
Cheers, Pete.

I agree with all those who said get a genuine cap.I bought a new cap from a landy dealer on ebay and had the same problem with water disappearing. To the point of an air lock and overheating. I would refill and problem would go away for a week or more then again. Took the cap to MR Automotive in Redcliffe and they tested the cap...would not hold any pressure at all....needless to say, new cap all the way. Then I found leaking o-rings at heater, just replaced them, should be good now.I hope....