WATER LOSS

[Deleted]

Whenever I go out I find that I lose about a half litre of water.
I have thoroughly checked many times to see if I had a leak anywhere but I haven't. I therefore assumed that it's pushing it out of the rad cap.
New cap fitted at the correct 15psi. - Same problem.
I then fitted an overflow bowl connected to the overflow pipe of the rad
as is fitted to later model V8's. This time I assume the water went in to the overflow bowl, but the rad level was still down.
My question is ? How does the water get back in to the rad from the overflow bowl ? How does an overflow bowl work ?
Your assistance or ideas will be appreciated.
regards, Mike

[Phil Nottingham]

There is a valve in the cap to allow air back in thus preventing a vacuum.

Water loss with no leaks suggests cylinder head gasket starting to fail OR the manifold vent pipe to top of the rad is blocked. This pipe should get hot after a few mins running. The very small bore tube in the inlet manifold blocks up very easily and causes airlocks which give some of the symptoms of head gasket failure so its always best to check this first. A very small drill bit is needed hand held

[Deleted]

Thanks Phil, but I still don't understand ? How does the water that's gone in to the overflow bowl get back in to the rad ? Or doesn't it ?
regards,
Mike

[Phil Nottingham]

If the coolant is in the pipe and the pipe end is in the coolant, it will be drawn (siphoned) back into the rad by the vacuum in the rad via the air valve. If the cap is removed or the end of the tube is not in the coolant it will not work

[Deleted]

That's it ! Thanks Phil. I found the return valve you told me about, and I confess to never having noticed it before. I filled the overflow bottle to the correct level and then did a 10 mile run during which the temp gauge sat nicely in the green. Normally, once the engine had cooled down, I would have to top up. This time - perfect ! Never lost a drop. So obviously the water bottle works. I wonder why these overflow bottles were never fitted on P5's ? I understand that they were on the P6 V8's, and on the Range Rover's etc., and on virtually every other car, including my Stag. A headgasket problem is the worst case scenario, so I'm hopeful the matter's now resolved.
Thanks, Mike

[Phil Nottingham]

The reason why they were not fitted is that they should not be necessary normally - are you overfilling?

The level should be just below the top of the oil cooler

[harvey]

Overflow (expansion) tanks were never fitted as standard to any of the P6 range although a lot of owners do fit them. The cooling system should not be filled right to the top because the coolant will expand as it gets hot and without some air to compress it will just blow out under the cap.

[Deleted]

I HAVE AN EXPANSION TANK FITTED TO MY P5B AND IT WORKS BEAUTIFULLY.

SORRY ABOUT THE CAPITALS

[theroveringmember]

philnottingham said:

There is a valve in the cap to allow air back in thus preventing a vacuum.

Water loss with no leaks suggests cylinder head gasket starting to fail OR the manifold vent pipe to top of the rad is blocked. This pipe should get hot after a few mins running. The very small bore tube in the inlet manifold blocks up very easily and causes airlocks which give some of the symptoms of head gasket failure so its always best to check this first. A very small drill bit is needed hand held

Saw this earlier on so decided to check mine as a matter of course. It was blocked so that's some good advice there & easy to check & rectify. It was cleared quite easily with the drill but I couldn't blow through it at all so the debris was effective at preventing water flow.

[lagain]

I fitted an expansion tank to my P5 many years ago, and it is a very successful addition.
I have a blank cap on the radiator and the pressure cap on the expansion tank. I no longer get gurgling sounds from the heater as this system cures air locks and I can see the waterlevel through the plastic bottle