Excessive water consumption

[SianB]

Can anyone help?
My 924S had a head hasket and top end re-build about a month ago. I set off for a 250 mile journey 2 weeks ago, topped the oil up and the water was fine. Before the return journey, the oil was topped up again and 3 pints of water added. We drove the 250 miles or so back and have done about 50 miles since and I added 2 litres of water last night. I drove it about 8 miles home from work and the water was below the minimum again.
There are no signs of a leak - nothing coming out under the car, and no steam from the exhaust. We've checked all the lines and can't find anything obvious.
The temperature has been running a little warmer than normal, but nothing too alarming.
Its going back into the specialist tomorrow, but wondered if anyone had any ideas what it could be?
It has also used about 4 and 1/2 litres of oil in 800 or so miles - is this usual?

 

[944Turbo]

Is the coolant cap in good condition? a weak spring or perished seal will allow the coolant to escape prematurely. An easy check is to put a container (soft drink bottle) at the end of the overflow pipe.
4 1/2 litres of oil sounds excssive in 850 miles especially as the rebuilt head should remove some of the escape routes.
Tony

 

[plhorner]

That oil consumption seems very high to me, is there any evidence of water in the oil?
I had the expansion tank cap go on mine, it would boil the water on shut down and spit it out of the overflow about 2 or 3 minutes after turning off the engine!

I would get it looked at pronto unless your handy with a spanner!

 

[plhorner]

Tony, you beat me too it!!

 

[SianB]

I haven't checked the cap on the expansion tank, but there is no sign of the water anywhere when its running or when the ignition is turned off.
I'm quite worried about the oil too.
I'm sure it will all be solved when it goes in tomorrow, I'm just not looking forward to having to dig deep!

 

[Guest]

If there is no water in the oil, or vice versa, then the head gasket would seem to be working correctly. It is unlikely the water or oil would be making it into the cylinder without mixing somehow.
The water cannot just disappear, so it must be going somewhere. The most likely cause is a leak, but it may not be so obvious.
The heater matrix for the internal heating or the car, uses the hot water from the engine I think.
A leak in there may not be so easy to tell.

For the oil consumption, if there is no sign of a leak, then it must be burning it. It could be leaking past the piston rings, although they would have to pretty bad in which case you would be losing compression and power I would have thought, or be leaking through the valve guides, which is possible.

 

[SianB]

The car went in to the specialist on Saturday and he seems to think the water consumption could be to do with the head gasket or a possible crack in the head itself.
It seems that the oil problem is down to the piston rings - is this something you would expect to be checked when having a new head gasket and top end re-build?

 

[Guest]

My understanding is that top end is the head. If you take the cylinder head off, you can check valves and reseat them, check clearances, cams/rockers/tappets, head gasket, and decoke the head. Plus you you could check to see if the mating surfaces of the head and block are flat (i.e. no warping) with a suitable flat piece is metal, which is quick easy and worth while on an older block, especially as the new gasket will not seal if it isn't.
While you at it you can check the carbs/injectors and throttle as well the inlet and exhaust manifolds and studs.

I would expect the pistons and block to remain in the car and not be removed. But if it were burning significant amounts of oil I would expect this to obvious through excessive carbon on the piston crowns, the spark plugs, etc.
If I did it myself I would turn the engine over (by puting it in gear and rolling it) to watch the pistons go up and down and have a look at the bores for wear and scoring. However, I don't know that a garage would do this.

If your head gasket was on the way out before, I believe they normally fail at one or two points, therefore if may have contaminated one cyclinder, but the others should have been in relatively good condition. If all four were bad I might have wondered if something else was at fault.
If the rings are cracked, you might get a ticking noise, and if the bores and rings are badly worn you might get some piston slap.

If you wanted to be thorough you also have done a quick compression test when it was back together after the gasket was done to check the state of the rings. But again this would cost, so it would likely be omitted.

I don't know how likely it is that the head would crack.

 

[924nutter]

I have just replaced a head gasket on a 944, and having seen inside, it is entirely possible for the head gasket to rupture in such a way as to leak no oil or water into the bores; this gasket had failed in exactly this manner, and the bore seal retained its integrity. This is because the engine is a dry-lined aluminium alloy block, and there is plenty of room for the gasket to fail "top to bottom", again, because there are three elongated figure of eight sections not under compression in between each bore, and when this happens water can circulate through the rupture in the gasket and not necessarily circulate around all the liners, leading to local boiling, overpressurising and venting off of coolant. I am putting my money on this. We have to make the assumption that a new gasket was used for the head rebuild, so there is an obvious question to be asked as to why it failed again so soon.

I would second Stuart's suggestion that the head is checked for flatness.

Finally make sure the head is tightened to Porsche's latest revisons of torque settings. (evenly in three stages, 40 n/m, can't remember the second but about 67 n/m, and finishing of at 90 n/m

The tappets (cam followers) are hydraulic, and clearance setting is automatic provided the follower has no leaks.