compression testing rings and head gasket

This is an addition to an ealier post (Overheating - head and/or head gasket) but coming from a different angle - so I've reposted....

L reg 850 NA 2.5 20V Engine.

Air being forced into header tank - not great amounts but enough to cause the tank cap to give up and loose water after about 20 miles of easy level driving.

I can see its possibly a gasket head or block problem so I've done the following up to now.

Checked oil water contamination - none other than crank gases in water - no oil.

Exhaust has slight water drops and possible steam - hard to tell.

Compression test is as follows and looks low to me.

In order L-R and in Lbs sq"

125 - 155 - 155 - 150 - 130

when adding oil to cyls and rechecking it read around the following:

200 - 250 - 250 - 250 - 250

should be between 188 to 218 Lbs sq" (13 to 15 bars)

I know adding oil into the cyls will produce a higher than normal reading at first but it believe this show ring/cylinder wear up.

When I first brought the car I found the crank case vent pipe off, so I replaced it. My question here is can the worn rings/bore cause exesive crank case pressure causing the head gasket to blow and so causing the header tank to fill with air.

I have to decide whether to replace the head gasket and put up with slight loss of power and run it for another 10 months and get rid. Or will I need to sort the worn ring/bores out to stop possible exesive pressure build up in the engine.

I also have to consider the fact the cams may have a worn lobe on due to the missmatch in compression between cyls - it may get to a point where I have to decide on a strip and rebuild or simply swap the head or the engine.

Any advice on any aspect of this problem is welcomed.
Regards,
Colin

old post:
http://www.volvoclub.org.uk/dc/dcboa...topic_id=12966

[sholtby]

Colin,

As I'm sure you know water is a byproduct of petrol combustion so unless you have a cloud of steam it doesnt help us much.

Were the compression tests done with the engine at operating temperature? If not the results will be inaccurate.

The first set of results dont fall within the spec given in the Haynes manual. The second set are very high. You must have added a lot of oil!

I dont think excessive crank pressure would cause a head gasket to blow. More likely the crankshaft oil seals.
Try and get the water leak fixed before you worry about worn cylinders/camshafts.
If you have excessive bore/ring wear you would have been using a lot of oil before your recent problem. Were you?
I'm not sure their is enough value in your car to do any extensive rebuilds. I think the head is more likely to crack than the block.
At the end of the day if you are sure you haven't got a water leak from a hose, radiator etc and there is no water in the oil then the water must be going into the cylinders.
Another test is to pressurise the coolant system to a pressure no higher than the coolant filler cap release valve. Remove the plugs and see if any of the cylinders fill with coolant. You could use a special hand pump, compressor or an inert gas bottle to create the pressure. But be carefull.
Simon

Cheers Simon,

>unless you have a cloud of steam....

Very little steam if any, drips a little water out of exhaust but that's normal I believe.

Did compression tests with the engine at operating temperature but I may re-do them before doing anything drastic.

>You must have added a lot of oil!

More than a table spoon possibly.

I am using a little oil but no more than I'd expect on an old engine, in fact not that much at all.

The water normally comes out of the header tank cap but it has also shot out of an hose, I think it finds the easiest route which is normally the cap - this is why I can't see any evidence of steam in the exhaust.

As for the pressure test I may take it into Speeds Volvo if it not too costly and let them test it for me.

My only concerne is fixing only half the problem, but I'll just have to investigate it further before I jump.

Cheers for now.