Blown Head Gasket

I've got a 91 240 (100 000 miles)that's leaking anti-freeze between the head
and block just behind the water pump. The dealer and another mechanic are
positive it is the head gasket while another mechanic is certain it's just
the o-ring between the pump and head. The motor has started to shake as if
it's running on 3 cylinders when first started in the morning-shakes last
for a few minutes then it runs fine. Could this be a build up of
anti-freeze in the cylinder once the engine is shut off-and a verification
of the blown head gasket? Also, how major is the job of replacing the
gasket on this car-it's in excellent condition otherwise-I've had to replace
the works in the past year-O2 sensor, AMM, idle control valve, just to name
a few parts. Are there any pitfalls in removing and re-installing the head
that could lead to worse probs? Thanks in advance for any advice!

 

Yes. Definate HGF.

Pull the plugs first thing in the morning and with a torch look down into
the cylinders- am certain you will see coolant sat ontop of one piston.

Tim..

 

That seal on the water pump is very common and I would certainly try
replacing that before doing a head gasket. If you're having someone else
do the work then it may be better to have a leakdown test done.
Replacing the head gasket isn't something I'd do for fun, but it's not
too bad either if you have a well lighted and heated shop and all the
right tools on hand. Last one I did took a long evening.

 

Yes, make sure you correctly diagnose the problem before undertaking
repairs.

The last thing you want is to replace the O-ring, only to find out that
wasn't the problem.

 

Well you should replace the O-ring either way, but you do want to
diagnose the head gasket before pulling the head off.

 

Yes, of course the O-ring must be replaced in either event, but there
is no sense misdiagnosing the problem, only to find you are replacing
the O-ring twice.

 

You don't want to run a car for long with a bad head gasket.

Among other things, water can be very, very bad for bearings, as it
hasn't the lubricating properties of motor oil.

Running an engine with a blown gasket can cause a depletion of coolant,
which will cause overheating which can warp the cylinder head and cause
the engine to sieze.

 

Thanks to all. I agree that it would be a shame to replace the O-ring twice
but doesn't the fact that the motor appears to run on 3 cylinders for a few
minutes after startup point the finger at the head gasket vs water pump
seal? One mechanic put dye in the rad and with uv glasses we could see that
the leak appeared about an inch behind the water pump but it still wasn't a
definite diagnosis-the anti-freeze may have travelled that far undetected
under the head before dropping down. There is one other question. If it is
the gasket, I can live with it for a while (keep an eye on the reservoir)
but can burning anti-freeze damage the valves or cause other probs? Thanks
again.

 

And a head gasket problem can get very much worse very quickly. If you
pull the plugs and compare them, you should see a difference if there's
a problem.

--
Mike F.
Thornhill (near Toronto), Ont.

Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)

 

I agree, although I think that I would try retightening the water pump
bolts first to see if that makes a difference. I can't see the problem
with determining if the leak is coming from the pump mounting point of
the cylinder head. Seems to me that that would be a fairly simple
observation, so I don't know what the problem is there. I can't
remember when Volvo went to the non-retorqueable (Is that a word?)
cylinder head bolts but I think that I'd try re torqueing them to see if
that makes a difference. If your engine has the one torque type of
bolts, then don't go there, but I'd definitely look at the pump first.

 

My experience with the top seal on the water pump is that if disturbed it
will leak, whether it did before or not. Since the bolts don't actually snug
the pump against the head it's probably a losing proposition.

Mike

 

I use a thin skim of blue RTV on the top "O" ring and also on the
smaller "O" ring on the end of the water pipe.

 

That works well on a new ring, but if it is leaking now the ring has
deteriorated to the point it will not seal no matter what. Believe me, I've
tried 8^P

Mike

 

I agree, I wouldn't think it realistically possible to reseal the
failed "O" ring on top of the water pump.

It seems almost a "black art" to make them seal correctly.

While you must put upward pressure on the pump while tightening the
bolts, if you put on too much, it can leak (I know, it happened to me).

I always take a wire brush to the head surface to prep it.