Oldsmobile/Buick Repair: 1996 regal custom running (really) rough, head gasket leak, intake manifold gasket


Question
Hi there,
Our '96 regal is running really poorly, it makes a knocking noise when
running, and is really slow to accelerate.  This was only a slight problem
because after the car ran for a little while the noise stopped and once the car
got up to speed the first time it accelerated fine.  We did have some problems
with antifreeze leakage, and my husband's co-worker (once mechanic)
changed the water pump for us (he was pretty certain that the seal on the
bottom of the pump was shot).  Now the check engine light is on and the car
is running worse than ever.  Any suggestions?  Oh, it has about 155,000
miles on it, and although we've done regular oil changes on it we've done
little else.
Thanks so much,
Julia

Answer
Hello Julie,
Do you still have a coolant leakage problem?
Or, to be more correct, are you loosing coolant? Be sure to check inside the radiator when it is cool, not just the coolant recovery tank.
A coolant leak into the combustion chambers can cause a knocking,(while the coolant is in a cylinder), which can go away after the coolant is blown out of the cylinder. That cylinder will even miss while the coolant is in it, cause it shorts out the spark plug.

Check that coolant level in the radiator.

One way to check for an internal coolant leak is, like after it has sat overnight, remove all the spark plugs, and while they are out, have someone crank the engine over a couple revolutions. Be watching the engine, but don't be leaning over it too close. If there is coolant leaking, some will be blown out one or more of the sparkplug holes.

You should also look at the spark plugs as they are removed, to see if the electrode end on any of them is wet with coolant.

They could also be wet with gasoline, in which case, I would say an injection system problem.

Possible causes of a coolant leak are intake manifold gasket leak, and head gasket leak. Both fairly common.
A cracked head is another possibility, if it has been run low on coolant and overheated.

Van