Overheating engine.. Does this seem like a blown head gasket

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Al Kondo - 29 Nov 2005 16:08 GMT

I have a 96 Sentra GXE. The engine has been overheating recently and
I have conducted quite a bit of diagnosis on it to determine the
problem. There a bunch of things I have eliminated because I have
changed the parts in a similar overheating problem last year. I have
changed out the thermostat, water pump, radiator cap, and had the
radiator flushed approximately 8 months ago. Now, I am thinking I
have a blown head gasket.

The main symptoms of the possible blown head gasket are these:

1. I am losing antifreeze at a very high rate... and, I can't find any
liquid under my car at any time.

2. I did a leak down test on my four cylinders and found that two of
the cylinders leaked down very quickly. Also, I could hear the leak
in the adjacent spark plug hole from where the compression was
applied.

The one thing going against my theory is that there is no residue
showing up at the radiator throat. I would expect that there would be
some.

I would appreciate some thoughts about my assumption. This would be
very helpful before I begin taking off the head.

Thanks, Al Kondo

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HLS@nospam.nix - 29 Nov 2005 17:02 GMT

When you have substantial loss of coolant and cant find where it is going
externally,
then you have a pretty good case for an internal problem. Sometimes
external leaks
are slow and difficult to find, but usually if you carefully examine the
head mating
area, the hoses, the heater core area, 'freeze' plugs, water pump, etc, you
can normally
spot a leak.

If you have strong leakdown on two cylinders (particularly if they are
adjacent cylinders)
and you can hear the gas in the cylinder not being tested, that is another
good indication.
The compressed air is either going through a blown head gasket, a crack in
the block or
in the head, or past the rings and into the crankcase.

Just because you dont see oil in the coolant, or coolant in the oil is not
conclusive.
These things can leak coolant directly into the cylinder or exhaust gas
directly
into the coolant, and it may not be obvious.

My cloudy crystal ball suggests, dimly, that you probably have an internal
problem,
but it is a lot easier to rule out the externals postively than to start
pulling the head.

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Mike Romain - 29 Nov 2005 18:47 GMT

'Usually' when antifreeze gets pumped through a cylinder or two, the
spark plug(s) in that cylinder will be super clean, almost like new.

The coolant also can get full of tiny bubbles when the engine is running
with the rad cap off. I start off with a cold engine, open up the rad
cap and watch what happens. If it starts foaming up like it has dish
soap in it, the headgasket is dead. You also can sometimes see exhaust
coming out the open rad cap or even feel the compression puffs if you
put your hand over the opening with the overflow tube pinched closed.

You also can have a leakdown test done on the rad. Or I guess have the
rad cap off when you do the cylinder test to see if you hear air out the
rad.

They also sell a paste you can smear on the dipstick that goes from gray
to pink if there is water in the oil.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
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> I have a 96 Sentra GXE. The engine has been overheating recently and
> I have conducted quite a bit of diagnosis on it to determine the
[quoted text clipped - 22 lines]
>
> Thanks, Al Kondo

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