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Car Forum / Chevrolet / Chevrolet Trucks / January 2007

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96 5.7 Vortec external coolant leak. Help please.

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nogd@aol.com - 02 Jan 2007 03:01 GMT
Hi,  I am haveing trouble locating a large coolant leak on my 96 GMC
Sierra.  It is running off of the starter bolts on the P/S of the
vehicle.  Any one have any suggestions where I may want to look?  I
have read the posts on the intake manifold gasket but the top of the
engine appears to be clean and the fluid is running out pretty heavily.
Thanks.
Augustus - 02 Jan 2007 03:47 GMT
> Hi,  I am haveing trouble locating a large coolant leak on my 96 GMC
> Sierra.  It is running off of the starter bolts on the P/S of the
> vehicle.  Any one have any suggestions where I may want to look?  I
> have read the posts on the intake manifold gasket but the top of the
> engine appears to be clean and the fluid is running out pretty heavily.
> Thanks.

The heater lines go into the firewall just above this area. Another
possibility is the intake gasket at the rear of the head. They always seem
to go on these engines. My 94 Suburban did this. For weeks I was finding
coolant dripping down the oil filer area onto the ground trying to figure
out where it was coming from
phinq - 02 Jan 2007 04:51 GMT
How many miles are on the truck? If near 100K, it is probably the intake
manifold gaskets. The base material of the gasket is plastic, and after many
hours of heat it breaks down. The water runs off the back of the head, and
off either the starter, oil filter or torque converter cover. Been there,
done that, got that t-shirt. Mine leaked for a long time, then finally blew
out the top of the gasket. I think it is leaking again because it smells
like anti-freeze again. There goes a Saturday.

> Hi,  I am haveing trouble locating a large coolant leak on my 96 GMC
> Sierra.  It is running off of the starter bolts on the P/S of the
> vehicle.  Any one have any suggestions where I may want to look?  I
> have read the posts on the intake manifold gasket but the top of the
> engine appears to be clean and the fluid is running out pretty heavily.
> Thanks.
nogd@aol.com - 02 Jan 2007 14:01 GMT
> How many miles are on the truck? If near 100K, it is probably the intake
> manifold gaskets. The base material of the gasket is plastic, and after many
[quoted text clipped - 10 lines]
> > engine appears to be clean and the fluid is running out pretty heavily.
> > Thanks.

Thank you both for the help,  it has 136,000 mi. When it thaws this
morning I will go and check again,  I initially ruled this out because
the top of the motor is so clean,  Would a pressure check identify this
area (intake man) of leaking?
Augustus - 02 Jan 2007 16:08 GMT
> Thank you both for the help,  it has 136,000 mi. When it thaws this
> morning I will go and check again,  I initially ruled this out because
> the top of the motor is so clean,  Would a pressure check identify this
> area (intake man) of leaking?

It should.
Whitelightning - 03 Jan 2007 17:59 GMT
...
> > Thank you both for the help,  it has 136,000 mi. When it thaws this
> > morning I will go and check again,  I initially ruled this out because
> > the top of the motor is so clean,  Would a pressure check identify this
> > area (intake man) of leaking?
>
> It should.

Top of the motor, i.e. intake manifold,  will be clean most of the time.  It
will leak between the manifold and the cylinder head, and run down the back
of the head, along the top of the block and down to ground.  If its the left
bank it will run down the oil filter housing, if the right bank the starter
will be wet.  There are two other possibilities, I believe there is a small
freeze plug on the back of the cylinder head, and there is also one behind
and slightly above the starter.  Chevy small blocks are not noted for eating
freeze plugs, but it is still a possibility that cant be over looked.  A
mirror will be needed to get an good eye ball on the back of the head.
Usually the manifold will stop or slow as the engine warms up, the manifold
expanding as it gets hot.  If the volume is as large as you suggest, and
there is no coolant in the oil(if the manifold gasket gets bad enough it
will leak into the oil galley as well) it may be a freeze plug.  Also if it
has been leaking any length of time, the coolant can groove the manifold
(erosion happens to metal too, especially soft ones like aluminum) be
prepared to replace the manifold as well.

Whitelightning
nogd@aol.com - 03 Jan 2007 18:10 GMT
> ...
> > > Thank you both for the help,  it has 136,000 mi. When it thaws this
[quoted text clipped - 22 lines]
>
> Whitelightning

Thank you
phinq - 03 Jan 2007 23:40 GMT
>> ...
>> > > Thank you both for the help,  it has 136,000 mi. When it thaws this
[quoted text clipped - 35 lines]
>
> Thank you

One other thing, the new gasket set will also have new upper plennum seal
that seals the two halves of the manifold. Unless you are having performance
problems, don't use it, as the new gasket will probably leak. This is
because the plastic half has adjusted to it's current position and gasket,
and won't really fit again once it is removed. Buy an extra tube of the
silicon "gasket in a tube" and save a trip back to the parts store.

phinq
nogd@aol.com - 04 Jan 2007 16:37 GMT
> >> ...
> >> > > Thank you both for the help,  it has 136,000 mi. When it thaws this
[quoted text clipped - 44 lines]
>
> phinq

Thanks,  it's a blizzard and  I found a reputable shop in town that for
$400 the will replace the manifold and rocker cover gaskets, replace
the quick disconnects and check the cooling system,  we'll see how it
goes and what the final cost is.  I'll keep you guys posted for anyone
in northern Ut.
nogd@aol.com - 04 Jan 2007 16:39 GMT
n...@aol.com wrote:

> > >> ...
> > >> > > Thank you both for the help,  it has 136,000 mi. When it thaws this
[quoted text clipped - 50 lines]
> goes and what the final cost is.  I'll keep you guys posted for anyone
> in northern Ut.
 
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