Head Gasket 1988 740

If the head gasket has gone then one of the problems will be air will enter
the cooling system.
If air is entering the cooling system caused by a blown or leaking head
gasket then is air is replacing the water would it first cause the heater to
stop working.

 

Is this a question?

Stricktly speaking it is not air that pushes the water out, but
combustion gases - exhaust. If the coolant level drops low enough,
then the heater will stop working. IME, on a 740, this happens before
the temperature needle registers anything wrong.
--

TSH


For email, replace 'SpamOnlyToHere' with my initials

 

That's my experience, too - anything that causes the coolant level to drop
causes the heater to stop working at idle. You will also hear gurgling
noises from the heater as the engine revs until the level drops too low to
pump coolant up to the heater at all.

A good screening test for exhaust gasses getting into the coolant is to take
the reservoir cap off when the engine is cold, start the engine and place
the palm of your hand over the reservoir. If you feel pressure build in a
couple of seconds, or a pulsating pressure, that is bad news. Be aware the
pressure will normally build if the engine warms up much while your hand is
over the reservoir - don't mistake that slow rise for exhaust leakage.

Mike

 

Will exhaust gases not act just like air if it enters the cooling system
and cause an airlock.

 

What I found usually happens is it leaks coolant into the cylinders when it
cools, drawing air in through the reservior or overflow tank to replace it.
The gas blown in acts like air but shouldn't cause a lock, just rises to the
top of the system until it has more air/gas than coolant - if it's leaking
that fast it is likely to not start because of a cylinder full of water.
There is often no evidence for where the coolant went & that loss is usually
my first indicator.

 

That's possibly why the heater is the first thing to stop working. But
the exhaust gases will keep pushing their way into the cooling system
at high pressure, and will tend to keep pushing the water out. It's
not like an air bubble that simply didn't get purged when the system
was filled.

--

TSH


For email, replace 'SpamOnlyToHere' with my initials

 

Another thought to keep in mind is that the heater core can leak without
drawing much attention. So in addition to being the high spot it can also be
a leak point.

When my heater core leaked 2 years ago, it was soon after being recored by a
shop I trusted. (Nobody bats 1000, I guess.) I was especially concerned that
the fogging vapor from it increased a lot when I accelerated hard because I
was afraid that meant the boost was forcing more gasses into the system and
that blew the heater in the first place. No - it was just the rpm pumping
coolant into the nearly empty heater core that was doing it. I wasn't all
that relieved, though; accessing the heater core is a lot of work in the
740/760.

Mike

 

If the heater core leaks where does the water end up inside or outside the
car

 

Either several different people, all with worries about their head
gaskets on their '88 740s, have remarkably similar headers to their
posts (including Posting Host, and client version), or one person
keeps changing identity, and then asking the same questions again.

Since last November or before, several experienced guys pointed 'Les'
to his head gasket. We did the same for 'Rock', and now 'Andy' has the
same symptoms.

The thing is, whoever you are, we're all happy to try and help out
with an honest worry; that's what this NG is for, and it's a pretty
friendly group as these things go. But what you're doing is a bit
rude.

Changing you ID and then asking the same questions again is making a
monkey out of all of us. As people realise, you will be considered a
troll.

Whoever you really are, we understand your concerns about needing to
be sure what the problem is, but we've been as helpful as we can be
several times.

In the end, we can only suggest our best guess. We can't make that
final decision for you - you have to consider whether we are making
sense or not; you have to make that final leap of faith that it really
is the head gasket and get it fixed.


--

TSH


For email, replace 'SpamOnlyToHere' with my initials

 

Mine ended up in the carpet at the driver's feet. It leaked quite a lot
before I noticed it, but if I had looked it would have been obvious long
before that.

Mike

 

Maybe it's the "mechanic" who buggered my nissan van a few years ago - he
thought every problem originated from the head gasket. Perhaps he just wants
to be sure before he does it again, the customer will wait... some are as
stupid as I was.

 

Hi.

I have changed my ID from Rock to Andy Mann but not out of choice but
advised that tomtom.com was a domain name which I was requested to change so
decided to change also the user ID from Rock to Andy Mann.

I really love my 740 Estate so does my wife and we don't want to scrap it
based on cost, I have an MOT in May so depending on that cost will depend on
what I do with the problem with the cooling system.

I am nearly 60 and don't know how to change the head gasket that is if it is
the head gasket at a cost of £200 and then find the problem is still there
and it was the heater matrix.

So apologise and hope I have clarified my reasons for postings, I am going
to now try the hand on the reservoir to see if there is instant pressure.

 

You can call yourself what you like on the internet - nobody has a
right to know your true identity. But when several different people
all post from the same computer, and all cover the same ground, it
makes troll alarms ring.

Using other people's domains is a bit naughty. If you want to
obfuscate your email address completely, you could use
The owner of this set it up especially for people who don't want to
disclose their addy on forums, and allows anybody to use it thus.
Although your earlier noreply@invalid would do also. You probably
realise that tom_tom.com is an impossible domain, because of the '_'
in it.

We sympathise with that. But let's recap what you have described under
your various IDs:

From memory:

Your heater makes gurgling noises and stops working.
You are losing water from the cooling system, but there is no apparent
leak.
The cooling system becomes pressurised, even before the water has had
time to heat up.
The system remains pressurised, even after the engine is long cold.
There are strange smells in the header tank that might be exhaust
fumes.

Together, all of these point inexorably to head gasket failure. It
*may* be a cracked head (unusual), or even a cracked block (very
unusual), but these faults will require the same initial amount of
dismantling to find out. Head gasket failure seems fairly common on
older red block engines.

It *may* be that you have several different problems causing some of
the above symptoms, but taken together, most people will suggest head
gasket.

What you won't get from anyone who has any experience, is a 100%
absolute guaranteed diagnosis, no matter how many different ways you
describe the symptoms.
--

TSH


For email, replace 'SpamOnlyToHere' with my initials