1992 Volkswagen (VW) Jetta Diesel TDI Overheat Coolant Leak Issue

Hi Everyone,

I just wanted to post a problem I had experienced with my 1992 VW Jetta
TDI, and what I finally figured the solution to be.

I read an awful lot of posts regarding engine overheat w/diesels, and
almost every one was pointing to cracked head gasket... I also read in
a few posts that the fan has high/low speed; this is true. The low
speed will come on if you turn the environment control to anything with
a snowflake on it (might only be on models equipped with AC). The high
speed is controlled by thermoswitches (as I understand).

The problem was that my car would need coolant every once in a while,
but seemingly only after long trips on the highway. The problem got
progressively worse as the summer came on. As I would drive down the
highway, the temperature gauge would be running fine (around the 1/2
mark), and then all of a sudden (usually after an hour of driving), it
would spike up to 3/4 (where my coolant boils), until the low coolant
light started flashing. I thought, "that doesn't make sense... on the
highway I should have plenty of cold air going through my rad". I
would then stop at the side of the highway, fill my reservoir up, and
start driving. Sometimes, I would have to pour in a gallon of water,
depending on how long the low coolant light was on. After I refilled,
and started driving, the temperature gauge would spike right back up
within 10-30 seconds. Low coolant light came on after about another
minute. Needless to say, it made long highway trips even longer.

I was thinking thermostat...

I brought it to my mechanic, and he did some re-wiring to fix a
thermoswitch. He said the fan wasn't coming on when the engine got
hot, so it would overheat. He said he was 99.9% sure that the
thermoswitch wiring would fix it, because the fan would now come on
when the rad was hot. Didn't make sense to me (on the highway, I'm
going 120 km/h anyway, so why would that tiny fan help?). I told him
to replace the thermostat anyway (he already charged me for the
wiring).

No noticeable difference. Same problem next time I was on a long trip.
After enough troubleshooting, I learned that my car would only
overheat AFTER it had lost enough coolant. I couldn't find signs a
leak anywhere, except for at my reservoir steam vent, and a pressure
test at Canadian Tire didn't show any leaks in my rad (btw: the
Canadian Tire mechanic thought I had a cracked head gasket, but I
didn't see any discoloration in my oil, or bubbles in my coolant, so I
didn't change anything. He also said that my car overheated because I
had too much water in my antifreeze... I noticed that when I was
running close to 80% antifreeze, the boiling point was just past the
3/4 mark on the temp gauge; with 95% water, it boils right at the 3/4
mark. It boiled either way. Lesson: Don't go to Canadian Tire.)

So, I was confused. I read all over the internet that it's usually a
cracked head gasket (but I never actually let my engine run past the
boiling point of my coolant, and couldn't see bubbles in my water, or
water in my oil). My mechanic was stumped (he said thermoswitch is all
he could think of, so my fan would come on). My rad was obviously
fine, as it passed the pressure test, was fine in the city, and good on
the highway for an hour. My thermostat was new. I was even running a
good mixture of antifreeze in case there was a glitch in the matrix,
and the Canadian Tire mechanic was actually right. I was absolutely
stumped...

I put paper towel near my reservoir bowl vent to confirm that this is
where it was leaking. It leaked once in the city (only a small
amount), and on my next 2 hour highway trip (a whole lot). Should I
plug up the steam vent? Why not?

Didn't help -- water still found its way out of the reservoir where I
tried to plug it. I finally ran the car in my driveway (3000 rpm) for
a good hour, watching the coolant level in the reservoir. After the
engine warmed up, the coolant level came up in the bowl, close to
overflowing. Then the fan switched on automatically, and the level
dropped. The fan turned off, and the water level crept up again, same
thing. Again... Uh oh... this time the fan didn't come on, so the
level didn't drop... coolant started leaking out of my top of my
reservoir (I plugged the steam vent). Leaking BAD. I turned on my
enviro control to the snowflake (to start the rad fan). Fan came on,
level dropped.

Everything suddenly made sense. When it was winter, I kept the
environment control on Defrost the whole time, so the rad fan was
always on, and whatever valve the rad fan opens stayed open (so I never
had any problems). When summer set in, I ran with my windows down, and
my environment controls off (simply because my AC doesn't work). When
I turned that fan off, the associated valve wouldn't work properly, and
my engine would spew coolant out of my reservoir until it was low, and
then I'd *overheat*.

Being as cheap as I am, and frustrated over how much I've already
spent, I've decided to run the car as is, but with the fan on all of
the time (enviro controls left on defrost). It's funny, but the
mechanic was actually right... George Orwell would say he understood
how, but not why. He told me HOW to fix the problem, but not WHY (he
only knew from experience, and drew his own conclusions). He said that
the thermoswitch will stop the overheating, because the fan cools the
coolant in the rad when operating properly.

Not entirely true. The thermoswitch will stop the overheating, but
because it electronically opens a valve when the engine is warm,
allowing the coolant from the reservoir back into the engine for proper
circulation. When this valve fails to open, coolant will boil out of
your reservoir, because the 1/4" line between the top rad hose and
reservoir will still feed coolant into the reservoir, but it can't go
anywhere, so it will overflow. I noticed someone else had this problem
years ago, but never posted any success.

I'm not sure where this valve is (maybe where the reservoir hose
connects to the engine), but it sure caused me problems. It's the
first I've heard of a cooling system having 2 valves, but I figure
that's the only thing that makes sense. Why else would the level drop
INSTANTLY when the fan runs? Why would the level in the reservoir
climb in the first place? It MUST be a valve. Nothing else can
over-heat an engine full of water in 10 seconds except for a closed
valve (which is why I initially thought thermostat). That's my theory
anyway. I hope someone saves themselves a few hours (and hopefully
more than a few dollars) from this. Thermoswitch or mysterious valve:
whatever you want to call it. What a frustrating problem...

Anyone care to comment?

I'm going on a long trip this weekend. I'll post again if my hack
solution doesn't solve the issue.

-Randy

(PS: My power steering pump leaked. I didn't want to spend $200 for a
rebuilt one, so I disconnected the belt, and get my daily workout
steering manually. I was going to run it with the belt on, but
apparently, the power steering fluid lubricates the whole pump
assembly, so if you don't take that belt off, you'll cease your pump
and snap the belt eventually without any PS fluid. Good advice.)

Try getting a new cap for your resrve bottle, they run on a pressurized
setup and if the cap doesn't hold the pressure the coolent will free
flow to the ground. Had this problem a couple of years ago and spent
several monthes fiddling before a mechanic suggested the cap. never a
problem since.

Rand-E wrote:
> Hi Everyone,
>
> I just wanted to post a problem I had experienced with my 1992 VW Jetta
> TDI, and what I finally figured the solution to be.
>
> I read an awful lot of posts regarding engine overheat w/diesels, and
> almost every one was pointing to cracked head gasket... I also read in
> a few posts that the fan has high/low speed; this is true. The low
> speed will come on if you turn the environment control to anything with
> a snowflake on it (might only be on models equipped with AC). The high
> speed is controlled by thermoswitches (as I understand).
>
> The problem was that my car would need coolant every once in a while,
> but seemingly only after long trips on the highway. The problem got
> progressively worse as the summer came on. As I would drive down the
> highway, the temperature gauge would be running fine (around the 1/2
> mark), and then all of a sudden (usually after an hour of driving), it
> would spike up to 3/4 (where my coolant boils), until the low coolant
> light started flashing. I thought, "that doesn't make sense... on the
> highway I should have plenty of cold air going through my rad". I
> would then stop at the side of the highway, fill my reservoir up, and
> start driving. Sometimes, I would have to pour in a gallon of water,
> depending on how long the low coolant light was on. After I refilled,
> and started driving, the temperature gauge would spike right back up
> within 10-30 seconds. Low coolant light came on after about another
> minute. Needless to say, it made long highway trips even longer.
>
> I was thinking thermostat...
>
> I brought it to my mechanic, and he did some re-wiring to fix a
> thermoswitch. He said the fan wasn't coming on when the engine got
> hot, so it would overheat. He said he was 99.9% sure that the
> thermoswitch wiring would fix it, because the fan would now come on
> when the rad was hot. Didn't make sense to me (on the highway, I'm
> going 120 km/h anyway, so why would that tiny fan help?). I told him
> to replace the thermostat anyway (he already charged me for the
> wiring).
>
> No noticeable difference. Same problem next time I was on a long trip.
> After enough troubleshooting, I learned that my car would only
> overheat AFTER it had lost enough coolant. I couldn't find signs a
> leak anywhere, except for at my reservoir steam vent, and a pressure
> test at Canadian Tire didn't show any leaks in my rad (btw: the
> Canadian Tire mechanic thought I had a cracked head gasket, but I
> didn't see any discoloration in my oil, or bubbles in my coolant, so I
> didn't change anything. He also said that my car overheated because I
> had too much water in my antifreeze... I noticed that when I was
> running close to 80% antifreeze, the boiling point was just past the
> 3/4 mark on the temp gauge; with 95% water, it boils right at the 3/4
> mark. It boiled either way. Lesson: Don't go to Canadian Tire.)
>
> So, I was confused. I read all over the internet that it's usually a
> cracked head gasket (but I never actually let my engine run past the
> boiling point of my coolant, and couldn't see bubbles in my water, or
> water in my oil). My mechanic was stumped (he said thermoswitch is all
> he could think of, so my fan would come on). My rad was obviously
> fine, as it passed the pressure test, was fine in the city, and good on
> the highway for an hour. My thermostat was new. I was even running a
> good mixture of antifreeze in case there was a glitch in the matrix,
> and the Canadian Tire mechanic was actually right. I was absolutely
> stumped...
>
> I put paper towel near my reservoir bowl vent to confirm that this is
> where it was leaking. It leaked once in the city (only a small
> amount), and on my next 2 hour highway trip (a whole lot). Should I
> plug up the steam vent? Why not?
>
> Didn't help -- water still found its way out of the reservoir where I
> tried to plug it. I finally ran the car in my driveway (3000 rpm) for
> a good hour, watching the coolant level in the reservoir. After the
> engine warmed up, the coolant level came up in the bowl, close to
> overflowing. Then the fan switched on automatically, and the level
> dropped. The fan turned off, and the water level crept up again, same
> thing. Again... Uh oh... this time the fan didn't come on, so the
> level didn't drop... coolant started leaking out of my top of my
> reservoir (I plugged the steam vent). Leaking BAD. I turned on my
> enviro control to the snowflake (to start the rad fan). Fan came on,
> level dropped.
>
> Everything suddenly made sense. When it was winter, I kept the
> environment control on Defrost the whole time, so the rad fan was
> always on, and whatever valve the rad fan opens stayed open (so I never
> had any problems). When summer set in, I ran with my windows down, and
> my environment controls off (simply because my AC doesn't work). When
> I turned that fan off, the associated valve wouldn't work properly, and
> my engine would spew coolant out of my reservoir until it was low, and
> then I'd *overheat*.
>
> Being as cheap as I am, and frustrated over how much I've already
> spent, I've decided to run the car as is, but with the fan on all of
> the time (enviro controls left on defrost). It's funny, but the
> mechanic was actually right... George Orwell would say he understood
> how, but not why. He told me HOW to fix the problem, but not WHY (he
> only knew from experience, and drew his own conclusions). He said that
> the thermoswitch will stop the overheating, because the fan cools the
> coolant in the rad when operating properly.
>
> Not entirely true. The thermoswitch will stop the overheating, but
> because it electronically opens a valve when the engine is warm,
> allowing the coolant from the reservoir back into the engine for proper
> circulation. When this valve fails to open, coolant will boil out of
> your reservoir, because the 1/4" line between the top rad hose and
> reservoir will still feed coolant into the reservoir, but it can't go
> anywhere, so it will overflow. I noticed someone else had this problem
> years ago, but never posted any success.
>
> I'm not sure where this valve is (maybe where the reservoir hose
> connects to the engine), but it sure caused me problems. It's the
> first I've heard of a cooling system having 2 valves, but I figure
> that's the only thing that makes sense. Why else would the level drop
> INSTANTLY when the fan runs? Why would the level in the reservoir
> climb in the first place? It MUST be a valve. Nothing else can
> over-heat an engine full of water in 10 seconds except for a closed
> valve (which is why I initially thought thermostat). That's my theory
> anyway. I hope someone saves themselves a few hours (and hopefully
> more than a few dollars) from this. Thermoswitch or mysterious valve:
> whatever you want to call it. What a frustrating problem...
>
> Anyone care to comment?
>
> I'm going on a long trip this weekend. I'll post again if my hack
> solution doesn't solve the issue.
>
> -Randy
>
> (PS: My power steering pump leaked. I didn't want to spend $200 for a
> rebuilt one, so I disconnected the belt, and get my daily workout
> steering manually. I was going to run it with the belt on, but
> apparently, the power steering fluid lubricates the whole pump
> assembly, so if you don't take that belt off, you'll cease your pump
> and snap the belt eventually without any PS fluid. Good advice.)

I'm stumped again. While it didn't lose as much coolant as usual with
the fan on, a lot still leaked out of the vent in the side of the
reservoir (my cap seals tight). If it leaked because the system is
pressurized, wouldn't it leak in the city too? (Only seems to leak on
long highway trips.) It always leaks out of what appears to be a steam
vent in the side of my plastic reservoir bowl (checked by shoving a dry
paper towel in). Thanks for the suggestion.

Frustrated,
Randy

In article .com>,
Rand-E > wrote:
>I'm stumped again. While it didn't lose as much coolant as usual with
>the fan on, a lot still leaked out of the vent in the side of the
>reservoir (my cap seals tight). If it leaked because the system is
>pressurized, wouldn't it leak in the city too? (Only seems to leak on
>long highway trips.) It always leaks out of what appears to be a steam
>vent in the side of my plastic reservoir bowl (checked by shoving a dry
>paper towel in). Thanks for the suggestion.
>

you have an air pocket in the system.

Its supposed to self-purge, but only if you follow the correct procedure
AND the small hose that goes from the head to the top of the reservoir is
not plugged.

Disconnect the hose, see if the hose is clear and the hole it goes to in
the head is clear and then fill with water, start the engine, wait until
the temp is reaching halfway and stop the engine. wait an hour, refill
again, and repeat until no more water gets in.

never let the system boil. if it boils, an air pocket WILL form and youll
have to start again.


--
Eduardo K. | To put a pipe in byte mode,
http://www.carfun.cl | type PIPE_TYPE_BYTE.
http://e.nn.cl | (from the Visual C++ help file.)

Check your belt and water pump bearing, maybe your water pump is not
working properly and is slipping at high revolutions, my bearing was
going and overheated the car at 120, but once it cooled I stuck to side
roads in the city, and it was fine. The belt tension will give the
same effect (bearing actually was so gone it relaxed the belt).


Rand-E wrote:
> I'm stumped again. While it didn't lose as much coolant as usual with
> the fan on, a lot still leaked out of the vent in the side of the
> reservoir (my cap seals tight). If it leaked because the system is
> pressurized, wouldn't it leak in the city too? (Only seems to leak on
> long highway trips.) It always leaks out of what appears to be a steam
> vent in the side of my plastic reservoir bowl (checked by shoving a dry
> paper towel in). Thanks for the suggestion.
>
> Frustrated,
> Randy

Check your belt and water pump bearing, maybe your water pump is not
working properly and is slipping at high revolutions, my bearing was
shot and overheated the car at 120, but once it cooled I stuck to
between 60 and 80 on side roads in the city, and it was fine. The belt
tension will give the same effect (bearing actually was so gone it
relaxed the belt).


Rand-E wrote:
> I'm stumped again. While it didn't lose as much coolant as usual with
> the fan on, a lot still leaked out of the vent in the side of the
> reservoir (my cap seals tight). If it leaked because the system is
> pressurized, wouldn't it leak in the city too? (Only seems to leak on
> long highway trips.) It always leaks out of what appears to be a steam
> vent in the side of my plastic reservoir bowl (checked by shoving a dry
> paper towel in). Thanks for the suggestion.
>
> Frustrated,
> Randy

Thank you for your responses.

Eduardo,

You are right. I neglected to mention that while I was on the highway,
if I ran low on coolant, I would have an air-lock problem. This is why
the car would heat up again after only 10 seconds of driving AFTER the
coolant boiled, and the low coolant light came on. After the quick
overheating happened about 10 times, I finally filled the rad from the
top rad hose (drank about a gallon), and it worked fine for the rest of
the trip. You're absolutely right, every time the coolant boils, if
enough boils out, and the low coolant light comes on, it develops an
air pocket in the system. The small top hose that connects the top rad
hose to the reservoir isn't plugged - I checked (that was my first
course of action after discovering the air pocket). But you are right
about the air pocket.

However, this doesn't solve my problem, it only gets me home safely
after boiling... The problem is that I am leaking coolant out of my
reservoir (for some reason). When enough coolant leaks out, my car
overheats. I don't understand why it leaks out. It only leaks out on
long highway trips (mind you, I've never had a city trip over an hour),
and at random intervals (not seemingly dependent on outdoor temperature
either). I have to admit that having the fan on helps, but doesn't
solve my problem. It only leaked out ONCE in the city (when I had
connected my AC, so I d/ced it again). I have never had an overheating
problem in the city (unless I am low on coolant from the highway).

It's extremely wierd... I watch my temperature gauge, and it is fine
for roughly an hour (sometimes 1.5 hrs). Then, it will slowly and
painfully climb to about 5/8s. Then I know I have a problem, and pull
over to fill the reservoir (turning the heat on will bring the temp
gauge down to half until I pull over). I put paper towels beside the
steam vent in the reservoir, and they're drenched whenever this
happens.

What I don't understand is why this only occurs on long trips. If the
bearing in my water pump is shot, then it would be a sure thing, and it
would overheat pretty quickly at high rpms (not after an hour of
maintaining temp at 1/2 mark). I think there are 2 or 3 belts going
over the water pump, so I can't see slipping (and it wouldn't make much
sense again for the same reasons). Do you agree E? How long did it
take for your car to overheat when you were on the highway w/your
bearing issue? I also ran the car for 5 minutes while it was warm in
my driveway at 3000 RPM (where it revs on the highway), and the gauge
wouldn't budge (I had just filled the coolant though).

I'm almost positive that the only place that I'm leaking is the
reservoir (I can always see antifreeze on my control arm when it
happens, and the paper towels are soaked). I think the coolant boils
close to the 3/4 mark on the temp gauge (at least it used to), so why
is it coming out of the reservoir at 5/8? I can't make sense of it.

When I did my little test in the driveway (with my fan controls to the
'0' mark), the coolant level would creep up in the reservoir, but would
go down after some valve (thermoswitch triggered?) opened. After
repeating that cycle a few times, it crept up and overflowed from the
reservoir - it didn't seem like it would stop either, so I turned the
fan on, and the level went down again, and was fine for another 10 mins
of running. Could whatever valve controlling this be giving me
trouble? Why is it leaking from the reservoir so much, and at random
intervals??

Thanks for all of the suggestions; I appreciate everyone's help. I
would love my car if it didn't have this problem...

-Randy

"Rand-E" > wrote in message
oups.com...
> Thank you for your responses.
>
> Eduardo,
>
> You are right. I neglected to mention that while I was on the highway,
> if I ran low on coolant, I would have an air-lock problem. This is why
> the car would heat up again after only 10 seconds of driving AFTER the
> coolant boiled, and the low coolant light came on. After the quick
> overheating happened about 10 times, I finally filled the rad from the
> top rad hose (drank about a gallon), and it worked fine for the rest of
> the trip. You're absolutely right, every time the coolant boils, if
> enough boils out, and the low coolant light comes on, it develops an
> air pocket in the system. The small top hose that connects the top rad
> hose to the reservoir isn't plugged - I checked (that was my first
> course of action after discovering the air pocket). But you are right
> about the air pocket.
>
> However, this doesn't solve my problem, it only gets me home safely
> after boiling... The problem is that I am leaking coolant out of my
> reservoir (for some reason). When enough coolant leaks out, my car
> overheats. I don't understand why it leaks out. It only leaks out on
> long highway trips (mind you, I've never had a city trip over an hour),
> and at random intervals (not seemingly dependent on outdoor temperature
> either). I have to admit that having the fan on helps, but doesn't
> solve my problem. It only leaked out ONCE in the city (when I had
> connected my AC, so I d/ced it again). I have never had an overheating
> problem in the city (unless I am low on coolant from the highway).
>
> It's extremely wierd... I watch my temperature gauge, and it is fine
> for roughly an hour (sometimes 1.5 hrs). Then, it will slowly and
> painfully climb to about 5/8s. Then I know I have a problem, and pull
> over to fill the reservoir (turning the heat on will bring the temp
> gauge down to half until I pull over). I put paper towels beside the
> steam vent in the reservoir, and they're drenched whenever this
> happens.
>
> What I don't understand is why this only occurs on long trips. If the
> bearing in my water pump is shot, then it would be a sure thing, and it
> would overheat pretty quickly at high rpms (not after an hour of
> maintaining temp at 1/2 mark). I think there are 2 or 3 belts going
> over the water pump, so I can't see slipping (and it wouldn't make much
> sense again for the same reasons). Do you agree E? How long did it
> take for your car to overheat when you were on the highway w/your
> bearing issue? I also ran the car for 5 minutes while it was warm in
> my driveway at 3000 RPM (where it revs on the highway), and the gauge
> wouldn't budge (I had just filled the coolant though).
>
> I'm almost positive that the only place that I'm leaking is the
> reservoir (I can always see antifreeze on my control arm when it
> happens, and the paper towels are soaked). I think the coolant boils
> close to the 3/4 mark on the temp gauge (at least it used to), so why
> is it coming out of the reservoir at 5/8? I can't make sense of it.
>
> When I did my little test in the driveway (with my fan controls to the
> '0' mark), the coolant level would creep up in the reservoir, but would
> go down after some valve (thermoswitch triggered?) opened. After
> repeating that cycle a few times, it crept up and overflowed from the
> reservoir - it didn't seem like it would stop either, so I turned the
> fan on, and the level went down again, and was fine for another 10 mins
> of running. Could whatever valve controlling this be giving me
> trouble? Why is it leaking from the reservoir so much, and at random
> intervals??
>
> Thanks for all of the suggestions; I appreciate everyone's help. I
> would love my car if it didn't have this problem...
>
> -Randy


Maybe a hose (the lower one) that can be to thin(old)
and collapse at speed?

Well I don't hace a/c so I don't know about the belt layout for that,
but if it goes over the waterpump then I would think you'd likely not
be slipping, but to be sure just grab the pulley on the water pump and
try to move it up and down and front to rear, it should have NO
movement in it at all. Mine was really bad when I discovered it, but I
normally trravelled on city streets to and from work, but had to go
across the city that day and hit the main highway. I was running for
about 20 minutes before the highway and 10 mins on the highway. after
it cooled and I again used the city streets, I ran for over an hour
without trouble.

But I would check the pulley, costs nothing to check, on the other
hand, how old is your termo-stat? That would be the device that opens
when your car reaches temperture. It opens the connection between your
rad and the coolent in your engine. If it's getting sticky, it might
not be opening when it needs to all the time. If its's old it could be
faulty and sticking, just not all the time. Pain in the ass to change,
but if you have no other ideas, it's cheap if you can do it yourself,
and it would give you the chance to refill the system with proper mix
of antifreeze, after all the water you've been forced to dump in her,
there's probably not much mix left.

Good luck.

Oh yeah, the coolent system is pretty well sealed and the vent on the
reserve tank offers the "path of least resistance", that's why it comes
out there, otherwise it would be like we had in the 70"s, blowing
hoses.

Just so you know why it only seems to leak there.