Interesting overheating problem 1991 Subaru Liberty 4wd station wagon.

[traveller888]

I have an odd problem with my 1991 Subaru Liberty4wd station wagon. The
car has recently had cooling system flushed and then a head gasket
redone. Now when driven in traffic or city roads for middle distance
the temperature gauge moves to half way and stays there. If I take the
car on the freeway and drive for a long distance the temperature gauge
again is perfect at half way.
BUT after I return to city conditions and stop at a traffic light or
drive in traffic at under about 1500 rpm the temperature steadily rises
to 4/5th the way to high.
Then if I begin driving (or put the car in neutral) and take the revs
to above 2500-3000 the temperature very quickly drops to normal (half
way again).

Any thoughts on this would be greatly appreciated as my mechanic is at
a loss.

Thanks

david

 

[l.lichtman]

I can think of an explanation, but it may not be the right one. Let's
suppose that when you go out on the freeway, you lose coolant.
However, with the high air flow, the radiator is still able to cool the
engine. As soon as you slow down, however, you lose the high air flow,
and with the low radiator fluid level, the fans can't handle it. What
makes me only half-believe this, however, is: the mechanic should have
observed the low coolant level and figured this out himself.

 

[traveller888]

Good thought - but it doesnt seem to loose coolant but i will be more
observant to see if it does.

The one that amazes me is still the fact that after it heats up at low
revs just puting it in nutral and reving it a bit cools it down again
!!!!!

 

[l.lichtman]

(clip) The one that amazes me is still the fact that after it heats up
at low

revs just puting it in nutral and reving it a bit cools it down again
!!!!!

^^^^^^^^^^^^^^^^^^
That suggests the possibility that the water pump is not working at low

rpm. Possibly a loose drive pulley, or a loose impeller?

 

[schema]

check the fan when the temp rises. My guess it the fan is not working.

 

[traveller888]

tx

I made this sugestion earlier to my mechanic and his responce was that
the impeller is driven off the timing belt so it either works or it
doesnt and if it was loose we would hear it

but ..... I may ask him to check it again.

 

[Kurt C. Hack]

Fan isn't working. Probably forgot to hook it back up when the head
gasket was done.

-Kurt

 

[Cam Penner]

Fan isn't working. Probably forgot to hook it back up when the head
gasket was done.

Perhaps the fan was put in backwards? (Or maybe the leads
were hooked up backwards?) I don't know if that's possible
on your car. I did it on a VW I had once. The fan was
blowing air FORWARDS through the radiator. At a stop, it
was fine, and at highways speeds it was fine, but when
driving slowly, the airflow from driving and the airflow
from the fan cancelled each other out.

Stand in front of the car when the fan is on and feel which
way the air blows.

 

[Andrew Garth]

OK sounds almost identical to the problem i had in my 1990 Liberty Wagon.

I had a similar mysterious cooling problem......I replaced the radiator
hoses, the thermostat, had the radiator professionally inspected (it was
only two years old), etc etc.

After trying everything else, and contrary to the advice of the subaru
dealership, i replaced the water pump. That solved the probelm.

Turns out that the water pump was on its last legs and wasnt circulating the
water. So, short trips it would be fine, because the water in the block and
the small circulation kept everything cool enough...a drive on the freeway
was fine, because of the extra airflow...But drive too long and into a
headwind and after about 40min it would boil..

The giveaway (once you know your thermostat is fine) is that after driving
for a while, the lower radiator hose was still cold. You expect it to be
much cooler than the top hose, but not cold.

Hope that gives you a little food for thought

Cheers
Andrew

 

[traveller888]

Hi Andrew

My mechanic continues to be sure its not the water pump. He tells me
that there is no way it can be sending reduced flow throught the system
and only cool the system properly when the revs are high.

Do you happen to remember what the problem was with the waterpump ? How
did it fail?
I have been told it will be au$320 to replace it and have spent enough
on the car latly ;-)

Thanks in advance

david

 

[Andrew Garth]

Hi David
Unfortunately by the time i actually replaced the water pump i was so over
the whole process that i didnt actually keep the water pump to figure out
why it failed!

Subaru had pressure tested the system, and the first time they did it there
was a tiny pin-hole leak on one of the seals on the water pump. They
dismissed it originally.

When i finally had decided that the water pump was the ONLY thing left to
replace, the Subaru mechanic i spoke to looked at the report and suggested
that the pin whole leak may have been sucking in air occasionally. If it
sucks a bit of air in, the impleller cavitates and doesnt pass any water
through the system!.....So based on everything else he agreed with my
diagnosis.

I bit the bullet asked for it to be replaced and sure enough it worked. I
also figured that after 250,000 kms, the waterpump had seen a lot of wear
one way or the other!

If you want to compare symptoms and have a chat about it (im in
melbourne),...Email me your number at
andrew dot garth at aues dot aerospace dot gknplc dot com (sorry, just dont
want my work email spammed)

I can totally sympathise with you...sorting out my cooling system took me
about 4-6 months and cost a lot of $$ overall

cheers
Andrew

 

[l.lichtman]

Andrew Garth wrote: (clip)the Subaru mechanic i spoke to looked at the
report and suggested that the pin whole leak may have been sucking in
air occasionally. If it sucks a bit of air in, the impleller cavitates
and doesnt pass any water through the system!(clip)
^^^^^^^^^^^^^^^^^^^
I hate to bring this up now, but do you suppose a drop of epoxy or a
piece of tape over the pinhole might have fixed it, or at least
verified the diagnosis?

 

[Andrew Garth]

Thanks guess it might have.
Compared to the grief it had caused me trying to track down the
issue.....the $320 was the best money ever spent

cheers
Andrew

 

[conmadre]

david,
did you ever find out what was wrong?? 99 Outback Wagon 2.5L, and i have
exactly!!!EXACTLY! the same symptoms of overheating at stops when engine
is good and warm, and then the temp going down with high rpm's... i have
replaced the waterpump, cleaned the radiator, new radiator cap and
thermostat....i am about to have the head gaskets done even though a
compression test shows nothing...please let me know what you found out
thanks
david

 

[Jim Stewart]

david,
did you ever find out what was wrong?? 99 Outback Wagon 2.5L, and i have
exactly!!!EXACTLY! the same symptoms of overheating at stops when engine
is good and warm, and then the temp going down with high rpm's... i have
replaced the waterpump, cleaned the radiator, new radiator cap and
thermostat....i am about to have the head gaskets done even though a
compression test shows nothing...please let me know what you found out
thanks
david

Make sure your fans are coming on when
the engine gets hot.

 

[traveller888]

David
Ya that sounds exactly like my problem.
My current guess is that it's a bubble in the cooling system at low
revs this bubble is siting over the temperature sensor so the heat is
gathering on the sensor. When you rev the bubble is moved and water
again gets to the sensor quickly cooling it down.

The problem seems to have stoped in my car which could be because its
getting cooler here in Australia or I am using the heater and have
moved my bubble to the heater coil as I now hear bubbles in my heater
coil if I drive with the heater on and no radio