ive been having overheating problem with my car.

 

99 legacy sus. automatic, 2.5l engine 130k owned it for 2 years now.

 

it overheats randomly. i just did a hydrocarbon test on my coolant with a block tester and there was no hydrocarbon in the system. im not losing any coolant. coolant level is good. i changed the radiator cap. thermastat is working good. i bleed the system of air. radiator fan turns on just fine and still having problems. it does not happen everyday. only happens sometimes randomly. what do you think could be the problem?

Edited October 20, 201510 yr by legacysus

is it possible my water pump stops working at times and starts working again? could i still have a head gasket leak even thou i dont have any trace of oil or hydrocarbon in my cooling system?

What year, model, engine?  What kind of tranny?  How many miles on it?  How long have you owned it? 

99 legacy sus. automatic. 130k owned it for 2 years now.

2.5l engine

2.5l engine

How do you know the Thermostat is working well, Did you test it?  Look for bubbles in your radiator over flow tank while its running.

yes i tested the tstat with boiling water several times. it opens and closes. i noticed bubbles in my res tank one time when it overheated and the coolant started to boil over into the tank. but i dont currently get any bubbles at the moment. im not sure if the bubbles were just steam. or combustion gasses.

Edited October 20, 201510 yr by legacysus

is it safe to say that if i have no trace of hydrocarbon in my radiator or cooling system then i dont have a head gasket leak?

 

or is it an inaccurate test?

 

 

"hy·dro·car·bon

ˌhīdrəˈkärbən/

nounCHEMISTRY

a compound of hydrogen and carbon, such as any of those that are the chief components of petroleum and natural gas."

Edited October 20, 201510 yr by legacysus

Ok next question. What brand thermostat is it. If it is not an OEM  it may be sticking.

Sounds like an after market T-stat or a failing T-stat. Buy a new OEM or Stant EXact stat or Napa has a premium T-stat made by Tama IIRC. If it doesn't cost $20+ bucks you are not getting the right thermostat. I believe my Tama brand T-stat cost $26

I am betting it is a head gasket problem. Subarus with 2.5 motor in 1996-1999 cars are famous for bad HGs. Having blown head gaskets in a 98 and 99 Outbacks, I have some experience. A blown head gasket won't present itself all the time, but most likely to do so, when stressed at highway speed, or climbing steep grades. Then, the temp gauge spikes to HOT in a hurry. Bubbles in the rad over flow is classic symthom of a bad head gasket. It is caused by exhaust gas leaking through the bad HG into the cooling system, so produces bubbles in coolant, and causes motor to over heat.

 

I don't think trying a new T-stat will help the issue. Some people have removed the T-stat, and driven for a while to mitigate the over heating problem. But, that is not much fun driving that way in winter, as it results in minimal cabin heat. What ever you do for the present, do not drive the car when the motor is over heating. Continuing to do that will destroy the motor. Subarus don't like to be over heated.

 

There is a much written on this issue in the archives of this forum. Use the forum "search" feature to do this. Read what others have written, and I think you will come to the conclusion, that bad head gaskets is your culprit.

Edited October 20, 201510 yr by Rooster2

Still, he did test for hydrocarbons... That's a pretty diffinetive test for an internaly leaking head gasket on a subaru

Edited October 20, 201510 yr by mikaleda

Still, he did test for hydrocarbons... That's a pretty diffinetive test for an internaly leaking head gasket on a subaru

Since the over heating problem is not consistently severe, but randomly,  there may not be sufficient hydrocarbons in the cooling system to show up on a test, so it still could be bad head gaskets.  I am also guessing the owner is ocassionally replacing coolant, after experiencing a coolant boil over, so that too could lessen hydrocarbons in a test.

Your right, it is possible... But I'm just saying let's not doom it just yet.

"A blown head gasket won't present itself all the time, but most likely to do so, when stressed at highway speed, or climbing steep grades. Then, the temp gauge spikes to HOT in a hurry"

 

stress seems to make no difference at all. i push this car very hard everyday. i hit 6k rpm on high way and up hills all the time. but like i said sometimes it will run just fine without overheating for 3-4 days. if im pushing it hard everday why would the gasket not leak for 3-4 days?

sometimes it overheats when the car is just sitting there warming up. so stress doesnt seem to make a difference.

 

i havent been adding any coolant, because the res tank does not overflow. it all gets sucked back into the system.

 

ive also tested for hydrocarbon 5mins after the car overheated and still no trace of hydrocarbon.

 

what about the water pump is it possible for a water pump to work Intermittently?

 

can my water pump pulley seize up and then break free? seize up again and break free again? or does that never happen? would the belt just slip past it and keep spinnin?

Edited October 21, 201510 yr by legacysus

what if i take the tstat out just to see if the problem will continue?

 

if i take the tstat out and the car still overheats does that mean its not a head gasket leak?

 

im thinking if i take the tstat out it can still overheat with head gasker leak because if it creates a gas chamber around the pump impeller then the pump wont circulate the coolant. what do you guys think?

 

hmmm or maybe no since the pump sits at a preaty low spot in the system and gases normaly rise unless it gets caught.

Edited October 21, 201510 yr by legacysus

what about the water pump is it possible for a water pump to work Intermittently?  No, water pump works full time, when motor is running.


can my water pump pulley seize up and then break free? seize up again
and break free again? or does that never happen?   No, water pump works full time, when motor is running.

 

 

would the belt just
slip past it and keep spinnin?  No, that could not happen.

 

The next time you start to see the temp gauge climbe above normal, stop the car, open the hood, and check for bubbles in the rad over flow tank. If you see bubbles, it is a sure bet that it is a bad head gasket.

You had a scientific test performed that ruled out hydrocarbons. This would indicate that
you do not have a head gasket issue.   I have a non-scientific answer.  After being around this forum for years I have seen several
people report your results to only see it come down to a bad head gasket.  Given the car, engine, miles, the year I think
you could have a bad head gasket.  The one sign for me is the blow back coolant into the reservoir.  If you let that go long enough it would then
blow out of the tank.  You also bled the coolant so that is ruled out.

​

could there be a bad temperature sensor?

ok the car overheated again today. i looked for bubbles in res tank as the car was overheating and there was no bubbles. none at all not even one. the tank filled up almost to the top. i waited and about 5mins after the car cooled back down again.

ok once again it just overheated. this time i do see some small bubbles in the res tank. i tested the res tank for hydrocarbon as the bubbles appeared while the car was overheating. and still no trace of hydrocarbon. what the smokes is going on here.

Edited October 21, 201510 yr by legacysus

i think these bubbles are just steam. just like when you boil water u get some bubbles. if they were combustion gasses then why im not getting any reading while the car is overheating. the liquid in the tester should have turned atleast green for small amounts of hydrocarbon or yellow. but no it stays blue even though the bubbles are appearing during the test while the car is overheating.i dont get it.

Edited October 21, 201510 yr by legacysus

The bubbles you are seeing is from the coolant turning to steam due to the temperature rising and the pressure blowing it back into the res tank.  If you drove it long enough the res tank would fill up then would blow out of the tank down your driver side fender leaking all over your tire.  On rare occasion on this forum I have seen the root cause as air being in the system.  All other root causes were a head gasket.

so its been a few weeks and i did some tests and found some problems. even tho i was not losing coolant and noting seemed to be leaking, i did a pressure test at 15 psi and found many leaks. fixed all the leaks and niw the system holds 15psi for over an hour. it still overheats. i was think the system was airlock because i heard in some cars u can only remove all the air if you use an airlift tool that puts the system in a vaccum so u can vaccum fill. i bought the tool and i cant the right amount of vaccum. the vaccum drops fairly fast. i dont get it i can hold 15psi but i cant hold a good vaccum. if there some kind of pressure test i can do to know if i hav a head gasket leak? i dont see any bubbles in the radiator or the res tank anymore. maybe my radiator is clogged any ideas on how to test tat. its looks clean as far as i can see.

Edited November 28, 201510 yr by legacysus