Weird overheating on 1990 2.0 Turbo Legacy

[New Subaru Fan]

My old 1990 2.0 turbo Legacy (190 000km) starts overheating after 10-15 min of driving.

The engine was rebuilt about 3 weeks ago. We replaced head gaskets, timing belt incl. the tensioner, water pump, thermostat and radiator. After the rebuild of the engine the car ran greatly, no overheating even under severe driving conditions. No leakage of coolant could be observed. But a couple of days ago (about 200 km after the engine rebuild) the engine overheated suddenly just during normal driving. I also would like to mention that on the day before the overheating I drove the car frequently (about 10 times) but for very short distances (1-2 km). And usually I never do it. Maybe this information could be of some significance.

I’ve been struggling with this overheating for the last couple of days now. The car overheats much quicker than as it had the head gaskets blown, so I don't think it's head gaskets this time. I ruled out following problems:

1) Leakage in the cooling system (I just ran car hot and couldn't find any coolant leakage apart from the coolant overflow container)
2) Thermostat (just took it out for the moment)
3) Air-pockets (bled the cooling system thoroughly)
4) Clogged radiator (I simply blew some air through it and I couldn't notice any clogging)
5) Head gaskets (while revolving motor at higher rpms (over 3000) there were no bubbles coming out of the cooling system so I assume the head gaskets are fine).
6) Core heater (I removed it from the cooling system by short cutting the pipes leading to and from it)

My observations:
- while bleeding the system the both upper and lower radiator hose seemed to be pretty cool or just warm (the radiator fans were not on!): it looked to me there was no circulation through the radiator
- also while bleeding the coolant level in the reservoir was almost constant even if I turned off and on the engine - the coolant was not sucked in as it should be

It's unbelievable: the only thing that I can consider as a problem for overheating at the moment would be a water pump. But it was brand new as I installed it!
I know it's not easy to check whether the water pump is working properly. But are there any typical symptoms that would indicate a faulty water pump?

WHAT COULD BE THE REASON FOR THIS WEIRD OVERHEATING ???

I’m going mad, it was such a big effort to rebuild the engine and now it overheats again!
I really want to keep this car cause I love it too much.
Thanks for your help.

[New Subaru Fan]

FINALLY SUCCESS!!!

After 4 days of struggle I figured it out. There was just a tough air pocket.
Apparently those older Legacies are meant to be bled under vacuum, because there's no air outlet valve on the radiator. My friend has a 1999 Legacy and the bleeding was not an issue at all because the air trapped in the cooling system was coming out freely as we were adding more coolant.

In my case I just lifted the right side of the car as much as I could, disconnected the upper radiator hose and turned it upwards. Then I turned on the engine and was slowly adding coolant until it appeared in the hose. Shortly after that the coolant started to come out of the radiator. Then I quickly connected the hose to the radiator. Although pretty pessimistic I decided to give her another go. She didn't overheat this time!!!!

And now my car is back and I can happily celebrate the New Year's Eve!

You have a good one too! Cheers :D

PS: By the way I'm driving without a thermostat now. Do you guys think it would be a good idea to keep it like that? This turbo engine tends to warm up very quickly even without a t-stat.
What are the pros and contras of not a having it?

[mike-tracy]

Con's: Even though you warm up quickly, long straights or high speeds will cool down the motor considerably. Since the motor runs most efficiently at operating temperature (whatever your OEM t-stat was), you'll have worse gas mileage. Also, your heaters won't be working as good, which sucks in the winter. They'll go from nice and warm around town to chilly on those aforementioned higher speeds.

Pros: well, when my HG's went, and I had decided to swap the engine, this prolonged my 'bad' engine's life. I used, no, I thrashed that motor for 40k more miles. No more overheating! (that motor still lived when I finally hauled it back to the junkyard)

YMMV

[New Subaru Fan]

Con's: Even though you warm up quickly, long straights or high speeds will cool down the motor considerably. Since the motor runs most efficiently at operating temperature (whatever your OEM t-stat was), you'll have worse gas mileage. Also, your heaters won't be working as good, which sucks in the winter. They'll go from nice and warm around town to chilly on those aforementioned higher speeds.

Pros: well, when my HG's went, and I had decided to swap the engine, this prolonged my 'bad' engine's life. I used, no, I thrashed that motor for 40k more miles. No more overheating! (that motor still lived when I finally hauled it back to the junkyard)

YMMV

Yeh, I'll definitely put the t-stat back when the snowboarding season begins and I will be traveling long distances. At the moment I'm thinking about leaving the engine without the t-stat, as the area here is quite hilly and I'm driving only about 10-20 km a day up and down those hills anyway.

Actually I should have taken the t-stat when my gaskets were blown. I wouldn't have to refill the engine with coolant every second day and should have saved my nervs.

How often (how much coolant) did you have to add when your HGs were blown?

[mike-tracy]

When my HG's blew, on my 2.2 Legacy, it would fill up the overflow bottle (this was an N/A model). I would use a turkey baster to put the "extra" fluid back to the engine. Every time the car cooled down it would fill the bottle but I only refilled the radiator every morning or if I needed to go out of town. This worked for me, and remember I wasn't worried about damaging the engine since I had a replacement already lined up.

[New Subaru Fan]

Yeh, finally the car runs well now! Thanks for your help in this matter. A thermostat is indeed important for a normally functioning engine. I found that it took for the engine ages to warm up without a t-stat.
And I'm also good at bleeding the air out now. I've recently added some radiator-flush into the system. It will hopefully remove all the rust and other crap.
Now having fixed this leakage problem I'm moving on to the other issues: check my recent topic 'My Legacy 1990 turbo 2.0 (manual) starts to jerk when I push her hard'. Maybe you can suggest a solution to this one. Cheers