Subaru overheating, a new theory;

[svxfiles]

My Father has a 1999 Subaru Outback 2.5 automatic wagon with 246k.
I replaced his head gaskets, water pump, timing belt and front seals about three years ago.
Friday night on a mountainous road it overheated.
That night I replaced the thermostat with a new stock Subaru one,
and it overheated about a mile later.
After getting it towed to my garage I was able to look at it today.
Changed the upper rad hose.
Flushed and replaced the cooked coolant with strait water,
checked the cam timing.
It was correct.
The fans work properly.
Reassembled the car and took it out for a test on "Head gasket Hill."
About 72° ambiant, AC on the coldest setting, ran up the seven mile long, seven° incline.
The AC remained ice cold, and the gauge stayed at below the normal position.

Untill two miles past the top of the mountain.
Now the gauge spikes, and water is boiling into the overflow.

I check the upper hose, VERY HOT,
check the lower hose, 100°f or less.
Aparently improper coolant flow!

Top hose hot,
bottom hose cold,
bad flow.

I THINK that I will find out tomorrow why.
I THINK that because he has a slight power steering reservoir leak that the ATF has saturated the timing belt,
and under load causes the water pump to slip,
causing overheating only under substantial load.
Hopefully, more on this tomorrow!

[Huskymaniac]

Interesting theory. I also wonder if the whole headgasket/overheating thing isn't a chicken and egg scenario as well. Does a car overheat because of a bad gasket or does the gasket leak because of stresses caused by an overheating event?

I went to the US Army Military Academy in West Point on Friday and Saturday for a basketball coaching clinic. I didn't realize how high of a hill/mountain/cliff it sat on. It was such a steep climb and such a long climb that I grabbed my OBD2 reader to check the engine temperature as I was curious. I was happy to see it only reached 203F at the top of the hill. What was maybe more amazing is that is hit 183F by the time I hit the bottom of the hill/mountain. I guess that shouldn't have been too much of a surprise as normal is around 193F when I am cruising down the highway. I have just never seen the temperature get that low once the car warms up. I guess coasting down a long hill will do that. The temp gauge never moved out of its dead zone the whole time. 14 months after the TEMP SENDER saga and all is still well...........

On the way home I checked the "highway" gas mileage and it came in at 29.25MPG. I thought that was pretty good considering that RT86/RT17 in NY is a pretty hilly highway. My TC unlocked a few times on the drive as some of those hills can be long and steep. Plus there were lots of annoying construction zones.

[Conn SVX]

How high is WEST Point??/ Last time I was there we watched eagles soaring BELOW us . That is a good test of a car for sure. I bet altitude may have played a part also.

[Tapani]

Maybe a severely restricted radiator (not enough flow)? Did you check while flushing the system?

Tapani

[kwren]

Originally Posted by Huskymaniac

Interesting theory. I also wonder if the whole headgasket/overheating thing isn't a chicken and egg scenario as well. Does a car overheat because of a bad gasket or does the gasket leak because of stresses caused by an overheating event?

Well, of course, it could be either one. Overheating can cause the head to warp and blow a head gasket... Also the age of our vehicles seems to take its toll.

Originally Posted by Huskymaniac

On the way home I checked the "highway" gas mileage and it came in at 29.25MPG. I thought that was pretty good considering that RT86/RT17 in NY is a pretty hilly highway. My TC unlocked a few times on the drive as some of those hills can be long and steep. Plus there were lots of annoying construction zones.

I also get better gas mileage driving down hill, but frequently get about 30 mpg on long road trips.

Keith

[svxfiles]

Originally Posted by Tapani

Maybe a severely restricted radiator (not enough flow)? Did you check while flushing the system?

Tapani

The radiator is an aftermarket one that is only a year old, or less.
It is a single row, just like the stock Outback radiator, that year.

[kwren]

Originally Posted by svxfiles

I check the upper hose, VERY HOT,
check the lower hose, 100°f or less.
Apparently improper coolant flow!

Sounds like you nailed it. Water pump pumping and then not continuing to pump... as long as coolant "stays full" when this thing begins to malfunction.

Keith

[92snowmachine]

i have seen this happen twice, on the same car. car came in for similar reasons and after taking off the timing cover i could spin the water pump by hand with the belt still on. told customer it needed new belt and ps pump. customer declined ps pump but replaced belt. returned several months later for new belt and ps pump for the exact same problem. the difficult thing was finding new timing cover gaskets (for a cheap customer that wouldn't replace the cover with a new gasket) because they had swollen so bad they wouldn't fit back into place.

[Uncamitzi]

Originally Posted by 92snowmachine

i have seen this happen twice, on the same car. car came in for similar reasons and after taking off the timing cover i could spin the water pump by hand with the belt still on. told customer it needed new belt and ps pump. customer declined ps pump but replaced belt. returned several months later for new belt and ps pump for the exact same problem. the difficult thing was finding new timing cover gaskets (for a cheap customer that wouldn't replace the cover with a new gasket) because they had swollen so bad they wouldn't fit back into place.

I noticed that when I was changing my water pump/timing belt last month... what I did was trim them down...and used a good gasket maker to "stitch" them back to be air and water tight..

[davew833]

Ah, the EJ25 is such a GREAT engine...

[svxfiles]

OK, time to eat crow.

New timing belt,
new water pump,
still overheats.
I now realize that it has a leaking head gasket, or cracked head ...
Moreonthis later...

[kwren]

The key...

Originally Posted by kwren

as long as coolant "stays full" when this thing begins to malfunction.

Keith

There you go!

Keith

[Subaru Alliance]

did you bleed the cooling system after re filling it and replacing the t-stat?

I had a similar issue coolant was full, fans worked but still got random overheating, come to find out it was air bubbles hanging out over top of the t-stat, then when the coolant warmed up, the t-stat stayed cold because it had the air bubbles keeping the t-stat from opening. the air bubbles kept the hot coolant from warming the t-stat enough to open and allow circulation.

Not even sure if it's still necessary to do that, just a thought.

[kwren]

To eliminate that problem, I simply fill the radiator, then disconnect the end of the big hose at the top of the radiator, move the end over far enough to poor collant down the hose and the air trapped on the other side of the thermostat come right out. It made sense to me, so I tried it one day! Works every time for me... so far

Of course, I always fasten the end of the big hose snugly back to the top of the radiator

Keith

[92snowmachine]

another good trick is to jack the front of the car up as high as you can. this puts the radiator cap high in comparison with the rest of the cooling system and tilts the surfaces a little so air has a harder time trying to find a place to hide.