Overheating 1994 Legacy

[TURNER]

Advice Needed On What Might Be Wrong? Have Replaced Radiator And Cap, Water Pump, Thermostat, Head Gaskets. The Overheating Only Happens After Hiway Speeds Of 75mph, The Temp. Will Start Slowly Climbing Up And The Heater Starts Cooling Down. If I Rev Up The Engine It Will Cool Down For A Little While.

This Leads Me To Think Air In My Heater Core, But How Is It Getting There After New Head Gaskets ? I Have Burped The Cooling System Several Times. Where Else Could This Air Pocket Be Coming From.

The Radiator Has Been Pressurized And No Leaks.

[Reveeen]

If, as you say, you have covered all the bases, did you check the heads for cracks?

[bcward]

This sounds similar to a problem I am currently having with my 99 outback. Running warm at sustained 65 MPH (~2500 RPMs), but punch it up to about 72 MPH (~3000 RPMs), and the coolant temp drops for a while. Same deal, new headgaskets, t-stat, water pump - and my mechanic says they use a system of filling it that prevents air bubbles, so that shouldn't be it.

 

Have you tried elevating the front end and adding coolant till it flows out the vent plug hole?

 

Just after it runs hot, does it show any signs of bubbling in the surge tank?

 

What brand t-stat and water pump did you use?

[TURNER]

This sounds similar to a problem I am currently having with my 99 outback. Running warm at sustained 65 MPH (~2500 RPMs), but punch it up to about 72 MPH (~3000 RPMs), and the coolant temp drops for a while. Same deal, new headgaskets, t-stat, water pump - and my mechanic says they use a system of filling it that prevents air bubbles, so that shouldn't be it.

 

Have you tried elevating the front end and adding coolant till it flows out the vent plug hole?

 

Just after it runs hot, does it show any signs of bubbling in the surge tank?

 

What brand t-stat and water pump did you use?

 

I HAVE TRIED TWO, "STAT" AND ONE FROM O'RELLY.

HAVE YOU TRIED CHECKING YOURS FOR EXHAUST GASES IN THE RADIATOR?

I PLAN TO TRY THAT NEXT, AFTER I LEARN HOW TO GET IT TO FAIL CONSISTENLY.

[TURNER]

If, as you say, you have covered all the bases, did you check the heads for cracks?

 

I KNOW MY MECHANIC MILLED THE HEADS AND SAID THEY LOOKED GOOD.

I AM NOT SURE IF HE JUST LOOKED AT THEM GOOD OR MAGNAFLUX THEM.

HAVE YOU TRIED CHECKING FOR GASES IN RADIATOR ? IF SO, DOES THE TESTING HAVE TO BE DONE AT THE EXACT TIME OF THE LEAKING ?

I SURE CAN'T CHECK IT AT 75 MPH, AND WHEN I STOP AND LOOK IN THE RADIATOR OVER FLOW TNK, I NEVER SEE ANY BUBBLES.

THANKS

[Wayne Boncyk]

This sounds EXACTLY like the issue I had with my '96 OBW, when I had a non-Subaru thermostat installed. Here's the deal - the Subie t'stats are located near the bottom of the engine, in the coldest part of the system. The way the Subie coolant loops are designed, there needs to be a little bypass of coolant past the t'stat even in the coldest conditions, or you get a pretty large thermal gradient between the top and the bottom of the block. That can lead to a case where the loop into the radiator is never opened, even though the block temp sensor (up top) shows higher than normal temperature. Subie t'stats have a little bypass hole in the plate, and further a little plug loosely riveted in that hole. I don't know exactly how that modulates the coolant flow, but with a genuine OEM subit t'stat I have never seen the high temp at low RPMs when the outside air temps are below freezing. Hoever, with TWO different makes of aftermarket t'stat (neither of which had the little bypass hole and rivet thingie) I saw exactly the behavior that you are describing.

[TURNER]

This sounds EXACTLY like the issue I had with my '96 OBW, when I had a non-Subaru thermostat installed. Here's the deal - the Subie t'stats are located near the bottom of the engine, in the coldest part of the system. The way the Subie coolant loops are designed, there needs to be a little bypass of coolant past the t'stat even in the coldest conditions, or you get a pretty large thermal gradient between the top and the bottom of the block. That can lead to a case where the loop into the radiator is never opened, even though the block temp sensor (up top) shows higher than normal temperature. Subie t'stats have a little bypass hole in the plate, and further a little plug loosely riveted in that hole. I don't know exactly how that modulates the coolant flow, but with a genuine OEM subit t'stat I have never seen the high temp at low RPMs when the outside air temps are below freezing. Hoever, with TWO different makes of aftermarket t'stat (neither of which had the little bypass hole and rivet thingie) I saw exactly the behavior that you are describing.

 

WHEN IF FIRST GOT THE CAR THEY HAD ALREADY REPLACED RADIATOR, WATER PUMP AND IT HAD A FACTORY THEROSTAT. I CHANGED IT FIRST BECAUSE IT WAS THE CHEAPEST THING TO DO. I DIDN'T KNOW IT HAD ANY PROBLEMS WHEN I BOUGHT IT 2 MONTHS AGO. I DID KNOW THEY HAD COOLING PROBLEMS, BUT I THOUGHT THE DEALER HAD FIXED IT.

THANKS TURNER

[nipper]

A few things, like everyone has said, make sure there is a SUBARU t-stat in the car.

 

Next fill the cooling system the old fashioned way (you will never get air in the system). Start the car with the cap off. Let it run till the t-state opens (the car should spit up some fluid). Top off the coolant, make sure you have a 50/50 mix.

 

Next thing to look at is the condition of the timing belt, if its glazed and slipping. Are there any oil leaks or oil on the belt.

 

Lets go for some long shots, what brand water pump? Is the AC condenser free of dirt and debree?

 

Does this happen with the ac on or off?

 

The radiator is it new or used.

 

How is the altenator. Low voltage can give you a high temp reading.

 

Rent a code reader and look at the ECU engine temp vs the gauge temp. Mid point should be 200-210 (thats what my cangauge says). If the gauge is highs and the reader says 200 ish its the sender.

 

nipper