97 outback 2.5 overheating

[cardoc]

Don't use any "sealer" like Bars Leak in the coolant. It will cause more damage than good. Clogged radiator, gunked up water pump and thermostat, clogged heater core, clogged coolant ports in the engine. It will just add to repair cost.

Has the HG been truly verified?

It is possible, if you know which side, to only repair the side with the leak, cutting cost for the short term. The opposing side should also be done for safe measure, but can be eliminated for now. Although, the best way to perform the work is to remove the engine, and the engine will be out for the repair, its not much more in labor to do both sides, doing one side will cut the cost a couple hundred.

Its your car. Its your budget. Pros/Cons time. No easy way about it.

[crshbandit]

Too late. I already added a bottle of that crap 2 my radiator. My mechanic suggested it! Someone else suggested trying one of those pressure relief rad. Caps. Tried driving with the valve open on that and it still over heated. Also my upper rad. Hose totally collapses every time it overheats.

[Xnander Bishop]

A cars cooling system is based on pressure. If you increase how much pressure it can hold the higher the boiling point. If you raise the boil point, the less likely it will over heat. Creating pressure to keep the boil point high keep it from generating bubbles, in turn keeps air pockets out and keeping the motor from over heating. Mt. St. Helens is an example (in a way). All that dirt kept the water in and the lava heated it up but when the dirt gave it blew, all that water that was 600-700 degrees when to steam in a flash. Anyways, either one; you have a HG leak, at which a leakdown test will find that out, or two; you have a leak some where in the system (hose, waterpump, or heatercore for examples), or three; the cooling system has not been properly filled and not bled right to eliminate possible air pockets.

[plain OM]

While the symptoms seem to be HG, the upper rad hose should never collapse.

As already explained, pressure is a critical part of the cooling system function. The rubber hoses play a role in this through their ability to stretch and return to their original shape.

Coolant, in liquid form cannot be compressed, at least not much. Moreover, most of the engine cooling system is solid metal and it too cannot stretch or contract to any great degree.

In order to build up pressure inside the cooling system when it's full of liquid, something has to compress or stretch, and in this case it's the hoses. They stretch out as the liquid coolant heats up and expands. As the coolant reaches full engine operating temperature, the hoses begin to resist stretching any further and additional expansion of the coolant is released through the radiator cap into the external reservoir.

As the car is driven, the stretched rubber hoses maintain the internal pressure in balance with the pressure setting of the rad cap, thereby preventing boiling.

When the engine is stopped, and starts to cool, the liquid coolant starts to contract (shrink). As it does, the rubber hoses contract back to their original shape. When the coolant continues to cool, the hoses are supposed to maintain their original shape, and, consequently, a negative pressure is built up inside the cooling system. This causes the vent valve on the rad cap to open, drawing coolant back in from the external reservoir.

If all of this is working properly , the engine shouldn't overheat, and the coolant inside the engine will always be full to the top of the radiator (at the rad cap neck).

But what happens if the rubber hoses are incorrect or weak? A hose that cannot limit it's stretch will continue to balloon out as the engine heats up instead expanding a bit and then resisting any further stretching. Because the hose is weak, there won't be the proper build up of internal of pressure and, going back to the system explanation in the previous post, if the pressure isn't maintained the coolant can boil.

Similarly, if the hose cannot maintain it's original shape and resist collapse as the engine cools down, there won't be any vacuum, and whatever coolant had been expelled to the external reservoir won't be drawn back into the engine through the rad cap vent valve. The next time the engine is run, there will be a shortage of coolant inside.

And if the rad cap isn't working properly with the hoses to maintain pressure, or if the rad cap is loose (same effect), without internal pressure the coolant can boil. (Temperatures around the cylinder walls and head can reach into the 1000 degree range. The pressure on the coolant, combined with the high rate of flow provided by the water pump, is usually sufficient to prevent the coolant that comes in contact with those surfaces from boiling. But if the pressure isn't there and/or the flow isn't fast enough, the coolant will boil and release bubbles into the system.)

A collapsed hose is an important symptom. It's telling you that the hoses might be weak or that the system is unable to draw liquid back from the external reservoir as the engine cools. An incorrect rad cap is one possibility. Another is the hose going to the external reservoir might be blocked (especially if there's some material down at the bottom of the reservoir).

While this doesn't negate the possibility that there is a HG failure, the collapsed hose could be a sign of a compounding problem.

[crshbandit]

Wow, that was an awsome explanation! I may be screwed but at least I learned something! I am going to take a HUGE financial loss on this car. I don't even know what it's worth if I were to try and sell it now with a blown hg. It sits covered with snow out at my mom's and I don't honestly know what to do with it.

[Xnander Bishop]

What about getting a new reservoir cap. If a hose collapses then maybe the cap is letting pressure out but allowing it to come back in.

[crshbandit]

How can the blown hg be truly verified? Is it true that a compression test will not indicate whether you have a bad hg? Does the engine have to be torn down to be 100 percent sure it is the hg? I checked into the kit for testing for exhaust gasses in the rad. fluid but it is pretty expensive and I don't want to spend the money for it if there is another way. The car never seems to miss while driving and I don't notice any loss of power. My mechanic, ( who I completely trust) did a leak down test and he said it checked out fine.

[Xnander Bishop]

Not really but a leak down test can tell you where a leak is at. Here is a video that shows how it works.

How To Perform A Leak Down Test - EricTheCarGuy - YouTube

How To Perform A Leak Down Test - EricTheCarGuy - YouTube

[jbwood5]

Originally Posted by crshbandit

How can the blown hg be truly verified? Is it true that a compression test will not indicate whether you have a bad hg? Does the engine have to be torn down to be 100 percent sure it is the hg? I checked into the kit for testing for exhaust gasses in the rad. fluid but it is pretty expensive and I don't want to spend the money for it if there is another way. The car never seems to miss while driving and I don't notice any loss of power. My mechanic, ( who I completely trust) did a leak down test and he said it checked out fine.

Some HG leaks only occur when the engine is fully warmed up so the leak down test may not be giving you an accurate diagnosis. You could try shopping for the test kit, either online or looking for coupons online for a local auto parts store. You should be able to find the kit for about $20 or $30 less than you were quoted. Often Advance Auto Parts has 20% coupon codes (try AP20). You purchase online and pick up at a local store. Perhaps even E-Bay is cheaper if you ever use them.

Once again, top off the coolant and run the engine for a bit to bleed the air out while adding some coolant or distilled water. Once you heater output is pretty good, you got most of the air out. Put the rad cap back on (inspect the rubber seals for any tears or deformities). Continue to run the engine while you look in the overflow container. DO NOT LET THE ENGINE OVERHEAT. If you are seeing bubbles, take a wiff (smell) of the coolant. If it smells like exhaust, the HG(s) is certainly bad internally. Any strong discoloration of the coolant, white steam out the tailpipe (on a fully warmed up car), or any cross contamination of fluids is a sign of HG failure.

[crshbandit]

I am about to take the plunge and have my mechanic replace the hg's on my 97 outback 2.5L . He offered to do the job for $1000 which I think is really reasonable. I have known him for years and I do trust his work. He will send the heads out to be checked for warpage and have them milled if needed. Is there anything else I should talk to him about before he starts this job? Should he use an aftermarket hg rather than the OEM Subaru hg? I have heard this is a good idea, just can't remember what brand was recommended. The car now has 153,000 mi. on it. He already replaced the waterpump and the car has a new timing belt also.