New Overheating Thread

[Nomake Wan]

Okay, I'm gonna make a new thread to attack this one, again. For reference, here's the old thread:

http://www.subaru-svx.net/forum/showthread.php?t=40723

Anyway, I just got done doing a trip up to San Francisco and back from Orange. It's about 400-something miles, with almost 6 hours straight of driving. The drive back is what really gave the most clues to my problem.

First, the car has no problems around town, ever. Even on the freeway, it just has no issues around where I live. Even if I stomp on it, it still doesn't push the heat.

Now, the trip from Berkeley back? This was actually a great indicator that something odd is going on. It was 4 hours of straight driving, on almost completely flat roads. Here's a map:

Google Map

Now, we stopped to get gas before we hit the Grapevine. It was when we came to a stop at the gas station that the car began to overheat. It had been fine this whole time, but as soon as we stopped, it heated up. I kicked the heater in, the temps dropped a bit, and I turned the car off. We got gas, and by the time we were finished at the station, it was back to normal operating temp. We hit the grapevine.

Predictably, the high load on the grapevine caused another overheat the very first time we had to slow down because of some idiot moving into the fast lane and doing 50. I then moved over into the slow lane and limped us up the hill, the temps staying about 3/4 of the way up the gauge. As soon as we got downhill, the problem vanished.

The final time was when we hit gridlock traffic on the 5 South. There was a major accident, and everyone was stopping to look at it, which had completely stopped traffic for miles and miles. Again, as soon as we slowed down, the temps crept up. I put the heater on, and it seemed to help a little, but not much. What actually helped the most was putting the shifter into '1' so that the revs stayed up. We never moved faster than 10 MPH for the whole time, so keeping the revs around 1500-2000 seemed to keep the temps manageable.

Now, my analysis was that there didn't seem to be enough capacity in the system, since turning on the heater adds a circuit to the cooling path and thus increases the volume of the cooling system. My dad's analysis, though, after driving the car around Orange and such, was a little different. He thinks there's something caught up in a pathway somewhere that's blocking flow; not enough to completely block coolant, but enough that after running for extended periods, the heat is too much. And that turning on the heater isn't really adding volume as much as it is dropping pressure in the system, which is jolting whatever it is that's stuck. He says it feels like something 'thermostatic'.

The Subaru dealer did a test on the cooling system and concluded that it was not a head gasket (block test) and that they actually couldn't get it to overheat (supposedly the car was driven about 100 miles). Aside from the block test, I don't know if they did anything else. I assume not. I also did block tests on my own which all came up negative. My dad also doesn't feel like it's a head gasket.

Thermostat is new but hasn't been tested for operation (I would assume it works since I don't overheat around town). Water pump is original; new one will be going in soon, but somehow I don't think that's it. Radiator has about 15000 miles on it; there are no obstructions on it; fins look clean. The fans both kick in properly. The passenger's footwell isn't damp, so I'm assuming that my heater core is fine as well.

Where else should I look, or what tests should I have done? Let's see what this new information brings.

[kwren]

while the temperature is heating up?

[crazyhorse]

Can you look to see if the lower hose is collapsing when the car is overheating?

It seems to me, that you're picking up a restriction somehow. IIRC you never actually lose coolant, so that's not the culprit.

This is a REALLY cornfusing problem.

[Dessertrunner]

I have had two SVX's do head gaskets and both when tested were said to be okay. Yet it was found both had headgaskets gone. You need to understand a couple of things about the svx cooling system.

-- The heater is always on its just that when you turn it on at the dash it blows air past the evaporator.
-- Its possiable for the heat gasket to cause the coolent to boil into the overflow tank but when the engine cools down it sucks the coolent back so when you later check its still full.
-- The fans only go on to low if the AC is off unless you are with in a certain speed range.
-- Let car idle with the AC off and the fans should turn on and off as the engine passes 95C temp. If this doesn't happen your problem is fans.

The other reason the car overheats on long trips and not short is that you could have a leak from the compression chamber and this pressure builds over time in the radiator.
One suggestion I have is get the car hot after driving for say 50 miles then use a rag and remove the radiator cap. The coolent may boil as the pressure drops and if you top it up (with the engine running) then with radiator cap off rev the engine up. If its a head gasket it blows the water out. Depending on how bad the leak is the coolent will jump 6in above radiator. Hope that helps
Tony

[Nomake Wan]

Originally Posted by kwren

while the temperature is heating up?

Yes, both fans are running full-blast.

Originally Posted by Desertrunner

I have had two SVX's do head gaskets and both when tested were said to be okay. Yet it was found both had headgaskets gone. You need to understand a couple of things about the svx cooling system.

-- The heater is always on its just that when you turn it on at the dash it blows air past the evaporator.
-- Its possiable for the heat gasket to cause the coolent to boil into the overflow tank but when the engine cools down it sucks the coolent back so when you later check its still full.
-- The fans only go on to low if the AC is off unless you are with in a certain speed range.
-- Let car idle with the AC off and the fans should turn on and off as the engine passes 95C temp. If this doesn't happen your problem is fans.

The other reason the car overheats on long trips and not short is that you could have a leak from the compression chamber and this pressure builds over time in the radiator.
One suggestion I have is get the car hot after driving for say 50 miles then use a rag and remove the radiator cap. The coolent may boil as the pressure drops and if you top it up (with the engine running) then with radiator cap off rev the engine up. If its a head gasket it blows the water out. Depending on how bad the leak is the coolent will jump 6in above radiator. Hope that helps
Tony

So lemme get this straight. Run the car for 50 or so miles. Stop. Remove the cap (which it says not to do). Dodge coolant. Refill so the coolant level is at the neck. Rev the motor.

If revving the motor shoots coolant out the neck, it's a head gasket?

Really?

[Dessertrunner]

You use a rag over the cap to stop it sprayng you and undo the cap part of the way slowly to let the pressure off before you remove the cap fully. The reason you do it this way is that when the engine is cool or cooler the head gasket won't leak and thats why it always passes the pressure test.
One other trick I know is even after smaller trips 20 miles when you stop listen for air bubbles in the overflow tank. You can hear the noise.

[Nomake Wan]

So just curious. What would a normally-operating vehicle do if you removed the radiator cap while the engine is at normal running temperature and then revved the motor?

[Dessertrunner]

When you remove the cap the pressure will realease the same way but they won't boil as badly and to the same extent. Once the pressure is released on a normal engine the water settles down fast. Then if you top up and rev the engine the coolent just flows around the cooling loop with out getting thrown out of the radiator. If the head gasket is real bad you may get the engine to blow the coolent out even when the engine is cold. I have seen engines do this as well. SVX engines operate below boiling point 95c or the fans turn on. When the head gasket leaks you add pressure & tempreture and that's the problem.
By the way the fans may look like they are flat out but they are 3 speed as long as they are running its not the fans.
I don't want to sound like a smart a__ but in my company I would own about 40 engines in cars, trucks, tractors & irrigation pumps and they I have not counted any less then 100 hp with the biggest motors 12.5 litre 600 hp John Deere diesels.
Tony

[crazyhorse]

Desertrunner's test WILL work.
A normal runner will maybe overflow a bit around the neck. A blown HG will spew water like a fountain.

WATCH YOUR FACE when you open the rad for the 1st time. Go slow, with a rag over the cap. Wet the rag in cold water to help keep the hot stuff off you. When it gets loose, keep pressure on top of the cap then rock it side to side to relieve the 13psi, or so that the cap holds.

Do this test, but be dadgummit careful, ER's suck as do burns!

[Nomake Wan]

Oops, I didn't put enough downforce on the cap when I went to unscrew it. I unscrewed as slowly as possible, but the second it came off the edge of the latch, BAM, all over the place. Didn't get on me, I moved out of the way, but it made a lovely mess of the front of my car. I'll clean it, so no biggie there. Wouldn't be the first time.

Refilled the radiator up to the neck (took almost a whole bottle, hahahaha), let it settle, then revved the motor. Nothing. Didn't shoot out the neck, it just flowed faster. No fountain.

Just a fountain at the beginning when 13lbs of superhot coolant suddenly found no restriction.

[YourConfused]

Originally Posted by Nomake Wan

Yes, both fans are running full-blast.



So lemme get this straight. Run the car for 50 or so miles. Stop. Remove the cap (which it says not to do). Dodge coolant. Refill so the coolant level is at the neck. Rev the motor.

If revving the motor shoots coolant out the neck, it's a head gasket?

Really?

After the pressure of the cooling system is released there should be no more gushing of coolant. If a head gasket is blown and letting combustion gas into the coolant then you will get a fountain effect. The fountain may not be there at idle (prob will be though from the # of cars I have seen), but rev'n it will make it known.
But...
Sounds to me like the water pump impeller is gone. I don't work on cars anymore, so it's just a thought.

[Nomake Wan]

Luckily I have another water pump ready to go in.

Oh, and I should comment. The fans were at full blast when the cap blew off, but after filling the radiator they slowed down... and after I was revving the motor a few times trying to blow coolant out the neck, the fans actually turned off, apparently because they weren't needed. It was a little interesting to see that.

[Dessertrunner]

were did you get the thermostate and when did you can it

[Nomake Wan]

Thermostat was purchased from the local Subaru dealer, and what?

[Dessertrunner]

Sorry was trying to type, eat and get dressed to go out. Ment when did you change it. Trying to figure if there is a different reason for your problem.
If the car isn't boiling and the only signs that it is actually overheating it might be some thing simple like the sender unit. If a car is boiling it will get worse the longer its driven. What happens is evently the tempreture goes off the gauge which I didn't think you said happened. This is mainly due to the loss of water when the car boils.