legacycentral bbs

Ok, seems like my car wants to have issues. Whenever I run the A/C the temp rises, and approaches redline. I'm in Tucson, AZ and this generally happens when I'm stuck in traffic. 105 degrees today, sitting in trafic, turn the A/C on and the temp starts climbing. Any thoughts? It doesn't overheat, but it gets pretty high. There's plenty of coolant, and I've done a good purge of all air bubbles. Strange.

Seems like a fairly normal situation: when the A/C runs, it'll naturally increase the heat load under the hood, couple that with the fact that you're already in a hellaciously hot environment (105 degree ambient air temp. is pretty goddamn hot), and idiling in traffic... obviously you're going to be running sorta warm.
If anything, I'd say it soundsl ike the car is running normally. I live in NE Ohio, and my temp gauge tends to rise a bit above normal when I drive around with the A/C on.
I wouldn't worry about it if everything is operating the way you say it is.

to alleviate this situation, you can always upgrade to a sport sedan which has a much beefier cooling system. i never see my heat spike in hot conditions with the a/c on.

Ahh, if only that were possible... I'd love to get my oily hands on a turbo, but unless money starts falling from the sky, well, let's just say I'll have to content myself with my trusty (if somewhat opinionated) n/a.
She can be a bitch sometimes, but all of the good one are .

I don't get the needle past a little over the halfway mark if everything's working properly. You shouldn't be getting near the red.

Steve

Do both cooling fans come on and stay on when the AC is on?

You say you purged air bubbles, so i'm assuming that you flushed the coolant... was there any crap in there? Also, what is the condition of the radiator and how old is it? If its not functioning good, that could be what's causing the temp needle to move.

Also, it is known that the temp guages on these cars aren't very good. You could be doing damage even before the needle gets to the red.

I don't think that the needle should move past the halfway mark. I live in Florida where it can get near 100 degrees and my needle is rock solid below the half mark with the AC on.

Andrew

Yes.....if everything is working right....you should not have ANY issues with overheating.

I'd check for bubbles & burp the system. Any idea the condition of your water pump? When's the last time it's been replaced.

Ok, the fans both run with the A/C on. The coolant looked good coming out, and seems to flow well when the cap is off while the car is running. Radiator is the original. Water pump was changed when the engine was installed, so it has about 35k on it now. The temp never gets over the half way mark when the A/C is off. And trust me, once the temp climbs, I don't push my luck. Already blew one head gasket on the old engine, though as I recall it acted the same way for overheating: only with the A/C on.

I'd say get a new radiator just to be safe. Check the one you have now for damaged fins or anything that might be blocking flow through the fins. It'd be worth paying for a new radiator if it saves your engine. At least it is not hard to do yourself.

Sounds reasonable enough. Especially since I don't truly know the condition of the radiator after the monkeys at the old shop did the engine change. Did I mention that these same monkeys were the CAUSE of the engine change? grumble grumble grumble

Lesson learned: check the simple stuff first. I had the car sitting idling in my driveway with the A/C on, and the temp never raised a bit. Drove around the block, temp went up. So when I got back to the house, I shut the car off and pop the radiator cap: no pressure. Not even a small amount, which is odd for a HOT engine. So I replaced the cap, took it for another drive, and the temp is even lower than before, and never climbed when the A/C was turned on. Damn, and that cap only had about 10k miles on it. I won't knock it though. Guess I need to get back to changing caps every other oil change like I used to do on my old cars.

Weird, I've never changed mine. I do live in a totally different environment, though.

Steve

was that an oem cap?

hmm.....yeah my cap is OEM original as well.

I need to be educated here. How can a malfuncitoning radiator cap make the temp rise that high when driving at low speeds?

It was a standard Stant 11227 cap, which is their "OEM" replacement. I have no idea what came on the car originally, but even the dealer back East carried the Stant caps.

Now as far as how a failed radiator cap can cause overheating at low speeds, that might best be answered by someone else, but I'll try to remember some of my water-cooling theory from school. Near as I can figure, the water boiled at a lower temperature due to the low pressure, which was adequate for "normal" cooling while driving without the A/C or idling with the A/C running. The whole point to having a radiator cap is to cause the water to boil at a higher temperature, thus keeping it in a liquid state at all times. Liquids exchange heat much better than gases, at least as far as water goes. If the water boils at too low of a temperature it becomes a gas that can no longer provide substantial cooling. Thus, the higher pressure "STi" radiator cap will actually allow the water to get even hotter than a standard cap without boiling, providing greater cooling. The drawback is that your system (mostly the hoses) has to be able to handle the higher pressure.

Ugh, after working all night, that nearly hurts the brain!

well if I understand it right, the cap is only supposed to let the real hot coolant into the overflow resivoir, if it wasn't doing this it would have just be flowing hot coolant through the system until it eventually got too hot for the fans to cool down (since you aren't driving fast enough to have a good flow of ambient air). Is that right?

The cap releases pressure when the water boils. When the water boils, it becomes a gas, and gases take up more space than liquids. This increases the pressure in the system to higher than the cap rating, which opens the cap allowing the gas to escape and cool (condense) in the coolant tank (reservoir).

sorry we posted at tthe same time, I wasnt trying to correct you or anything Yeah that stant cap couldve been the reason why it failed so early. A Subaru OEM cap should last a long time. Much longer than 10k

You guys touched on parts, but the cap keeps the system pressurized. As pressure increasese, the boiling point of water increases. You do not want your cooling system to boil.

If the cap opens too soon....the system never reaches the required pressure and it boils.

The caps are supposed to open to relieve pressure once it gets too high....so you don't blow it up.

THAWA wrote:sorry we posted at tthe same time, I wasnt trying to correct you or anything Yeah that stant cap couldve been the reason why it failed so early. A Subaru OEM cap should last a long time. Much longer than 10k

LOL, yeah, I realized we posted at the same time. It was still on the brain, so I just kept on spitting out theory.

Anyway, like I said, back East the local dealer sold Stant caps, so I figured that was an acceptable OEM replacement. Never trust a Subaru dealer that also sells Mazda and Ford, huh?

that's funny. i was gonna say check that first before putting a whole radiator in there. guess i forgot.

doesn't it feel good when you finally figure out what the problem is and fix it?

Thanks for the education, guys. I recalled some of the points you all mentioned but not all of them.

Brat4by4 wrote:that's funny. i was gonna say check that first before putting a whole radiator in there. guess i forgot.

doesn't it feel good when you finally figure out what the problem is and fix it?

No sweat. I had totally forgotten about the cap myself, and it was a fluke that I checked it. And yes, it does feel good to figure out a problem and fix it. Just hope next time I figure it out faster.

Ok, just when I thought the problem was licked, go for a longer drive and it comes back. Looks like either the radiator or water pump then.