1997 subaru legacy overheating

no white smoke, no water in the oil. I think the antifreeze is not circulating. thermostat? plugged radiator? faulty water pump? air blocked? I have had heat in the car when the gauge is on “H” and then cool air when in the same place. Have loosened the radiator cap and the engine appeared to cool off quickly then when it got up on “H” again opening the radiator cap just to relieve pressure did nothing. The next time i let it idle and it started to come down, then accelerated to 2000 rpm and it cooled quickly. The next time repeated this same type of thing and did no good. Next time the gauge said “H” i kept moving and the heater blew hot air for 4 miles then it blew cold air?
Start with a thermostat? Try bleeding the heater? replace radiator? take a compression test?

Are your fans on when it overheats?

A bad radiator cap can cause weird overheating problems like that. I’d start there because it is cheap.
I’d check the radiator with this tester: http://www.harborfreight.com/radiator-pressure-tester-kit-69258.html

A new thermostat would be another quick cheap thing to try. If you don’t remember doing it, it may be due.

I’m worried about you having allowed it to overheat. Subarus (actually most cars nowadays) are highly intolerant of that.

I was not driving it when it over heated so… not sure it was. I note the heat gauge rises then seems to stop on “H”. I have not seen any steaming or boiiing out of antifreeze but it appears it is going somewhere. no white smoke, nothing in oil… will do the radiator cap. Thank you.

In a 16 year old car, the radiator may be partially clogged. If there is no overheating at low speeds, but it happens at higher speeds or engine loads, the radiator is incapable of providing enough cooling.

I would do what others suggested, and if that does not work, have the radiator and the rest of the cooling system flushed out. If the radiator has never been flushed, you may be better off just replacing it.

Do your fans come on when it overheats? Note this is an important thing to check:
While sitting still for extended times, driving slowly or running with defrost/ac on, those fans are protecting it from overheating so make sure they work before you start replacing parts.

If those fans never come on when it overheats but do come on when you turn the AC on, it may very well be a thermo sensor.
If those fans never ever come on, it likely is electrical in nature. There are fuses and relays that are in the electrical path. Check those, if that is the case.

There’s no point flushing out a 16 year old plastic/aluminum radiator

The plastic tanks will soon crack and/or leak anyways

Speaking from experience here

this subaru i have noticed that the radiator does not get warm or hot, the top hose has lots of pressure (it is hard) and the coolant gets forced back in over flow tank where it will over fill and run out. Sometimes the gauge is on hot and it blows warm air sometimes it blows cold air, but i think when cold air it is because it has blown coolant in over flow tank. It definitely looks like a circulation problem.

Sounds like a thermotat problem and this needs to be cured before it becomes a head gasket or fried engine problem.

I’m curious how everything worked out. I’m considering buying a used 1998 Legacy and have heard that Subarus often have head gasket problems (which might look like overheating at first?).

Anyone who buys a 16 year old car without first having a qualified mechanic inspect it is being…very foolish. And, even as the contented owner of my third Subaru, I have to say that buying a Subie from that era without first having a thorough inspection by a mechanic familiar with Subarus is…close to insanity.

All good comments above. A cooling system simply won’t function properly if the radiator cap is kaput, the thermostat isn’t working, or there’s air in the system. One thing I’ve done as a diagnostic on an overheating problem is to remove the top radiator hose from the radiator, then idle the engine from a cold start and over the course of the next 10 minutes watch the dash gauge, the radiator fan, and the top radiator hose. As the coolant gets hot, approaching but not reaching the red zone on the gauge, coolant should start coming out of the top hose, and not just a trickle, it should really gush out. And the radiator fan should come on. You have to be careful when doing this to prevent the radiator from running low on coolant of course. On my Corolla the top radiator hose comes into the radiator near the radiator cap, so I can do this without removing the hose, just using a flashlight and, after removing the cap, peeking inside the radiator.

I also have a 1997 subaru legacy outback and had that same problem. I fixed it. The head gaskets are shot. Exhaust gases are blowing into the cooling system. That causes the overheating and also does not let the cooling system to function properly. When the coolant cools it causes a vacuum to pull coolant back from the reservoir. With this problem the added pressure prevents that from happening. The gas bubbles also collect on the radiator side of the thermostat preventing it from opening to circulate coolant. If you can’t do the head gaskets immediately, you can put a couple holes in the rim of the thermostat to allow air bubbles to pass through. However, you will still need to top off your coolant almost daily to be safe. I did this for a year before I was able to tackle the head gaskets. The head gaskets are layered metal and , on mine, the inside layers rusted up and deteriorated and failed allowing passage of coolant and gases to where they didn’t belong. The holey thermostat hack saved me from scrapping the car. You will be able to tell when the coolant needs topped off because it’ll start overheating again. Basically, the air pocket prevents the thermostat from achieving its magical temperature to activate and do what its supposed to. After the head gaskets are replaced it’ll run like new and you’ll feel great again. EDIT: A tell tale sign of exhaust gases in the coolant is to get the car to running temperature and look into the coolant reservoir. If you see bubbles then the above is for you.