My dad has a 1993 Subaru Legacy L 2.2L (no turbo) with a perplexing cooling problem. It overheats, and there doesn't appear to be flow through the cooling system.

The upper radiator hose is extremely hot, the lower radiator hose is cold.

The thermostat has been replaced 3 times now. They have all been put in boiling water, and they all opened.

The car has been parked on an inclined and filled with coolant, been jacked up and filled, we've used the cap to vent, we've used the bleeder to vent.

For a while, he ran without a thermostat, but the seals in the water pump failed.

I just got home from replacing the water pump. The car still overheats. Again, upper hose hot, lower cold. The radiator is cold by the lower hose, then warm in an arc around the cold section, then hot along the top and on the entire passenger half of the radiator. Radiator fluid overflowed the overflow.

I'm at a loss; it seems like there's a no flow condition, but a garden hose in one end of the radiator got water flowing out the other end and the thermostat(s) have all been tested. Is it possible to have coolant flow through the engine blocked?


  1. I would love it if it were the radiator as it's extremely easy to swap out, but a garden hose on one end passed (clear) water through without backing up on the inlet side. I would think that any flow through the radiator would get the whole thing at least warm and definitely warm up the lower radiator hose. Is there another test we can do to check it?
  2. This will sound crazy, but neither radiator fan works. HOWEVER, as there is no flow through the radiator (lower radiator hose and bottom driver's quarter of the radiator are COLD), my first concern is getting flow through the radiator and then I'll worry about the radiator fans.
  3. Everything worked fine with no thermostat (and no radiator fans), but the seal failed in the water pump after maybe 5-10k miles. The car was purchased used and had cooling issues from the start. The garage that sold the car replaced the water pump after the sale, then when that didn't fix anything they said the radiator was clogged and flushed it. Things got a little better, but the car still overheated. This was when the first two thermostats were installed. Eventually Dad removed the thermostat entirely and the car ran fine until the water pump seal failed. When I replaced it yesterday I suggested we install the thermostat, et voila, heat issues return. There is a bypass line before the thermostat, but I don't remember looking at a coolant schematic so I couldn't say where that line goes for sure.

:EDIT 2:

The car overheated on 3 mile test drive and didn't cool off at all despite coasting the second half of that drive at 35mph with a manual transmission.

:EDIT 3:

There is no heat from the car with the heater on and the fan at full speed, but there is also very little air flow from the vents. The no heat situation persists regardless of engine temperature; what little air there is feels the same with the engine cold or fully overheated.

  • 2
    I would look again at the radiator ... Seems if it isn't getting warm near the return side, you have blockage going on. Oct 25, 2015 at 4:33
  • You mentioned nothing about the radiator fan. Is it electrical or does it run off the serpentine? If electrical, does the fan turn on when the car overheats? If mechanical, can you stop the fan with a newspaper roll when the engine overheats?
    – Zaid
    Oct 25, 2015 at 7:40
  • When you ran the car without a thermostat, did the problem go away?
    – HandyHowie
    Oct 25, 2015 at 8:31
  • One more question: does the overheating happen only when the car is stationary, or does it happen even when the car is on the move for, let's say, 5 minutes?
    – Zaid
    Oct 25, 2015 at 13:58
  • I still sounds like a problem with the thermostat. Is the temperature gauge showing a high temperature?
    – HandyHowie
    Oct 25, 2015 at 21:19

4 Answers 4


If this was in my bay I would proceed as follows:

Repair fans: It will overheat at idle without the fans. The first test for this is to turn on the A/C, both, one or none will come on. Test and repair as needed.

Test for system flow: Remove the inlet hose to the heater at the firewall. Test pressure and flow rate. A lot of water should be pushed out when the engine is revved. The pump should make at least 10 psi. This gives the relative heath of the water pump. The most common cause of poor flow in a Subaru is air trapped in the engine block.

I would flow test the radiator and visually inspect the radiator interior. The flow tests is not very helpful. A radiator can flow great but not transfer heat if it is fouled with coolant scale deposits.

From your description I would repair fans first, replace the radiator, put it all back together. Test after repairs by timing the fan run time. If the fans are off most to the time and the fans run only about 20% of the time and the fans blow warm air it is fixed. If the fans run most to the time and the air coming out is cold it is not fixed.

  • 1
    It WAS the radiator. You were correct; water flowed through the radiator but apparently heat did not. Replacing the radiator was 4 bolts and 2 connectors to get the fans off, then 2 bolts and 2 hose clamps to get the radiator off. Pretty easy and we'd tried about everything else. New radiator, problem solved!
    – Chuck
    Nov 2, 2015 at 2:50

I was having a similar problem with my '97 Accord.

My fans weren't working so I thought that was the cause of the overheating. I shorted them to always be on, but it kept overheating.

I checked the thermostat in boiling water. Opened as usual.

When I refilled the system with coolant after checking the thermostat, I poured the coolant directly into the radiator, instead of the reservoir. And the overheating stopped! The fans then went on automatically too.

Though my reservoir was always at the right level, I guess I had a tiny leak in the radiator. When the radiator emptied, the coolant wouldn't flow and the fans wouldn't go on. I didn't think the radiator could be empty with the reservoir full. So that was a learning experience. So long as I put coolant in the radiator periodically, the car ran fine.

If you've got a small leak in your radiator, you might not have noticed it by flushing it with your hose. See if it still overheats after filling the radiator directly (not via the reservoir). If that works, try some StopLeak or egg whites. :)

  • I've never actually filled a radiator by putting coolant in the overflow; I've only ever filled via the radiator cap.
    – Chuck
    Oct 26, 2015 at 12:18
  • 1
    Can you explain the use of egg whites as a solution? Nov 17, 2016 at 4:56
  • @DucatiKiller - Put raw egg whites in the radiator coolant while the coolant is cold. When you start the car, the water pump should mix the whites and coolant. Wherever there is a leak in your radiator you will now have coolant + liquid egg whites flowing through the leak. Once the engine gets to temperature, all the egg whites curdle, including the portion that is in the middle of leaking out of the radiator. Whites turn from a liquid to a solid and the hole is plugged. This would also leave scrambled egg whites (a la egg drop soup) in the radiator, your engine block, etc.
    – Chuck
    Nov 20, 2018 at 19:48
  • The route I've usually heard (and would have preferred) would be to put finely ground black pepper into the radiator, to get a "clotting" action similar to platelets. Put it in while everything's cold, run the car, and the pepper should find its way to the leak and then swell after being "steeped" for lack of a better phrase, in the hot radiator fluid.
    – Chuck
    Nov 20, 2018 at 19:50

Have you filled the system and started the engine with the radiator cap off? See if system circulation is there or blow back meaning a head and / or head gasket.


I fixed the Same problem by taking off the Heater Hose on the Passenger side then put a tall but sizeable funnel into it an fill slowly through the hose..it basically back feeds the water to the block an what not. Once it's full it will be full at the radiator cap. hope that helps ya out man. #Subaru

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