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Subaru Legacy cooling fan issue

Hey all- Have a 2001 Subaru Legacy GT, 5 speed manual, 194,000 miles.

A few months ago, I started noticing that my cooling fans are running more often. Even when it is cold out and the temperatture gauge was at normal temperature. The fans would turn on, and just keep running. Obviously, they would turn off when I shut the car off, but if the car is on, they will stay on. However, I found a trick to get them to turn off. If I am in neutral, and I race the engine up to around 3000 RPM’s or so for about 10 seconds, and let it come back down to idle speed, the fans are now off. Works almost every time, not just a coincidence.

I know my car, and this has never done this before. I know it is not normal. I have replaced the following- thermostat, coolant temperature sensor, flushed the system, changed the fan relays, and most recently, I put a brand new Subaru radiator in. All of this, and the issue is still there. I am beginning to wonder if it is the water pump. Coolant not circulating fast enough, so the fans come on to help cool down, but when I race the engine, the water pump works harder circulating coolant faster? Also recently, the temp gauge starts to climb going up long steep grades. If I pull over and race the engine, the temp gauge drops almost immediately back to normal. The pump is not leaking or making any noise, so I’m not sure if it could go bad any other way.

Before I go ahead and but a $140 pump, I’d like to hear some other possibilities.


Did you also install a new cap and thermostat to go along with the radiator?

sure did!

You have electric cooling fans, right?
There are two of them, right next to each other?
I believe you have a radiator fan and a condenser fan. The condenser fan should come on with the AC engaged. And the radiator fan comes on "as needed"
Are both of them coming on, even with no AC?
I’d try to find a wiring diagram somewhere.
I’m not really familiar with your car, but hopefully some of this helped narrow it down.

Electric cooling fans, two of them. One main, one sub. Both of them come on- I’ve never seen only one running. With no AC, both of them are running when I see the problem… happens every day. With the ac on, only extra thing it does is kick the compressor in.

Your new radiator cap may be defective or not the right pressure range. I would replace it with another new one, first check the required range. Might also look for any defects around the seat where the cap mounts.

I think your Subie has two temperature sensors: one for the dash and one for the ECM. You replaced the one for the ECM, I take it?
The one for the ECM is towards the top of the engine. If there’s an air bubble in the system, it will misbehave. You may want to fill the engine up from the top radiator hose with a funnel first, then quickly put the hose on the radiator. Then burp the system (I take it you know how?).

All above good ideas to check. It appears to me though you have a more serious problem. Something may be blocking a passage in the cooling system, the water pump isn’t pumping water like it should, the new radiator is somehow plugged, or a head gasket is leaking directly into the coolant jacket.

If the comments above don’t work, well, there’s a couple of things to try. Make sure the water pump turns freely. I’m assuming it is belt driven. Your mechanic will have to loosen the belt that drives it, and turn it by hand, and compare the friction and axial freeplay observed with a new one. If still unsure about the water pump, I think it is possible — I know I’ve done this w/my Corolla – to loosen the top radiator hose and observe how much fluid comes out as the thermostat opens. That yields some idea of the water pump operation and efficiency.

If all that doesn’t work, then it’s time for a pressure test of the cooling system, and if it is still a no-go, then a leakdown test for the head gasket. At 194K? I’m thinking head gasket.

I will get another cap since they’re cheap. And yes, there are two sensors. I replaced the one on the motor, underneath the airbox and hoses. Just don’t see why they’d go off after I rev the engine

I believe your water pump is driven by the timing belt.
So replacing it would be a major expense.
When is the last time the timing belt was replaced?

Timing belt was done at about 183/185,000 miles. About 10k ago. Water pump was inspected and was not leaking or making any noise, so decided not to replace it. Since they rarely actually give out

Head gaskets have already been done. Everything new but a water pump.

You’re pretty luck with that water pump, then.
Some cars don’t get half as many miles before the pump goes.

Are there other ways the pump can go bad besides leaking or making some sort of bearing noise?

The impeller could become pitted if it’s cast iron.
The impeller could actually break if it’s plastic.
The impeller could slip on its shaft, causing the pump to not flow enough coolant.

I don’t advising you to run out and get a pump . . .

I’m just explaining that a pump that isn’t noisey and/or leaking is not necessarily 100% okay.

I know. I actually planned on buying a pump already, because what else is left? My friend and I can do the work, so that’s not the issue. I just hate replacing parts that don’t solve the issue.

So the coolant temperature gauge only rises on long, steep grades?
Perhaps your coolant system is okay.
I’d look for that wiring diagram if I were you.
I may have gotten a little sidetracked with the pump, because the fans were your original concern.

Yes. That’s really the only time it rises. And it’s more of a new symptom. Electrical issue you’re thinking?

That wiring diagram could show you what’s controlling the fans.
So, let me ask you this.
Do the fans come on with the ignition on, engine not running, and the AC control panel turned off?

The temperature sensor should have two wires going to it. The sensor for the dash gauge only has one wire tied to it. I was thinking headgaskets until I saw they were already done. Hopefully they aren’t bad again. You could have the coolant checked for exhaust gases to see if that is the trouble. There may be an air pocket causing the trouble as was already suggested. Filling from the top radiator hose has helped some folks get rid of a air bubble. I think that is the most likely culprit here.

The coolant sensor ties to the ECU and the ECU turns on the fan relays by making a ground connection to the relay coils. Check the OBD 2 data and see what temperature the coolant is when the fans turn on. Sometimes there is a problem with the ECU for the fan circuit but that usually causes the fans to not turn on at all.