Water Pump Failure

2003 Subaru Baja
157,846 miles

Car temp gauge was fluctuating slowly between max and normal operating temperature. Thermostat works properly, fans work properly. I’m pretty sure my water pump is leaking from the weep hole, and plan to replace it ASAP.

Could a failing water pump make the temperature bounce back and forth like that?

Sounds doubtful to me, can you relate the driving conditions related to temp rise?


Check the serpentine belt for wear.


Was probably driving 50-60mph when it initially occurred, but seemed to happened regardless of speed afterwards. Wasn’t an abnormally hot day. Car seemed to be driving normally except for a squeaky new serpentine belt (alternator and power steering) that I tightened today. Disregarded this because it doesn’t drive the water pump or fans.

I tried turning on max heat when it was overheating, it didn’t seem to help much.

Any specifics that could help?

If the water pump is leaking and the coolant level is low the engine will overheat.


Serpentine belt is new and does not run the water pump. Don’t know the condition of the timing belt though. I plan to replace it with the water pump, but no other problems with the car to suggest timing belt issues.

It’s only leaking a little bit. I’m watching the coolant levels and they are fine.

After flushing and burping the system it has not overheated again. I don’t think the water pump would make the temperature rise and fall repeatedly like that.

Could air have been getting in through the weep hole over time, creating air pockets? Not sure if that’s practical, but would explain why it works after flushing.

Worst case I replace the water pump and take it to a mechanic afterwards if it overheats again. Thanks for all the replies btw. Much appreciated.

You have to check the coolant level cold in the radiator, not the remote tank.

Because it is a high mileage Subaru, the first suspects when overheating are always the head gaskets.


if its leaking through the weep hole you need to change the pump. it wont get better. it will only get worse.


Speaking from experience my first thought was a head gasket when the temp fluctuates. For me it would cool down again at speed when the pump was pushing the coolant faster. The other thing is a radiator filled with bugs in the front can lose it’s ability to cool efficiently or the radiator could be coated inside.


Yes, I said I will replace it ASAP. Waiting for new water pump.

How would I go about checking the head gasket? I believe oil would be mixing with coolant, so I’ll check for that. Are there any other things to look for?

I will definitely check that. Any tips for checking the head gasket?

Check for bubbles in the radiator or combustion in the coolant with a tester or test paper I guess. Never had to do that myself.

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oil in coolant.
coolant in oil. looks milky
white smoke out the exhaust
a lot of bubbling in the radiator or overflow
any of the above


Last time this vehicle had problems it was a cracked radiator. You aren’t helping identify the issue.

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maybe not but it was funny.

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Then it is leaking too much.