air getting in cooling system - old car

[bluebelle]

I drive an old car.  2 weeks ago it started to over-heat, I could keep it within normal operating temperatures by driving with the heater and fan on high.   I assumed it needed a rad flush or new rad (old original rad), rad fluid looked full....honest mechanic checked it out, said there was air in the system, and burped it.   Less that 2 weeks later, it started to overheat again.   Obviously burping my rad once a week is not a viable option.   I see nor smell any leaks,  oil is clean, so I doubt it's a blown head....any guesses how air is getting into the system and what my options are?

[ChickenStash]

Did you do a flush and was it done before the first overheat incident? Some vehicles are just a pain the butt to get all the air out so it's possible it might take a few "burping" sessions to get it all out.

Has anyone done a pressure test on the cooling system? There's equipment available for rent (free, usually) from many auto parts here in the US to do the test DIY, not sure about Canada, though. The idea behind the test is to pressurize the system to near the cap pressure and watch for a pressure drop over time that would indicate an opening to the air someplace.

If the overheat happened first, it's quite possible for the head gasket to have failed such that it's letting combustion gasses into the coolant passages creating your air pockets. There's test kits available at most auto parts stores to check for combustion byproducts in the coolant. If they show a positive result then it's time for at least a new head gasket along with a check to make sure the head and block surfaces are still flat.

[six-car-habit]

 Some cars have an "overflow" tank with a hose going from the radiator to the bottom of the tank. If the heat / pressure gets too high, some cooling fluid will flow into the overflow tank,- conversely when the system cools after the car is shut off, a vacuum can be created, and if the overflow tank is empty, or the hose is not set at the bottom, it can pull air into the system.
  The temperatures in the cooling system are kept lower by having a pressurized system. On old cars the pressure was "set " by a relief valve in the radiator cap. Have you tried replacing the cap ?   Also there is a additive called "water wetter" it's red and comes in an approx 12oz bottle, it helps transfer heat out of/ into the coolant . You can try adding this, costs about $10. 
    Is your radiator cooled by a fan driven by a belt and pulley [mechanical], or by an electric fan{s}.  Sometimes the electric sending unit that senses the temperature and tells the electric fan to start goes bad, resulting in the fan not starting and/ or starting at a higher temp than factory setpoint.

[bluebelle]

Did you do a flush and was it done before the first overheat incident? Some vehicles are just a pain the butt to get all the air out so it's possible it might take a few "burping" sessions to get it all out.

Has anyone done a pressure test on the cooling system? There's equipment available for rent (free, usually) from many auto parts here in the US to do the test DIY, not sure about Canada, though. The idea behind the test is to pressurize the system to near the cap pressure and watch for a pressure drop over time that would indicate an opening to the air someplace.

If the overheat happened first, it's quite possible for the head gasket to have failed such that it's letting combustion gasses into the coolant passages creating your air pockets. There's test kits available at most auto parts stores to check for combustion byproducts in the coolant. If they show a positive result then it's time for at least a new head gasket along with a check to make sure the head and block surfaces are still flat.

haven't had the flush done yet.   And I'm not sure if a pressure test was done or not, my mechanic often doesn't charge when there are no parts involved - so I don't have an invoice.   I know they put at least a litre of antifreeze in 2 weeks ago..... 

I think a pressure test is definitely needed, thank you for the suggesting - air is leaking in somewhere and now at an alarming rate or they didn't get all the air out two weeks ago - I just added nearly 2 litres of antifreeze today.   Overflow is 2/3 full, so it appears that my car can't draw from the overflow.   I've never had a car with rad issues, so this is new to me....man I love you-tube, learned how to burp my rad.....and to think only 2 weeks ago, I didn't even know that was a thing.

[bluebelle]

Some cars have an "overflow" tank with a hose going from the radiator to the bottom of the tank. If the heat / pressure gets too high, some cooling fluid will flow into the overflow tank,- conversely when the system cools after the car is shut off, a vacuum can be created, and if the overflow tank is empty, or the hose is not set at the bottom, it can pull air into the system.
  The temperatures in the cooling system are kept lower by having a pressurized system. On old cars the pressure was "set " by a relief valve in the radiator cap. Have you tried replacing the cap ?   Also there is a additive called "water wetter" it's red and comes in an approx 12oz bottle, it helps transfer heat out of/ into the coolant . You can try adding this, costs about $10. 
    Is your radiator cooled by a fan driven by a belt and pulley [mechanical], or by an electric fan{s}.  Sometimes the electric sending unit that senses the temperature and tells the electric fan to start goes bad, resulting in the fan not starting and/ or starting at a higher temp than factory setpoint.

Thank you for the pointers....I know the mechanic checked the fans 2 weeks ago, they are definitely coming on.   Thermostat was changed a year ago.

adding the extra antifreeze resolved my problem for now....but adding 2 litres of antifreeze every 1,000km is not a good solution.   I'll keep trouble shooting.

[alsoknownasDean]

No leaks from the waterpump? Maybe it's faulty if it's not circulating coolant around the system? Potentially even a blockage somewhere? Any traces of white (or other coloured residue) around any connections (including radiator end tanks)?

Is there much white smoke from the exhaust? When you take the radiator/overflow cap off and run the engine, how much bubbling is there in the coolant?

Ultimately if you're losing coolant, you're either leaking it or burning it.

[Model96]

Yep, it's either leaking out to atmosphere or being burnt in the engine.
Check for leaks on the ground under the car. Check that your radiator cap rubber seals are in good condition (when the engine is cold!).
Often the head gasket is leaking into a cylinder, but no oil is leaking into coolant or vice versa. Sometimes this will make bubbles in the coolant which might be visible in the radiator.
I would revisit your mechanic and let him know it is still losing coolant.....he may recommend adding a stop leak product into the radiator to extend the life of your old car or narrow down what the problem is cheaply....for e.g. if the radiator is blocked up or the water pump faulty the additive won't help, but it will help if you have a small head gasket leak.

[bluebelle]

Yep, it's either leaking out to atmosphere or being burnt in the engine.
Check for leaks on the ground under the car. Check that your radiator cap rubber seals are in good condition (when the engine is cold!).
Often the head gasket is leaking into a cylinder, but no oil is leaking into coolant or vice versa. Sometimes this will make bubbles in the coolant which might be visible in the radiator.
I would revisit your mechanic and let him know it is still losing coolant.....he may recommend adding a stop leak product into the radiator to extend the life of your old car or narrow down what the problem is cheaply....for e.g. if the radiator is blocked up or the water pump faulty the additive won't help, but it will help if you have a small head gasket leak.

thanks.....mechanic is assuming a small leak in the head gasket, he can find no leak under the car (she's spent some time on a hoist).   He added a stop leak product.   I haven't driven the car enough in the last two weeks to really tell if it helped (like everyone else - I'm staying home).   Easy fix for now is to add  a coolant every 1,000km.

[Model96]

You should be ok for quite a while then, assuming your radiator cap is ok.
If you are still losing coolant, and the level in the radiator overflow bottle never seems to get lower, I would recommend to change the cap for a new one.

[bluebelle]

You should be ok for quite a while then, assuming your radiator cap is ok.
If you are still losing coolant, and the level in the radiator overflow bottle never seems to get lower, I would recommend to change the cap for a new one.

thanks - I wondered about swapping out the cap as a cheap check, mechanic said it was okay....the overflow never gets lower, but there will be air in the rad after its been driven X miles (I haven't found the sweet spot, probably 500km)

[Reddleman]

Sorry to say, this is probably a head gasket leak.  It has all the symptoms.  It will get worse, possibly when you least expect it. 

The easiest way to make sure is to use a chemical test kit.  It lets you know if combustion gasses are getting into the coolant.  https://www.blocktester.com/

A mechanic can do it, or you can pony up the $50 for one at your local NAPA.  They are good to have if you are the type of person who buys used cars.  You can test every car you look at for head gasket leaks for about $1 a piece.

If it is a head gasket leak, you should get it fixed sooner rather than later.  If overheating continues it can lead to a warped head- much more expensive than just replacing the gasket. 

Also- it wouldn't happen to be a Subaru, would it?  Those are notorious for eventually dropping head gaskets.

[bluebelle]

Sorry to say, this is probably a head gasket leak.  It has all the symptoms.  It will get worse, possibly when you least expect it. 

The easiest way to make sure is to use a chemical test kit.  It lets you know if combustion gasses are getting into the coolant.  https://www.blocktester.com/

A mechanic can do it, or you can pony up the $50 for one at your local NAPA.  They are good to have if you are the type of person who buys used cars.  You can test every car you look at for head gasket leaks for about $1 a piece.

If it is a head gasket leak, you should get it fixed sooner rather than later.  If overheating continues it can lead to a warped head- much more expensive than just replacing the gasket. 

Also- it wouldn't happen to be a Subaru, would it?  Those are notorious for eventually dropping head gaskets.

yes, it's a 17 year old Subaru, she's been a good car and doesn't owe me anything.   I had not heard that they were bad for dropping head gaskets.   It's a very slow leak, I just check the rad level every week.   Mechanic added a sealant, it may have resolved the issue, car didn't need coolant last time I checked.

[JLee]

Sorry to say, this is probably a head gasket leak.  It has all the symptoms.  It will get worse, possibly when you least expect it. 

The easiest way to make sure is to use a chemical test kit.  It lets you know if combustion gasses are getting into the coolant.  https://www.blocktester.com/

A mechanic can do it, or you can pony up the $50 for one at your local NAPA.  They are good to have if you are the type of person who buys used cars.  You can test every car you look at for head gasket leaks for about $1 a piece.

If it is a head gasket leak, you should get it fixed sooner rather than later.  If overheating continues it can lead to a warped head- much more expensive than just replacing the gasket. 

Also- it wouldn't happen to be a Subaru, would it?  Those are notorious for eventually dropping head gaskets.

yes, it's a 17 year old Subaru, she's been a good car and doesn't owe me anything.   I had not heard that they were bad for dropping head gaskets.   It's a very slow leak, I just check the rad level every week.   Mechanic added a sealant, it may have resolved the issue, car didn't need coolant last time I checked.

I actually have a 17yo Subaru in my garage (friend's car) that's getting a motor swap because it blew up a replacement engine a few months after it blew up the engine she bought it with..I hope you have better luck with your fix!

[bluebelle]

Sorry to say, this is probably a head gasket leak.  It has all the symptoms.  It will get worse, possibly when you least expect it. 

The easiest way to make sure is to use a chemical test kit.  It lets you know if combustion gasses are getting into the coolant.  https://www.blocktester.com/

A mechanic can do it, or you can pony up the $50 for one at your local NAPA.  They are good to have if you are the type of person who buys used cars.  You can test every car you look at for head gasket leaks for about $1 a piece.

If it is a head gasket leak, you should get it fixed sooner rather than later.  If overheating continues it can lead to a warped head- much more expensive than just replacing the gasket. 

Also- it wouldn't happen to be a Subaru, would it?  Those are notorious for eventually dropping head gaskets.

yes, it's a 17 year old Subaru, she's been a good car and doesn't owe me anything.   I had not heard that they were bad for dropping head gaskets.   It's a very slow leak, I just check the rad level every week.   Mechanic added a sealant, it may have resolved the issue, car didn't need coolant last time I checked.

I actually have a 17yo Subaru in my garage (friend's car) that's getting a motor swap because it blew up a replacement engine a few months after it blew up the engine she bought it with..I hope you have better luck with your fix!

I've had very few issues with the subie over the years.   The O2 sensor failed a few years back, the thermostat a year ago.....but other than that, just general maintenance.