Cooling System noise after running car

Hi All,

I am having an issue with my 1969 OTS I could use some advice on: after running the car I can hear what sounds like liquid moving on the exhaust side of the engine. I assume it is the cooling system, but not sure.

A bit of background on the car and the cooling system:

  • the car sat in a garage for 45 years before I acquired it a year ago. I have been going through every system in the car. The engine runs strong with good oil pressure.
  • cooling system: I have replaced all the hoses, the heater pipes, the heater case and matrix, had the radiator re-cored, and flushed the system several times. The coolant in the system looks good, same color as what I put in and is clear.
    Heater matrix gets hot, the thermostat opens and cooling fans go on as engine gets hot.

I am thinking there might be air in the system? I filled the system with the front of the car raised.

Any thoughts about what might be going on?



When you filled the cooling system, did you have the heater valve open? Do you have the pressure cap on the header tank and the blank cap on the radiator? When cool, is the radiator full to the top?

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Yes, filled with heater valve open, the radiator is full when cold and has a plain cap and the expansion tank I believe the expansion tank has the right pressure cap (it has a a spring with rubber washer at the end which seals the neck of the expansion tank).

Use a mechanics stethoscope (inexpensive ones are available at any auto parts store) and locate the exact source of that noise.
BTW, the coolant level in your expansion tank on the firewall should achieve a consistent level after a few drives of about 3 inches below the mouth of the tank after the engine cools. Any more and it will be expelled through the overflow when the engine heats up.


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Air can take a few heat cycles to work its way out. Depends on how hot you get it and how long you drive it. And if you open the heater valve.

After shutdown, a hot engine could still push coolant into the expansion tank. And then as it cools it was suck it back. I would think this would be quiet because the flow rate is low

I will listen more carefully to see if I can hear mine.

When you say coolant noises…do you mean boiling coolant? I’ve seen engines where people put in a couple cans of stop leak, this settles in the bottom of the cylinders and can cause the coolant to boil after the car is shut down.

Went for a drive. After shut down I hear very quiet fluid flow noises in the area of the expansion tank. It only lasts about 5 seconds, so not long or loud enough to locate. Or to worry about.

Thanks for all the responses.

My helpful assistant (lovely wife) h gave me a hand and had a listen. She was able to better identify where the noise is coming from: seems to be the cam cover area near the oil filler. Is it possible the noise is oil going back down to the pa n?

Sounds good to me

I think that’s much more likely than hearing any flow in coolant, especially since coolant doesn’t really flow in the strictest sense when the engine’s not running.

I hear this every shutdown. If I didn’t I’d be worried, very worried. I’d be looking for a huge oil slick where the car had been, or making an appointment with an audiologist.

The XK engine cylinder head (camshafts) should be awash with oil when the motor is running, even at tickover.

I know the oil flows to the camshafts through the oil feed pipes at the back of the engine, how does the oil flow from the camshafts back to the pan?

Down the front, and through return holes at the back.

Thanks Paul.

So where I am hearing the noise makes sense, correct?

Given the car sat for 45 years I have been paranoid about every noise and issue I encounter!

There are three or four oblong holes in each cam area of the head casting that match up with holes in the block. Gravity takes care of the flow.

Thanks John and everyone. One less thing to worry about!!


Remember that the oil is @40psi or so when you turn the engine off. So there will be some movement in the oil system until it bleeds down. The original filter canister doesn’t have an anti-drain valve, either. So it’s dripping back into the sump.