knocking noise

[Wallio]

Hello All

It's been one thing after another. A little bit of history first.

Four years ago..had a blown head gasket.
Had it replaced and all was well. Later during that year had an issue with oil being pumped... (no oil pressure) Had no time and place to fix.
GN ended up stored for four years. I wanted to do the work myself.
Didn't know what it was until I removed the oil pan...and WOW the sump pump was clogged...which seems to me was a small piece of rag which could of been left in there while the head gasket job was done. I now do my own work and refuse it to bring it anywhere.
The problem I'm having is like a thumping sound when the car warms up. It's seems to be coming from the coolant system from what I can tell...it continues with the ignition off. It will disappear as it cools off or remove the radiator cap to relieve the pressure. I took out the thermostat and checks out OK. The cooling fan works.
I removed the radiator cap and revved up the engine at maybe 1500 after a few minutes I saw coolant coming out of the radiator,but then it was flowing out of the filler neck of the rad and I put back the cap.
No white smoke, no shaking or misfiring of the engine. I did a compression test before doing any work on the car and all six cylinders were around 150.
The gauge might be off not a high tech one.
It doesn't seem like a head gasket issue as the compression is good. No coolant bubbling up in the over flow tank.
Any help would be appreciated.

[pajeff87]

How about pressure testing the cooling system?

[Wallio]

Is it something I could do? Never done before.

[kenmosher]

Could be just air "burping" out of the system? Was the car totally up to temp?

Use an IR handheld thermometer and see what the coolant temp is in the neck. Should tell you about how accurate the gauge is.

Pressure testing the coolant system is pretty easy ... you just need a kit like this:

Radiator Test Kit

[pajeff87]

You can probably rent a pressure tester from your local parts store. Just make sure you keep the pressure within reason for the test as you do not want to blow out your radiator -- no more than 15-16 psi maximum (a good rule of thumb is to go just above the rating on your radiator cap). Also, you want to perform the test with the engine cold and ensure that there are no leaks in the connection to the radiator.

[Wallio]

Yes, the car was at the proper temperature. I drove it for a couple of miles and that was when I herad the thumping sound. Didn't know what it was, then shut off the car and the sound continued on. I let it cool down and drove it back. By the time I got home it started acting up again.
First time I see this.
I'm thinking it's air also, but how do I eliminate the air in the system?

[pajeff87]

Most modern thermostats have an air bleed built in to them. Unfortunately, older style thermostats do not have this feature, however, they can be carefully drilled using a 1/8" drill bit to create an air bleed:



You then install the thermostat with the hole at the 12:00 o'clock position. This helps air escape as you fill the cooling system.

Other tricks to bleed the air out of a cooling system include raising the front of the car, as air will automatically move to the high spots, and squeezing the upper and lower radiator hoses to burp out the air as the system is filled. Once filled, you can start the engine and continue to "burp" the hoses and add more coolant as needed. I also blip the throttle to accelerate the water pump and increase the speed of the coolant moving through the engine.

Be careful that you do not air lock the thermostat and overheat the engine. Usually, with the hole drilled in the thermostat it will not air lock. I would still recommend pressure testing the cooling system when you get a chance.

[Wallio]

Thanks for your input guys. Won't have time to take another shot at it until Friday. Will post the out come.

[Wallio]

Hey Guys

I removed the thermostat and drilled a small hole in it for the air to escape, but the problem is still there. Seems to me it could be a head gasket. When I hold the bootom rad hose you can feel the knocking for a minute then stops.
One more test is take off the spark plug and make sure both valves are closed and put in air and see if it bleeds out in the rad. I think this should give me an idea if the head gasket is bad. I'm running out of ideas.
Never seen this issue before.

[larrym]

blowing bubbles in the coolant tank? that's usually the sign of a head gasket.