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.:steam:

[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 (http://www.harborfreight.com/radiator-pressure-tester-kit-69258.html)

[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:

http://i667.photobucket.com/albums/vv39/pajeffro/1987%20Regal%20Turbo/DSC06987_zps792bc244.jpg (http://s667.photobucket.com/user/pajeffro/media/1987%20Regal%20Turbo/DSC06987_zps792bc244.jpg.html)

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.

[Wallio]

No bubbles in the tank.

[pajeff87]

Do you have a white color to your exhaust after the engine warms up or does it have the sweet smell of coolant? If coolant is entering one of the combustion chambers it generally cleans all the carbon out and will look very different from the other cylinders. You may even be able to see a difference on the spark plugs if you pull them.

Only reason I mention this is that there is both positive and negative pressure in a cylinder as the piston progresses through the combustion cycle, so it may be drawing a small amount of coolant into the affected cylinder(s) as well as pushing air into the cooling system.

[Wallio]

It's alive and kicking again.
After work today I tackled this issue again. I was not convinced it was a head gasket. A friend of mine had a pressure tester which we installed. Noticed the pressure getting higher and higher. We shut off the car after a while running. He then heard the noise I was talking about. He said maybe the head gasket, but again no white smoke or bubbling in the overflow tank. We started the car up again and let it run. I noticed my cooling fan would never came on. I said there is probably air at the thermostat. We took out the hose going to the upper intake from the water pump. Coolant game out we then made the car run again and removed the pressure tester and a splurge of coolant came out. I kept it running and added more water. After a while I noticed the sound of the car changed. It was then my cooling fan came on and that's when I knew it was air the problem. After a while running ... checked the temp on the upper hose and it was 163 and thermostat opened.
All seemed to fall back in place. Drove a good part of the night and it's all good so far. Bottom line it was air which was stuck in the system and was hard to come out.
Unless it's a head gasket on his way out? All I can say...happy to drive it again after four years of storage.

Thank you much everybody for your help.:bye:

[pajeff87]

Glad to hear that you are up and running again.