No Circulation / Overheating

[stsdriver03]

Quick Background: 94 STS NorthStar started losing coolant, about half a gallon every couple of weeks. Generally you could smell it but not see any liquid on ground or presence in exhaust. Then vehicle started overheating. Came to this board and performed all the tried and true advice. Pressure test provided no signs of head gasket leaks and chemical test seemed to confirm this.

Replaced water pump and thermostat but there seems to be no circulation. Radiator was 167 degrees on one side (nearest tank) and 60 degrees on other. Removed radiator to inspect for blockage. Water flowed through fine.

Inspected pump tensionor and replaced belt (a little cracked). Put back in old thermostat in the open position and still no circulation. Inspected nipple on bolt (found somewhere on this board) and still no sign of plug. Essentially it seems the water in the block is not passing though radiator. Anybody got any suggestions?

[winterset]

Make sure you are putting the thermostat in the correct way. It's easy to have it facing the wrong way, as the flow in a NS is the reverse of a "regular" engine.

[BodybyFisher]

Make sure your lower radiator hose is not collapsing, thereby restricting the flow

make sure your water pump is turning and that the tensioner didnt loose its tension and the water pump is slipping, make sure the tensioner is not bound up and that it is applying pressure

Disconnect the bleed line at the coolant tank and make sure you are getting coolant coming out, that will confirm that your bleed line is not blocked at any point and you are not getting the air out and cavitating

You make this statement "Put back in old thermostat in the open position and still no circulation" what does "in OPEN POSITION mean? The stat is normally closed. The long end goes into the block.

I am not sure how you determined that your radiator is flowing but I don't know if you can determine that easily, you might want to take it to a radiator shop to have them check it, I am thinking that you might have a radiator flow problem

How did you determine there was no circulation, the uneven temps? You didnt take the plastic end tanks off the radiator did you?

Tell us the history of the car, did you just buy it? Has it been fine and all of a sudden this happened?

[MAC]

1) Make sure thermostat is installed correctly; 2) Make sure air bleed line is not blocked; and 3) If you recently dumped stop leak into the expansion tank it's possible it blocked a line.

[stsdriver03]

Little history as requested on the car... Purchased the car from original owner with 48,000 miles on it two year ago. It belonged to a church and assigned to the priest, hence the low mileage. Vehicle originally had a transmission problem but since I picked up the car at such a low price it made sense to have it rebuilt. Only other repair was an A/C pump about a year ago. This became a progressive problem. First from the loss of coolant then by overheating weeks later.

To determine there is no flow from the block, we cut out the center of the old thermostat so that the coolant should start flowing towards the radiator before reaching temp. We verified the operation of the pump, tensioner, belts etc. Also there is no heat in the vehicle as well even when temp sensor displays over 200 degrees. Am I missing something here?

[BodybyFisher]

There is a hose at the top of the coolant tank, pull it off while the car is idling and see if you have coolant flow from it, be careful not to burn yourself. Report back what you find, all of your symptoms point to air in your system that is not getting out and you are cavitating and not circulating.

We have not heard of many radiators clogged to the point of creating an overheating problem, this is sounding like air

[stsdriver03]

Quick question on something I'm not sure of. Had mechanic friend perform something he described as a "leak down test" on vehicle. Here is the issue. He placed a device with a pressure gauge on the coolant tank. It created a vacuum on the system using a compressor. After this he disconnected the compressor and the vacuum released with air resonating from the rear of the motor. He stated that this was indicative of a bad head gasket or cracked head. Normally the vacuum would adhere.

The question I have is after searching about leak down tests and their findings, nothing I saw looked like the gadget he used. More came with instructions of removing sparkplugs and placing heads at TDC. Anyone have a clue what type of test he was performing and if it actually reveal anything about the state of the head gaskets. Seemed to me simply like a way to introduce coolant in the motor.

For anyone wondering my about my stupidity level, my killset is very limited I am trying to make sure I don't get hosed here.

[BodybyFisher]

I don't believe I have ever seen this vacuum test, I have seen a cooling system pressure test, did he create a VACUUM or PRESSURIZE the system. Pulling a vacuum on the tank could potentially damage it, if you ask me, its been holding PRESSURE.

A leak down test typically is when you pressurize a cylinder on its compression stroke and see if it holds pressure, if not its usually an indication of a bad valve or head gasket leak, this will normally cause bubbles in the tank if the head gasket leaks..

I don't like his test. You did a combustion by products test right?

[Ranger]

Usually, the "cooling system" test your mechanic did is to pressurize the system and look for a leak. Nor sure why he used a vacuum. That said, Northstar head gaskets rarely leak externally. IF you where drawing air from a head gasket, you'd have a bad coolant leak at that point with the engine running. When you say "After this he disconnected the compressor and the vacuum released with air resonating from the rear of the motor", I assume you mean by the firewall (rear of the motor is actually the drivers side). There are two heater core lines that run along the rear head that tend to rust out and leak. Might have a look at those.

The leak down test you speak of is pressurizing each cylinder individually while at TDC, compression stroke, with 125 - 150 psi shop air. If a head gasket has a breach, the pressure will leak down and air will be forced into the cooling system resulting in telltale bubbles in the surge tank.

[wiz6728]

IT SOUNDS LIKE HE PRESSURE TESTED YOURS SYSTEM TO CHECK FOR LEAKS I WOULD CHECK THE HEATER HOSES FOR LEAKS LIKE HE SUGGESTED

[stsdriver03]

So after a little research it turns out that the test performed indeed was not a leak down test but a pressure cap vacuum test. It turns out this test sold by Mityvac to be used in conjunction with a pressure test. Questions is, can this vacuum test determine a head gasket leak. Remember, the pressure test performed well as did the chemical test for the presence exhaust gases in the coolant.

I will not get the opportunity to check the lines leading to the heater core until after the weekend so I'm just feeling around for something concrete right now.

Thanks you've all been very supportive.

[BodybyFisher]

I am more concerned with the line leading to the coolant TANK, and less concerned with the lines leading to the heater core. The heater core could be blocked 100% and the engine will not over heat, you just wont get heat in the car.

Check the bleed line connected to the coolant tank

That test he proformed has confused me

[Ranger]

So after a little research it turns out that the test performed indeed was not a leak down test but a pressure cap vacuum test. It turns out this test sold by Mityvac to be used in conjunction with a pressure test. Questions is, can this vacuum test determine a head gasket leak.

No.