: air in coolant system?

09-04-11, 12:05 PM
hi all!

this is another issue with my 97 sts. i've got about ~160k miles on it and am worried about it's coolant system.

if i'm travelling on uneven terrain, while going uphill i see the temp gauge quickly climb to a point that borders on the red-line. it was really worrying me but it other cars i've dealt with, this happens when there is air in the coolant system. i've topped off the coolant and tried to get all the bubbles out of it - a few times i've gotten the system to "burp" and at the moment there doesn't seem to be any air left in it.

we found a leak in the heater core that wet the passenger side floorboard and the quick fix was to bypass it with some hose. no leaks there and the car runs fine and maintains a good temperature unless i'm in very slow moving traffic on a hot day, the temp will climb a little above normal - just a little - and then drop back to normal once i start moving again.

where should i look? thanks so much for any pointers! :)

09-04-11, 08:18 PM
This is not a Northstar forum. Northstar has an air purge line which sometimes gets clogged and causes overheating. Make sure there is flow from that tube.

Otherwise, overheating is not a good sign particularly for a Northstar since it may be caused with failed headgsakets. A very expensive repair involving removing the engine.

09-04-11, 09:13 PM
Yeah, this needs to be moved to the Northstar forum. I'm not a mod here so I can't do it. but will alert those who can.

Assuming that your purge line is clear and flow coolant like MC said, borrow a block test kit from any parts store like Autozone that has a loan-a-tool program and test for exhaust gases in the surge tank. Overheating on a hill climb does not sound good though.

09-05-11, 10:03 AM
OK - Sorry! I posted to the wrong group...

for starters, i don't think it's actually overheating and if it is, it's barely getting above nominal. the rate at which the temp starts to climb and then immediately cools off seems unrealistic. that's why i suspect air in the system. if you get a large bubble, the water pump might cavitate or if the bubble lingers near/over the sensor, it'll throw the measurements.

anyway - regarding the air purge - where? i haven't seen anything like that. sorry, but i don't have any manuals for this car yet. a google search took me to a thread here, but i found no pointers to what it looks like or where it is - any help is greatly appreciated!

i have yet to find the system with a lot of air in it and it hasn't lost any coolant since i bypassed the heater core. i know my bmw can trap air when refilling the radiator and parking on an incline helps greatly - i was hoping there was a similar trick for this.

thanks for pointers!

09-05-11, 12:42 PM
The purge line is the 3/8" line that runs into the side of the surge tank near the top. Pull the line, stick it in the open surge tank and start the car. If it flows coolant (flow will increase with RPM), and it should, the line is clear.

09-05-11, 12:54 PM
First, update your profile to show your car, year, model, mileage. It sure helps. look at my header ^^^

The water pump system is at the rear end (driver's end) of the engine.

Remove the engine beauty cover. Trace the small coolant hose coming from the nipple on the top side of the coolant reservoir - it will run to a hollow bolt/nipple just rearward of the water pump/thermostat cover. With the engine cold and the reservoir properly filled (halfway up - at the seam - no higher), remove the line from the reservoir and hold it in the open filler neck. Have an assistant start the car - does the purge line flow a small but steady stream of coolant ? Good. If not, remove the purge line and check it and the hollow bolt/nipple for obstruction. The bolt can be cleaned by carefully using a proper sized drill bit as a reamer. If the hose/line is clogged, it can be replaced with a proper size/length of reinforced fuel hose from any parts store.

Replace the heater core, don't worry about the thermostat, replace all coolant with a fresh 50/50 DEX-COOL mix (use distilled water from the grocery store).

With no A/C function called for the cooling fans go to SLOW at 224 degrees - almost to the first tick past 12 o'clock. Fans go to FAST at 236 - about 1.5 ticks past 12. With any A/C or DEFROST function set, fans run in SLOW all the time. With a good coolant reservoir pressure cap the coolant boils at 265 degrees at 16 psi. Without a good pressure cap, coolant boils at about 222 or so - right where fans go to SLOW in normal traffic. The thermostat begins to open at ~188 and is fully open at 206. A good, healthy normal running temperature for a Northstar is 205 - 212 degrees.

I believe there's a way, in your pre-2000 car, to call up coolant temp in the DIC. Or use an IR temp gun. Or look at www.scangauge.com (http://www.scangauge.com) - ScanGauge-II.

The ECT (Engine Coolant Temperature) sensor is down low on the rear of the right cylinder head/block - just about in front of where your gas pedal foot sits.

Oooooppppppssssss !!!!.............Ranger beat me to it..........

09-05-11, 04:01 PM
great information - thanks a lot!

i'll start updating my profile to help out as i use the forums here more. i have been neglecting the car and not using the forums as much as i should have... i'll have to change that.