Is there a way to evacuate air from a slant six cooling system?

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cruiser

cruiser

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Hello All: I've noticed something unusual about my cooling system performance whenever I open the system up. Usually, it happens when I backflush the system and install new coolant. I have the 225 six in my 1974 Duster. The cooling system is completely stock, the only addition being a backflushing tee in the heater inlet hose. After I refill the system, I always notice that once I start the engine, the system temperature rapidly climbs up to about 205 degrees, then settles back to the normal (195 degrees) value. I suspect that this might be because air is trapped somewhere in the system and hasn't worked its way out. I always thought that in a completely normal system, the engine temp should rise steadily to 195 and then settle there. But mine wants to overshoot, then go back to 195. Do you think there is air trapped in the system, and if so how do I get it out? Thanks!
 
I drill about a 5/64 hole in the flange of the thermostat close to the outer diameter and install it in the 12 o'clock position. Allows the air to bleed out into the radiator.
 
I more suspect that it's heating up before the thermostat opens, then cooling back down after. Normal operation.
 
How long does this take?

The factory gauges will move fast the first time the key is turned on (by design) once the IVR normalizes they react very slowly.
 
Removing & then refilling a cooling system ALWAYS results in some trapped air. Fill the system & get the enngine up to operating temp. That will purge the air. Let cool down overnight & then top up the system. Repeat the process [ may take 2-4 times ] until you can no longer add coolant.
 
Bewy said:
Removing & then refilling a cooling system ALWAYS results in some trapped air. Fill the system & get the enngine up to operating temp. That will purge the air. Let cool down overnight & then top up the system. Repeat the process [ may take 2-4 times ] until you can no longer add coolant.
Click to expand...
With the coolant recovery bottle, I think the process that you described occurs automatically. Presumably, the engine heats up and expels trapped air through the rubber hose attached to the top of the radiator. When the engine cools overnight, the process reverses itself and any void created by trapped air is filled with coolant sucked out of the recovery bottle. I was just wondering if there is a way to speed up this process by somehow manually releasing the trapped air.
 
When I refill some engines I fill through the heater hose holding it up higher than the rest of the system.

Rad cap off and when fluid starts to come out of the heater barb I put the heater hose back on and finish filling into the rad.

Then a few heat cool cycles.
 
They make Air Vac's (cooling system refiller) Lisle also makes a funnel that seals to the top of the radiator so the air can burp out without making a mess.
 

cruiser What you describe is pretty normal. I wouldn't worry about it. I also do as stated in post #2. Not critical, but does make it easier to purge any trapped air on the first fill.​

 
I think it's normal too. The gauges in our cars are not perfectly accurate, so it's probably opening at 195 the way it's supposed to. The temp. maybe climbs up a little and then settles at 195. Check your hoses and make sure nothing is collapsing. Maybe the thermostat is not functioning just right. But again, I don't think you have any problems
 
used to just run em till they burp then top off...youll know they will push some coolant out the top of the rad then the level will draw down when the thermostat opens...
 
Just so you know,
1) the CTS cannot measure air temp very accurately. If it was to sit in an air pocket, above the hot coolant, it would read lower than the liquid temp actually is.
2) I have been running my system at 207 at the stat-house, on purpose, for a couple of decades.
 
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