Anyone with cause to replace coolant such as during a flush or water pump replacement has undoubtedly come up against trapped air. Usually this is seen as a rapidly fluctuating temp guage needle.

Yesterday, I found a method that seems to work - the first time around. I have a 'flush port', an aftermarket T-connector installed in the upper heater hose near the passenger side inner fender. By chance, this is also the highest point in the cooling system. I bought a standard female garden hose couping with a barbed outlet connection and attached a two foot piece of clear, vinyl tubing. I filled a small coffee can half full with water and submerged the open end of the tubing holding it in place with a small clip/clamp. I put the can near the A/C accumulator with the tubing rising upwards approximately 1 ft then looping back into the can.

After replacing coolant until visible in the upper radiator, start engine and keep adding coolant as level in radiator drops. You will see a surge in colored coolant up the vinyl tubing, followed by several large air bubbles over a period of several minutes. Continue to leave radiator cap off and add small amounts of coolant as engine comes to operating temperature and more air is displaced when the thermostat opens.

There will likely be coolant remaining in the tubing afterwards. You can do it the messy way and simply disconnect at the T, but you will spill residual coolant until you can get the T connector re-capped. Alternatively, you can wait until the engine cools and the fluid in the tubing drops back into the heater hose and is replaced by more dilute solution from the can, before disconnecting everything.

The key is not overfilling the radiator to begin with. As the coolant heats up it surges in the neck of an overfilled radiator and spills over the top. I left the level at just where I could see the uppermost cooling tubes covered during the refill process and had no 'surge over'. Top off the radiator when finished.

This is the first time I've done major work on the cooling system without suffering through several weeks of temp gauge fluctuation while the system purges itself.

 

That's a great idea, a loop of hose from the T fitting submerged in a can.

I would offer that that the T fittings that come with those Prestone flush kits also work quite well. I've never thought to use the hose loop there, but now I will.

 

Great idea Aero, I am going to need to remember that the next time I flush the system.

 

Aero"C"-Nice job. I had a buddy back when i was stationed up in Minot North Dakota 15 years ago who had just purchased a new Dodge Ram van with a 318 in it. I never knew he had been driving it around a whole week with his 3 small daughters in it with no heat. I had read an tech. article and put it to the test. His heater core-not unlike ours is high up in the dash. Since the air likes to travel to the highest area of the cooling system we needed a "quick fix". I had him drive up on a curb making the radiator cap the highest part of the cooling system. I simply opened the cap and within 5 minutes he was thanking me for the furnace coming outta his dash. I never forgot that and use the same method today.----Boz

 

I've had this problem of fluctuating temp gauge, first time there was air in the system. The next time (at about 310,000kms) it turned out to be a sticking thermostat, which eventually caused a heater hose to fail, I believe that the pressure build up caused a rupture when it opened after allowing the engine to heat up beyond normal temp. Nice & steady now though!

 

and it is for that very reason that I simply either jack up the front of the van or drive it up the ramps that i open up my radiator cap to release any "air pockets" that might have settled in. Up and running for just the amount of time it take for the thermostat to open-(with the cap and van running- you can see the fluid suck down then percolate like coffee being made) once this is going on for about 2 minutes-shut it off-replace the cap-done and corrected.--Boz

 

I have used this same method of running the driver side up on to a ramp to bleeb the air. It appears the heater core clogging it the main issue. once i flush it out (every year) the air will release from the system. I seem to have a bigger problem getting my 4.0 93 xl up to operating temp including new ford stats. any ideas or comments on the same issue would be helpfull.

 

Does your heater have a valve in the hoses? If that's not working properly, it will not allow coolant through to the core. Otherwise, check to see if the heater door is working properly.

 

Brian what 90 said is right. The plastic valve with the vacuum assist on it (if equipt) when not working properly will allow this to happen. It had a small black vacuum hose-on my 94 4.0 it traces to the inside of the fire wall to the vacuum assist for the A/C booster. If your configuration is the same-simply remove the vacuum hose from the black vacuum adapter that your heater hoses goes through (next to your pass. fender/black ignition module) and un-plug the hose and place a small stoper in it (like a golf tee). Pro's vs Con's now=I run without a module going to my heater hoses-heat is like lava-really hot. The function is to help in not allowing your heater to be soo hot which I should re-install my new one again-removing the vacuum hose and "Teeing" it off will not allow your A/C booster to work correctly. It will always be in "BOOST" mode always recirculating your cabin air.

 

the Ford temp gauge is not accurate and the sender is subject to contamination in the cooling system.
drive the rig on the road for 10 miles and check the top hose inlet to radiator with an infared heat gun gauge. should read over 190d

pull the old one, single wire sender, and clean the part that goes in the coolant with acetone. clean the electric connector on sender and wire
if that doesn't bring the heat gauge up to your liking, put in a new sender.

what temp of thermostat did you put in? hopefully a 195d F. one.