Coolant bleeding proceedure details

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Nov 25, 2011
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Seattle, WA
Just replaced a bunch of gaskets and coolant system components on a Ford 4.0 OHV in my Ranger.

I think my standard bleeding proceedure is leaving air in the system because I keep getting a fluctuating temperature reading. Meanders towards the middle, then drops, then repeats.

Today I parked on an incline, and used a coolant funnel in the radiator and let the car idle, no bubbles appeared. Once warmed up, if I rev the engine and hold it there, coolant stays at its level. Once I release my foot off of the gas, I get a geyser of coolant as it comes back down to idle.

Another geyser when I shut it off (with the cap off).

I can't find any info on why it would geyser like that as it returns to idle. Most sites say to rev the engine to force air out. Or is this wrong?
 
The geyser is not normal, have you checked that your radiator is not partially blocked up? What was the condition of the coolant that came out of the radiator when you changed it? Revving the engine during bleeding is optional, it just speeds up how fast the engine reaches operating temperature and the thermostat opens up. Are you sure that the thermostat opened when you did the bleeding procedure, did both radiator hoses have the same temperature to the touch?
 
Don't rev it with the cap off! I find that varying the rpm in quick succession will force the thermostat to open faster (From idle to @ 2500 rpm). The temperature might rise a little past normal then drop like a rock....This is how you know the 'Stat opened.
Shut the engine off & allow the pressure to bleed off if any is present in the system.
Add coolant 'til full. Put the Rad cap back on, Start the engine & rev it to @ 2500 RPM to bleed the rest of the air out of the system. (Both Rad hoses will be HOT)
Shut the engine down & allow to cool, Add coolant as needed.


I don't recall the 4.0L Ford being difficult & needing all the above? But sometimes even systems that aren't known to airlock will anyway!

Glad I bought a Coolant Refiller....Saves alot of time!!!
 
I've had plenty of different engines geyser when bleeding the cooling system while coming back to idle after running at high rpm, so in my experience that is pretty normal, as long as it doesn't continue to bubble through your funnel if you let it sit and idle for a few minutes. Did you notice a fluctuating temp gauge before the repairs you performed? Used to see a lot of cracked heads and blown head gaskets on the 4.0 ohv engines, and a fluctuating temp gauge was usually a symptom.
 
It doesnt bubble at all, besides the geyser-ing as mentioned above.

I have a thermostat with a jiggle-valve in it, which I suppose would have taken out most of the initial air. There wasnt a big drop in fluid level when the thermostat opened up.

I did do a leakdown test this afternoon and did not see any bubbles in the radiator. It was done cold as I didnt have time to warm up the car. I'm wondering if I need to take the thermostat out to see bubbles with that approach.
 
This sounds identical to when I did coolant work on the 4.2L V6 in my old F150. I saw the same fluctuations in the gauge,

Does the Ranger have an overflow reservoir (degas chamber) or are you fiddling directly with the radiator cap opening? This could be one important difference and why you are getting gushing.

On the F150, the incline trick worked for me with a little bit of accelerator input to "burp" the bubble out.. which felt like it was near the heater core. I had the degas chamber cap off at the time and the coolant level in the chamber was on the lower side of things, so if there was a "gush" it was minimal due to the space available. I don't recall ever fiddling with the radiator cap on the F150 or if it even had one.
 
A quick search over on Ranger-Forums.com or therangerstation.com might be helpful.

Could you list the "bunch of gaskets and cooling system components" you replaced?
 
The Lisle coolant funnel is awesome
smile.gif
 
I work on a fleet of about half ford 4.0. They still give me trouble occasionally after 6 years of working on them. I always fill with a funnel and remove one heater hose. Sometimes I can get all the air out of the heater hose but usually not.
 
I would use a scan tool to see exactly what your temperatures are doing. Ford has had bad sending units in the past or to verify an actual air pocket problem.
 
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It doesnt bubble at all, besides the geyser-ing as mentioned above.

I have a thermostat with a jiggle-valve in it, which I suppose would have taken out most of the initial air. There wasnt a big drop in fluid level when the thermostat opened up.

I did do a leakdown test this afternoon and did not see any bubbles in the radiator. It was done cold as I didnt have time to warm up the car. I'm wondering if I need to take the thermostat out to see bubbles with that approach.
So what was the cause of overheating? did u solve your issue?
Head gasket was okay?
 
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