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4.0L engine coolant disappearing

  #1  
Old 3 Days Ago
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Location: Montgomery
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4.0L engine coolant disappearing

Engine coolant in reservoir is disappearing and this is what I have checked:
1. Reservoir is not leaking
2. Heater is not leaking
3.Radiator is not leaking
4.Radiator hoses are not leaking
5.Water pump is not leaking
6. No moisture is on the oil check stick
7. Oil is not "milky"
8. The oil fill cap is totally clean on underside---no residue
9. No colored exhaust or noticeable odor.
10. Tested radiator air for engine combustion CO2---Negative
11. Check for air in engine block, lines and heater. No air burped out.

Just completed a driving test of 30 days, 428 miles, all locally & 95% at less than 60 mph. Reservoir coolant was down by 20 oz.
Engine never misses and runs smoothly at all speeds.

What am I missing here?
 
  #2  
Old 3 Days Ago
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Location: Vancouver, BC
Posts: 10,894
Its most likely to be an rad/engine leak since you don't see coolant on the ground, it is not leaking until system has pressure which is after coolant gets hot, so coolant is leaking at a place where it is evaporating before it can drip to the ground

Couple of ways to find it
You can rent a pressure tester, basically a Rad cap with a gauge and a hand pump
You pump up the COLD cooling system to 20-25psi and watch for pressure to start dropping, and if it does then look for the coolant leaking out and dripping to the ground

UV(ultra violet) Dye, you can get UV dye kit with UV flashlight, you add the dye to the coolant and run the engine for a few days, then in the dark use the UV flashlight to see if there is a dye trail leading to the leak point.
The UV Dye is safe for engine, AC or oil systems, and can not be seen without UV light so no visible marks or trails

Check the Overflow/reservoir hose, mine had a small crack, where it ran on top of rad, and leaked only when hot, and coolant on rad evaporated pretty fast
 
  #3  
Old 1 Day Ago
03R44Edge's Avatar
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Join Date: Jun 2010
Location: WA
Posts: 36
I had a similar situation a few years ago....with my 03 4.0...
Turned out to be the lower plastic thermostat housing.......Very common deal....
It would huff the contents of the overflow bottle in a100 miles......and was difficult to spot the leak...because hot engine evaporated leaked coolant
Bought a Stant replacement parts kit from Rock auto....about $35......I think?
Can be done...without taking the intake off.....Was a bit fiddly.....but not too bad...
 
  #4  
Old 1 Day Ago
djfllmn's Avatar
Ford parts guy
Join Date: Mar 2009
Location: PA
Posts: 5,820
Originally Posted by captflx View Post
Engine coolant in reservoir is disappearing and this is what I have checked:
1. Reservoir is not leaking
2. Heater is not leaking
3.Radiator is not leaking
4.Radiator hoses are not leaking
5.Water pump is not leaking
6. No moisture is on the oil check stick
7. Oil is not "milky"
8. The oil fill cap is totally clean on underside---no residue
9. No colored exhaust or noticeable odor.
10. Tested radiator air for engine combustion CO2---Negative
11. Check for air in engine block, lines and heater. No air burped out.

Just completed a driving test of 30 days, 428 miles, all locally & 95% at less than 60 mph. Reservoir coolant was down by 20 oz.
Engine never misses and runs smoothly at all speeds.

What am I missing here?
check thermostat housing
 
  #5  
Old 1 Day Ago
cliffdog2004's Avatar
Member
Join Date: Jul 2018
Location: Irvine
Posts: 151
Originally Posted by 03R44Edge View Post
I had a similar situation a few years ago....with my 03 4.0...
Turned out to be the lower plastic thermostat housing.......Very common deal....
It would huff the contents of the overflow bottle in a100 miles......and was difficult to spot the leak...because hot engine evaporated leaked coolant
Bought a Stant replacement parts kit from Rock auto....about $35......I think?
Can be done...without taking the intake off.....Was a bit fiddly.....but not too bad...
Mine, too.

At about 85000 on the clock, I noticed my coolant level low. I don't see anything coming out. I filled up the rez and drove off. A week later, same.

With a pressure test, I Found my housing was leaking and going into the valley and probably evaporating as the engine got hot.

I took off my intake because I hate being restricted LOL

New housing and thermostat. I'm good.

Got a new knock sensor while I was there, too
 
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