Explain this one (loosing coolant... sorta)

[Rot Box]

If I fill up my coolant overflow reservoir to the mark it will slowly use up the coolant up until the reservoir is empty. Sometimes within just a few hundred miles.

That said the coolant in the radiator will never get below 3/4" of an inch below the radiator cap no matter how many miles I drive the truck. Once it's to about 3/4 or 1" it stays there for good.

Radiator cap looks good. No visible leaks whatsoever. No coolant on the dipstick and no noticeable white smoke from the exhaust. Sometimes I'll catch a whiff of coolant when I shut the truck off and pop the hood but I've looked it over a hundred times and haven't seen so much as a drop.

Makes no sense to me any ideas?

 

[riotwarrior]

Purple coolant farries drinking from reserve....

 

[MtnHaul]

I'm certainly no expert but can you see any dried coolant residue on the rad fins or fan/fan clutch assembly? I once had a tiny leak in the line from rad to overflow res. Just a thought.

 

[MtnHaul]

The fact that your coolant level doesn't dip below a certain point makes me think the leak is in the upper radiator.

 

[Rot Box]

Purple coolant farries drinking from reserve....

Hope they enjoy it that ELC aint cheap!!

I'm certainly no expert but can you see any dried coolant residue on the rad fins or fan/fan clutch assembly? I once had a tiny leak in the line from rad to overflow res. Just a thought.

The fact that your coolant level doesn't dip below a certain point makes me think the leak is in the upper radiator.

No signs of dried coolant anywhere. No hissing sounds or bubbling.

On that note in recent history I've installed a new Motorcraft water pump, all new hoses, and a new Champion radiator. None of which made any difference in helping this issue. I keep a really close eye one everything so far I'm stumped.

 

[Hydro-idi]

Maybe heater core leaking?

 

[IDIoit]

the best way to find it, is to pressurize the cooling system with a tester, and digging in like a tick when youre getting shelled.
I have done a lot of intensive coolant testing to find out I had a cracked block.

use a pressure tester and pressurize the coolant system, then start deleting items until you find it.
I have made block off plates for the water pump, oil cooler,

the way you explain it, I would suspect the radiator also.

 

[Leroy]

mine used to slowly lose coolant .. the old rad leaked at the top seam ..

not no more after i put in a new radiator .

 

[Sorro71]

Rot Box I had similar type of problem before I rebuilt the engine. I did the same sort of things to try and solve it. But every time I refilled the reservoir bottle and radiator, within a couple hundred km the res bottle would be down to about 2 to 3 centimetres full and the radiator would be about 5 centimetres down from the top. Then it would sit at that level. It turned out to be a cracked cylinder head. I hope you don't have that problem. But that's what I ended up finding on mine. Since the rebuild and some replacement cylinder heads I haven't needed to touch the coolant.

 

[Thewespaul]

Pull the overflow tank out and fill it up on a bench and make sure thats not whats leaking

 

[Shawn MacAnanny]

The fact that your coolant level doesn't dip below a certain point makes me think the leak is in the upper radiator.

When coolant leaks down into radiator and the cap seals air tight you get essentially a bladder tank. As the coolant expands it generates pressure maybe 1 to 2psi but the air absorbs it rather than expanding in the closed system and overflowing into the tank at cap pressure. I bet it leaks further with a leak tester.

 

[IDIoit]

is there foam in the CDR?
when ive delt with cracked heads and a cracked block,
I had the radiator leak down constantly it would never stay at 1 level.
im not saying its possible, but the water enters the engine via the lower radiator hose.
if there is a break in the cooling system, I don't see how it will maintain a certain level.
even with a heater core, it would continue to leak down.
I believe cavitation would display a constant leak down also,
while the engine heats up and expands, the water pump keeps cycling the coolant, charging the block.
what about it leaking through the thermostat housing? kinda hard to get in there with the brackets in place.

 

[Rot Box]

Thanks for the reply's everyone its been very helpful. I'm thinking I'd better pressure test everything to get a better idea of what's going on. Oh man, if the heads or block are cracked that would suck really really bad!

Sorry for the novel but I should probably add a little history to this. I've owned the truck since 2009. Previous owner had the engine rebuilt 100k miles ago and I 'think' it's been sleeved in two cylinders but I can't confirm. I've been very meticulous when it comes to maintenance and I've changed the hoses and coolant (I use CAT ELC) at the proper intervals also added a Champion radiator not long after purchase.

In that time (guessing somewhere around 40,000 miles) I've never had a full reservoir---even if I top it off it slowly goes 'somewhere' leaving the reservoir empty. Coolant always stays about an inch below the radiator cap and I've never had to add coolant to it. Doesn't seem to fluctuate much if any. For better or worse I've just left it alone and drove it


Over the weekend I changed the coolant. Filled the reservoir and drove it about 100 miles. Reservoir is empty and that's when I started this thread. Well last night I drove it home from work and turned on the defrost..... Instantly the windshield went cloudy. Aha! Must be the heater core! Pulled the heater core box cover off today and sure enough there's antifreeze dripping off some of the fins. One of the hose clamps on the heater core wasn't very tight (I just replaced the hoses) and there was some antifreeze dripping around it. I'm hoping that's why the heater core had antifreeze on it....

Here's my thoughts right now.

-Reservoir empty and radiator level down one inch (air pocket in the top of the radiator). Not enough pressure to make the heater core leak.

-With the reservoir full and the radiator full of coolant is there just enough pressure to make the core leak until I get an air bubble in the radiator then it stops leaking. Does that even make sense?


That said the radiator, water pump, engine, carpet... everything is completely spotless. No antifreeze anywhere. I keep thinking that in 40,000 miles I would have noticed it leaking somewhere--anywhere right?


Fwiw the heater core is aluminum. And no foam on the CDR or moisture under the oil cap. Blow by looks good too.

 

[IDIoit]

crossing fingers for ya.

 

[icanfixall]

My guess was a leaky overflow reservoir. Second was the heater core.. Glad you appear to have solved the issue now.