Disappearing coolant

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I am wondering if anyone's tractor does this same thing. Coolant level up to full in radiator and overflow bottle. I'll run tractor for an hour and anywhere from 1/4" to 1/2" coolant level diminishes. No matter how many times I'll fill it up, does the same thing. First suspected a bad radiator cap but this tested 0k, then a bad head gasket. No external leaks and no wetness on radiator rods and not the slightest, smallest drip on ground. Tested for CO in coolant - negative. No weeping at water pump. Tractor (JD 750) runs strong with no tell tale of head gasket leakage such as white smoke or grey residue on oil cap nor coolant detection in oil. (which CO test confirms) The coolant just seems to "evaporate" but the engine never gets hot and runs very cool.
I know JD has a "non evaporative" coolant and was wondering if this is the reason why as I have not used their coolant. I know a bit about car engines but not as much with small diesels so this is a bit of a mystery to me.

 

[Midniteoyl]

You are losing only 1/4"-1/2"? Or losing that much each time you run?

I believe you are filling up just a little too much for what your system requires and it is spewing it overboard. Its very little, so it would go unnoticed. If it stays 1/2" low, just leave it. it will be your new normal..

 

[arrow]

You are losing only 1/4"-1/2"? Or losing that much each time you run?

I believe you are filling up just a little too much for what your system requires and it is spewing it overboard. Its very little, so it would go unnoticed. If it stays 1/2" low, just leave it. it will be your new normal..

That's the trouble Midnite: it won't seek a steady level. Yes, each time I run it this happens. I idled it for an hour yesterday at different rpm's with the hood off looking for any tell tale….nuthin. No spewing, seepage or anything. It'll empty an entire bottle over time if I let it go. Pressure test on radiator reveals no leakage. Thought it had to be a head gasket but all testing reveals nothing of the sort. One would think with a compression ratio between 20-22 to 1, a blown head gasket would be quite evident on a diesel.

 

[Midniteoyl]

Ya, definitely sounds like a slow head gasket leak. At the moment though, and something to think about - I have a car that is losing coolant too. Mine I am sure is a small leak as I can get a faint whiff of hot coolant smell while idling, say at a drive-thru. I too cannot find any hint of just where it is leaking, but I know it is. Its just soo small a leak it turns to gas as soon as it escapes. They make a radiator dye that i am gonna try next. You put it in, drive a few times, then check with a black light..

UVIEW Radiator Coolant Dye 6 - 1Oz Bottles: Heating, Cooling, & Air Quality : Walmart.com

 

[3930dave]

It's sounds like you've covered most of the usual suspects already Arrow. I couldn't tell from your description if you've had the crankcase oil lab tested (UOA) - if not, I'd send off a sample for a lab test.

I don't know these new coolants as well as I'd like, but from your description it sounds like the volume you are losing should be visible in the oil if it is a head leak. But, given how little I know about these new coolant formulations, maybe not (?).

Strange one, pls keep us posted.

(P.S. - is "very cool" running typical for your model of JD ? If not, that may be another clue.)

Best luck, Rgds D.

 

[Soundguy]

1/4" to 1/2" each run and does not stop.

that's not alotta water. surely not enough to see steam out the stack. it could very well be burning it at a microscopic level.

with that lil.. i bet if you pull an injector it might not even be celan.. though would not hurt to look.

 

[arrow]

Ya, definitely sounds like a slow head gasket leak. At the moment though, and something to think about - I have a car that is losing coolant too. Mine I am sure is a small leak as I can get a faint whiff of hot coolant smell while idling, say at a drive-thru. I too cannot find any hint of just where it is leaking, but I know it is. Its just soo small a leak it turns to gas as soon as it escapes. They make a radiator dye that i am gonna try next. You put it in, drive a few times, then check with a black light..

UVIEW Radiator Coolant Dye 6 - 1Oz Bottles: Heating, Cooling, & Air Quality : Walmart.com

That's another corundum for me. I wouldn't think a diesel would be capable of a "slow" head gasket leak considering the compression they run at. I'm wondering if a small crack in the head may be more the culprit but as I said, don't know about these little diesels. But in either case, I'm thinking the fluid in the test container would have turned green with even the slightest amount of CO in the radiator.
Dave, good points about the lab test. For the amount I'm losing, you would think 1. it would be visible. 2. the oil level would go up. I as well do not know the behavioral characteristics of the newer coolant formulations. The JD has always run cool.

 

[arrow]

1/4" to 1/2" each run and does not stop.

that's not alotta water. surely not enough to see steam out the stack. it could very well be burning it at a microscopic level.

with that lil.. i bet if you pull an injector it might not even be celan.. though would not hurt to look.

SG, could you elaborate on this please? I'm thinking you may have meant the injector may not be "clean" but you are still losing me if that is indeed what you are saying.

 

[arrow]

- I have a car that is losing coolant too. Mine I am sure is a small leak as I can get a faint whiff of hot coolant smell while idling, say at a drive-thru. I too cannot find any hint of just where it is leaking, but I know it is. Its just soo small a leak it turns to gas as soon as it escapes. They make a radiator dye that i am gonna try next. You put it in, drive a few times, then check with a black light..

UVIEW Radiator Coolant Dye 6 - 1Oz Bottles: Heating, Cooling, & Air Quality : Walmart.com

Midnight, this could be a bad backing plate seal behind the water pump. This is especially so if your vehicle is a Chrysler product in the 318-360 range.

 

[PRF]

Sounds to me like a cracked head or cylinder wall and its blowing it out the exhaust. We've had that happen in our big diesel trucks before. Good luck, hope you solve it.