The mysterious case of missing coolant...

[DMC5180]

When you get out of the car after a drive, do you smell any odd or sweet odors around the engine? Do you have a metal or plastic header bottle? If plastic you can fill the tank to the low level line. Start the car and let it warmup till the fans cycle on and off. Watch the level in the tank To see if it rises to near the top. Then shut the engine off after the fans cycle off. Watch how quickly the level recedes. Report back on the results.

[Jonathan]

Wouldn't there be some evidence of that? I changed the oil a couple days ago and it was clean? Compression test yielded normal results. I DID do the compression test cold. I gotta think losing coolant at that rate, due to a bad head gasket, would cause catostrphic failure.

Definitely rely on others for the final yay or nay on a head gasket problem as I have no experience with them. My train of thought was more Mr. Spock than anything else in that once you rule out the impossible, whatever left, however improbable, is the answer. The coolant has to go somewhere, and if you don't see evidence of it outside the car, then it must still be within the car, and that points to the head gasket. If we got lucky and it was just a leaky connection on a hose underneath that only seeps fluid while driving at temp and pressure, I would still try to let it sit and idle in the driveway and monitor underneath and hopefully catch it.

[DMCMW Dave]

Wouldn't there be some evidence of that? I changed the oil a couple days ago and it was clean? Compression test yielded normal results. I DID do the compression test cold. I gotta think losing coolant at that rate, due to a bad head gasket, would cause catostrphic failure.

There are multiple leak paths for blown head gaskets.
--coolant into oil (oil will look like chocolate milk) (no impact on compression)
--coolant into combustion chamber (goes two ways, will cause steam in the exhaust and exhaust into the cooling system typically causing the heads to run dry and blow coolant out the overflow (compression test might find this, but might not on a very low key failure. It will get worse over time)
--coolant out the side of the gasket and down the side of the block. (no impact on compression).

I've also seen radiator leaks that only show up at certain temperatures. You can have a radiator that leaks but never leaves drips on the floor if it only leaks hot and the coolant goes out as a mist, and seals back up when it cools off or the pressure goes away.

You may have a valley leak that you don't see when the car is sitting still but it sloshes out when you drive.

Most leaks are worse cold if there is pressure. That's why the pressure tester is key. Leaks may seal up hot, or leak only when hot with pressure, only when cold, only at certain temperatures, etc. . .

[PJ Grady Inc.]

That low cylinder could be a prime suspect but a "leakdown test" would be much better at pinpointing internal engine problems.
If the clt cap checks out OK and there are no external leaks (lest we forget the VOD!) then you should seek the services of a shop with a leakdown tester.
Rob

Hello all. It's been a long time. Due to issues with my daily driver, I've been forced to temporarily put my D into daily use. I have this mysterious condition where coolant disappears. Every couple DAYS, I'll be driving along, and I'll watch the TEMP needle climb. I pull over and will need to add at least a gallon of coolant.

I did a compression test. Every cylinder was at 140PSI except one that was at 133/135.

Changed the oil and noticed no signs of coolant.

Oh, and NO NOTICEABLE leaks. So where does this gallon of coolant disappear to every couple days?

[David T]

That low cylinder could be a prime suspect but a "leakdown test" would be much better at pinpointing internal engine problems.
If the clt cap checks out OK and there are no external leaks (lest we forget the VOD!) then you should seek the services of a shop with a leakdown tester.
Rob

That's a LOT of coolant to be losing over a short time. Either you are leaking it externally or burning it internally (popped head gasket). I would do a combustion gas test on the coolant and/or a leakdown test to confirm a blown head gasket. You could very well be blowing it out the overflow BECAUSE of a popped head gasket, NOT a bad cap.

[congerz83]

If I rent the two testers (combustion & leak down) are they easy enough to figure out?

[DMC5180]

Yes, but rather me trying to describe to how to use the pieces. I would suggest you do a how to search on YouTube. I'm sure their are plenty of descriptive videos on the subject.

[DMCMW Dave]

Yes, but rather me trying to describe to how to use the pieces. I would suggest you do a how to search on YouTube. I'm sure their are plenty of descriptive videos on the subject.

Combustion tester should come with instructions. A agree with Dennis on the leak down, its a very common process and lots of words to explain.

[PJ Grady Inc.]

Before you rent the tester if you haven't already done so pressure test or replace the cap. It would be the quick and easy thing to do. If you have access to a tester that would be prefered so you will know wether it is the likely problem or not. Anything weaker than about 13# or so will loose some coolant and below 10# you'll lose a lot in hot weather. I've seen this often enough to know. If it happens to be just a bad cap you will have saved yourself a lot of work.
I have seen certain brand NEW 16# caps that have an internal spring loaded sealing plate that would not close and allow coolant to flow out at rates approaching your description. Not all places carry original style 15# caps and if you can't find one use an 18# cap as I've never seen that problem with them. Use a 15# if you can get it but if not I'd avoid the 16#. By all means test/replace the cap and drive it again to see if you're a lucky guy who just saved himself a lot of work. Head gaskets on this car are not a good job candidate for the average DYI'er as a lot can go wrong without the proper tools and experience.
Here's wishing you good luck!
Rob
'

That's a LOT of coolant to be losing over a short time. Either you are leaking it externally or burning it internally (popped head gasket). I would do a combustion gas test on the coolant and/or a leakdown test to confirm a blown head gasket. You could very well be blowing it out the overflow BECAUSE of a popped head gasket, NOT a bad cap.