The mysterious case of missing coolant...

[congerz83]

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?

[Bitsyncmaster]

My guess would be you have a bad cap not holding pressure and it spits out the overflow.

[DMCMW Dave]

Do you need to re-bleed the system after adding coolant?

To add to Dave's suggestion - is there coolant evident in the overflow tube?

Under some circumstances this is indicative of a blown head gasket.

[Jonathan]

You can zip tie an empty plastic water bottle upright on the inside of the rear fascia and then drape the overflow hose into it. Don't seal it though. If you go do some driving and find you need to fill your coolant again, you'll know whether you can rule out the reservoir bottle cap by seeing if there is coolant in the plastic water bottle or not.

[congerz83]

I purchased Hervey's "self-bleeder" system when I bought his radiator a couple years ago. Today I bought a new radiator cap. 16lbs (I know stock is 15) with a safety valve. I noticed No evidence of dripping from the overflow tube. Soda bottle... Here I come!

[AugustneverEnds]

I would borrow a pressure tester from AutoZone and test for leaks. You may have a slow leak in a difficult to see place possibly the hoses under the intake manifold or the heater control valve which doesn't tend to leave a visible trail.

[congerz83]

I would borrow a pressure tester from AutoZone and test for leaks. You may have a slow leak in a difficult to see place possibly the hoses under the intake manifold or the heater control valve which doesn't tend to leave a visible trail.

I will do that, but how slow could it be if I'm adding a gallon of coolant every 72-80 hours?

[mluder]

I will do that, but how slow could it be if I'm adding a gallon of coolant every 72-80 hours?

It might not be slow when the system is pressurized.

Cheers
Steven

[Jonathan]

Adding a gallon every few days is quite a bit of liquid. It has to be going somewhere and it might not be that much more complicated than what has already been discussed. If it is going out the overflow hose, you'd probably see at least signs of it splashed all over the inside of the rear corner of the engine bay (or in the plastic bottle if you try that method). Otherwise, it's probably the head gasket problem others mentioned. If it was somehow a leak that was sealed when cold and parked in your driveway but leaking when out on the highway at temperature and pressure, you could always just let it sit and idle for a while in your driveway and then keep watching underneath to see where it goes. If you just can't see it going anywhere, then it's the head gasket.

[congerz83]

Adding a gallon every few days is quite a bit of liquid. It has to be going somewhere and it might not be that much more complicated than what has already been discussed. If it is going out the overflow hose, you'd probably see at least signs of it splashed all over the inside of the rear corner of the engine bay (or in the plastic bottle if you try that method). Otherwise, it's probably the head gasket problem others mentioned. If it was somehow a leak that was sealed when cold and parked in your driveway but leaking when out on the highway at temperature and pressure, you could always just let it sit and idle for a while in your driveway and then keep watching underneath to see where it goes. If you just can't see it going anywhere, then it's the head gasket.

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.