Coolant loss mystery - a real one...

My fiance took my Golf IV for a 5 hour all highway trip with some stop and go traffic. The next day, we got in and the low coolant light went off. The expansion globe was nearly empty! I checked the coolant level a week before and was within the checkered range.

1) I have no head gasket symptoms at all - engine runs great.
2) It was about 45F-50F outside - eliminates the very cold coolant contraction phenomena.
3) No abnormal oil loss (small consistent, predictable leak from oil pan corner)
4) I ordered a MittyVac coolant pressure tester: it held pressure on a cold engine of 18 PSI.
5) There was no pressure measured when the engine was started.
6) There was no loss of pressure when I pumped up while engine was running to about 148F (car never got hotter due to 40F day) and the pressure held steady.
7) There is no evidence of leaks anywhere no any trace of dried coolant.
8) There is no smell of coolant in the cabin or around the engine bay.
9) Never overheated - both temp sensors working and the fans work (at least of last summer)

Where did it go? And should I be alarmed? I've read dozens of posts and not sure what to make of this case.

Mhm egr cooler failed perhaps?

Wouldn't I lose pressure with the tests I performed?

what color is the coolant expansion globe!

and what mods do you have?

Globe is normal translucent color. Coolant, pink.

Mods are .205 nozzles and Malone 1.5 chip. 275K

Checked water pump area ?

Yes, no leaks. Thinking EGR cooler.

As suggested by the above post, I had the same issue - left home with a full coolant reservoir....five hours and two mountain passes later, coolant light came on and reservoir was empty.

No trace of a leak anywhere.

Filled up and it stayed. But then occasionally, it'd be low.

Changed my timing belt about a month later and found out where the coolant was leaking from.
(dried coolant all around the water pump)

Replaced the water pump (of course) and 10K km later - coolant level hasn't budged.

couple hard to find coolant leaks that I've had in the past..

heater hose at firewall and small 8mm hose coming off the back of the head.

Of course heater core can leak "into" the car. Minor egr cooler leak could "use" coolant with no symptoms. Minor head gasket leak could use coolant and not cause a symptom (less likely though)

elicon200 said:

Wouldn't I lose pressure with the tests I performed?

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You lost antifreeze over a 5 hour drive, and possibly for weeks leading up to that. Did you leave the pressure test on for 5 hours and weeks?

You lost antifreeze over a 5 hour drive, and possibly for weeks leading up to that. Did you leave the pressure test on for 5 hours and weeks?[/QUOTE]

- Good point, but the standard practice is to perform a static pressure test and then an observed test of the engine on to measure of - if any - accumulated pressure.

I know the coolant went somewhere, so I guess I will check my pump which is only 45k old. Otherwise, I'm leaning on EGR cooler though I don't want to throw parts unless I can prove it.

I had a similar issue; got the warning light, filled the reservoir, then it came back about 2 months later. Very slow, and I couldn't find evidence of a leak anywhere.
After the second time I filled the reservoir, I looked a little harder. Eventually I had found some residual coolant and corrosion on the ends of the radiator that I never seen before. It didnt get bad enough to leak on the ground for several weeks later, when I replaced the radiator.

i would like to point out one more spot. in the last few years ive had to replace several hard coolant pipe seals. this is the black steel coolant line that feeds in behind the accessory bracket next to the thermostat. often people dont see a leak because it runs down behind the bracket and on to the ground. while driving the wind blows the coolant away and no tracer is left.

you can sometimes see the leak by using a pen light and peeking behind the bracket or around the thermostat housing.

o ring is a special one. depending on your car there are two different designs (single ridge or double). these are not interchangeable. do go OEM for this part.

if this is the source of your problem make sure to clean the hole on the block VERY VERY well. i use a hard wire tube cleaner. also use a little bit of grease upon install so the seal wont roll over on install.

possible head gasket leak that only shows itself under heavy boost. Had one on my 98 TDI, could drive easy all day long with no coolant loss. Hit the highway or drive a little hard and it would empty the degas bottle within 100 miles or so.

if your thinking its the head gasket as a last ditch effort you should try to retorque the head bolts. this has worked for me as well.

An update:
I crawled under and looked all over. No leaks or evidence of leaks anywhere. I really, don't believe it's a head gasket since I pressure tested and it runs great - getting into the high 50s for MPG and getting great acceleration. Additionally, it has never over heated.

Probably the EGR cooler.

Any traces in the oil? Oil cooler. However, I'm thinking that you'd see oil in the coolant as well?

Any traces in the oil? Oil cooler. However, I'm thinking that you'd see oil in the coolant as well?

elicon200 said:

An update:
I crawled under and looked all over. No leaks or evidence of leaks anywhere. I really, don't believe it's a head gasket since I pressure tested and it runs great - getting into the high 50s for MPG and getting great acceleration. Additionally, it has never over heated.

Probably the EGR cooler.

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Is there a difference in coolant loss between driving easy and driving hard?

There is no traces of oil in the coolant nor any leaks concerning the oil cooler.

Interesting question about coolant loss with the type of driving. I will experiment and observe.

I drove hard (2.5 hours @80-85 mph) and no coolant loss.

Must have been an air bubble. I hope...

Pressure tests won't always reveal a head gasket issue until it gets really bad. Don't discount a failing head gasket just because the cooling system passed an 18 PSI pressure test.

It might not be a bad idea to have an oil analysis done. It only costs around $20 and then you'll know for sure if there are any traces of coolant in the oil.

drsven said:

It might not be a bad idea to have an oil analysis done. It only costs around $20 and then you'll know for sure if there are any traces of coolant in the oil.

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In my experience, the only time there is cross-contamination between coolant and oil is when the oil cooler fails. This may not be an indicator for a head gasket failure on a typical diesel, as the failure mode there is usually just combustion gas in the coolant, with everything else staying where it belongs.

It's still worth looking into, though.