losing water mystery

[jettaman8691]

I have posted a bit about my builder over the years. I used to call it my therapy, but now I think therapy is what I need to keep at it.
The body is from a 1991 16V. That motor has been replaced with a 1.6 td with a radiator oil cooler and intercooler. I rebuilt the ACN transmission, replacing 4th & 5th with gears from a 7A tranny to give a smoother, more sensible transition from 3rd on up. I can actually go to 60 in 4th now, at around 3200 rpm (when I need to get up to speed fast) and 70 at around 2800 rpm. Helps a lot in the fuel efficiency; averages 50 mpg, ranging from 48 to 56, depending on how much weight I am carrying, weather, how many hills to climb, and how hard I push it. I have used wax in the fuel during warm weather; 2-cycle oil now that it is cold. And I use Stanadyn additive, after testing out many others. All in all I have been pleased with how the rig rides.

I have had a curious thing going on with disappearing water recently. There are no leaks from the head, water pump, or anywhere that I can find. I can be driving along without any problems whatsoever when all of a sudden I will lose water. Sometimes it is slow, causing the low water light to blink, so I can just stop and top off the resevoir. At other times I lose almost all the water suddenly. When that happens I can stop, crack to resevoir cap to release pressure, and refill while the car is running. It almost seems as though there is a vapor lock or something.
I have considered that perhaps there is a break in the head gasket, but that would not explain why I can drive most of the time with no problems at all, and no loss of power at all. The heater core is fine; no leaks. I do not see any leaks from the raditor grill. The water pump is fairly new, as is the thermostat.
Has anyone else run into this kind of situation? What did you do? Thanks ahead.

[VWCaddy]

I had a similar issue in my old '81. It would run fine and then every once in a while lose coolant. Turns out it had a very minor leak in the head gasket due to a coolant passage that had eroded and enlarged and got close enough to the top of one cylinder bore to cause a leak but only at high pressure. It was only a cylinder -> coolant leak. It would cause the cooling system to be pressurized and periodically the radiator cap would release that pressure and with it a little coolant if the overflow tank was too full. For a test, you can check the coolant with a chemical test kit (NAPA sells one) to check for exhaust gas in the coolant. Or you can pressure test the cooling system and look for the pressure to rise with the engine revs (this was the test we did on mine). This test would also tell you if you have some other sort of leak that only shows up at high pressure. In my case, I never saw any leaks because the vented coolant was hot and evaporated almost instantly and only did that while driving at high engine load, like up a long grade.

[coke]

I fill mine almost weekly as the plastic coolant flange on the front of the head is leaking. Its hard to see if you don't know what to look for, but that is where mine is leaking. I can't offer any other advice other than that. Coolant leaks that hide are hard to find. Only other thing I can recommend is having a peek at the metal line that runs from the pump to the heater core. They rust out and crack at the bends and leak coolant.

Do you smell coolant? I can smell it when I get out of mine, but it doesn't leak on the ground.

[jettaman8691]

Thanks. I do not find any, and I mean any, leaks. VWCaddy's suggestion was something I had thought of, and can certainly find plausible. Don't really want to change out a head gasket, but may look anyway. Need to change the timing belt soon anyway.

[vanbcguy]

I just had to do one of the plastic flanges on Jezzie too. The leak was practically invisible except I was noticing I had to add a touch of coolant once in a while. In the end it really let go, but even then you couldn't see the crack unless you looked REALLY closely, and even then only after I'd removed it from the engine.

I think it basically would only leak while under sustained load for a long time. When it started leaking significantly I'd been on the interstate for 3+ hours already, but even then when I pulled off the leak was basically impossible to see. I only found out because the "low coolant" light started flashing.

That particular flange I think had been leaking for about 3 years before it got REALLY bad.

[jettaman8691]

A little update; while driving today I stopped and checked my radiator hoses and found that even though the car was up to heat on the gauge, the lower radiator hose was stone cold. Ah, ha, says I, the thermostat! So I bought a good German-made thermo and put it in (after checking to be sure it would open when under heat, of course).
Wellm the car got up to heat, and then some, and the thermo didn't open. I shut off the car and took off the upper radiator hose to get out the air, and that seemed to do the trick, the engine took all the water back in that had been drained out and the thermo opened like it should.
I am not completely convinced that the thermo has been my problem. The water pump seems to be operating properly; the pulley is not spinning on the shaft. Well, a road trip will tell if this takes care of the problem.

[Fatmobile]

Seems like the water coming from the radiator should be cold.
It should also bleed the air out by itself, is the little hose going to the resevoir putting out a steady stream?

[jettaman8691]

Well, new info; and Fatmobile hit it right smack in the kisser. I had read about a restriction in that small return hose iin an old posting, but had not seen it on my hose............until Friday. That sucker was plugged solid!. Evidently some junk got into my water system and did the dirty deed. I initially just cut the hose off behind it, but after speaking to a diesel mechanic, understood while my water light kept blinking; the water was simply recycling from the hose to the resevoir, instead of passing through the radiator. I found a small tube with a hole slightly larger than the one in the original restriction, and I have a happy car again.
As I was initially thinking about why and how the engine was losing water, it just seemed to me that there was an air blockage someplace. Well......there was. Learn something all the time.

Thanks to all who responded to help.

[coke]

Interesting. There is a restrictor in the hose going to the reservoir? I installed a new radiator in my car that had a separate nipple for the small reservoir hose so I just ran a hose to it.

Mine is loosing coolant pretty steadily. I have to refill it about once a week (just the tank). The only place I can seem to locate any sort of leak is that coolant flange. It must be spraying out pretty good at steady speed but I can't actually see it leaking when its just idling.

[82vdub]

Yes, on some models the small coolant line going to the top of the coolant jug has a restrictor in it. It's a very small oriface, and the slightest bit of debris will clog it. The water has nowhere to go and after a while depending on loading, the coolant cap will puke the water out.