Need help from VW techs re fluctuating coolant overflow tank levels

you may have the beginning of a leak, but it's to small to detect yet. Just keep an eye on the level and see what happens. Some fluctuation could be caused by the expansion/contraction of the coolant and hoses at various temperatures. after all the hoses are rubber.

Thanks. I don't think there's a coolant leak because the level recovers at times. As a follow up, I brought the car to the dealer. When I drove it to the dealer the cold level was a 1/4" below the MIN. The dealer did a pressure check and said everything's okay. The next morning, the cold level was 3/4" above the MAX. This is a pretty big increase in overflow level. I'm thinking re-pressurizing the system to do the pressure check resulted in the big increase in the overflow level. That's another reason why I don't think there's a coolant leak.

I live in Phoenix, so we don't have much of a temperature variation. Also, the car is garaged overnight. So, the garage temp is equal to or even above the outside temp here in the winter. Wondering if I have a slow pressure leak, which, when the pressure drops too much, the system re-pressurizes itself and then goes thru the cycle again, and again? Or, could going from a warm garage to a colder outside have something to do with this? I would like to think the hoses are less sensitive than this because they have to deal with coolant temps at 190 degrees F for normal operation. Oh yea, the car does not overheat and the coolant temp, when hot, is the same now as before this all started.

A pressure test may show leaks where the hoses or something is letting fluid out. You can have head gasket leaks that pressurizes the system or maybe pump some air in a passage. This air could displace the coolant and make the coolant appear high. If you get the right condition where this air burps out the coolant could read low.

Coolant temps are hotter than 190. You are read>Thanks. I don't think there's a coolant leak because the level

Jim B.

letting

Are you saying I have a head gasket leak? Wouldn't there be other indications of a head gasket leak, such as coolant and oil mixing?

though.

I'm reading the water temp off the dash gauge. Isn't the purpose of a sealed pressurized cooling system to capture boiled water vapors (using the overflow tank) so the cooled back into water can be put back into the radiotor (using the pressurized vacuum)?

I'm confused. Are you saying I might have a head gasket lead (even without any other indications) or that my cooling system is functioning normally? Thanks.

There are 3 passages in a head gasket. Or 3 types of openings. The combustion chamber, the coolant pasages and the oil passages. The passages in the gaskets are not all close to the outside of the engine. Some may be right in the middle of the block or head. You can have head gaskets leaking with no external signs. It is possible that there is a void between the combustion chamber and a water passage.

I am saying that something weird is going on. I am saying that you could have a leaking head gasket. I am saying that pressurized tests do not always show leaks. When you work on air conditioning systems you can leak test using pressure. You can leak test using vacuum also. Note that there are some tests done with a hot engine, some done with a cold engine. I define a hot engine as one with the oil temperature at the normal temp after the car has been driven at highway speeds for

15-20 minutes. A gas engine can show normal water temp in 10 minutes of city driving but the oil temp has not risen to normal temp.

Have you ever looked at a head gasket? Ask at the parts store if they have one you can look at and if the parts counter person knows about the egine for the gasket he/she can point out how all those holes have different functions. Oil, water and combustion.

A good radiator sh>

Jim B.

Our shop hasn't had a head off a VR6 in over 5 years! That said, if you have a leak sooner or later you will be adding coolant. Just keep an eye on the level and don't add any until the low coolant lamp comes on... and note how many miles & time(days) until coolant was needed. There are 2 places more prone to leakage than the headgasket which are thermostat housing and after run electric coolant pump. But very unlikely on such a low mile car. My suggestion is if the coolant level varies up & down slightly... don't worry be happy! BTW, VW has been using multi-layer metal head gaskets for several years since about 1996 or so. And yes, it's normal for an engine to need coolant every now and then.

Thanks for the encouraging words about the head gasket. Now, the car doesnt' really lose coolant, because the warm level is always the same. (Also, I only added 6 oz of distilled water when the light originally went on. That was enough to bring the overflow tank level to MIN. Then, last week after the dealer did a pressure test, the following morning the level was about 6 oz above the MAX. It stayed there for 4 days, and yesterday it was about 4 oz or 1/2" above the MAX.) It's just the cold level that varies. And, it varies up and down. The cold level does not continue to fall. Some mornings its down below the MIN and some mornings its above the MAX. The car is always garaged overnight, so the outside temperature variations should not have much of an impact.

My best (weak, admitedly) guess is that the system pressure/vacuum varies a lot. Some times the pressure/vacuum is strong enough to "suck" more cooled coolant from the overflow tank back into the radiator than at other times. It's this pressure/vacuum variance that concerns me.

It seems to me that if the system were fully pressurizing, and the coolant amount remained constant, then, when cold, the amount would be pretty similar from day to day. If the system didn't always reach full pressure, then less cooled coolant would be sucked back into the radiator, leaving a greater amount in the overflow tank. When the system would reach full pressure, then more cooled coolant would be sucked back into the radiator, leaving a lesser amount in the overflow tank. If this makes sense, then its the wide changes in system pressure that concerns me.

Woodchuck wrote:

My diesel Eurovan has needed coolant on the first cold (-10C) morning each fall. Probably since new it had a crack letting a small flow of coolant near the intake on one cylinder. This wasn't diagnosed until a -20C morning when the gasket let go completely. The crack was "repaired" by welding, but after several years has cracked again.

This time the cooling system was building pressure and then losing coolant when the pressure relief went off. The first sign of a problem was that I had to go to full-on heat to get any heat at all -- probably a small bubble causing a vapor lock that was cleared by the full flow. If you idled the engine without the coolant cap you could see little puffs off steam.

I think you are right to worry. Make sure coolant isn't getting into the oil, and watch carefully for signs of overheating or vapor lock (no heat).