After I drive the car in 100+ outside temps - I think it occurs more when I when on the freeway for a while where the speeds average 73 mph. After this when I stop the car I lose coolant out of the overflow of the reservoir. After about 5-8 drives it was almost empty (the warning light did not come on). The car is not really overheating - when I drive around town or the freeway if it is at least 105-110 the gauge may get to one small hash over the half way mark - sometimes a bit more after I stop and restart again after say 15-30 minutes and the car has not cooled much. It seems like after the car is driven hard and then parked the coolant get overheated and then overflows. BTW I am assuming it is overflowing from the expansion tank since the puddle of coolant on the ground is right below it.

I changed the water pump, thermostat Nov 2018 and the radiator a couple months ago. Prior to these changes I did not have this problem even though I had a water pump that was going out and the radiator had a very small undetectable leak. also prior to the changes the car ran hotter yet no overboil.

Any help would be appreciated.

 

Try replacing the cap on your reservoir tank.

 

It is only 3 years old but I will definitely do that first since it is not expensive.

There is another symptom which I thought was normal but maybe not... If I drive the car for a while and then turn it off - then get back into it say 15-25 minutes later and start it up again the Temp gauge moves to the 2./3 mark past the half way mark. If the engine has had more time to cool this does not happen and when I drive it will cool down again to just over the half way mark. Is that normal for it to do that.. or should it dissipate the heat better. It is like the coolant overheats after the car is turned off.

Thanks again.

 

Wanted to give an update. Before I bought the cap I thought I would test it. I rented a Cooling System Pressure Kit from Autozone. None of the fittings fit but I was able to remove the nipples to make it work. See the pic of the setup (let me know if I did it wrong). If you have the time and can help me interpret what I found (to verify what I think), I would be most appreciated. When I tested it and started to pressurize the tank (system) at about 5-6 psi I started to hear a hiss sound. When I put my finger over the overflow downtube (see pic of the overflow at the bottom of the expansion tank) I could feel the pressure (air) coming from it. I interpret that to mean that the Cap is bad. Am I correct or do I need to check something else.




Thanks again.

 

NP.

I would replace the cap and see if it still bleeds out. If the cap is bad, then the engine is going to get hot (as it is currently). The cap is the cheapest and quickest way to find out. Always try the easiest and cheapest fixes first, then dive deeper if you have to. That's my opinion anyway.

G/L

 

Thanks again appreciated... will replace and update.

 

NP. G/L

Let me know how it goes.

 

Well I pressure tested the cap and I could still hear (and slightly feel) the air coming out of the overflow at the bottom. When I put my finger over it I thought I could hear air seeping from around the cap. So I plugged up the overflow so the tank would be completely sealed. I then pumped 10 -15 psi of air into the tank.

It should have held the pressure correct?

I put soapy water around all the connections and air was seeping from only around the cap edge - I could not see it anywhere else. What does this indicate? A bad tank? Is the cap and tank not sealing? Or is it not supposed to work this way and hold the pressure?



Thanks again for the help - always appreciated.

 

Are you sure the tank isn't leaking at the seam? (Been there ... done that on my 1996 A4.)

 

Update... I bought a new tank and while off the car pressure tested it and though I could not hand pump it to 22psi only got it to about 18 psi it held and did not appear to leak. So it appears the other seal between the cap and the tank was bad.

Thank you for all the help - much appreciated as always.