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Discussion Starter · #1 · (Edited)
Hey guys. I'm sure yall have read my previous post in the new member section. I have a 2001 beetle 2.0l GL Automatic. I bought it with a coolant leak. I traced the leak to the upper coupling on the radiator. I installed the radiator this weekend however, its still overheating. After so much coolant at an expensive rate, I started to use just water to test. After about 10 minutes of idle, the reserve starts boiling over. I bled the system, let the car sit for 2 days and its still boiling over. The fans work with the A/C. Without the A/C, the fans came on but only for a second. The thermostat works due to the bottom hose getting hot after a while, the radiator is new, the water pump is working perfect. NO white smoke out of the tail, the oil is just oil and the coolant remains just coolant (well just water at this point) I coudln't find any leaks whatsover. Heat works strong. Its just boiling over. Since I was using just water, I'm gonna bleed it one last time and fill it with G12. Hope this works :(
 

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Check out this thread; for basic things to check:

http://newbeetle.org/forums/1-8-liter-turbo/124898-flashing-red-temperature-warning.html

Many times; the plastic impeller on the water pumps, are cracked or spinning on the water pump shaft. THis can make a situation; where it is partially cooling the system but once it warms up or is driven, it will overheat as it cannot cool the system efficiently.

Worst case scenario; you might have the system pressure checked for more leaks and run a combustion leak test, to confirm the head gasket is ok.
 

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Pressure test!!!!


My recommendation is to change the thermostat if it's boiling over. If you are doing the thermostat might as well do the temp sensor. Two very inexpensive and first-to-go parts. After that I would recommend a pressure test. How are the hoses when s/he overheats? Is one hot and one cold? Both hot? Both cold? This is a big help in giving a hint if something is stuck in your cooling system, or if your thermo isn't opening.

Sometimes the engine cooling system is more finicky than it should be. Start small, then start thinking big. After thermostat/temp sensor you may want to buy some UV liquid and a light from an auto parts store. You'll be able to see where its leaking out if it is indeed leaking.

Lots of luck to you! Had plenty of issues with mine before I got it sorted for good, keep us posted.
 

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Discussion Starter · #4 ·
Yeah I pulled that small top hose and coolant is circulating just fine. Once the water starts boiling in the reserve, I felt the upper and lower rad hoses and both were hot to the touch. They weren't hard or anything just soft and HOT. While all of this is happening, my fans don't come on unless I turn on the A/C then both turn on just fine however, I don't run the A/C cuz the car overheats faster. And I guess according to the sticky, the light only flashes red and beeps so I'm just low and not necessarily overheating?
 

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Discussion Starter · #5 ·
Also, the coolant boils in the reserve but it never leaks out until I remove the coolant cap. Once, I remove the cap, I can hear the water rush back to the reserve and then it leaks out.
 

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Also, keep in mind; if you remove the thermostat, that gives you access to the water pump impeller. Then you can put your fingers on the impeller; see if it is cracked or moves on the shaft. If you do not have any hot air from the heater and the fans aren't coming on; I would say you may have air in the cooling system. Check for blockages;in the return line and vacuum fill the cooling system, to remove any air in the system. How many miles on the car and when was the last time, the waterpump was replaced?
 

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Discussion Starter · #7 ·
I have hot air. Which leads me to believe the heater core is not clogged and circulating just fine. I figured I wouldn't have to check the water pump any further due to the small hose at the reserve circulating coolant just fine. At idle it circulates great and it increases as I increase RPMs. Also the thermo is fine due to the bottom hose getting hot after the engine warms up. No apparent leaks anywhere after the new radiator. Just 10 minutes of idle and water boiling in the reserve as well as no fans kicking on. The only thing I can think of is: the water is boiling faster than coolant would therefore, its not hot enough for the fans to kick on and its just boiling in the reserve??? I think I just have to buy a pressure tester and test the system.
 

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Well, a thermostat is a cheap replacement; that would confirm the waterpump is ok by giving you access to it and also the new thermostat would eliminate that as a variable. Do not rule out the possibility; the waterpump is partially working and on its way out.These cooling systems; can be confusing, don't overanalyze it, check the basics and go from there.

Here are some videos; showing, how the plastic impellers can spin on the shaft. Note: the pumping; can progressively get worse, as the impeller starts to spin on the shaft:

https://www.youtube.com/watch?v=H_7De5aU4dI

https://www.youtube.com/watch?v=OcW...yC55kUPcPYqUJ7_4mZVQV4CQKskqlv1jlfMbwTpxI_ymw

https://www.youtube.com/watch?v=Xc77wsYhRhk
 

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Discussion Starter · #9 ·
Thanks billymade! Just needed someone to calm my brain down a bit!! I'll replace the thermo and check the pump while I'm in there. Ill check in with you guys afterwards. Also, I made a how-to with pics for the radiator replacement. After finals, Ill post that bad puppy up.
 

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Yeah, I have been there; pulling my hair out, trying to analyze what the problem is. Before, I did my first vw water pump; I just couldn't believe it was the problem, kept thinking of everything else but that; drove me nuts, having tried all kinds of different things to fix the overheating issue. Most of the time it is: a bad waterpump, bad thermostat, air in the cooling system. clogged return line or head gasket failure. Let us know; how things go and what you find out, through your testing and checking procedures. A cooling pressure tester and a vacuum fill tool; have really helped me diagnose my problems easier, over the years. Read the other linked thread; for specific tools and sources for these.
 

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Agreed agreed agreed! Air in the system is what did me in last time for a boil-over issue. Replaced my plastic impeller WP around 57k to steel so if you haven't done that yet, as billy said, would be good to do.

Do you have a temp gauge to test the coolant in the reservoir? This might help diagnose as well. :)
 

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Discussion Starter · #12 ·
Ok so rushed home to look at and test the thermostat. Thermostat opened right up in boiling water and closed right up once I took it out. Also the water pump impeller is not the plastic and it was on there nice and tight. I'll have to invest in a pressure tester to inspect for a head gasket or any potential leak ?
 

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Discussion Starter · #13 ·
Haven't added the g12 yet. I am gonna install everything back in and burp the system with g12. I' don't think this will fix the issue but I'll report back when complete
 

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Good, you are making some progress; I would have replaced the thermostat but at least it opened. It sounds like your waterpump; is ok?!? :)

As seen here; make sure there are no restrictions in the return line:

https://www.youtube.com/watch?v=ln4grYe3WnE
 

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Discussion Starter · #15 ·
That water pump looks great! It looks new. I might still replace the thermostat just in case. I just bought the car a few weeks ago it has 108k I'm trying hard to save this baby lol
 

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Discussion Starter · #17 ·
Ok will have to put off until tomorrow. I installed the same thermostat again but couldn't get a good deal. Have a good leak coming from the bottom near that dreaded bottom bolt. Will just purchase a new thermostat tomorrow and install again. Thanks for the info brother!!
 

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A new plastic coolant flange; may not be a bad idea, they tend to warp, crack and end up leaking. All of the plastic cooling parts; typically end up leaking, I usually replace them. I have learned through experience; they just seem to leak and need replaced; the heat makes them fragile, brittle. They don't cost that much either and a new o-ring seal, is definitely recommended. One of the mechanics videos (exovcds); he drills a small 1/8" hole in his thermostats, to help bleed the cooling system. This might not be a bad idea; I know other thermostats I have seen, have included a small brass 'jiggle valve' to do the same thing.

Engine Coolant Thermostat Housing
Beetle; 1.8L, 2.0L.
06A121121C

Engine Coolant Thermostat
Beetle; 1.8L, 2.0L.
050121113C

Engine Coolant Water Outlet Seal .
Part Number: 037121688
 

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Just 10 minutes of idle and water boiling in the reserve as well as no fans kicking on. The only thing I can think of is: the water is boiling faster than coolant would therefore, its not hot enough for the fans to kick on and its just boiling in the reserve???
This has been my experience as well, that the cooling system won't work right on plain water. The fans come on the low speed at a temp of 197-206 in the radiator. Trouble is, by the time that happens the metal in engine block is already above boiling temperature. The steam you see coming out the reserve is a good thing. It means the hose from the driver's side of the block over to the reserve tank is open. You can pressure test with water, but once everything is sealed you need to switch to coolant mix.
 

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I agree with red99. You're not going to have a properly functioning cooling system if you only fill it with water.

The other thing that concerns me is that it appears the pump is good and that the thermostat was good (opened in boiling water). But, you said the cooling fans aren't coming on. I would recommend that you figure out why the cooling fans aren't coming on. If it is getting hot enough to boil over, the fan(s) should be running. There are good how-to threads on this topic on this site.
 
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