# 1.8 Radiator Bubbling After Head Gasket Replacement



## xrufx (Sep 27, 2008)

Hello, dear community. I've searched google and the forums but can't quite find the exact answer to my question. So I turn to the experienced. I would appreciate any aid.

79 Rabbit, engine swap from a 1.8 8v cabby. The Cabby had been in an accident and had a broken exhaust stud in that had to be replaced. Pulled off the head and extracted the stud (fairly easy thankfully) and properly replaced it and torqued down with new gasket. However There is a problem. When I started it up and it warmed up the coolant started to surge up and bubble out of the radiator fill spout. It'll surge up and spill out.. then draw back slightly for a moment, then surge again. sometimes it will spill continually but the surge is still present as evident by the amount that comes out (in a surge). There is also a very slight waft of steam (but as far as I can tell it doesn't seem to smell explicitly like exhaust) I jacked up the left side of the car (where the spout is) and keep pouring water into it and squeezing the top hose but it would not stop surging. I give up and turn it off and leave it. I've done this for several days trying to see if there is air trapped that I need to get out but it continues to bubble over.

I've heard advice from a buddy that the head could be cracked or the block, or the gasket is seated incorrectly.

Does this sound like a water pump impeller spun problem, tstat, or head/block problem?

Before I dig into it I'd like to hear if anyone has any experience or suggestions. Please help me get another bunny back on the streets. I miss it.


----------



## WaterWheels (Aug 14, 2005)

Sounds like an air pocket in the coolant system. Most times they form right at the thermostat and because air is trapped there and no coolant, the coolant in the engine starts to boil because the thermostat does not open. Three common ways to clear it out. First you can run it while making sure there is always coolant in the system untill it finally clears out. I don't like that way as it is dangerous, engine damage not to you. Second is to remove the hoses before and after the thermostat and make sure they are filled with coolant. This does not ALWAYS work but it is the "text book" method. Third, and my method, is to drill two or three small holes (1/8" is more than fine) in the thermostat and fill the coolant system and start the engine. The holes allows fluid to pass through and avoids any air pockets from forming. Most times when the engine is run it only requires a small top-off once warmed up.


----------



## xrufx (Sep 27, 2008)

Thank you for the suggestions. They all sound like things that should be easy to try. I hope that can fix the issue and get things sorted out. I thought I was doomed to sit there and wait for it to bubble itself over until it finally fixed itself.

Thank you WaterWheels, I am anxious to try those methods!


----------



## ziddey (Apr 16, 2006)

did you torque the head bolts properly? used new ones?


----------



## xrufx (Sep 27, 2008)

Torqued to spec in the correct pattern and stepping. New head bolts


----------



## chickenfriend (Jan 31, 2005)

The coolant system can be pressure tested. If it does not hold pressure, there is a leak somewhere. 

The coolant can also be tested with a kit that detects combustion gases in the coolant. Sometimes the local auto parts stores rent this. if it tests positive, that means a headgasket leak or cracked block or head. 

Check the coolant as soon as the engine is started (before warm-up) to see if it bubbles, if so that means a cracked block, head, or leaking headgasket. 

If you are sure all the air is out of the system, and it only boils over when warmed-up,; it may be failed closed or partially closed thermostat, faulty cooling fan, loose drive belt on coolant pump. 

--- 
I do not think it is necessary to drill a hole or holes in the thermostat. The VW thermostats are located at the bottom of the system, and air will travel upward through the system. There is little for the thermostat to trap. 

When air entrapment is a problem auto engineers with specify a jiggle valve in the thermostat. An old trick is to hold open the thermostat with an asprin tab. 

It is important to open the heater valve after refilling with coolant, until the engine warms up. I suggest also suggest blurping the system by squeezing the big hoses all around.


----------



## xrufx (Sep 27, 2008)

Waterwheels, thank you for the suggestions. I think the air was trapped in there somewhere. Now all hoses are hot and it doesn't bubble over! I finally got everything hooked up and took it out for a 15 mile drive. All was well and temp stayed at ~200 almost the whole time. For the life of me I could not get the stock gauge to read. I tried the cabby's water temp sending unit, modified the one from the original rabbit motor, even tried to put resistors in line with the sending units to make it read properly. I finally broke down and bought an aftermarket coolant temp gauge and modified it to fit into the cabby motor's plastic housing. Seals, seats and sends (with a little clever wiring). 

Chickenfriend, I'm not sure if you remember but almost two years ago you helped me diagnose an alternator problem where the alt wouldn't start charging until i revved it up and you helped me figure out a way to do a temporary fix with the exciter wire going to the pos+ coil with a resistor. You were a huge help back then and my dad and I still talk about how cool it was for you to help me out so much. And although the motor didn't have any of the problems you suggested, I really appreciate you chiming in yet again with your endless wisdom. If you were local I'd have bought you more than a few beers by now. 

Well, onto the next problem... why turning the parking lights/and/or/headlights on turns the car off.. lol. 

Thank you again, guys.


----------



## chickenfriend (Jan 31, 2005)

xrufx said:


> Thank you again, guys.


 Always a pleasure to help a gentleman.


----------



## Glegor (Mar 31, 2008)

WaterWheels said:


> Sounds like an air pocket in the coolant system. Most times they form right at the thermostat and because air is trapped there and no coolant, the coolant in the engine starts to boil because the thermostat does not open. Three common ways to clear it out. First you can run it while making sure there is always coolant in the system untill it finally clears out. I don't like that way as it is dangerous, engine damage not to you. Second is to remove the hoses before and after the thermostat and make sure they are filled with coolant. This does not ALWAYS work but it is the "text book" method. *Third, and my method, is to drill two or three small holes (1/8" is more than fine) in the thermostat and fill the coolant system and start the engine. The holes allows fluid to pass through and avoids any air pockets from forming. Most times when the engine is run it only requires a small top-off once warmed up.*


 this is the method i use, but instead of drilling 2 or 3 holes, i drill only one, and usually SMALLER than 1/8"... 

and only drill them in the outter portion of the thermostat (the frame, not the actual valve) 

ive noticed longer warm up times when more than one hole is drilled..


----------

