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Discussion Starter #1
1998 New Beetle diagnosed with bad head gasket -- engine leaking but not exhibiting any symptoms of overheating.

Mechanic replaced head gasket, but now engine overheats.

Any suggestions on cause?
 

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i'm almost in the same boat as you,

make sure that there the coolant is topped off in the reservoir,

burp the cooling system,

personally i'd do a compression test on the engine, if there was a blown head gasket, it'll mainly be because of previous overheating and the head was warped.

if you replace the HG but didn't resurfaced the warped head, the HG will blow again and you'll burn through coolant
 

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Discussion Starter #3
Thanks ... will burp the system and double-check coolant levels.

Strange thing is that the engine wasn't overheating prior to the HG replacement but it is after the repair.
 

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then the mechanic may have improperly did the coolant when it came time to refill it

double check that plastic coolant piping that is connected to the right side of the engine as well to make sure everything is normal
 

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Is it possible that two issues are not related but just a coincident? Broken water pump if plastic?
 

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Discussion Starter #6
Thanks for the water pump suggestion. I'll definitely have it checked out, but the water pump should be OK. It was replaced in early July.

I haven't seen it heat up yet, but the guys at the garage tell me it starts to overhead pretty much immediately.

Will post more info after I see it in person.
 

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Is it overheating or just getting the coolant light come on? Huge difference! And if its the light, the coolant level needs to be topped off most likely. My bet is that there is some air in the system that needs to be burped out.
 

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but the water pump should be OK. It was replaced in early July.
In this case you are fine as it is impossible to find one with plastic impeller these days.
My bet is that there is some air in the system that needs to be burped out.
Is it just a matter of time? AFAIK there is no special valves to bleed air out, right? I still didn't try to start engine after I've changed WP & TB...
 

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Discussion Starter #9
The shop has assured me there is no air in the system. I would like to check that out myself when I get the car home early next week.

What are the steps to take to burp the system?
 

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The shop has assured me there is no air in the system. I would like to check that out myself when I get the car home early next week.

What are the steps to take to burp the system?
IMHO do NOT take the car from the shop until they get the overheating resolved. If they did the HG then THEY need to figure out and correct why it is overheating. With them telling you it heats up immediatly I would bet on wrong HG or air in system. Nothing else makes sense.
 

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Discussion Starter #11
Here's the latest.

Stopped by the garage this morning. Engine starts and sounds like it's running like a top.

Antifreeze soon begins to bubble in the plastic reservoir -- and it seems like it takes longer than it should for the blue light to go off.

Once the light went off, I turned the heat on but only cool air came out. Hoses never did heat up to a level you would expect.

My guess is that we have an antifreeze circulation issue of some sort. First step is to replace the thermostat to see if that takes care of the problem.

Will post results.
 

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I can't speak for this particular situation, but there are head gaskets that fit sevearal different heads and have "knock-outs" for some water ports that are not on all heads.

As said, the car doesn't leave the shop until it's correct. Any subsequent damage that may result in driving the car is going to be on your nickel, not theirs! I'm am beside myself that a shop would pull off a head, have a problem, and then not continue to diagnose and fix it. Perhaps they need to come here to learn how to do the procedure (lol). Is this a generic shop or an independent VW Specialist? I suspect a generic, because I don't believe you would have had a call from a shop specializing in VW. There are many methods that are very specific to VW. Also special tools and knowledge. Aside from going to the Dealer, I would be hesitant to take it anywhere but a shop that specializes.

A light doesn't indicate that it is overheated, necessarily, just that it may be low on coolant, or has air in the system.. If the shop is not using the proper equipment for filling the system, air DOES need to be purged from the system. There is a specific procedure for this. Perhaps review it, and then asked them about THEIR procedure (in a tactful way, trying not to come off as a know-it-all). Go here -

Bentley drain and fill procedure
http://newbeetle.org/forums/questions-issues-concerns-problems-new-beetle/52130-beetle-overheating.html#post753690

The purging process must be followed to the letter. With the "hand" procedure, it may still need to be driven, and then filled again to purge all of the air. They should drive it, close to the shop, and as soon as the light comes on, it should be stopped, and the level checked.

You didn't say what the original symptoms were, compression problem? water in the exhaust, or oil? Oil in the water? Oil getting into a cylinder chamber an fouling a spark plug? It's possible, depending on the failure, that the head could be warped or cracked. Especially if the bad gasket had caused an overheating problem. Depending on different factors, a shop will send the head out to have it checked. But again, who does this needs to know the VW, I understand the head is not magnaflexed as a normal head is checked, and if done that way can actually cause damage to the head.

MORAV
 

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If you have bubbling in the expansion tank these are your options...

1) Incorrect head gasket replacement was used
2) Head Gasket/Cylinder Head not installed properly
3) Cylinder Head should have been planed

The coolant system is being pressurized which prevents the coolant from circulating. This thread might be helpful.
 

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First, the coolant light indicates either coolant level low or overheat and if it overheats almost immediately then it's probably coolant level low. Second, according to service manual, beetle engines take 2 complete warm-up and cool-down cycles to bleed the cooling system so make sure with the shop they did this accordingly.

If they did the coolant system bleeding properly and coolant still bubbles when startup, I'll suggest that either the head gasket is not installed properly or the head is warped. (another possibility is that they did clean the gasket mating surface thoroughly which is a stupid mistake) The bubble is probably passed from combustion chamber and you can try smell the coolant, there can be burned smell. Also try looking at the tail pipe to see if there is any coolant getting out...

Thermostat is easy to check before you replace so don't waste your labor.


Here's the latest.

Stopped by the garage this morning. Engine starts and sounds like it's running like a top.

Antifreeze soon begins to bubble in the plastic reservoir -- and it seems like it takes longer than it should for the blue light to go off.

Once the light went off, I turned the heat on but only cool air came out. Hoses never did heat up to a level you would expect.

My guess is that we have an antifreeze circulation issue of some sort. First step is to replace the thermostat to see if that takes care of the problem.

Will post results.
 

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Here's the latest.

Stopped by the garage this morning. Engine starts and sounds like it's running like a top.

Antifreeze soon begins to bubble in the plastic reservoir -- and it seems like it takes longer than it should for the blue light to go off.

Once the light went off, I turned the heat on but only cool air came out. Hoses never did heat up to a level you would expect.

My guess is that we have an antifreeze circulation issue of some sort. First step is to replace the thermostat to see if that takes care of the problem.

Will post results.
Vagcom to tell what temp the CTS is seeing, try to see if the engine thinks it is overheating.

Bubbles in the reservoir are either air in the system coming out, combustion gases or steam bubbles from serious overheating.

BUT

The system is designed to run under 15psi pressure so make sure she does overheat with the system cap in place and sealed.

Check the rad fans run (try with a/c on, both fans should run at low speed continuously)

You can get a testing kit for combustion gas in the reservoir, that will rule out HG installation leaks and leave you with air, boiling or circulation as the causes. Circulation comes down to pump, thermostat and air pockets.

Low/no heater output points to air in the system - run engine at 2000rpm and check the small pipe going into the reservoir near the top, there should be some flow here. Run at 2000rpm for 5mins and see if that will purge the air.
 

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Discussion Starter #16
The saga continues ... the thermostat was replaced and there seemed to be no improvement.

Today, though, I went back to the shop and took the car on a short test drive.

After a couple of miles, the heat suddenly kicked on. The red temperature light never did come on.

However, I didn't notice the fans coming on.

So that's the next step ... a check of the fans.
 

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As I suspected they probably didn't bleed your cooling system properly. My feeling is that the AEG's water pump is a little bit weak that it is not powerful enough to bleed at idle speed. At idle, the coolant seems not moving a lot. This means you need to use a higher rpm to bleed this is likely either run on the road or pump gas. The heat suddenly kicked on means that the heater was bleeded and coolant was running through heater. The same thing could happen on radiator, too. Be sure to check the coolant after you drive the vehicle and then COMPLETELY cool the engine down TWICE! This is according to the service manual.

Fans are easy to test. Simply turn on your A/C and then both fans should be on at low speed. If either no on, it's probably bad or fan control module is bad. Also when running, the fans might turn on if you are driving in local. On highway when speed is more than 40mph the fan would probably never turn on.


The saga continues ... the thermostat was replaced and there seemed to be no improvement.

Today, though, I went back to the shop and took the car on a short test drive.

After a couple of miles, the heat suddenly kicked on. The red temperature light never did come on.

However, I didn't notice the fans coming on.

So that's the next step ... a check of the fans.
 

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Jitterbug
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The saga continues ... the thermostat was replaced and there seemed to be no improvement.

Today, though, I went back to the shop and took the car on a short test drive.

After a couple of miles, the heat suddenly kicked on. The red temperature light never did come on.

However, I didn't notice the fans coming on.

So that's the next step ... a check of the fans.
So now we think it never did overheat, just had air bubbles in the reservoir coming out???
 

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Discussion Starter #19
I think that may be the case.

When I took it for the drive this morning, I had the heat on and it was blowing cool air. All of a sudden it switched to warm.

It's not showing any signs of overheating. The bubbles in the reservoir tank happen only when the cap is off and the car gets up to temperature -- probably takes 10 minutes or so before they appear.

When the cap is on, there are no bubbles and the red temperature light doesn't come on.

No white exhaust smoke, no odd smells, nothing that indicates the engine is overheating. Coolant level seems to be staying level too.

The smaller of the two cooling fans has kicked on now, as well, after a period of in-town driving.

I think there was air trapped in the system that was causing the problem.
 

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To reiterate my FIRST post in your thread (sometimes I feel invisible!)...
A light doesn't indicate that it is overheated, necessarily, just that it may be low on coolant, or has air in the system.. If the shop is not using the proper equipment for filling the system, air DOES need to be purged from the system. There is a specific procedure for this. Perhaps review it, and then asked them about THEIR procedure (in a tactful way, trying not to come off as a know-it-all). Go here -

Bentley drain and fill procedure
http://newbeetle.org/forums/questions-issues-concerns-problems-new-beetle/52130-beetle-overheating.html#post753690

The purging process must be followed to the letter. Note running engine at 2000 RPM, not idle. With the "hand" procedure, it may still need to be driven, and then filled again to purge all of the air. They should drive it, close to the shop, and as soon as the light comes on, it should be stopped, and the level checked.
And now to add a link for checking the fans, since you seem convinced they are not running when you think they should be (fan diagnostices are toward the end) ...
Bentley Cooling System Diagnostics
http://newbeetle.org/forums/2-0-liter-gas/52013-overheating-problem.html#post753256

Now, to pose the question again, that I asked earlier...
You didn't say what the original symptoms were, compression problem? water in the exhaust, or oil? Oil in the water? Oil getting into a cylinder chamber an fouling a spark plug? It's possible, depending on the failure, that the head could be warped or cracked. Especially if the bad gasket had caused an overheating problem. Depending on different factors, a shop will send the head out to have it checked. But again, who does this needs to know the VW, I understand the head is not magnaflexed as a normal head is checked, and if done that way can actually cause damage to the head.
What do you think is normal for the blue light to go off, indicating the engine has warmed to operating temperature? 8-10 minutes isn't unusual after a total cool down, say overnight. So... they/you were getting a red light (low coolant), what made them/you ever think it was overheating?

I really have my doubts you have any issues.

MORAV
 
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