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Overheating?

Tiny
DYLANFRANK
  • MEMBER
  • 2003 VOLKSWAGEN JETTA
  • 175,000 MILES
The car listed above has a 2.0. Car will idle for 30-45 minutes before overheating. When driving, car will overheat with 2-10 miles. I have A/C and heat in the cabin. There’s water flow from the return line to the bowl once the engine heats up and the top and bottom rad hose become under pressure (and sometimes before). I’ve replaced the fan control module, radiator temperature unit, coolant temperature unit, thermostat (and felt the water pump fins - felt fine and no free play) When hot, both lower and upper radiator hoses are hot. I’ve purged the system and have put 2 gallons of G12 coolant in it (which took days of running, stopping, adding). Fans don’t kick on until the temperature gauge is 2 lines above 190. Both fans turn on low when A/C is pressed (manual climate control system). Each repair I’ve made (detailed above) the car drives further than before, before over heating comes back. Can it be some really stubborn airlock messing things up?
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Monday, May 22nd, 2023 AT 4:18 PM

32 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,755 POSTS
Hi,

Does it overheat at highway speeds? Also, you asked about air in the system. Was the system drained or extremely low at any point? As far as the radiator hoses getting hot, that is normal and needed.

Also, since the fans are turning on, we may have an issue with a head gasket. Take a look through this link and let me know if anything mirrors what you are seeing:

https://www.2carpros.com/articles/recognizing-the-symptoms-understanding-a-blown-head-gasket-in-your-vehicle

Also, I need to know what engine is in the vehicle. There were several options. See pic below.

Let me know.

Joe

See pic below.
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Monday, May 22nd, 2023 AT 8:47 PM
Tiny
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Thanks for the reply. Read the article about head gaskets. The only symptoms are over heating (rapidly, within 10 miles under load) and warning lights on my dash. Coolant level stays pretty consistent though I do too it off after an overheat. No white smoke.
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Tuesday, May 23rd, 2023 AT 1:13 PM
Tiny
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Sorry. The last drive, it didn’t overheat at highway speeds for about 2 miles. It did overheat returning home driving up a steep grade.
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Tuesday, May 23rd, 2023 AT 1:14 PM
Tiny
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And it’s a 2003 2.0 engine.
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Tuesday, May 23rd, 2023 AT 1:22 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,755 POSTS
Hi,

When it is running, check to see if there is any evidence of air bubbles in the coolant. You can remove the reservoir lid when the engine is cold and then start it. See what happens.

You've replaced nearly everything. The idea that it didn't overheat until it was under a load near home leads me to think there is compressed air getting into the cooling system. However, I've been wrong before and will be again, so this is just a theory.

Let me know.

Joe
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Tuesday, May 23rd, 2023 AT 8:56 PM
Tiny
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I’m thinking the same thing and wondering if the air is coming from the combustion gases via a bad head gasket. On start up with the lid off there’s no movement in the coolant bowl. When it overheats, there’s sometimes bubbles in it.
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Wednesday, May 24th, 2023 AT 6:18 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,755 POSTS
Hi,

When you see the bubbles, could the coolant be at its boiling point, or do you notice air bubbles before it overheats?

If you want, the link I attached above provides the directions for testing the head gasket for leaks. There is a specific one that is related to this concern.

Let me know.

Joe
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Wednesday, May 24th, 2023 AT 6:56 PM
Tiny
DYLANFRANK
  • MEMBER
  • 21 POSTS
Thank you. Read it through. I just did one of the gas mixture blue turns to yellow test via the float bowl and the color of the dye didn't change from blue.
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Thursday, May 25th, 2023 AT 11:12 AM
Tiny
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  • 21 POSTS
I’d guess the bubbles are from the coolant boiling. It’s like a pot of water in the stove.
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Thursday, May 25th, 2023 AT 11:23 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Then the coolant isn't pressurized by a faulty head gasket. When you installed the thermostat, was the brace vertical when installed? See pic 1.

Also, how does it run before it overheats? I ask because we could have a plugged catalytic converter. Also, if the timing is off, that can cause an overheat. How old is the timing belt?

Let me know.

Joe

See pic below.
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Thursday, May 25th, 2023 AT 8:16 PM
Tiny
DYLANFRANK
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Thank you. I believe the previous owner stated the timing belt was changed within 45,000 miles. The car runs great from startup all the way through overheating. If it wasn’t for the gauge and warning lights (and seeing the coolant bubbling after checking under the hood) I wouldn’t even know it was overheating. As for thermostat, I can’t confirm the vertical placement, but I know I installed it spring side towards motor.
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Friday, May 26th, 2023 AT 10:25 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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You're going to hate me, but if the support wasn't vertical, there could still be air in the system. Don't laugh, but does the heater work properly?

Let me know.

Joe
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Friday, May 26th, 2023 AT 9:43 PM
Tiny
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Really? That’s the first I’ve heard of that! I have a OEM VW thermostat in the car now. This was after I used a non-OEM and drilled a little hole in it to help with air release (I read about that online. It didn’t help with the overheating problem. The OEM thermostat doesn’t have a hole). Heater works great, so does A/C.
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Saturday, May 27th, 2023 AT 9:25 AM
Tiny
DYLANFRANK
  • MEMBER
  • 21 POSTS
The one thing I’ve noticed is that with every part I’ve changed, the car drives longer without overheating. And with every repair, I’m adding a little more coolant and burping the system more. It took dozens of times to finally get 2 gallons of coolant in the system. If it was air pockets, would it take weeks to get them out? Just seems crazy...
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Saturday, May 27th, 2023 AT 9:29 AM
Tiny
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... And if so, there’s got to be something that is letting air in I’d think. I even used one of those tools to suck air out via the over flow bowl and force coolant in. I witnessed some hoses collapsing, the gauge read 20 and didn’t drop for 5 minutes (I’d assume showing an air tight system) but only sucked in about 1/2 gallon before the pressure was done.
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Saturday, May 27th, 2023 AT 9:32 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

I agree, it does sound crazy. But you have done nearly everything there is to stop it from happening. That is the only thing I can think of that wasn't done.

As far as the hole you drilled, (don't laugh) but that is called the jiggle valve. It is designed to allow coolant to enter while air escapes.

Let me know your thoughts.

Joe
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Sunday, May 28th, 2023 AT 1:16 AM
Tiny
DYLANFRANK
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  • 21 POSTS
My thoughts are that air is either not escaping (through maybe some partial blockage) or air is getting into the system (through some faulty connection/seal) under load. I’ll remove the housing again and check the position of the OEM thermostat. Should I drill a jiggle valve into it also?
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Sunday, May 28th, 2023 AT 10:16 AM
Tiny
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Did I mention earlier that I removed one end of every coolant hose and blew through it? There was no noticeable blockage in hoses so that would mean if there was one, it’d be in the engine block I’d assume.
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Sunday, May 28th, 2023 AT 10:18 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,755 POSTS
Hi,

I agree. I don't feel there is a blockage. I may have asked this before, but does the heater work properly? That is usually the first thing affected by an air blockage.

Let me know.

Joe
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Sunday, May 28th, 2023 AT 8:25 PM
Tiny
DYLANFRANK
  • MEMBER
  • 21 POSTS
The heater works properly. I did notice once when it was over heating while driving it would get cold then hot again, in relation to the temp gauge raising and lowering, but now it seems consistently hot.
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Monday, May 29th, 2023 AT 9:01 AM

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