Overheating?

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.

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.

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.

And it’s a 2003 2.0 engine.

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

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.

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

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.

I’d guess the bubbles are from the coolant boiling. It’s like a pot of water in the stove.

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.

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.

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

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.

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…

…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.

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

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?

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.

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

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.

One more, I think I may have forgotten to mention: when it overheats, and I shut it down, the two fans stop also. I’d think the fans should still be running once the ignition is off for a while if the engine is hot but I don’t know…

Okay. So, I took it out today on a 5-mile run in city, country and fwy driving. The temperature stayed right at 190 (normal). It wasn’t until I got back home that it began to overheat (in the driveway, idling. On that 5-mile trip I drove it like I stole it).

The AC worked; the heat worked. The top and bottom radiator hoses were hot and firm.

Neither fan turned on until the temp gauge reached 2 lines past normal, then they both turned on high but couldn’t cool the engine down. I revved the engine to 35k RPMs which brought the temperature down to almost normal. While idling afterwards the temp gauge went back up in short time.

I’ve read these fans should kick on before it overheats and stay on afterwards (when the ignition is off to help cool the engine - this didn’t happen). I’m about to replace the fan control module, the radiator fan switch and the coolant temperature switch (all of which I’ve done before, which didn’t make a difference, using parts I’ve bought from Amazon at a fraction of the cost of OEM parts). The OEM parts are about $450 together, but I’m at my wits end. Am I being crazy? Replacing parts I already have? But, maybe I need to do OEM and it will solve all my problems? I’m stumped.

Hi,

You aren't being crazy. These things can cause a person to go crazy. As far as it not turning the fans on until it already has overheated, we have a sensor not working.

Do me a favor. The 8th digit of the VIN should be a K, L, or a T. Let me know which you have. Also, I found the temperatures when the fan should turn on. I attached it below.

Let me know.

Joe.

See pic below.

Thanks Joe! That is helpful!
The 8th letter on the VIN is an M.
Since I’ve replaced all those parts, how would I locate a bad sensor? I’m good with nuts and bolts but multimeters have always been a mystery to me…

Hi,

Just for curiosity, how close to the temperatures I listed do the fans turn on? As far as the coolant temperature sensor is concerned, I attached a pic below of the location. In red, I circled a plastic horseshoe-shaped clip. First, disconnect the electrical connector and inspect it. If it is good, then when the engine is cold, gently press down on the sensor and remove that clip. Pull straight up on the sensor to remove it. Have a new one ready to install to prevent too much coolant loss. Lubricate the new o-ring with coolant before installing it. Gently press the new sensor into position and reinstall the plastic clip and connector.

See if this takes care of the issue.

Let me know.

Joe

Hi Joe. Hard to say about fans cause I’m just going by the temp gauge inside the car. The fans come on when the needle reaches almost two lines above the middle 190 mark. And as for that sensor, in the radiator, I’ve switched that out already with no difference (along with the fan control module).

If the fans turn on at 190, that's actually too soon. The thermostat isn't designed to fully open until it reaches 195 F.

As far as the sensor, the one I'm referring to isn't on the radiator. Was it replaced as well?

Let me know.

Joe

Oh, sorry. Yes, the sensor in the radiator and the one I think you’re talking about (in the hose near the block which sends info to the gauge in the dash of the car) have both been replaced.

And got it. The issue with the fans turning on is that they don’t turn on until the engine has already begun to over heat, and at that point can’t cool it down. Also, they turn off when I turn off the ignition, even if the engine is at an over heated state (I’ve heard they are suppose to continue until the engine cools down when car is off).

Hi,

The only thing left would be to have the computer updated if there is an update available. That is something you would need a dealer to do. I wish I had a better answer, but you've done a lot already.

Let me know.

Joe

Thanks Joe. Never heard of a dealer computer update for these cars.

Hi,

I'm not showing one under any technical service bulletins. However, I don't have the most updated info from VW. You may want to contact a dealer and ask if there are any updates related.

The only reason I'm suggesting this is because you have already done so much work. There really isn't anything other. If the cooling fans are turning on too late and the sensors and PCM are recognizing the temperature, something is preventing the PCM from turning the fans on sooner. In my mind, which sounds like a programming issue. I've been wrong before and will be again, but that is what is making sense to me at this point.

Let me know.

Joe

Thanks Joe.