2003 V6 Overheating?

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Thread: 2003 V6 Overheating?

  1. #1
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    2003 V6 Overheating?

    My passat gives me a overheating light, telling me to stop. It starts out fine, with the temp gage going from 90 (bottom of gage) to 190 (normal operating range) in about 5 minutes. Then in about another 5 minutes it goes up to the red, and I get the warning light. It doesn't seem to be as hot as it says, but I'm not sure. I have had the timing belt & water pump replaced about 15000 miles ago, and everything worked fine until a week ago. The fan clutch was weak and replaced, but that didn't fix the issue. I don't know if it is thermostat, CTS, water pump, or an air lock. Any help in diagnosing this would be appreciated.

    The fans are working properly, and the oil looks good (head gasket not likely the issue). The heater blows heat after a few minutes.
    Last edited by tsloss; 05-09-2019 at 07:16 AM.

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  3. #2
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    CTS is a ten dollar part and a quick fix once you've done one or if you do some searching on how to do it. really shouldn't take even 30 minutes.

    https://www.amazon.com/gp/product/B00OYI9XW0
    Last edited by ar393; 05-09-2019 at 07:34 AM. Reason: Added Part link

  4. #3
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    To test the water pump, run the engine to normal temperature with the coolant reservoir cap REMOVED, remove the small hose that goes to the top of the coolant reservoir and put it into a can or jug, it should be pumping coolant out that hose. If it's not then you water pump is bad.
    If it is pumping coolant then either your thermostat is stuck shut, or you have a faulty CTS (coolant temperature sensor).

    Start with the CTS as it is the easiest to swap out and it's only a few dollars for a new one.
    axenstar, cchief22 and PassatPatch like this.

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  6. #4
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    Replacing the CTS is a reasonable first step. The trick is to first remove the MAF sensor-to-throttle body flex duct, which is nearly over the CTS. Then, tie fine string or dental floss to the retaining clip, which otherwise has a habit of flinging off and getting lost. The old CTS should pull out of the socket with a little twisting, and be sure to retrieve the old O-ring, which is easy to overlook. After clipping the new one in, be sure to spray the harness contacts with contact cleaner, or WD-40, before clicking that back on.

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    Is the system supposed to be burped after replacing the sensor?
    Is the extension tank cap supposed to be on or off while replacing it?


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    Is the system supposed to be burped after replacing the sensor?
    Is the extension tank cap supposed to be on or off while replacing it?


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  9. #7
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    Quote Originally Posted by axenstar View Post
    Is the system supposed to be burped after replacing the sensor?
    Is the extension tank cap supposed to be on or off while replacing it?


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    I can't say for 1.8s. For the V6, you'll have to drain some of the coolant, unless your the kind that just lets it run out all over the place.
    Getting in behind the right bank head just blows, especially people with bigger hands, like me.
    There was at least one instance I had the intake manifold off my V6 for some other repair, even though it didn't need it, at that point in time I replaced the CTS just because it was that much easier.
    I personally have not needed to burp the system after replacing the CTS.
    Last edited by AndreasPassat; 05-10-2019 at 07:23 AM.

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    Quote Originally Posted by AndreasPassat View Post
    There was at least one instance I had the intake manifold off my V6 for some other repair, even though it didn't need it, at that point in time I replaced the CTS just because it was that much easier.[/FONT][/COLOR][/LEFT]
    I personally have not needed to burp the system after replacing the CTS wards.
    When I did this on my adopted 2.8L ATQ, I already had the intake manifold out because I also was doing the VCGs.

    I think taking the round part with the two hose clamps is pretty painless and fast and will make the rest of it go pretty painlessly.

    I did not burp the system as the coolant reservoir tank was still closed so nothing major should have (and nothing really did) come out the CTS port given it would have needed to create a vacuum somewhere in the cooling system.

    /small hands, smell like cabbage

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    Replaced CTS. No help. Replaced clutch fan. Also no help. Water pump and thermostat were replaced 2 years (15,000 miles) ago, with good (non-plastic impellers).

    Car warms up to 190 in a few minutes. After a few more, it goes to 260 and the warning light comes on & tells me to stop. When you look at the overflow tank, you can see boiling liquid. The top radiator hose is warm, but not boiling hot. Should I backflush the system to make sure nothing is plugged? If not that, I'd guess the t-stat is stuck closed, or the water pump failed. I hate to take half the car apart to change t-stat and water pump, but I can't see anything else to check. I see above someone said to pull the top hose off the overflow tank while car is at temp (with cap removed). Is that effective? Not sure what that would save me, since I wouldn't tear the car apart & only replace the t-stat. Any advice?? Thanks.

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    Quote Originally Posted by tsloss View Post
    I see above someone said to pull the top hose off the overflow tank while car is at temp (with cap removed). Is that effective? Not sure what that would save me, since I wouldn't tear the car apart & only replace the t-stat. Any advice?? Thanks.

    That'd be me.
    The smaller hose that attaches to the top of the coolant reservoir is the bypass flow of coolant.
    If you don't have any flow out of that hose when the engine is at temperature, then your T-stat might be stuck closed or your water pump is not pumping as it should.
    I only mentioned to remove the hose because most cars our age the reservoir is so discolored you can't see if the coolant is flowing or not.

    The V6 takes the heat pretty well, but with your temp going all the way to the far end of the gauge indicates something is way wrong.
    My guess is that you're going to have to bite the bullet and investigate both the water pump and t-stat.
    I myself have had one faulty t-stat on my '98 V6. About 6 years ago I installed a brand new one it lasted about a month. Awful lot of work just to go in and replace a $30 part. The other possibility is that the pump impeller came off the pump shaft. It's been known to happen.
    Last edited by AndreasPassat; 05-20-2019 at 01:31 PM.
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    t-stat
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    Is there a certain amount of flow I need, or is anything OK? I can see the hot coolant moving from the small hose into the overflow tank. I can take the hose off to see how much. Any ideas?

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    It's kind of a subjective amount. I might say a small stream and someone else will say, that's only a trickle.
    I'll take a video of mine so you can make a comparison.

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    Here's another piece of info. Last night, it heated up pretty quickly, and it was making a lot of noise (gurgling and pressure blow-off). So, after it cooled down, I topped of the coolant. Today, I ran it with the coolant tank cap barely on to allow pressure to escape. I ran it at least twice as far as I usually do, and the temp stayed at 190. Was not blowing any heat with the heater on. What does this mean? Can I run it all the time with the cap loose? Do I need a new cap (assuming it's designed to relieve some of the pressure)?

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    By 'Was not blowing any heat with the heater on' do you mean the temp gauge said 190 but there was no heat from the vents? It sounds like you have air in the system.

    Without the cap on, the temp will not get above boiling since it will just boil off. The system is supposed to be pressurized so this doesn't happen. It acts like a pressure cooker instead of just an open pot of boiling water.

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    Quote Originally Posted by tsloss View Post
    Here's another piece of info. Last night, it heated up pretty quickly, and it was making a lot of noise (gurgling and pressure blow-off). So, after it cooled down, I topped of the coolant. Today, I ran it with the coolant tank cap barely on to allow pressure to escape. I ran it at least twice as far as I usually do, and the temp stayed at 190. Was not blowing any heat with the heater on. What does this mean? Can I run it all the time with the cap loose? Do I need a new cap (assuming it's designed to relieve some of the pressure)?
    it means you better address the situation before catastrophic failure

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    I'm trying to address the situation, but I don't know what I need to do. With the cap off, the temp gauge went to about 190 (fluctuated a bit), but no heat from the vents. There was almost no loss of coolant, possibly even no loss. With the cap on, I get all kinds of pressure (and generally heat from the vents). Is there a good way to ensure there is no air in the system?

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    Quote Originally Posted by tsloss View Post
    I'm trying to address the situation, but I don't know what I need to do. With the cap off, the temp gauge went to about 190 (fluctuated a bit), but no heat from the vents. There was almost no loss of coolant, possibly even no loss. With the cap on, I get all kinds of pressure (and generally heat from the vents). Is there a good way to ensure there is no air in the system?
    Check your local autopart stores if they rent coolant vacuum fill tools. Try to fill the system using it, checking for any leaks.
    You can buy it as well.
    https://www.ecstuning.com/b-schwaben.../024948sch01a/


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    Quote Originally Posted by Iowegian View Post
    It sounds like you have air in the system.
    I agree, and that would account for the gurgling noises too. You need to ensure that all air is out, and if done correctly, that takes maybe 15 minutes. First, don't attempt this with the coolant hot: you don't need to get scalded. Also, Don't run the engine.

    Remove the screws holding the reservoir to its mounts, disconnect the sensor wiring underneath it, then support it as high as the hoses allow. Fill it and leave the cap off. Now find the bleeder screws on the metal coolant pipe, which need to be unscrewed several turns to allow air to vent. When coolant begins to burble out, close the screw(s).

    One of the heater hoses at the firewall, adjacent to the battery, should have a white ring marked around a small punched hole. Release and move the clamp so that the hose can be pulled away from the firewall, which may require some twisting to break it free. When the punched hole is moved out far enough, a small nail will go through and prove the hole is past the end of the heater pipe. Wait until the coolant burble occurs there, then push the hose back into place and re-clamp. Reinstall the reservoir, then try driving the car again to see if that corrected the problem.
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  22. #20
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    Quote Originally Posted by tsloss View Post
    Here's another piece of info. Last night, it heated up pretty quickly, and it was making a lot of noise (gurgling and pressure blow-off). So, after it cooled down, I topped of the coolant. Today, I ran it with the coolant tank cap barely on to allow pressure to escape. I ran it at least twice as far as I usually do, and the temp stayed at 190. Was not blowing any heat with the heater on. What does this mean? Can I run it all the time with the cap loose? Do I need a new cap (assuming it's designed to relieve some of the pressure)?

    So with the cap on you don't get any heat.
    That might be a sign you have a air pocket or air-lock inside the cooling system.

    Burping the system might take care of this problem.
    I would try this first before anything else as ylwagon suggests.

    Bypassing the heater is a simple procedure and can be done without any harm to your car.


    If the burping of the system doesn't yield satisfactory results, here is something that may be happening:

    What I'm concerned about is that you are getting to much pressure with the reservoir cap on. That indicates an internal leak in the system.
    What condition is your coolant in the coolant reservoir? Is it pink / violet in color? Is all coolant/water or does it have any milkshake appearance to it or anywhere inside the coolant reservoir?


    Leaving the cap off in this particular situation sounds like you are getting a build up pressure that is beyond what the system is designed to hold.
    I don't know the actual VW spec on the optimal pressure in the coolant system is, but a round about average (most cars) will allow a max of 15psi in the coolant system.

    When mixed properly and with the proper operating pressure of the coolant system you should be able to exceed 250°F without boiling.
    With the cap off that drops down to approximately 225° - 230° (with properly mixed coolant).


    Also, check the oil dipstick. The oil should be of very light brown or brown (or black depending on your oil change habits). If there is anything that looks like a milkshake on the end of the dipstick you need to let us know for diagnosing.

  23. #21
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    when "burping/venting" air at the heater core, be cautious as to twisting,pulling and wriggling the hose back to get it past the little vent hole in the heater core pipe, unless you have one of the new heater cores with aluminum tubing, the OEM plastic piping becomes brittle and susceptible to cracking or breaking... when all this stuff is happening is your radiator warm/hot at all ?

  24. #22
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    I would try a new tank cap and bleed the cooling system. The cap can go bad and cause your issue.

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    Quote Originally Posted by cchief22 View Post
    when "burping/venting" air at the heater core, be cautious as to twisting,pulling and wriggling the hose back to get it past the little vent hole in the heater core pipe, unless you have one of the new heater cores with aluminum tubing, the OEM plastic piping becomes brittle and susceptible to cracking or breaking... when all this stuff is happening is your radiator warm/hot at all ?
    yeah, or when you break one doing a reverse heater core flush. I still need to find out the inside diameter when I have time and get something in there. you don't know off hand what could go in the outlet/inlets in the firewall because I cracked the joint of the outlet one, and it leaks (just enough to be annoying) and there is also another coolant leak somewhere, but again minor that I haven't had enough time to check it.

    My titan has been taking up free time i've had.

    On the plus side....i got that effin' broken exhaust manifold stud out!

  26. #24
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    get me the exact I.D. measurements , I will look on my 03 parts car ,I have an idea for a repair

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