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

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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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    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?


    Sent from my iPhone using Tapatalk

  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?


    Sent from my iPhone using Tapatalk
    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; Today at 01:31 PM.

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    t-stat

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