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Coolant Temp. Sensor

36K views 63 replies 11 participants last post by  jfoj 
#1 ·
So i recently got that dreaded check engine light so instead of driving over to advanced auto or bringing my car to the shop i bought the vag maxiscan off of amazon because i heard it was a good scanner but not a ross tech that for sure. It does have some vag functions though and overall I'm happy with it. So anyway i scanned my car and i got a code(don't remember the exact code #)for a coolant temp sensor inaccurate readings. Recently i replaced this part for Advanced Auto for like 10 bucks. Since then i have filled up like twice so thats about 700 miles ago. So first i opened the hood as i thought the sensor was loose and gave it a nudge and then reset the light. 25 miles later bam theres the light again. So did i just have bad luck with the sensor as its aftermarket. Should i go to the stealer-ship and get the OEM one or should i just replace it again with an aftermarket one.
 
#2 ·
Coolant temp issues are very often mis managed for many reasons.

If you got a green top temp sensor from Advance you are probably in decent shape. The coolant sensors get blamed all the time as they are the easier item to change, but rarely the source of the problem.

Thermostats fail open or open too early and cause the engine to run cold VERY often. Some stats only last 2 years at a time. If you think you have the original stat, change it. A bit tricky, but I did not remove or disconnect my Alt on my car, just 1/4" ratchet, wobble extension and I was able to do it.

Also you need to read up on the plastic impeller water pump. These are problems.

You need to figure out if your temp code is too low or too high. Also see if you have any freeze frame data with your codes. Not sure your tool reads real time data, but my car with a bad stat only ran about 170-180F, with the newer 185F stat, the engine now runs around 200-205F.

Thermostat will likely run too cold, water pump likely too hot. There could also be some fan issues, would cause too hot as well.

Most thermostat codes are due to cold conditions caused by bad thermostats.
 
#49 · (Edited)
If you think you have the original stat, change it. A bit tricky, but I did not remove or disconnect my Alt on my car, just 1/4" ratchet, wobble extension and I was able to do it.
Thanks so much jfoj.

I told my German mechanic friend about your trick when I wanted to replace my stat. He said "it can be done that way if you are really good." I changed my stat yesterday using your advice here and did it all by myself. My mechanic handed me the tools and said "your beetle friends said you can do it so go ahead. I am going inside and I am not coming out to help until you are crying. I mean tears falling out of your eyes." I walked in less than ten minutes later holding the housing in my hand. That time included stopping to take pics and going to look for a magnet when the socket fell off the extension when I broke open that bottom hidden bolt. His jaw dropped and he said "really?" Made me feel so proud. I guess that means I'm really good...lol :D If I can manage it with very little DIY experience then anybody should be able to for the most part. It is a huge PITA; but, much less so than taking apart the throttle body to dance the alternator out which appears to require some sort of exorcism to accomplish. All I had was a small socket wrench, an extension that was probably twelve inches long, a 10mm socket that pivoted in all directions, later an extending magnet to retrieve said socket more than once, and a repertoire of German swears so I fit in with the German mechanic. I also needed a pick to get the old stat out since its in there good and snug.

At the end of that extension is the pivoting socket almost on the hidden bolt behind the alternator. View attachment 99497
And the new stat in its place View attachment 99498
Now Iggy has a new stat and housing, held a vacuum (talk about easy to refill the coolant system with that), and passed the pressure test (at least at the stat. Found lots of leaky loose hose clamps and going to have to take a lot of Iggy apart to locate one leak behind the engine today).

All this accomplishment I feel is thanks to you posting that it could be done and what you used.

THANKS AGAIN JFOJ!!! YOU'RE THE BEST :)


Sent from AutoGuide.com Free App
 
#4 ·
So I went and changed the sensor again. The first time I did it I had no coolant loss but this time I forgot to de-pressurize the system so I had some leakage. I wrote the code down but I can't seem to find it but hopefully the code doesn't pop back up again. Recent discovery while I managed to drop that stupid black plastic U clip I reached down to find it and grabbed what I thought to be a leave. In reality it was a plastic bag with a cts o ring which is brand new and an oem dealer one as well. This is from the previous owners dealer in NJ. How they managed to not find it is besides me and the fact that its probably been lodged in there for quite some time without coming out. Also side note I recently had an oil change and they only put in 4 qts of oil. Isn't are capacity like 4.2 or something a little more than that.
 
#9 ·
Be prepared to replace the thermostat, trust me.

Hopefully the coolant sensor is your issue, but more often than not the thermostat is the problem.

You should not relay on trouble codes for indication of the running temp, you need a scan tool that reads real time data. I think the one you have may?

If the coolant sensor reads correct at ambient temp, it likely will read correct at operating temp.

But in any event, let us know what you find as it will likely help others here.
 
#10 ·
I will have someone check out that other fault code and as far as the thermostat I hope the cts fixes my prob. What should my temp be running at when warm and what is considered out of range. Off topic I had a friend that went to a public auction yesterday and a 2009 black beetle with 75,000 on it sold for $3500 plus 8% tax. Someone got lucky :D. If I was only there.
 
#12 ·
WOW, High Mileage for an 09. I guess someone loved his Beetle and drove it a lot ;) Still an excellent deal for only $3500 bucks. I Paid $3600 including tax for my 2000 Beetle. Still running strong at 160k miles ;)

I would swap out the CTS. More often than not ;) it is the Coolant sensor when the P0116 code comes up. Personally, I had never had a Thermostat fail in my 2 Audi TT's 1.8 and now my New Beetle 1.8, however I always changed them with the timing belt service at around 75k to 80k miles. If you do change the Termostat don't get a cheap aftermarket unit. I only use the True OEM VW type that the dealer sells. I had so many friends that used the aftermarket kind like the Whaler brand just to have them fail in a very short time. Since it is a little tricky to swap out the thermostat I wouldn't skimp on that particular part and get the real deal.

But for now I would just swap out the CTS and see what happens. When I bought my Beetle it still had the old Black CTS in it and I immediately swapped it for a new Green one.

Again, in this case I do prefer the Real Deal but a lot of people have been using the cheaper aftermarket sensors and most of them haven't had any issues.

Volkswagen New Beetle 1.8T > Search > Coolant Sensor > ES#264174 Coolant Temperature Sensor With O-Ring & Clip - 4 Pin - 078919501CKT

Volkswagen New Beetle 1.8T > Search > Coolant Sensor > ES#2535452 Coolant Temperature Sensor With O-Ring & Clip - 4 Pin - 059919501AKTU

Volkswagen New Beetle 1.8T > Search > Thermostat > ES#261231 87C Thermostat - 050121113C

If you do swap the Thermostat I also suggest a new Thermostat housing.

Volkswagen New Beetle 1.8T > Search > Thermostat > ES#259316 Thermostat Housing - 06A121121C

Good Luck and Keep us posted.
 
#11 ·
My car typically runs in the 204-206F range when I have checked it. I just returned from testing a few things and it was 50F out and I was right around 204F.

I just replaced the stat about 1k miles ago, the older one was opening at about 160F.

I only once ever had a stat code, and cleared it and it never came back. Unfortunately at the time I had a cheaper scan tool that did not display real time data and since there is not temp gauge in these cars I could not tell where the temps were until I put my newer tool on the car and started to monitor the data.

Just because you do not get a code does not mean things are correct and in proper operating order!
 
#13 ·
Quick question. Did you already replace the water pump and timing belt in your Beetle? If not you may want to put that on your to do list since the old Plastic Impellar Water Pump can really be a huge problem and could cause that code if the impellar blades are breaking up.
 
#14 ·
I couldn't believe the price of that beetle though, still a really good deal. No check engine light yet but it still hasn't passed the readiness test on my scanner yet. Praying that it was only the cts. As far as the timing belt and water pump I couldn't find any shop around me to do it so vw dealer got me on that one.
 
#16 ·
Code is back for inadequate readings from cts. I've noticed there seems to be another sensor that plugs into a coolant flange by the power steering res. could this be my problem. I'm also going to put some connection cleaner in where the cts plugs in. My scanner doesn't display live data, I'm just hoping its not the thermostat now. I took it to a shop and they suggested that my water pump might have failed or the fans may not be moving. I'm pretty sure my water pumps good and my fans both run I turned on the ac to check. Any suggestions.
 
#18 ·
So did you have the water pump replaced recently?
You did say that the dealership did your timing belt and water pump? How long ago was this?
If I misunderstood than it is quite possible that it is your water pump. Those old pumps plastic
Impeller break very easily after they get old.
 
#17 ·
You really need to get a scan tool that at least displays freeze frame data and possibly live data. If you find a tool that displays freeze frame data, do not be surprised if you see a temp like 180-185. This still means your stat has failed.

Again, I expect your engine to be running too cool and you have failed open thermostat this happens far more than people really are aware of.

I do not believe there is a CEL/code for engine running too hot, just too cold.

If you had a fan or water pump problem you would likely have the red coolant light coming on and possibly a boil over issue. The water pump is a weak area, but deal with the low temp issue you likely have at this point. Also if you change the stat you can inspect/fell the back of the water pump impeller for damage or broken fins.

The thermostat and gasket is only like $20 as I recall and it really pretty easy to install if you have a 1/4" drive socket set and either a universal joint or wobble extension. 2 bolts and 1 hose clamp after draining the radiator which is a 1/4 turn and pull.
 
#20 ·
So I'm having an issue with the cts code again and I just didn't want to deal with it myself so I took it to a shop where they said they monitored the real time data and said they left it running in the shop and the temperature was climbing normally so they don't think it's the thermostat but maybe a short in the cts wiring now. I've noticed that the check engine light will only come on when I'm going down a big hill. Elevation have anything to do with this at all??
 
#23 ·
I would also suggest you listen to jfoj.

I had similar problem and it turned out to be a "soft" failure of the old thermostat of my car. jfoj successfully predicted the problem before I changed the thermostat.

Just look at these two figures for my 2001. Top one is the coolant temp for the old thermostat (temp never exceeds 178F/81C, which is abnormal), and the bottom one is the temp with a new one (constantly around 200F/93C, works perfect).


(Figures extract from my post on thermostat "soft" failure.)

No one can say with 100% confidence that your thermostat is "soft" failed. However, you can guide yourself to a clearer scenario by just investigating a real-time scan tool.

jfoj's suggestion is great, an Ultragauge for $75 can potentially save you $$$. If you are computer smart, you may want to try a Vag-Com for $15, and to get real-time data with the help of your laptop.

And, any response to Tom's suggestion on timing belt and water pump?
 
#22 · (Edited)
Problem is most shops and techs do not understand coolant temps properly. Many cars will not easily reach proper temp idling.

Best thing to do is bring car to shop and have them read temp after car has been running for 15+ minutes, this is 15+ mins driving. Temps should be around 205F. Anything under 200F you need a thermostat.

Temp will rapidly drop once driving if stat is weak. My car was running 170F and would not trigger CEL! It takes a REALLY bad stat to trigger CEL for engine temp.

A stat is like a battery, more than 4 years old, replace it!

We are talking about a $20 part here, unfortunately the alternator makes it difficult to replace the thermostat, however, I was able to replace my thermostat without removing or touching the alternator. I just used 1/4" drive sockets with a wobble extension.

2 bolts, 1 house clamp and catch coolant and I was done.

I cannot believe all the people that just do not get that thermostats are really maintenance items and do not last forever. They fail ALL the time, usually soft fail as the spring gets weak, they open too early and the engine runs too cold. I see this ALL the time.

Only way to confirm this is problem is to put a real scan tool or device that can read real time data on the car and drive it.

Given these stupid cars do not have a temp gauge, I would just invest the $75 in an UltraGuage and connect it to the car permanently. This way you can keep track of Temps, Fuel Trims, Voltage, read and clear trouble codes, monitor fuel economy and so forth.

You should really read this for more info on scan tools and software - http://newbeetle.org/forums/1-8-liter-turbo/59778-2002-glx-turbo-gas-mileage.html#post830803

If you plan on keeping your car and not going broke, you NEED some sort of scan tool to monitor your car. Even if you do not do your own repairs, you need these tools to keep an eye on problems and determine how critical issues are and to be able make informed decisions and not be at the mercy of some typical tech that sees the work Oxygen Sensor or Catalytic Converter in code and immediately jump on the fact that the part mention in the code description needs to be replaced, usually the issue is the exact opposite if you have half a brain in your head!
 
#24 ·
temp. sensor



Also because some freakin' engineer at VW or VW corp didn't put a temperature gauge in these cars makes it more difficult to troubleshoot engine temperature. Four years ago i chased around the different sensors for a week when it wind up being the thermostat staying stuck slightly open...UUURRRGGG! :p
 
#25 ·
Even if a temp gauge is put in the car does not mean it is anything close to accurate!!!

BMW buffers their temp gauges in some cars due to a electrically heated thermostat that can alter the baseline engine temp.

Also my GMC truck has a really screwy non linear temp gauge that shows the engine MUCH warmer after start up, then becomes more linear and accurate as the engine reaches "normal" operating temperature.

So the only real way to get a handle on what is going on is to have a tool that can read the real time temp info from the OBD stream and to know what your vehicle "baseline" temp should be.

As a rule of thumb, most modern cars and trucks should run about 200F-210F.
 
#29 ·
temp. gauge



Yea but with a temperature gauge on the dash I could have seen that the car was running slightly cold and point me in the right direction instead of troubleshooting goose chase. I am talking 4 years ago when technology didn't have these fancy code readers at a good price. I'm glad technology advanced so much now I can read the codes with my Iphone..LOL :p and reset them too
 
#27 · (Edited)
Thermostat

Proper operating temp on these cars is 205F +/- about 5F.

Most I see are 205-208F

You need to treat your car like your body, you can guess all day about the temperature, but using thermometer/scan tool will clearly answer the question without a doubt and there will be no question what is going on unless you are the type of person that "believes" since the car has a 185F thermostat that the engine should run at 185F, which is NOT the case!
 
#36 ·
new beetle operating temp.



Clarifying question here :confused: so the operating temp. on these new beetles is 205-208 (+/- 5f) ? is that correct jfoj? If so then mine is barely on the lower edge spec's cause i know mine runs at round 200-201 most of the time, during the summer it comes up a little more. Sure glad somebody answered the question directed to me about the OBD2 scanner, I bought mine on ebay for $35 (ELM32) then the iphone's application for $5.00 GOOD DEAL
 
#38 ·
My 2003 1.8t now runs pretty consistently around 205F with the new thermostat. The new stat was installed right at the time I installed the timing belt and water pump.

Before that the engine was running around 175F.

I am the original owner and I only received 1 CEL for coolant temp many years ago when I not have a scan tool that would read real time data and the freeze frame indicated the coolant temp was at 183F as I recall?

What happens to most of the thermostat is the main spring gets weak with age and temp cycling. I have tested quite a few soft failed stats and what I can say is they all seem to open the proper amount at the rated temp, but the spring gets weak and the thermostat actually opens too early.

If your engine is close to 200F, I would not get excited now, but I would likely watch the temps over the Summer and plan to replace the stat at least before next Fall.

I just had a friends Volvo Turbo 5 cyl here and looked at the engine temps. Was reading as high as 220F until the fan kicked in, then the temp dropped to about 208F and would just drift between the 205-220F. Today's outside temps were a bit higher than usual, about 60F so his car was running in the expected temp range.
 
#40 ·
Every car will differ a bit based upon both the thermostat and the temp sensor. Not sure on these cars if the temp sensor wiring is loose if the values would read high or low.

This is why you really need to benchmark your own car and keep a close eye on the temps.

Even things like differences in antifreeze concentration can cause the engine temps to shift slightly. So even though you can compare like cars, something like water/antifreeze mix may cause a difference in the baseline temps.

I just find that most every car/truck I check these days is at 200F or typically between 200-210F operating temp if the ambient temps are below 75F. After 75F ambient, you likely will be up 5-10F and more into the fan cycling window.

It is hard to track a soft stat in the Summer, many times you can cool the radiator with a garden hose to determine if the stat is soft, but you can always catch soft stats when the temps are 60F and lower.

3-4 years is the max I plan on keepinig stats these days based upon what I have seen over the years.
 
#41 ·
I see your points, very instructive! Thanks!

I guess the specific heat capacity and heat transfer coefficient of the coolant mixture affects the adaptive system controlling the engine operating temp, and thus the equilibrium temp. I begin to understand why the VW manual said the percentage of water added into coolant should never be out of the range of 40%--60%. It's not just an issue of the mixture's freezing point...

And I'm looking forward to "visualize" the fan cycling window that can be reflected from measurements taken in this incoming summer!

Really can learn at lot from jfoj :D
 
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