mechanic says thermostat needed. how can he tell?

just wondering what the thermostat does exactly? he says I need a new one. its not a big deal it seems. how can he tell?


what happens when your thermostat has gone bad?

Assuming you have one, does your temperature gauge reach normal operating temperature (195F)?

yeah. on the dash it hits the 12 o clock position all the time. stays there too except on -30 days with the heat cranked itll drop it down a bit but thats with no winter front.

Just because the gauge says 90 doesn't necessarily mean that is the actual temp. If you
have a scangauge what does that say? If you don't have one it may be worthwhile to get one or get a bluetooth adapter, usually 20 bucks for a good one and a torque pro app. Pair it with an
android phone and monitor your temps. The mechanic that said it needed one, why not ask him? Maybe he saw some leakage that made sense to just advise to replace the housing and thermostat.

BAFX Products Bluetooth Diagnostic OBDII Reader/Scanner for Android Devices https://www.amazon.com/dp/B005NLQAHS/ref=cm_sw_r_cp_apa_i_2dznCb4Y316B8

I wanted your guys/a second opinion.

I do have a cheapo obd reader that I can plug in and view engine temps but it’s too late now eh if he already put in a new thermostat.

That does seem like a neat little setup though. I will look into getting that.

Thank you

For the symptoms you describe, I would say your mechanic is padding the bill. Reject his recommendation. Consider finding a new mechanic.

Cheers,

PH

fouillard13 said:

just wondering what the thermostat does exactly? he says I need a new one. its not a big deal it seems. how can he tell?


what happens when your thermostat has gone bad?

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The thermostat opens and closes to regulate the flow of coolant through your radiator to keep the engine within operating temperature.

The thermostat stays shut to prevent coolant from flowing through the radiator so it just keeps cycling through the engine until the system reaches operating temp. Then it opens to allow coolant through the radiator so that it doesn't go above operating temp.

There are some pretty easy steps to diagnose a faulty thermostat now that you've got a picture of what it's doing in there: if your cooling system allows you to open the cap and look at the coolant you can simply watch whether it's flowing or not and under what conditions (cold engine + flow = stuck open, warm engine + no flow = stuck closed), you can grab both in and out hoses from your radiator and feel the temperature differential, or you can turn the car on from dead cold with the heater on blast and check how long it takes for it to heat up (for example, if it doesn't heat up, you know the thermostat is stuck open because it's allowing the coolant to flow through the radiator before everything is up to temp).

Once the thermostat is out of the car you can verify it was faulty by dropping it in water, heating it up to the temp range stamped on the t-stat, and seeing if the t-stat opens/closes correctly. If you want to do this test, simply ask the mechanic to give you the old one when you pick up your car.

BamaB4S said:

Assuming you have one, does your temperature gauge reach normal operating temperature (195F)?

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The dash gauge means virtually nothing, except that the engine is cold/warm/HOT. Every MklV VW I've owned will reach 190* on the dash gauge at coolant temp of aprox 164*, which is far from optimal operating temp (as well as very less than optimal for proper wintertime cabin heat).
Monitor coolant temps and other data points with a ScanGauge or similar device in real time driving and you get to see how things are working.

Hopefully the mechanic used an OEM or Wahler stat. I've had no success with most aftermarket ones reaching proper temp or staying that way. I know thermostat manufacture isn't rocket science but I tried a bunch.

fouillard13 said:

yeah. on the dash it hits the 12 o clock position all the time. stays there too except on -30 days with the heat cranked itll drop it down a bit but thats with no winter front.

Click to expand...

Based on that it doesn't sound like your T stat was too bad.

Metal Man said:

Based on that it doesn't sound like your T stat was too bad.

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I disagree, that gauge on the cluster is useless (to a point). My gauge read straight up and down unless it was -20C which it would then read a touch low. I hooked up my scanguage and the actual temp when the needle was straight up and down was 70'ishC; at -20C, the real engine temp dropped in the 50'ishC.

I also noted that my car was really slow to warm up, another tell tale sign that your thermostat is pooched.

The ECU monitors the coolant temp, and time stamps it at start up within a certain temp range, then times how long it takes to come up to a predetermined range.

However, in BITTER cold conditions, this time stamp is thrown out on the diesels, because in some cases they'll never reach that point. I am not sure just how cold it has to be before it throws this out, though. And I have encountered plenty of VAG engines, diesel and gas, that clearly have a poorly performing thermostat and no flagged DTC for coolant temp control range.

To be fair, thermostats are not like light bulbs, where they work 100% until they don't work at all. They fail gradually, and in many cases you won't even know just how "bad" they've gotten until you experience a new one.

I doubt there is a single ALH, BEW, or BHW engine on the road right now anywhere in North America aside from some freak very low mileage specimens that still have their original thermostat working at peak efficiency. This is why it is listed in my fuel economy thread, and is of significant importance in winter operation.

Hear hear!

I've personally come to consider them a wear item...they can fail suddenly but also just tend to gradually degrade over time as the internal wax pellet ages.

Not possible to see on the factory gauge because it's programmed to show straight up (90C in Canada) for a wide range of actual temps, but with an actual coolant monitor like a Scan Gauge over the years the engine slowly takes longer to come to full operating temp *and* "full operating temp gets lower and lower, particularly in the winter.

My current BEW generally got to about 84C at best when I first bought it a few years ago...shrugged it off as normal for the car...but last season it was more common to see 82C, and this season 78C unless I pushed her hard. All the while the dash reads 90.

New 87C factory stat...wow....back to a perfect 88C under all driving conditions *and* up to that temp in what seems like half the time. Dash still reads 90.

Old stat looked fine, opened and closed properly in a pan of boiling water, etc.

Too soon to tell, and we are on winter diesel ATM, but I know I will be seeing a lift in fuel economy too, having added nearly 10C to the average operating temp and also getting there sooner.

$35 bucks Canadian for a good t-stat and housing plus an extra half hour during a timing belt when the system is already drained...sure they say don't fix it if it ain't broke, but without a Scan Gauge being watched nerd-like you may not be aware it's slowly dying.


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oilhammer said:

I doubt there is a single ALH, BEW, or BHW engine on the road right now anywhere in North America aside from some freak very low mileage specimens that still have their original thermostat working at peak efficiency. This is why it is listed in my fuel economy thread, and is of significant importance in winter operation.

Click to expand...

Mine has it's original thermostat. Seems to work fine as the temperature stays very close to 90 C under a wide range of driving conditions. I'm using an Ultragauge to monitor it.

However, I have been thinking of changing it, because it's 15 years old now, with 290,000km on it.

January 18, 2004 is the day I picked up the car from the dealer. Maybe it deserves a thermostat for it's birthday. LOL

Mike_04GolfTDI said:

Seems to work fine as the temperature stays very close to 90 C under a wide range of driving conditions.

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Ah... a fellow gauge nerd... well done!

Powder Hound said:

For the symptoms you describe, I would say your mechanic is padding the bill. Reject his recommendation. Consider finding a new mechanic.

Cheers,

PH

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he diagnosed what I thought was a broken turbo. turned out to my be my homemade lower EGR block off plate had a hole fried in it. replaced that with a proper kit, replaced thermostat, and took a look at my vacuum lines. im sure all the tinkering and diagnosing took at least 1-2 hours plus parts. he charged me $105 canadian... about $70 USD for all that. I was actually considering buying him supper!!

thanks for the explanations guys. I got the "four stroke" app on my phone which allows me to have 6 gauges and going to get a bluetooth OBD adapter too so I can check it a bit more accurately.


I told the mechanic to throw the block off plate and t stat in the car so hopefully he did.

fouillard13 said:

just wondering what the thermostat does exactly? he says I need a new one. its not a big deal it seems. how can he tell?


what happens when your thermostat has gone bad?

Click to expand...

typically they fail in an open position, meaning it will allow coolant to flow, if this happens, your engine may not get up to temperature,

in the real world, they fail CLOSED, unlike most say, i seldom see one fail open, in this case the car will overheat when full of coolant and boil overs are very common.

The thermostat has a material in it that when its at a certain temp of higher (195F) it will expand and push against the spring and allowes coolant to flow to the radiator to cool off.
This job is not a hard job to do and the part is like $15. with a few hand tools and a shopvac that is CLEAN, you can do this job saving you BIG $$$

An actual mechanic can tell when the thermostat fails, he won't do it over the interweb.
Or he could be guessing, in which case he's just a guy that works on cars.
When they stick closed they will cause havoc, but on our TDIs they usually just get lazy causing reduced operating temperature.

I believe the mechanic did swap it (can I easily tell by popping the hood and taking a pic?) as well as a few others things, for virtually no money. I was expecting a $300 bill and it was only $100 so I cant complain.


hes a TDI speciailst. said there hasnt been a vw he hasnt been able to fix yet and I believe it.


heres some of his work.. I trust him

If you trust him why are you posting here about a cheap little part that probably needed replacing anyway due to neglected maintenance? There are probably many parts on your car that I would replace just because I thought it was a good idea at the time.

Lightflyer1 said:

If you trust him why are you posting here about a cheap little part that probably needed replacing anyway due to neglected maintenance? There are probably many parts on your car that I would replace just because I thought it was a good idea at the time.

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im just trying to learn here. wasnt asking if hes trying to rip me off, I know hes not.



like my first post said...

1. just wondering what the thermostat does exactly? (I shoulda known this... I installed one on my snowbike to disable the rads until the coolant heats up to a certain temperature, THEN it allows the rads to be utilized until its cooled off, but you dont want it too cold, so it blocks the rads off again once its cooled down to a certain temp. without the thermostat and the rads being used the whole time, the bike never gets warm enough in the winter and stays in "warm up mode" dumping excess fuel all day long)



2. he says I need a new one. its not a big deal it seems. how can he tell? (so I can maybe diagnose and figure it out myself one day... got a lot of years left in me, probably something I should know/learn)


3. what happens when your thermostat has gone bad? (again, related to question 2. I plan on keeping this car for a while, I should probably learn something simple like this) so here I am. thats why.

the reason I asked "(can I easily tell by popping the hood and taking a pic?)" is because his communication is bad (his only flaw). im 99% sure he replaced the thermostat. I just like to see for myself, ya know?


all 3 questions have been answered and explained amazingly, I thank you all again. its really appreciated!