2010 Passat 1.6 tdi overheating

yamaha4life · 02-03-2020 1:19pm #1

right so ill start my story with the missus needed a new car, i steer her away from bmw and audi due to chain and oil pump issues. got her to settle for a nice clean 10 plate passat 1.6 tdi.

so i test drive it all is well bar a rear shock bush lovely, bought it, drove it home 1.5 hour journey flawless.

day two, i was driving it up a bit of a hill and noticed the temp gauge started creeping up past the 90C was almost home so when i got home i topped it off with coolant about 500mls, checked for leaks no obvious ones anyway no drips on driveway. took it for another drive and the temp gauge is still creeping up it gets up to just under 120C and the rad fans kick in and bring the temp back down to 90C. after this i topped it off again only a little required.

left it over night no coolant lost and drove it circa 30km and was fine no overheating. so headed home again on the way i stopped off at a mechanic friends garage explained the situation to him and he reckoned it was an airlock that more than likely is after pushing out itself, i thought great left for home up a slight hill near top checked gauge up around 110-115C again heart well and truely sank it was up and down the all the next 20km until i got home and checked coolant levels still on max mark rad fans were on until temp dropped to 90C. it doesnt show any obvious signs of overheating like steam/ bubbling from expansion tank also the heaters in the car are no where near the 30 degrees they are set to warm at best not hot like my own audi.

to add insult to injury this car was bought to replace a very troublesome opel so this is a real kick in the teeth.

thats my story any input on where to look at next would be great? common issues that cause this? ive done a lot of googling and it doesnt seem like these passats overheat that often.

biko · 02-03-2020 1:59pm

It could be the water pumping not circulating the coolant well enough.

Start with free things - like burping the car to remove air pockets. https://www.youtube.com/watch?v=cRPEqO06O58

I assume the coolant is nice and clear?

yamaha4life · 02-03-2020 3:21pm

biko wrote: »

It could be the water pumping not circulating the coolant well enough.

Start with free things - like burping the car to remove air pockets. https://www.youtube.com/watch?v=cRPEqO06O58

I assume the coolant is nice and clear?

the coolant colour was a little murky red but diluted a bit with water also by previous owner id imagine, i put some generic coolant that can be mixed with all types so the bottle says.

i tried to burp it a bit last night but it was freezing and id had enough lol but i will give it another go when shes back with the car iv told her watch the temp gauge religiously while shes out.

the belt and pump were "done" 40,000km ago according to the writing on engine, no true way of knowing really so you could be right that its failing.

temperature only seems to be rising when the car is under load or driven on plodding along normally it will sit at 90C.

yamaha4life · 03-03-2020 12:54am

iv had a bit of an idea and seeing as the coolant has been diluted quite a bit with water and slightly murky i wonder if the P/O had a leak and put in rad weld type stuff and now has caused poor flow so im going to try a flush of system tomorrow but sadly removal of thermostat may not be realistic from google housings tend to break while removing. i really cant get over how the car never overheated on test drive or on the way home, shes only owned it for 3 days and worse case could b stung for a new head gasket

Whocare · 03-03-2020 8:14am

Is probably serious that it was sold. Head gasket cracked Head. Was it a private sale

Tea drinker · 03-03-2020 11:54am

Was there pressure in the system when you opened the reservoir ? Should have been seeming as you opened it when hot.
Be careful opening that when hot. ;-)
No wet carpets? And water's definitely not escaping from reservoir cap?
Oil filler cap doesn't have white stuff on it?

biko · 03-03-2020 2:19pm

Murky coolant doesn't have to mean something is broken. The car is ten years old, coolant could possibly be the original..

yamaha4life · 03-03-2020 3:47pm

whocare yes is was a private sale met the lad at where he "worked" in a small industrial estate.

tea drinker, system had plenty pressure in it i only opened the cap slighty and slowly left a big load of air and water out of it heard lots of bubbling at the other side of engine also. since doing that and topping it off the coolant level has stayed at the max mark and heaters in car are gone from warm to hot.

biko the coolant in this car is g12 its and suppose to be bright red and if you could see it its anything but, its a rusty brown colour. so i think a flush is in order a quick google revealed g12 doesnt mix well and can block up rad and heater rad im starting to feel this is the problem, there might be light at the end of this tunnel.

side note the oil temperature of the car has been quite high so i decided to change the oil and filter, the filter was disgusting and after collapsing i should have taken a picture, since this the oil temp on the display has dropped at least 20 degrees.

yamaha4life · 03-03-2020 10:58pm

right second attempt at this post thanks to very poor signal

i flushed out cooling system was not that fun, the heater matix was tricky and quite dirty.

i refilled it with generic coolant and bleed it out with cap off waited for no more bubbles.

i though i was on to a winner as on the test drive the temperature only rose slightly past 90C on the first test drive and came back and topped it off.

i went for a longer drive and all was good until the last few hills on the way home the temperature increased to 125C heaters went cold right outside the house so i switched it off and released some air from header tank and left it cool for a few minutes.

after this the car heaters were hot again and temp around 100C and dropping. topped coolant off.

i priced a new themostat inc housing from the dealer €41. its in an awkward spot altenator removal looks un avoidable. also priced a new coolant temperature sensor dealer again €40. ive been told aftermarket parts can cause issues.

if these parts dont sort it the head gasket must be cooked

Whocare · 04-03-2020 4:04pm

Come it unlikely it's the thermostat previous owner knew full well that I was f***** .if I was Me go to proper garage and get it diagnosed

yamaha4life · 04-03-2020 5:42pm

Whocare wrote: »

Come it unlikely it's the thermostat previous owner knew full well that I was f***** .if I was Me go to proper garage and get it diagnosed

its the last chance before it goes to a mechanic but reputable ones are in short supply in my area, not trying to be smart but i have worked in the trade for a couple of years before so im fairly compedent with a spanner hence why im trying to sort it before handing it off.

ive no doubt the P/O knew something was amiss but its the way things are now sadly i would never sell a car to someone knowing it had a major fault.

Tea drinker · 06-03-2020 2:24pm

yamaha4life wrote: »

its the last chance before it goes to a mechanic but reputable ones are in short supply in my area, not trying to be smart but i have worked in the trade for a couple of years before so im fairly compedent with a spanner hence why im trying to sort it before handing it off.

ive no doubt the P/O knew something was amiss but its the way things are now sadly i would never sell a car to someone knowing it had a major fault.

With you on that, but some people are a bit autistic when it comes to money... sorry to see you met a bit of a cnut.
Hopefully it's just a headgasket, I don't know what the chances are the head is damaged / cracked... I'll say a decade of the roasary for ya ;-)

06-03-2020 2:52pm

yamaha4life wrote: »

........... not trying to be smart but i have worked in the trade for a couple of years before so im fairly compedent with a spanner hence why im trying to sort it before handing it off...........

There's no way it's a stat or a CTS that's causing the overheating.

yamaha4life · 06-03-2020 4:59pm

Augeo wrote: »

There's no way it's a stat or a CTS that's causing the overheating.

i hope for my sake your wrong, ive had two ford focus with similar symtoms present at garage i used to work at the thermostat had failed on both (boiled them didnt open)

but anyway an update for ye i took the car for a long journey yesterday including some 120kph motorway and it didnt overheat at all.

so i managed to get a diagram of the cooling circuit and its quite complicated compared to a petrol car. theres basically two circuits one goes around the egr cooler, oil cooler, heater matix and head also contains a secondary waterpump which is electronically controlled to run at various times, this circuit in itself wolud be enough to stop the car over heating if the thermostat in the main circuit has failed and car wasnt working too hard but not if waterpump impellor is slipping or free wheeling (common on vw plastic waterpump).

anyway ill see what happens over the next few days might get lucky and just be the thermostat or unlucky and end up in a garage costing €1000 ish fingers crossed

yamaha4life · 12-03-2020 7:25am

well im back from the dead to update this thread ha ha. all jokes aside the car is still overheating but still not reaching the danger zone on temperature gauge.

things that have been done so far, drain coolant and flush rad and heater core with garden hose, fitted new thermostat old one had failed shut, new coolant temperature sensor, bleed system, new coolant bottle lid. bottle of leak stop.

there was a slight improvement that was short lived, there is only two culprits left the egr cooler (its like a radiator for exhaust gas before going to intake) or the head gasket is toast.

have not had a chance to bring it to a garage yet she uses it daily but only for very short periods but the parts have come up to around €135. not too bad really thermostat was a pain to fit and was needed anyway.

so heres the kicker the head gasket and egr cooler failing will cause similar symptoms neither are going to be nice jobs for poor me. neither are going to be cheap at a garage poor her lol.

the egr cooler online at the minute would be just under €100 delivered and probly 4-6 hours fitting by myself, is it worth the hassle gamble?

lastly there is a coolant flange housing on the side of the head which has about 3/4 outlet pipes on it, there seems to be some localised boiling/pressure build up there so either the headgasket is gone there on cylinder 4 or the coolant is being boiled in the egr cooler and causing the hotspot there very hard to tell though without taking it off.

yamaha4life · 21-02-2021 2:34am

Completely forgot about this thread, i have since completely sorted the overheating issue, just for anyone who might be having a similar issue.

After trying a second new thermostat (still overheated) and expansion tank cap, fresh vw pink coolant and trying other avenues of trial and error.

The solution i came to was to drill 6 3mm holes along the outer edge of the thermostat, the car takes slightly longer to get up to temperature but stays at 90C under all loads.

The car has covered at least 20,000km now without fault.

Unsure if this will help anyone but saved €€€€ on getting head done!

21-02-2021 4:03am

What do the holes do? Allow some coolant to pass when the stat is closed?

yamaha4life · 21-02-2021 5:02am

Augeo wrote: »

What do the holes do? Allow some coolant to pass when the stat is closed?

Good question,

Yes, basically it will leave an amount of flow past it while its closed more holes = more flow, i probably would have been fine with 2/4 but i wanted to be sure there would be enough on the first attempt. Thermostat is in a sh1te location!

The passat has two cooling circuits which enables it to get up to operating temperature faster also has egr cooler and a T-piece with a restrictor which can sometimes get blocked but it wasnt blocked on this car.

For some reason the radiator on the car even when it was getting too hot was always cold same with the hoses, even when the cooling fan was kicking in which is controlled near the head as apposed to down on the actual radiator.

Now the radiator is warm when the car is warm and kicks in and out only when it needs to.

Im not sure is it because the thermostat has no jiggle pin and a bubble of air was getting trapped at the thermostat not leaving it open or is there some underlying flow issue somewhere in the system.

I tested the flow to the expansion tank and it seemed good so really a head scratcher.

I trawed through many many posts on Vw/audi/skoda and seat forums with people that had this exact issue and no solution at all. Some traded in the cars, sold privately or there threads had all similar replys of change this that triial and error and report back.

I also joined and posted on a few forums and a vw tech in a different country told me the head is done only a new head and headset would cure it as cayc heads are not skimable due to being porous and some coating is applied to them during manufacturing to fix it.

The funny thing is i read a thread then that a person had all that carried out plus egr, radiator, heater matix, thermostat etc and the car still overheated!

John.G · 24-02-2021 9:53pm

In older cars the flow of water through the heater heat exchanger and hence the amount of heating was controlled by a adjustable valve from the dash, valve open, full heat to valve closed, no heat, because of this when the valve was/is closed there was no flow through the block and head or thermostat when closed so the stat had a jiggle pin to allow a small flow of water through it, also to release any air, some cars may have had a bypass pipe that was shut off by the stat as it opened but I don't recall it on my VWs. Because the heating temperature was slow to respond to any required change the heat exchanger now has full flow of water through it at all times and just diverting the airflow through/around it makes the heating much more responsive so no more need for jiggle pins/by pass pipes etc?

yamaha4life · 24-02-2021 10:00pm

This is a diagram from a golf i think its the same as passat as its 1.6 tdi cayc. It says to bleed system with vag com but i was told the passat doesnt have this function on vag com until the next model could be wrong though. Either way at least it doesn't overheated anymore!

Toyotafanboi · 24-02-2021 10:10pm

VAS 6096 is a pressure bleeder.

yamaha4life · 24-02-2021 10:17pm

Toyotafanboi wrote: »

VAS 6096 is a pressure bleeder.

i didn't know that, i may have been confusing the electric waterpump bleeding with vag com and this or maybe i just have no clue ha ha.

is that the only way to fill and get rid of air locks?

I wouldn't be allowed use it anyway, im not allowed my air compressor got attacked on another thread for having one.

John.G · 24-02-2021 10:23pm

I had a petrol bora for 19 years and changed the coolant maybe 3 times, I used to just leave the expansion bottle top off while refilling/venting air, the first time I changed the coolant, the temp gauge wet up to ~ 110C before the stat apparently opened but during the subsequent changes the gauge never moved beyond 90C, of course these coolant gauges are of very limited value as they will read exactly 90C between actual temperatures of 75C and 107C.

yamaha4life · 24-02-2021 10:47pm

John.G wrote: »

I had a petrol bora for 19 years and changed the coolant maybe 3 times, I used to just leave the expansion bottle top off while refilling/venting air, the first time I changed the coolant, the temp gauge wet up to ~ 110C before the stat apparently opened but during the subsequent changes the gauge never moved beyond 90C, of course these coolant gauges are of very limited value as they will read exactly 90C between actual temperatures of 75C and 107C.

Yeah thats the way I would do it too, i had similar when i did the belt and pump in my a4 temp gauge went up and then settled itself topped it off after it cooled down never lifted beyond 90c after, on the passat i was getting the temperature reading from diagnostic it was at 115c before gauge lifted from 90c sharply though to be fair.

I read on another forum they called it a comfort gauge instead of having it swing up and down holds steady 90c from about 70C to 110-115C i guess as not to cause concern when small temp fluctuations are happening

John.G · 01-03-2021 10:29am

Have been thinking about your problem/fix, the 6X3mm holes is equivalent to 1x7.4mm which is quite a big area, while not the same as having no stat installed, I would have expected the coolant temp to go below 75C (and actually display this) at motorway cruising speeds. Also you said the fan was coming on so there should have been some water passing through the stat as the fan thermoswitch is (or was) screwed into the rad header.
You problem may be the pump even though it was changed with the timing belt, some of the impeller tips on these break off and cause overheating problems, it would be interesting to see this pump if you ever remove it.
Did you run with the stat removed before you drilled those holes?.

Toyotafanboi · 01-03-2021 10:50am

I've only skimmed this thread but it was popular in early 1.6 B6's for the main rad to block up causing overheating under load.

To be fair, it kind of fits with what you are suggesting.

Is the car still on it's original rad?

yamaha4life · 01-03-2021 11:47am

Toyotafanboi wrote: »

I've only skimmed this thread but it was popular in early 1.6 B6's for the main rad to block up causing overheating under load.

To be fair, it kind of fits with what you are suggesting.

Is the car still on it's original rad?

Yeah it is id say, but it has been flushed out twice with hose first then ran rad flush through it. The heater matrix was full of crap the main rad not as much.

John.G · 01-03-2021 11:52am

But drilling the holes in the stat "cured" the o/heating problems subsequent to this.

01-03-2021 11:59am

Yes because the stat is now effectively always open to an extent........... that would mask an underlying issue or two.
Issue was intermittent prior to the stat mod iirc.

John.G · 01-03-2021 12:19pm

Thermostats, even when fully open cause a restriction to flow, and if the pump isn't developing its rated head then drilling the 6 holes to increase the open area by 42 mm2 can only help, which it clearly has.

01-03-2021 12:29pm

Yes no doubt, but there's still an issue there.
The issue isn't the stat.

Toyotafanboi · 01-03-2021 1:03pm

yamaha4life wrote: »

Yeah it is id say, but it has been flushed out twice with hose first then ran rad flush through it. The heater matrix was full of crap the main rad not as much.

yeah but if some veins are blocked, your flush will only be passing through the clear veins.

That was definitely a popular complaint with them. I know you've been throwing a few parts at this but i'd say new rad, all day long.

yamaha4life · 01-03-2021 6:43pm

Good to know, i still have a new non modified stat somewhere, ill see if i can talk her into a new rad at next service and will fit the other stat. Saying that though if it goes back overheating ill be murdered lol.

The rad used never get warm though even when the stat was suppose to be open but it does now but could just be the unblocked sections. The cabin heater prior to matrix being flushed was blowing lukewarm at best it's lovely and warm now.

I wouldn't recommend a vw passat 1.6 tdi they seem to have plenty issues other than over heating.

Apart from overheating, there has been 1 ruined ecu, binding handbrake, caliper, stop start issues, dpf blocking, broken wire in loom (guy i gave it to hasnt sorted it), oil pump suction gauze blocked sump removal required, central locking problems, window switches, tyre pressure moniter.

I could go on but i think ye will get the idea!

Toyotafanboi · 01-03-2021 7:45pm

Yeah, the B6 Passat in general is a disaster of a yoke, qouldn't recommend one to my worst enemy, particularly a 1.6. It's hard for people after the B5 was generally a decent yoke.

John.G · 01-03-2021 10:46pm

I hope Tea drinker hasn't been putting tea bags full of silica in the expansion bottle which can cause havoc with cooling systems in all VAG cars, what next?.

https://www.audi-sport.net/xf/threads/silica-bag-coolant-mqb-engines.382604/

Tea drinker · 01-03-2021 10:51pm

John.G wrote: »

I hope Tea drinker hasn't been putting tea bags full of silica in the expansion bottle which can cause havoc with cooling systems in all VAG cars, what next?.

https://www.audi-sport.net/xf/threads/silica-bag-coolant-mqb-engines.382604/

Beats that stop leak stuff any day! :pac:

2010 Passat 1.6 tdi overheating

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