Temperature dipping after turning heating on - new thermostat

BillyBruiser

Hi folks,

My Passat B6 1.9Tdi was having problems with temperature fluctuations last week so I bought a new thermostat and coolant temperature sensor, I put both in today and the car finally got to 90°c which it wouldn't reach before. It
Stays at 90°c which is great, then I turn on the heating and the temperature dips roughly 10° - 15°.
I am getting hot air and always was so Im not sure it's head gasket related. Could it be air in the system or what would be the cause of this?

crosstownk

Does the coolant temperature come back to 90 after a few minutes? I'd say it's normal. The air gets warm by taking heat from the coolant so it's reasonable to expect the temperature to drop slightly - more noticeable if it's a cold outside and the heater fan is on a higher speed setting.

BillyBruiser

crosstownk wrote: »

Does the coolant temperature come back to 90 after a few minutes? I'd say it's normal. The air gets warm by taking heat from the coolant.

I'm just back in from another spin there, so I started with the heating on 1/3rd of full power, drive about 15 miles or more and it just went to 75°c exactly and didn't move, then I turned the heating off altogether and it gradually went to 90°c, won't go above 75° when the heating Is on at all. Very strange

crosstownk

BillyBruiser wrote: »

I'm just back in from another spin there, so I started with the heating on 1/3rd of full power, drive about 15 miles or more and it just went to 75°c exactly and didn't move, then I turned the heating off altogether and it gradually went to 90°c, won't go above 75° when the heating Is on at all. Very strange

I wouldn't be too concerned. It's cool enough outside tonight. Monitor it over time - I'd say it's grand.

biko

It could be air in the system.

Was the job done by yourself?
Did you give hoses a squeeze and check for bubbles etc?

CoBo55

Looks like your new thermostat is a dud, where did you buy it?

0lddog

As Biko says.
If any doubt there are some YTs on avoiding airlocks etc.
We have an 02 TDI here that behaved more or less as yours.
A makey uppy baffle to reduce airflow to radiator improved matters muchly

CoBo55

0lddog wrote: »

As Biko says.
If any doubt there are some YTs on avoiding airlocks etc.
We have an 02 TDI here that behaved more or less as yours.
A makey uppy baffle to reduce airflow to radiator improved matters muchly

Jesus I haven't seen that since the aul lad had a Hillman Hunter:pac: Talk about curing the symptoms and not the disease...

0lddog

CoBo55 wrote: »

Jesus I haven't seen that since the aul lad had a Hillman Hunter:pac: Talk about curing the symptoms and not the disease...

<derail mode> IIRC some PHEVs and present Gen Prius have automatic version of this </derail mode>

( Official version available from VAG in cold weather countries )

CoBo55

BillyBruiser wrote: »

I'm just back in from another spin there, so I started with the heating on 1/3rd of full power, drive about 15 miles or more and it just went to 75°c exactly and didn't move, then I turned the heating off altogether and it gradually went to 90°c, won't go above 75° when the heating Is on at all. Very strange

Try leaving the cap off and starting the engine from cold, any trapped air should make its way into the expansion bottle. I still think your thermostat is faulty. It does happen.

BillyBruiser

biko wrote: »

It could be air in the system.

Was the job done by yourself?
Did you give hoses a squeeze and check for bubbles etc?

I did do it myself, I didnt check the pipes afterwards. Should I be checking to feel if I can feel any bubbling of water in the pipes? Just pressurised water is what should be felt?

CoBo55 wrote: »

Try leaving the cap off and starting the engine from cold, any trapped air should make its way into the expansion bottle. I still think your thermostat is faulty. It does happen.

I bought it from MicksGarage! Thanks, I had seen that mentioned elseware for bleeding the air out. Il give that a shot in the morning and if not do more extensive bleeding. Thanks!
Just on the note of the faulty thermostat, is micksgarage well reciceved among folks here? I havent had an issue with parts from them over the years but I have a few friends who wont buy from them? Just curious

CoBo55

BillyBruiser wrote: »

I did do it myself, I didnt check the pipes afterwards. Should I be checking to feel if I can feel any bubbling of water in the pipes? Just pressurised water is what should be felt?



I bought it from MicksGarage! Thanks, I had seen that mentioned elseware for bleeding the air out. Il give that a shot in the morning and if not do more extensive bleeding. Thanks!
Just on the note of the faulty thermostat, is micksgarage well reciceved among folks here? I havent had an issue with parts from them over the years but I have a few friends who wont buy from them? Just curious

No I won't buy anything from them anymore I got in trouble here for saying what I thought of them but no, I definitely couldn't recommend them. Did you price a thermostat from VW? Which brand did you get from MG? I see they sell a few different brands.

BillyBruiser

CoBo55 wrote: »

No I won't buy anything from them anymore I got in trouble here for saying what I thought of them but no, I definitely couldn't recommend them. Did you price a thermostat from VW? Which brand did you get from MG? I see they sell a few different brands.

I didnt honestly, if bleeding the air doesnt fix it I will get in one from VW. It was firstline thermostat, I went for that because it came with a seal and extra O-ring which I thought were necessary.
Is your problem related to customer service or just sending dodgy/incorrect parts?

CoBo55

BillyBruiser wrote: »

I didnt honestly, if bleeding the air doesnt fix it I will get in one from VW. It was firstline thermostat, I went for that because it came with a seal and extra O-ring which I thought were necessary.
Is your problem related to customer service or just sending dodgy/incorrect parts?

Parts and refusing to refund me when I returned it, they had two items listed under the same name on different pages (an oil cooler for a passat coincidentally) unfortunately I picked the wrong one and when I told them about the error they changed the listing on the site and said I had left a thumb print on the cooler which was a lie as I made sure it was spotless when I returned it. I would have picked either the Febi or the QH myself as they would be familiar brands to me.

Kopparberg Strawberry and Lime

I would not be the least bit concerned about buying an after market brand.

After all, the aftermarket brands are the people that produce the part for the main brand and just stick their logo on it.

You could buy a new air filter from volkswagen and it'll still have Mahle somewhere stamped on it so no issue there.

I'd be thinking on the lines of an air lock too, not so much a faulty thermostat, unless of course it's the incorrect one.

Just on a side too, micksgarage are ok but I find a good motor factors like rathcoole motor factors to be better for getting the correct parts and cheaper than micks garage. And even if something isint in stock, if your early enough, they can usually have the item in a few hours for you to collect.

CoBo55

Kopparberg Strawberry and Lime wrote: »

I would not be the least bit concerned about buying an after market brand.

After all, the aftermarket brands are the people that produce the part for the main brand and just stick their logo on it.

You could buy a new air filter from volkswagen and it'll still have Mahle somewhere stamped on it so no issue there.

I'd be thinking on the lines of an air lock too, not so much a faulty thermostat, unless of course it's the incorrect one.

Just on a side too, micksgarage are ok but I find a good motor factors like rathcoole motor factors to be better for getting the correct parts and cheaper than micks garage. And even if something isint in stock, if your early enough, they can usually have the item in a few hours for you to collect.

Some great factors here in town and as you say next day service too.