Tempature question ?

2010 G

I have a 2004 passat 1.9 tdi 130. It heats up to 90 degrees but after drivig 15-25 miles the tempature wil go to the bottom 50 degrees for a short time car will still run finr but why is this happening. Happened twice yesterday and a few times a couple of weeks ago. And the windows inside the car are always full of condensation its very hard to clear the door windows ?

Pkiernan

It sounds to me like the thermostat is sticking and staying closed a bit longer than it should.

If the stat was staying closed the car would overheat
The drop to 50 may well be the stat opening when it shouldn't, or possibly an air lock in the system.

Kid Nothing

Coolant Temperature Sensor was the first thing to come to mind..

E39MSport

Pkiernan wrote: »

It sounds to me like the thermostat is sticking and staying closed a bit longer than it should.

^^ What he said.

Avns1s

E39MSport wrote: »

^^ What he said.

At the risk of repeating an earlier post, if the thermostat was staying closed for longer than normal, the engine would be overheating. If anything, the stat is staying open longer than normal which is the most likely fault.

If it was a faulty coolant temperature sensor, then it would likely not go up to the 90 degrees in the first instance.

E39MSport

Avns1s wrote: »

At the risk of repeating an earlier post, if the thermostat was staying closed for longer than normal, the engine would be overheating. If anything, the stat is staying open longer than normal which is the most likely fault.

If it was a faulty coolant temperature sensor, then it would likely not go up to the 90 degrees in the first instance.

Good point. Ta.

I was thinking it might be sticking closed then fully opening rushing very cold coolant through thus reducing the temp in the entire system. But, yeah, that would probably lead to an overheat before hand.

The stat open or closed thing is something I always have to have a think about before I post or say anything

E39MSport

I think I felt a slap on the wrist there

E39MSport

E39MSport wrote: »

I think I felt a slap on the wrist there

Not at all 'tis like when you're under a car trying to loosen a nut with poor access and you're going through the anti clockwise / clockwise thing in your head for loosen and tighten :pac:

E39MSport

RoverJames wrote: »

Not at all 'tis like when you're under a car trying to loosen a nut with poor access and you're going through the anti clockwise / clockwise thing in your head for loosen and tighten :pac:

oooooh, I hate when that happens - feel a right fool.... lefty loosey I have to say to myself then picture my hand turning as you say. Works though !

Pkiernan

Normally I would agree with the thermostat sticking the other way.

But in this cold weather, I have noticed that my diesel engine is never hitting anywhere close to the mid temp mark - it is hovering about a quarter way above minimum even after 20 miles of driving.

I was thinking that in the OP's case the engine is getting to 90 degrees quickly because the coolant wasn't flowing. Then, when it does open it is being cooled by coolant effectively at -5 degrees or lower, causing the engine temp to drop.

E39MSport

Right. The lets get the OP's car to a carpark and get that thermostat out

Avns1s

E39MSport wrote: »

I think I felt a slap on the wrist there

Not from me anyway!! :)

Pkiernan

Pkiernan wrote: »

I was thinking that in the OP's case the engine is getting to 90 degrees quickly because the coolant wasn't flowing. Then, when it does open it is being cooled by coolant effectively at -5 degrees or lower, causing the engine temp to drop.

Dunno about that, the stat opens and closes loads and loads of times to maintain the temp at 90 degs or whatever it's rated to.