Passat Suddenly Overheating!
Discussion
Driving back from Gatwick on the M23 tonight and my Passat suddenly overheats and tells me to stop. Absolutely pissing down with rain, I'd recently driven through alot of pretty deep puddles before I got on the motorway. Anyway, I gave it just 3/4 minutes and the gauge was back on 90 degrees so I drove to the nearest garage off the motorway. Checked the coolant level....it was fine so its not losing coolant. Managed to get home but the gauge bounced around between 90 degrees and danger level. Could the water be something to do with this or could it be summat else?
If it was the impeller the temp would go up and stay up!
However, they do go as suggested so get it done asap as a matter of course.
It also sounds like the thermostat to me.
What can happen is they stick partially open and cause a bit of an airlock.
The likely cause could be going through deep water, cooling the bottom of the radiator to the extent that the stat closes, then opens a bit and sticks.
Ticking over will allow just enough coolant to get through, but driving will cause overheating.
Change the stat.
However, they do go as suggested so get it done asap as a matter of course.
It also sounds like the thermostat to me.
What can happen is they stick partially open and cause a bit of an airlock.
The likely cause could be going through deep water, cooling the bottom of the radiator to the extent that the stat closes, then opens a bit and sticks.
Ticking over will allow just enough coolant to get through, but driving will cause overheating.
Change the stat.
Well, it's not really an airlock as such, but best way to describe it.
There will always be a tiny bit of air in any system due to the gap in the coolant expansion tank. It's more like a vacuume problem in that the coolant simply cannot get through the tiny gap quick enough.
I have had similar problems in the past with Renaults as their stats manage to stick in the closed position as opposed to the fail safe open position.
A few years ago a friend had a Toyota Celica which was overheating and making extraordinary bubbling noises.
Three garages condemmed the head gasket so I was appointed the task of changing the gasket.
However, upon driving the car I found it was excellent untill it reached "normal" running temp.
It also idled for ever without overheating.
I decided to check the stat, did the boiling water test and found it was stuck partially open.
£16 later and the car ran beautifully.
He sold it a year later, still running perfect.
So much for the head gasket
There will always be a tiny bit of air in any system due to the gap in the coolant expansion tank. It's more like a vacuume problem in that the coolant simply cannot get through the tiny gap quick enough.
I have had similar problems in the past with Renaults as their stats manage to stick in the closed position as opposed to the fail safe open position.
A few years ago a friend had a Toyota Celica which was overheating and making extraordinary bubbling noises.
Three garages condemmed the head gasket so I was appointed the task of changing the gasket.
However, upon driving the car I found it was excellent untill it reached "normal" running temp.
It also idled for ever without overheating.
I decided to check the stat, did the boiling water test and found it was stuck partially open.
£16 later and the car ran beautifully.
He sold it a year later, still running perfect.
So much for the head gasket
Andoo said:
Well, it's not really an airlock as such, but best way to describe it.
There will always be a tiny bit of air in any system due to the gap in the coolant expansion tank. It's more like a vacuume problem in that the coolant simply cannot get through the tiny gap quick enough.
Can you run that by me again, vacuum problem? in where??There will always be a tiny bit of air in any system due to the gap in the coolant expansion tank. It's more like a vacuume problem in that the coolant simply cannot get through the tiny gap quick enough.
Andy Gardiner said:
Were you sitting in traffic and the temp went up, cooled down when you started moving again?
No, there was steam comming out when I stopped on hard shoulder. Thanks for replys, so what no I do next, start with the cheapest possible fix is what I tend to do. Would that be temp sensor?
It's hardly likely to be the temp sensor if there was steam coming out of it. That means it's actually overheating.
Usual causes would be a failed expansion tank cap seal stopping the system pressurising or a stuck thermostat. Both are cheap and easy to check first. A friend's Passat started to overheat and steam out in traffic many years ago and all that turned out to be was a failed O ring in the expansion tank cap which I sorted for him in minutes.
The stat can be checked in a pan of hot water but it's as easy to just change it once the old one's out. If the system isn't pressurising then the rubber hoses won't get hard to the touch when the coolant's up to temperature. A proper pressure test would be a better check but again the O ring or a new cap is cheaper than the test.
You'd be wise to attend to it before you really do seriously overheat it and blow a head gasket because then it won't be a quick fix any longer.
Usual causes would be a failed expansion tank cap seal stopping the system pressurising or a stuck thermostat. Both are cheap and easy to check first. A friend's Passat started to overheat and steam out in traffic many years ago and all that turned out to be was a failed O ring in the expansion tank cap which I sorted for him in minutes.
The stat can be checked in a pan of hot water but it's as easy to just change it once the old one's out. If the system isn't pressurising then the rubber hoses won't get hard to the touch when the coolant's up to temperature. A proper pressure test would be a better check but again the O ring or a new cap is cheaper than the test.
You'd be wise to attend to it before you really do seriously overheat it and blow a head gasket because then it won't be a quick fix any longer.
UPDATE :
Firstly thanks for all your replys.
Just taken car out for a 10 mile spin this morning to assess what's going on. Had to top up the expansion tank with half a pint but don't think its losing coolant. The temperature sat on 90 degrees for the whole journey, perfect, not a problem! However, the heater didn't want to get hot, just a little warm with the occasional spurt of hot air.
Added : I'm sure its got something to do with the amount of big puddles/water getting into engine compartment?
Firstly thanks for all your replys.
Just taken car out for a 10 mile spin this morning to assess what's going on. Had to top up the expansion tank with half a pint but don't think its losing coolant. The temperature sat on 90 degrees for the whole journey, perfect, not a problem! However, the heater didn't want to get hot, just a little warm with the occasional spurt of hot air.
Added : I'm sure its got something to do with the amount of big puddles/water getting into engine compartment?
Edited by Lordbenny on Monday 30th November 11:46
Simon Says said:
Andoo said:
If it was the impeller the temp would go up and stay up!
.
Not so,if the knurled shaft end starts to rotate in the plastic impeller(higher speeds)you can get all kinds of random circulation problems .
Edited by Simon Says on Monday 30th November 10:46
Every one I have attended to with a broken off impeller has overheated.
Perhaps one in a million will have the impeller catch on the shaft and rotate now & then, but not something I have encountered.
However, I am always open to suggestion
phumy said:
Andoo said:
Well, it's not really an airlock as such, but best way to describe it.
There will always be a tiny bit of air in any system due to the gap in the coolant expansion tank. It's more like a vacuume problem in that the coolant simply cannot get through the tiny gap quick enough.
Can you run that by me again, vacuum problem? in where??There will always be a tiny bit of air in any system due to the gap in the coolant expansion tank. It's more like a vacuume problem in that the coolant simply cannot get through the tiny gap quick enough.
Thats a vacuume.
Andoo said:
phumy said:
Andoo said:
Well, it's not really an airlock as such, but best way to describe it.
There will always be a tiny bit of air in any system due to the gap in the coolant expansion tank. It's more like a vacuume problem in that the coolant simply cannot get through the tiny gap quick enough.
Can you run that by me again, vacuum problem? in where??There will always be a tiny bit of air in any system due to the gap in the coolant expansion tank. It's more like a vacuume problem in that the coolant simply cannot get through the tiny gap quick enough.
Thats a vacuume.
Edited by phumy on Monday 30th November 13:44
esselte said:
Lordbenny said:
Definately not losing coolant, just very little heat out of heater! 
No heater suggests an airlock,is there a way of bleeding the system in a VW?I must admit that I am baffled as to why the car over heated last night but now is fine except for the heater not working though!
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