Overheat but with fans on

[dermotbell]

I arrived back in UK after 12 days away and had an uneventful journey home until i stopped at a gate.

It was 2am and I was pretty tired so didn't notice the temp gauge on the 25 min drive home. What i did notice was the fans were going, which was unusual as the drive home is open roads. The temp gauge was nearing 3/4.

My first thought is that it was the thermostat seized in the shut position but why then were the fans on. Surely if the thermostat was seized no water would get to the sensor as it is on the other side of the circuit.

When I stopped (eng off) the fans kept going and after 2-3 mins cooled the temp. Is it possible the thermostat opened at a higher temp to allow the water to circulate.

I am planning to replace the thermostat, and am now searching the site for alternatives to OEM.

[RayD]

Hi Dermot,

Thermostats rarely fail closed, and if it did there'd be enough temperature to trigger the switch, after a while. There’s usually a bleed hole in the stat allowing water through even when it’s shut.

Ray

[GeoffSmith]

If you haven't been topped up with antifreeze/corrosion inhibitor it could be grunged up and sticking. They do have a bleed hole but that would delay the response of the fans and obviously wouldn't provide full cooling. Look no further than the Wiki for replacements. Watch out for HGF.

[dermotbell]

Hi Dermot,

Thermostats rarely fail closed, and if it did there'd be enough temperature to trigger the switch, after a while. There’s usually a bleed hole in the stat allowing water through even when it’s shut.

Ray

I thought (and previous exp on fiestas) they always failed closed?

Geoff, yeah I keep a regular eye on the anti-freeze. Already done HGF 2 years ago, don't want another. Checked her this morning and the header tank is empty, not sure if this is a result of overheat, or if it has a leak. Was fine just before I went overseas. Am I right in saying that the Halfords version has no relief hole? I'm sure I read it somewhere.

[L.G.]

Did you ever change the water pump? I had a corrosion problem as Geoff described and as a result my water pump was in an unbelivable condition. Worth looking at if the car doesn't come back to normal.

L.G.

Edit: Grammar check

[RayD]

I thought (and previous exp on fiestas) they always failed closed?

Fair enough Dermot, if you have had them fail closed I’m sure you’re right.

There are also plenty of instances on the Internet of people saying the same.

Ray

[muley]

Hi,

I did have one fail closed (on the Blue Elan) a while ago.

It overheated - the fans were on while I was going along!

Jim

[RayD]

Unfortunately the fans won’t be much help with a closed thermostat

Ray

[muley]

Unfortunately the fans won’t be much help with a closed thermostat

Ray

I think they helped a bit...as there was some flow through the 'stat...

... better than nothing anyway.

Jim

[rip]

I thought (and previous exp on fiestas) they always failed closed?

I have had one failed stat:- It failed open. I thought that was normal, but it makes sense that closed failures would be more common because they would be in this state when parked up with cold coolant.

[Sy V]

Are you sure it was the fans running after switch off, and not the recirc water pump?

[dermotbell]

Ray, wasn't trying to suggest that you were wrong, merely my experience was the opposite. I have been wrong on enough occasions to welcome all advice and experiences.

Having got over my jet lag I investigated the issue, basically as the header tank was empty I turned the heater to hot and filled her up several time with engine running, no air in the radiator bleed screw. Seems to work perfectly now.

As she was fine before I went away, I can only assume a slow leak somewhere, can't see anything obvious but I guess the radiator is most obvious suspect.

[RayD]

Me thinking the thermostat won’t fail closed has an element of wishful thinking and a bit of optimism attached to it.

The number of people saying they only fail closed are so widespread it must be true. While some may have been mistaken by finding the stat closed when they came to remove it, the ones who tested it and found it wouldn’t open have to be right.

Ray

[rip]

The number of people saying they only fail closed are so widespread it must be true.

No way.

My stat failed open. No doubts about that because the engine would not get up to temperature.
The majority may fail closed, but definitely not all.

[RayD]

Thermostats rarely fail closed...

The number of people saying they only fail closed are so widespread it must be true. While some may have been mistaken by finding the stat closed when they came to remove it, the ones who tested it and found it wouldn’t open have to be right.

I agree with you RIP

Ray

[muley]

I think the majority fail open (luckily!)

I've had 2 fail open and 1 closed



Jim

[dermotbell]

Well I guess it's a bit of both then.

[Specky]

The other month I put a new thermostat in on Spec...

and guess what the new ones just failed open... the engines sounds like a bubbling geezer after shut down...

I must fit my old one ASAP...

TTFN

[RayD]

Good idea Dave,

There’s probably more to be said for cleaning the old one up every so often than putting a new one in that might be a lesser quality.

Ray

[Specky]

Good idea Dave,

There’s probably more to be said for cleaning the old one up every so often than putting a new one in that might be a lesser quality.

Ray

The new one was a Hal-Frauds...

TTFN