Thermal Sensor Switch and Temperature Sender

[gunner1x1]

The other day I realised that the fan on my 1.2 Vauxhall Nova had not come on when I was sitting stuck in traffic, so when I got home I open the bonnet and found that both the top and bottom rubber rad hoses were twice as hot as they had ever been.

I tried running the engine again to see if the fan would come on but it never, so I connected both wires from the Thermal Sensor Switch together and this time the fan did start running.

After buying a new Thermal Sensor I connected it to the rad, but after running the engine upto temperature the rad fan failed to come on again (but as above it did run when the wires were connected together:confused:)

I am at my wits end trying to track down the problem, so I hope that you guys can help.
The temperature gauge in the dash reads normal (or it did but more about that in a minute) and there is no loss of water. There is no oil in the water, or water in the oil, and after testing it the thermostat seems to be working alright.

Because I had to empty the rad to remove the Thermal Sensor, I thought that I might as well re new the anti freeze, so I used a flushing agent, and to let the air out while re filling the system I removed the temperature gauge sender. Then after putting everything back together I started the engine to see if the fan would run now, and the second I did the needle on the temperature gauge went crazy and flicked from side to side finally stopping in the red. It seems that I had forgot to put the blue wire back onto the temperature gauge sender and had left it on top of the engine.
I removed the plus and neg from the battery to see if the needle would go back to its proper place, but it never.

So now I am left with the rad fan not working, even with the new thermal sensor switch, and a temerature gauge in the red even with the engine off.

By the way when I was flushing the system with the hose pipe in the bottom rad hose (and the thermostat removed), the water came out of the bottom of the rad, but I could'nt feel and water in the top rad hose, and there was no water at all in the expansion tank. Is this normal?

Any advice you can give will be great as I do not relly want to use it just in case I blow the head gasket.

Many thanks

Mike

[Jon_nova1]

I assume your temp guage has gotten stuck when it had its fit, if all else fails with the fan you could always bodge it so it comes on with ignition?

[gunner1x1]

I assume your temp guage has gotten stuck when it had its fit, if all else fails with the fan you could always bodge it so it comes on with ignition?

Yeah it has got stuck right over in the hot part.

Bodging it to come on with the ignition is an option, but I really want to know what's wrong.

Thanks Jon

Mike

[AlexW]

Are you sure its not a airlock, Mine did the same, so i just left it running without the cap on and all of a sudden there was a big bubble in the header tank and the rad fan came on.

[gunner1x1]

Are you sure its not a airlock, Mine did the same, so i just left it running without the cap on and all of a sudden there was a big bubble in the header tank and the rad fan came on.

That's an idea mate (a good one at that), but could the system have got an air lock without anyone disturbing it, ie I had not done any work on the cooling system for at least a year. I would really love it to be something as simple to correct as that.

Many thanks

Mike

[Jon_nova1]

usually only if the coolant has gotten too low

[gunner1x1]

usually only if the coolant has gotten too low

Thanks Jon, well it's not that then because the system does not use hardly any water from one year to the next.

Many thanks

Mike

[Nova_Tek]

Hmm sounds awfully like my dads Cav, we had/have the same problem.

First do the abve to get rid of the airlock. Then run car upto temp. Carefully feel the rad to see if the top and bottom of the rad get hot.

On my dads Cav the car get up to temp but the top half of the rad is HOT and the bottom much cooler. As the switch is at the bottom and that part being cool the fan won't switch on. We at first thought it was a blocked rad. In comes in a brand new rad but same problem.

A mate of my dads (a mechanic) suspects exhaust gases in the cooling system, and it makes sense as there is a lot of hissing when the car gets up to temp.

Hopefully yours is much simpler but if all else fails its a possibility.

[gunner1x1]

Hmm sounds awfully like my dads Cav, we had/have the same problem.

First do the abve to get rid of the airlock. Then run car upto temp. Carefully feel the rad to see if the top and bottom of the rad get hot.

On my dads Cav the car get up to temp but the top half of the rad is HOT and the bottom much cooler. As the switch is at the bottom and that part being cool the fan won't switch on. We at first thought it was a blocked rad. In comes in a brand new rad but same problem.

A mate of my dads (a mechanic) suspects exhaust gases in the cooling system, and it makes sense as there is a lot of hissing when the car gets up to temp.

Hopefully yours is much simpler but if all else fails its a possibility.

Ah now we have just had a complete new exhaust system fitted (except the manifold), but how would the exhaust gases get into the cooling system, and how do you get rid of them?
If you could ask your dad or his friend it would be very much apprciated:)

Many thanks

Mike

[Nova_Tek]

Sorry fella didn't quite put an end to my post...

Exhaust gasses get in through the headgasket i.e. it's blown!

[gunner1x1]

Sorry fella didn't quite put an end to my post...

Exhaust gasses get in through the headgasket i.e. it's blown!

That is the first thing I thought of but as I said above there is no oil and water mixture at all. The expansion tank is clean, as is the camshaft housing and dip stick.
Although I do not think it is the problem is there any other way I can test to see if the head gasket is on its way out?

What else could cause the above symptoms?

Many thanks

Mike

[Nova_Tek]

Same here mate, no signs of the usual headgasket calling card, but we've tried absolutley everything, changed all cooing system parts, flushed, refilled, system bled, new rad, new cts, 2 switches (1 new and one we tested and found working). You name it.

Check to see if the rad is hot and the top and bottom when engine is at running temp or when the fan should come on.

Lazy water pump not circulating properly?

[gunner1x1]

Same here mate, no signs of the usual headgasket calling card, but we've tried absolutley everything, changed all cooing system parts, flushed, refilled, system bled, new rad, new cts, 2 switches (1 new and one we tested and found working). You name it.

Check to see if the rad is hot and the top and bottom when engine is at running temp or when the fan should come on.

Lazy water pump not circulating properly?

Water pump, yeah I will look into that too. I did check to see if there was any play in it when I had the cam belt cover off, and it seemed all right, but we all know that it can turn out to be that thing that we were sure was ok:wtf:

With reference to the temperature gauge stuck over in the red, what can I do about that? The rest of the instrument panel is working ok, but could I have blown (fuse is ok) something when I forgot to put the blue wire back on the sender, and instead left it touching a metal part of the engine?
If it isn't buggered how can I reset it?

Many thanks

Mike

[Nova_Tek]

Is the actual needle stuck past red?

Maybe it's just jammed itself on the metal dial face and doesn't have the power to return to cold (IIRC it happened to one of my mates Nova). Take the instrument binnacle out, remove the clear plastic lens off the dials and just reset the temp needle back to blue by hand (making sure you've put the wire back properly in the engine bay).

Run the engine to see if it works ok.

[CoolTiger]

Oil and water dont have to mix for a head gasket to go, You can have head gaskets go between cylinders, and also between a cylinder and water/oil way.

You could compression test though.

[gunner1x1]

Is the actual needle stuck past red?

Maybe it's just jammed itself on the metal dial face and doesn't have the power to return to cold (IIRC it happened to one of my mates Nova). Take the instrument binnacle out, remove the clear plastic lens off the dials and just reset the temp needle back to blue by hand (making sure you've put the wire back properly in the engine bay).

Run the engine to see if it works ok.

Cheers mate I will try that.

Cool Tiger,

Oil and water dont have to mix for a head gasket to go, You can have head gaskets go between cylinders, and also between a cylinder and water/oil way.

You could compression test though.

Sh1t I hope it isn't the head gasket. If it is what are the chances that the head has warped? Because until I noticed the rad fan was not running while sitting in traffic I did not know anything was wrong (The temperature never rose above normal, no water loss, no steam out of the exhaust etc), so the gasket could have been blown for ages:mad:

Many thanks

Mike

[gunner1x1]

Is the actual needle stuck past red?

Maybe it's just jammed itself on the metal dial face and doesn't have the power to return to cold (IIRC it happened to one of my mates Nova). Take the instrument binnacle out, remove the clear plastic lens off the dials and just reset the temp needle back to blue by hand (making sure you've put the wire back properly in the engine bay).

Run the engine to see if it works ok.

Yeah you were right mate it was only stuck on the other side:thumb:

Now if we could sort the rad fan problem out I would be well pleased.

Many thanks

Mike

[Nova_Tek]

Sh1t I hope it isn't the head gasket. If it is what are the chances that the head has warped? Because until I noticed the rad fan was not running while sitting in traffic I did not know anything was wrong (The temperature never rose above normal, no water loss, no steam out of the exhaust etc), so the gasket could have been blown for ages:mad:

Many thanks

Mike


Yeah you were right mate it was only stuck on the other side:thumb:

Now if we could sort the rad fan problem out I would be well pleased.

Many thanks

Mike

No worries mate,

The needles can sometime jam like that :)

As for head damage, if the guage was in the safe zone then you may get away with the head being ok and undamaged. If the coolant got really hot and boiled over i.e. towards or in the red zone then you run a higher chance of head damage (normally).

Headgaskets can sometime start to go and you won't even realise it everything may seem to be running fine. Only eventually will you see some clue as to it going. Compression test may shed some light.

Even if it's the headgasket, fortunately 1.2's are simple and you can buy a head set for peanuts, if you feel up to it and are confident with your skills you could do it yourself.

[gunner1x1]

No worries mate,

The needles can sometime jam like that :)

As for head damage, if the guage was in the safe zone then you may get away with the head being ok and undamaged. If the coolant got really hot and boiled over i.e. towards or in the red zone then you run a higher chance of head damage (normally).

Headgaskets can sometime start to go and you won't even realise it everything may seem to be running fine. Only eventually will you see some clue as to it going. Compression test may shed some light.

Even if it's the headgasket, fortunately 1.2's are simple and you can buy a head set for peanuts, if you feel up to it and are confident with your skills you could do it yourself.

Yeah I am confident enough to do it myself. I have changed the valve stem seals on a Mk1 Astra and another 1.2 Nova belonging to friends of mine, and that is basically how far down you go on a head gasket. That's right isn't it?
The first one I nearly messed up because we did not know that we were meant to use new stretch bolts (is that their name?), so I could have sheared them, but luckily I didn't:thumb:

Thanks for all your help

Mike

[Nova_Tek]

Yep new stretch bolts all the time. Some guy I know reused the bolts on his smart car. Funking lucky that it's still running.

If you've done all that then a headgasket change (if the block is fine) won't cost much.

[gunner1x1]

Yep new stretch bolts all the time. Some guy I know reused the bolts on his smart car. Funking lucky that it's still running.

If you've done all that then a headgasket change (if the block is fine) won't cost much.

Bleeding stupid ain't it:roll: For the cost of a few pints, these peeps risk snapping x number of bolts, and having a repair bill that equals the deficit of a small country:confused:

Many Thanks

Mike

[Nova_Tek]

lol

[gunner1x1]

Are you sure its not a airlock, Mine did the same, so i just left it running without the cap on and all of a sudden there was a big bubble in the header tank and the rad fan came on.

AW06 step forward and take a bow:thumb: :thumb: :thumb: lol lol :) :) :) :cool: :cool: :cool:. Up bright and early this morning and fitted the new thermal sensor switch. Let it run upto temperature, and then thought WHAT A :tard: I have not taken the expansion cap off like AW:cool: recommended. So I went and removed it, and then a couple of minutes later a few bubbles appeared before one big one hit the tank and the fan started:thumb:. I have run about in it all day and the fan works perfectly:thumb:

So no new head gasket needed.

Many thanks AW, Nova_Tek and the rest of you

Mike

[Nova_Tek]

Nice one. Glad you got it sorted and it didn't need any work doing.

[AlexW]

Told ya :p

[gunner1x1]

Sorted, nice one guys and thanks to you both.:thumb:

Mike