Mk3 Cavalier Owners Club | Vauxhall Cavalier Dot Com

I recently had my water pump and thermostat replaced.

I noticed yesterday that the temperature gauge has shot up to 100 by the end of the road! It cooled slightly when I got on the motorway but rolled up to over 100 as slowed, then bobbed down to midway as I continued.
When I arrived at my destination the rad fan was on full - it's making a nasty noise and need replacing but that's another story. it cooled down okay but again within 10 mins it was up to 100 again.

I suspect there may be an airlock - but is there anything else I should look at? I find it odd the thermostat has been replaced but the engine heats up so quickly.

Which car is this Dave, Archer I presume?

A brand new thermostat can like any component be faulty, so I wouldn't be surprised if it was stuck closed... Try removing it and pouring boiling water on it from a kettle, see if the valve opens slowly..

Most obvious question is fluid level.
Is the coolant header tank upto the Cold / Kalt mark when fully cold?

I would give your radiator hoses a good squeeze to swoosh the coolant and any trapped air out into the header tank.
Do this when cold obviously.

100 degrees by the end of the road?.
Blimey do you live on the M1?

A standard petrol car should take a couple of minutes / miles in normal traffic to get up to heat so that the thermostat opens.

In order of price - cheapest first..
1 - Swoosh out the coolant pipes with the header tank cap off.
Check / top up coolant level with a proper mix of coolant and water.

2 - Check that the gauge sender wire or the female spade connector on the front start casting is okay, and not shorting to earth, corroded or damaged.

3 - Check the thermostat opens when it should - dip in a jug of boiling water to see if it opens.

4 - Check that the water pump impeller is not loose on it's spindle.

As Andrei has said - new does not always guarantee a working part.
I have learnt this a few times.


My guesses are an air lock or a cack water pump.

Cheers lads. I'd be miffed it was the water pump or 'stat as they were both new! I had it running in the garage and the block heated up quick, so I had the cap off and squeezed the pipes a lot to move the water round. I am tempted to flush it even though it was done with the new stuff put on.

I'll check through other points and report back. I actually only live 4 minutes away from the M3 so it reached 100 within 5 miles!

I am not sure if the correct bleed method is-

Top up the header tank to the correct level. (Kalt mark when coolant is cold)

Then loosen the small pipe from it's stub on the front of the stat housing.

Run the engine for a short period to allow any air to escape from the stub.

Then reconnect the pipe securely.
As always - take care not to burn yourself.
Especially as your car appears to heat up so quickly.

I prefer my method, which is to leave all pipes connected.
Remove filler cap.
Squeeze any or all of the fat coolant pipes to swoosh air and coolant into the header tank.

The problem with re-flushing is that you may introduce another air lock.
Especially if you use the same method as last time.

I didn't do the last flush. It was done by the garage when replacing pump and stat.

I'm just aware that when I was trying to get the car to run with the HT leads the wrong way round I may have introduced air into the system by the rough running, jerky starts and stops.

Meh, I'll give it a go anyway, can't get worse. Can it?! lol

Right then.

I emptied the system and ran a hose through it via the expansion tank and the lower hose to flush out lots of rusty coloured water. Refilled with red antifreeze (is that right?) and water.

Been out a few times since and the temp gauge heads up towards 100, fans kicks in but seemingly has no effect as the gauge heads up to about 105-110 where I chickened out and slam the heater on full blast in an attempt to dump some heat, after a few minutes this seems to help and it drop to about 96. Switch off heater and it rises again. Bare in mind most of my driving is at motorway speed so I would expect the air rushing in through the grill to have some effect! I have checked pipes after a run and both were hot.

Today I extracted the thermostat housing and dunked it in a jug of hot water, nothing seemed to happen. I refitted it and topped up water/antifreeze and went for another run. Same thing, climbed to 100, fan kicked in but continued to rise to just over 100 when I arrived at home.

So, is the thermostat knackered?
Why does the fan not seem to have any effect?
Any ideas on what to do next? I want to get this sorted before tackling the fuel fumes that still pervade the car.

PS. Mods: We don't have a 'Faults and Fixes' section for the cooling system (rads/heaters/etc), perhaps it would be a useful addition?

lowrider dave wrote:...Today I extracted the thermostat housing and dunked it in a jug of hot water, nothing seemed to happen...

Hot water - or boiling water?

Yup needs to be boiling.

I know the stat was replaced, but new does not always mean working.

Although modern parts prices should mean that these things are plated in gold..
Not just working.

Yes, boiling water.

I'm not sure what the issue is
If you have checked both pipes after a run out and both were hot, it implies that the thermostat is working.
At least eventually.

It's not a winter thermostat that they've sent you, is it?

Re your question the fan will have no effect as it only supports the cooling of the engine when the vehicle is stationary. The bulk of the work is still done by the transfer of hot coolant out of the block, cooled coolant in; with the defective (or late-opening) thermostat effectively locking the heated coolant inside the block the fan simply can't cope with this much heat transfer on its own.

Possibly something crusty on your sender gauge got dislodged with all the new gear flowing past it and the gauge is now a little bit snappier to the mark. Or it's died of old age and you need a new one. Did you check it for serviceability as suggested further up the thread?

Yes, I gave it and the connector a good clean. All very odd.

Ont he way home - 5 miles - it climbed up to 100 then continued into the red but dropped when I put the heater on. Once at home I could hear it bubbling away. I can't help but think there is a bigger problem elsewhere - pump? HG?

If you can hear bubbling is it in the expansion tank or in the heater matrix, if in the expansion tank try a new cap.

lowrider dave wrote:Ont he way home - 5 miles - it climbed up to 100 then continued into the red but dropped when I put the heater on. Once at home I could hear it bubbling away. I can't help but think there is a bigger problem elsewhere - pump? HG?

I'd give another thermostat a shot first

Can't think why it would be the pump. In the meantime, some symptoms for HG might be:

- smell of combustion in the expansion tank
- coolant pipes to and from the radiator are super-hard after a run, sometimes even inflated around the jubilee clips

these are usually late-stage HG not-goods though

Thanks Colin and Ian.

The expansion tank has a new cap - but I'm beginning to wonder if that could be a cause? I don't recall it getting that hot when I drove it all the way home from Essex when I first bought it!

Yes, HG was a bit of a long shot as there is no water loss and it doesn't smell.

I have ordered a new Thermostat and coolant temperature sensor, so time will tell.

lowrider dave wrote:...and coolant temperature sensor, so time will tell.

Do you mean coolant temp sensor or did you mean temp sender gauge?

Sender gauge.

If its cooling via the heater matrix to an acceptable level then I'd be looking at the radiator or thermostat.
Run the car from cold touching the top pipe.
You will feel the pipe get very hot when the stat opens, follow the heat through the rad to the lower hose.
If the radiator isn't fully hot here's where the problems lies

If fan is not cooling down then likely stat is stuck and not letting water through rad to be cooled, feel rad if it is getting warm near the top and also feel in the middle. If it's freezing cold all over then it's likely stat or blockage of some sort. The rad should feel very warm at top, then slightly less warm as you progress down it. If boiling hot at top and freezing the rest of rad then either air lock/block. If cold all over then stat.

Thanks chaps,mwhen I get back on Saturday I'll have another look. Hopefully my new Stat will be waiting for me.

IF it;s been flushed one way then the other, I wonder if the heater matrix has got some kind of blockage.

I'd be tempted to bypass the heater matrix and see if that makes any difference.

Envoy CDX wrote:IF it;s been flushed one way then the other, I wonder if the heater matrix has got some kind of blockage.

I'd be tempted to bypass the heater matrix and see if that makes any difference.

The heater matrix is fine. It does a good job of cooling the coolant as not to overheat the engine.
Its thermostat or radiator related

I'd agree with the suggestion of a dodgy stat, it sounds like it doesn't have enough flow through the rad.

..... and to bleed, fill the system, run with the cap off until the thermostat opens, at which point it will almost boil then burp and swallow the water. Top it back up and put the cap on, that's it, no other trickery required.