Engine coolant temp sensor?

O.A.P

I have a 99 1.4 astra that is getting about 20 mpg for the last few weeks. The tyre pressure is fine, there are no leaks and I'm not over loading it or pulling a trailer. I gave it a full service(I did'nt change the fuel filter though) just after last Christmass and it has just under 5000 miles up since and I will be changing the oil and filter after Christmass. I dont think it would need anything else since its been nowhere.
I have heard that the engine coolant temp sensor might be the cause of it been so thirsty but I dont have anyway to check for sure. Have any of ye had experience with this before and if so am I on the right track? Its not that hard to replace one I hope?
Thanks for any help.

Hal1

Could well be the sensor.

the Engine Coolant Temperature Sensor which tells the onboard computer what the engine temperature is so that the optimum driveability is realized while the engine is warming up ( more fuel is added) and when the engine has reached operating temperature the engine is kept in that state ( via the fans ).

sorry there a bit big .

O.A.P

Thanks Hal I wasnt sure where to look. I will have to drain the coolant first I'd say but I should manage that, just hope it fixes it now cheers

Hal1

I found a more detailed description of what's involved. Link

coolant does leak out...best time to do it is with engine cool,and release any pressure from the system by releasing the coolant filler cap then retighten it..slacken the old sensor after removing the plug and remove it having the other one ready to screw back in and you will probably only lose less than a cupful of coolant

Source

shamwari

O.A.P wrote: »

I have a 99 1.4 astra that is getting about 20 mpg for the last few weeks. The tyre pressure is fine, there are no leaks and I'm not over loading it or pulling a trailer. I gave it a full service(I did'nt change the fuel filter though) just after last Christmass and it has just under 5000 miles up since and I will be changing the oil and filter after Christmass. I dont think it would need anything else since its been nowhere.
I have heard that the engine coolant temp sensor might be the cause of it been so thirsty but I dont have anyway to check for sure. Have any of ye had experience with this before and if so am I on the right track? Its not that hard to replace one I hope?
Thanks for any help.

Make sure your engine is reaching correct temperature first before replacing the CTS. I've had a few cars lately that are struggling to reach the correct temp in this cold weather and the problem is that their thermostat's are iffy, and not the CTS sensor. If the engine doesn't go over around 65-70 degrees C then it won't run closed loop, and that will push the consumption right up. Look for the simple things first!

O.A.P

I think thats the eariler type engine in that pic you posted, the sensor seems to be on the left of my engine as I face it . I could be wrong is that not it in the pics I have put up, sorry about the quality
Thanks for the tip Shamwari, I think it gets up to temp ok, definately at idle anyway but not sure about on the motorway with a 120 km below freezing wind hiting the rad. So I'll make sure first if I have some money left for petrol.

O.A.P

I took it for a run on the motorway an hour ago and when at 3000 revs or above its at between 80 and 83 degrees c but when I come off the throttle it drops way down between 60 and 70 within a minute, is that normal or is the thermostat giving up on me? The heater and demister work perfectly by the way.

shamwari

I'd replace the 'stat and take it from there, especially if it is the original one! The symptoms you describe are likely caused by a stat not closing when it needs to, especially if you find that the car is taking an excessively long time to warm up in the morning.

O.A.P

shamwari wrote: »

I'd replace the 'stat and take it from there, especially if it is the original one! The symptoms you describe are likely caused by a stat not closing when it needs to, especially if you find that the car is taking an excessively long time to warm up in the morning.

I'll do that in the morning and see if it works.Thanks again.

O.A.P

I still have this problem two months on thank God I dont use the car much.
I replaced the coolant temp sensor at the time but it made little difference, I did that first because replacing the thermostat is a pig of a job on the 1998-2004 astras it involves taking off the timing belt believe it or not.
Assuming that the thermostat is stuck open I have heard that it is possible to fit another thermostat in the hose coming from the top of the rad but close to the engine. The old Renault 5 one fits it I have been told . Do any of ye know about doing this ? or is it just a ridiculous idea thanks.

Slidey

TBH thats sounds like a real bodge job.

shamwari

O.A.P wrote: »

I still have this problem two months on thank God I dont use the car much.
I replaced the coolant temp sensor at the time but it made little difference, I did that first because replacing the thermostat is a pig of a job on the 1998-2004 astras it involves taking off the timing belt believe it or not.
Assuming that the thermostat is stuck open I have heard that it is possible to fit another thermostat in the hose coming from the top of the rad but close to the engine. The old Renault 5 one fits it I have been told . Do any of ye know about doing this ? or is it just a ridiculous idea thanks.

The stat should not involve removal of the timing belt on your engine, which is the 16V. Autodata quotes only 30mins for the job!

It was certainly timing belt off on the older 8v model (live the Vaux engine in the 2nd pic) as the stat housing was behind the rear timing case, and this involved removing the belt, camshaft sprocket, and finally the case. Where are you based by the way?

O.A.P

O.A.P wrote: »

I still have this problem two months on thank God I dont use the car much.
I replaced the coolant temp sensor at the time but it made little difference, I did that first because replacing the thermostat is a pig of a job on the 1998-2004 astras it involves taking off the timing belt believe it or not.
Assuming that the thermostat is stuck open I have heard that it is possible to fit another thermostat in the hose coming from the top of the rad but close to the engine. The old Renault 5 one fits it I have been told . Do any of ye know about doing this ? or is it just a ridiculous idea thanks.

problem still there as its a faulty stat.

shamwari

Ok, an update on this. I've attached a scan of the replacement procedure for the stat. It's definitely a DIY job and does not necessitate removal of the timing belts. Worst thing that needs doing is a drain down of the cooling system, and that only takes two minutes.

The replacement procedures is as follows with the engine cold*.

1. Set the heater control to HOT and drain down the cooling system. Capture the coolant in something clean if you intend to reuse it, or to facilitates its disposal if not.
2. Unbolt stat housing (3) from its base. Remove all of the old gasket in the joint between the housing and the base.
3. Remove the stat from housing (3) and replace with a new one. Note the way the old stat was installed in the housing and replace the new one the same way.
4. Reassembly is the reverse of the above. Make sure you use a new gasket between the stat base and housing. Don't go mad tightening the bolts thru the stat housing as you will crack it.
5. If you are using new coolant then make sure you dispose of the old stuff properly. Capacity is 6.3 litres. The system should not not need bleeding as it thru the header tank, which is at he highest point of the system, but be prepared to top it up after it the car has been run up.

* I accept no responsibility for any errors or omissions in this advice, which is intended as a guideline only. If in doubt, consult a manual or get your mechanic to do it instead.,

Frankie t

U will have to get d emissions checked on a 4 gs and also c is d lambda switching, I have a workshop on <snip>

firefly08

Correct if you have the 16v it's a 10 minute job to replace the thermostat and doesn't require removal of anything else other than the housing.

The new one should come with a cardboard tube like a toilet roll insert, that's useful for getting the old thermostat out of the housing (it'll be obvious when you look inside the housing)

You can test the old one by putting it in a pot of water and bringing it to the boil - you should see it opening. But you might as well replace it anyway, they're cheap.

Mine was stuck open and replacing it made it warm up much quicker - made the engine run smoother and got the heater working much sooner too. But the fuel consumption was not down to 20mpg! That's extremely low for this car.

Could the car be in limp mode? That would give around 20mpg, and very poor acceleration. You'd know because the check engine light should come on on the dash. This happened to my Astra (same model) and it turned out to the be the O2 sensor (aka lambda sensor) - part cost around 80 euro and was very quick & easy to replace.

O.A.P

Thanks for all the help lads espeically shamwari (I live in Ennis by the way)
I thought that the timing belt had to be removed because thats what it says in the Haynes manual anyway I got the thermostat today at the motor factors ,60 euro because the housing and stat are one part. It was 103 plus VAT at the main dealers :eek: but luckily they had none in stock. I flushed the system out while I was at it.
The temp gauge gets up to 87-88 quicker and stays there either in traffic or at motorway speed so I just have to wait and see now if the fuel consumption returns to normal. I will post again in a few days to let ye know.
Here are some pics of the big operation I dont know how to explain each one individually but I'm sure ye can work out whats what.

O.A.P

Some more.

-Chris-

Frankie t wrote: »

U will have to get d emissions checked on a 4 gs and also c is d lambda switching, I have a workshop on <snip>

Frankie t banned for spamming the forum.

This is a forum to help each other from a technical point-of-view, this is not a place to pimp for business.

Spammers will have their access to the forum(s) removed.

shamwari

O.A.P wrote: »

Thanks for all the help lads espeically shamwari (I live in Ennis by the way)
I thought that the timing belt had to be removed because thats what it says in the Haynes manual anyway I got the thermostat today at the motor factors ,60 euro because the housing and stat are one part. It was 103 plus VAT at the main dealers :eek: but luckily they had none in stock. I flushed the system out while I was at it.
The temp gauge gets up to 87-88 quicker and stays there either in traffic or at motorway speed so I just have to wait and see now if the fuel consumption returns to normal. I will post again in a few days to let ye know.
Here are some pics of the big operation I dont know how to explain each one individually but I'm sure ye can work out whats what.

`

Sounds like a result OAP! I'd be very very surprised if this didn't sort the problem out for you.

O.A.P

I said I would up date this when I knew how much better, if any the MPG is.
On a drive of urban roads and motorway-116.1 miles it took 10.46 liters that is 50.4 MPG
Over a week or more of short trips and city driving-329.2 miles it took 42 liters and that is 35.6 MPG
Im happy enough with that anyway. Thanks