Coolant Thermostat / Temperature Gauge - charlie_boy
Sorry, for the mamy postings but your help is greatly appreciated.

My 1993 TD Astra (Isuzu), the temp gauge rarely goes above the blue, even on runs over 30mins. I guess my thermostat has failed, and being Vauxhall the failsafe is that they fail opened.
I have been quoted 7.99 for a new one and contemplated using a paper type gasket with gasket sealant. Would this be suffice to seal the housing, or not. And is it easy job to fit? Any pointers on how to do it.

Coolant Thermostat. - Altea Ego
The thermostat may not have gone. Does your heater work OK? lots of nice hot air after 1/2 hour?

paper gasket and sealant? be a good boy and use a proper gasket set (which should come with the thermostat) 7.99 is not going to break the bank now is it!.
Coolant Thermostat. - charlie_boy
Yes, I get nice warm air after about 15-20mins or so. Apparently, the gasket dosesn't come with the thermostat, and they do not stock the gaskets. This is coming from a parts supplier, not a main dealer.

Is there a bigger probelm? I hope not!
Coolant Thermostat. - Dynamic Dave
If the engine design is the same as the petrol, then the thermostat housing gasket will be an "O" ring. £7.99 sounds cheap for a thermostst. I take it that's a pattern part as opposed to a genuine Vauxhall? As for fitting, a Haynes manual should point you in the right direction.
Coolant Thermostat. - charlie_boy
I doubt it is a genuine Vauxhall part. Will the paper gasket and sealant be suffice? Or where can I obtain a suitable O Ring?

Coolant Thermostat. - Dynamic Dave
Will the paper gasket and sealant be suffice?

Er, no. Water and paper don\'t generally mix too well.
where can I obtain a suitable O Ring?

Any decent car assessory shop, or try the main dealer.

But first check what type of gasket is fitted. I trust you have a Haynes Manual? If not, then the money you\'re saving by doing the job yourself instead of getting a garage to do it, can be put toward said manual. Once you\'ve got a manual it will pay for itself in no time.
Coolant Thermostat. - charlie_boy
One thing that worries me, is the removal of the three bolts to secure the housing. How can I remove them without the danger of shearing them? Would spraying them with WD40 prior to removal be worthwhile or not?
Coolant Thermostat. - Dynamic Dave
I've never had a problem undoing these bolts, but yes, spraying with oil prior to removal won't be a bad idea. Now you've mentioned the housing is secured by 3 bolts, I'm 99.9% sure it will have an "O" ring seal.
Quick help - charlie_boy
1993 TD Astra with Oil Fed Intercooler.

Temp gauge very rarely gets out of the blue on the dashboard, even when the coolant in the expansion tank is I guess that the thermostat needs replacing to solve my problem. Is this a correct assumption.

Just fitted a new waterpump yesterday.

Quick help - Dynamic Dave
By, have you actually measured the water temperature in the expansion tank with a thermometer?
Quick help - king arthur
It's more likely the temperature sender. I don't know where you'll find it on these, normally somewhere on or around the thermostat housing. If you can locate it, unplug the wiring plug and short the terminals, if the gauge now reads hot, change the sender unit.
Quick help - charlie_boy
So I can rule out changing the stat then? or shall I fit a new one as I have already bought it? What are the chances it is the stat? I was told that they were designed to fail openened. Would this cause it never to come out of the blue????
Quick help - Cyd
Does the radiator get hot or warm? If so, then this would suggest the stat is stuck open and needs changing.

Does the radiator stay cold, but the heater give out good heat? If so, it may be the stat doesn't need to open and the engine is getting enough cooling from the heater. The sender may need changing.

Does the rad stay cold and the heater give out poor heat? If so this would suggest the engine is not getting up to 'normal' running temperature.

How far has the car been driven before making these observations?

What does the coolant in the tank look like?

Stats normally fail open, but can fail shut. If it fails open then this would prevent your engine reaching normal operating temp except on a long journey on a warm day.
Quick help - charlie_boy
HEat comes from the heater after about 10mins. Radiator is warm. Drove the car for 40mins plus and the gauge not moved.

Coolant is brand new as a water pump was fitted. So drained and flushed accordingly.

Car has done 117k

Do you think it still is the stat?

Quick help - charlie_boy
How easy is it to replace the sender? More difficult than the thermostat?
Quick help - Dynamic Dave
First you have to establish whether it is the sender or not. Disconnect the wire going to it and connect it directly to the engine. ie, earth the wire. The temp gauge should go full scale - if not, then it\'s a faulty gauge.
Temp gauge - Astra - Again - charlie_boy
Sorry about this.

1993 Vauxhall Astra
1.7 TD (Oil Fed Intercooler)

Temperature gauge just about creeps up just over the blue portion of the gauge, on runs around 30mins. After this, coolant in the tankis redhot, as is the pipework. However, the radiator is very cool. The pipe that seems to feed the rad (at the top of the rad) is cool.

Changed the sender unit. Nothing really major changed.

A Vauxhall mechanic friend said that the Isuzu engines do run cold and the gauge reading is correct. And the radiatior will only run 'hot' after long journeys, then the fan will kick in. Is this correct? I would assume the coolant measure more or less 90 Degrees, not the 80 degrees that is the blue section of gauge, or am I wrong.

I am worried that the engine will overheat and cause damage. Will I damage the car by driving it as it is? Or with the coolant flowing round it as it is, the engine is cool enough - even though the pipes are red hot.

My next stage was to fit a new thermostat. Would this solve the problem as I have already fitted a new sender. How much should a garage charge to carry out such repair?

Or does this sound a major expensive job?

Anyone near Manchester care to help???LOL

Cheers Backroomers!

Temp gauge - Astra - Again - SkyMan
The sender unit only sends the temperature to the guage on the dashboard - nothing else. Because the pipes are hot but the rad not, I'd say it was definitely the thermostat.

Not sure about the mechanics advice - sounds a little "poo"

Temp gauge - Astra - Again - charlie_boy
Could the gauge be broken? It can\'t be can it if rises a little when the engine warms up, can it???

How do you know if you are in danger of overheating the engine? I know that after driving around for 30mins or so, the head is extremely hot.

Sorry if I sound naive, but I\'m learning fast from other more experienced backroomers!!!
Temp gauge - Astra - Again - king arthur
If the radiator is staying cool it does sound like the thermostat might not be opening properly. Did you say you've already bought one? Might as well change it if so.
Temp gauge - Astra - Again - charlie_boy
How much would it cost i.e. labour (I have the part) would a reputable garge in Manchester charge?

Would this solve my problem??? Or is there other things that could be serious.

I have a budget of £150 to bottom this problem.
Temp gauge - Astra - Again - Dynamic Dave
Just a note to say that later today I\'ll be moving this thread to the previous one you started, as they are all related to the same question.
Dynamic Dave
Back Room Moderator
Temp gauge - Astra - Again - Dynamic Dave
As previously asked by myself, did you try shorting the wire that is connected to the sender directly to the engine and seeing if the temperature gauge went full scale or not?

Now perhaps you can see why I\'m going to attach this thread to the other one you started, as it cuts down on repetetive questions and answers!!

Temp gauge - Astra - Again - charlie_boy
Can ask a dumb question?

"What does the coolant thermostat actually do?"

Temp gauge - Astra - Again - Dynamic Dave
"What does the coolant thermostat actually do?"
Temp gauge - Astra - Again - charlie_boy
Do you think I have a problem or not????

Temp gauge - Astra - Again - charlie_boy
What I cannot understand is that if the thermostat has failed:-

1) Failed Open - Then I would asume that the rad would get warm, and the fan kick in. It does neither (Not tun the car more than 35mins though)

2) Failed Shut - Then the rad would not get warm, the fan not kick in (as it is now), but the gauge read hot (it reads cold).

I have had new water pump which definately works.

I'm sorry if I sound 'thick' but I am learning fast.

What could the problem be, if there is a problem. Do diesels take alot longer to warm up than petrol? As my gauge on my petrol laguna goes to half way after about 15mins.
Temp gauge - Astra - Again - SpamCan61 {P}
I had exactly the same symptoms on my 1.8 petrol cavalier; replaced thermostat (12 quid from vauxhall) and everything has been fine since. Mind you I lived with the fault for 5 years before bothering to fix it; during which time the electric fan only kicked in twice!

Life being what it is; once the thremostat was fixed this increased the pressure on the water hoses round the back of the engine; which split one morning on the M3. Ho Hum.
Temp gauge - Astra - Again - RichardW
Bit difficult to tell if you've got a problem or not as you have not reported any findings back.

Have you tried earthing the gauge to see if it will go full scale as has been suggested more than once?

Does the gauge have numbers on it, or just blue, white and red zones?

Yes diesels tend to take longer to heat up than petrols, but should be up to operating temperature within about 5 miles normally.

Your assumptions about stat operation are about right. To find out if yours is working try this:

Start engine from cold and leave it idling. After about five minutes the thermostat housing should be getting hot. Feel the top hose - warm (as the housing?) or cold? Warm = thermostat probably failed open, cold = still closed. Leave it run longer and keep feeling the difference between the top hose and the stat housing - correct operation should be signified by the top hose not getting hot until the housing is so hot you cannot keep your hand on it (most stats open at around 80 - 90°C). Once you've ascertained if it is working or not take the car for a run round the block to get it properly warm. Keep the engine running when you get back - the rad by now should be hot all the way across (Keep you fingers out of the fan!!), and eventually the rad fan should come on - for about 30s - 1 min. Watch the temp gauge - it should be higher when the fan comes on, then fall back as the fan does its job. This cycle should repeat about every 5 minutes or so.

If your stat was failed closed the car would overheat in a very short time, so no problems there I think.

For reference, my Xantia runs at a steady indicated 80°C, unless you're in traffic, it's a hot day or it's being worked hard, when the gauge climbs to about 90°C. In traffic the gauge will climb over about 5 mins, then drop back as the fan comes on.

Please report back so we can close this one out!

Temp gauge - Astra - Again - charlie_boy
Some more inforamtion.

Night before changed water pump.

Last night changed the temperature sender.

Tested the gauge by shorting the temperature sender wire with another wire. Gauge goes upto the top of the dial (110), mid point is 90.

Tested the fan, again by shorting it. The fans spins as it should.

Drove the car for 6 miles or so, the gauge crept over the blue(for once) not by much I might add. Top of the radiator was as hot as the engine (pretty hot - could only keep myhand on it for about 10 secs or so), but the bottom of the rad was stone cold. The bottom hose to the radiator was stone cold as well.

Going to it 10mile run on the motorway to see if the fan kicks in tonight.

Any more suggestions???

Temp gauge - Astra - Again - Dynamic Dave
Any more suggestions???

You could of course park up in a supermarket carpark and ask any owners of simliar model Astra's where their temp gauge usually sits.
Temp gauge - Astra - Again - EnormousDerek
Charlie Boy -

Did you ever get to the bottom of this?

I've got a '93 Cav TD (Isuzu engine) and I've been wondering if the thermostat was knackered ever since I bought the car in 1997. I came to the conclusion that everything's working correctly, as I asked a mate at work who had one, and his temp. gauge sat at the same place.

My gauge normally sits at 78C after a good run up the A14. It takes ages to get there (about 10 miles). Even after 40mins at 70!MPH on a hot August day, it only gets up to 82C, but no hotter. The only time I've seen it get anywhere near 90 is in traffic. The fans then kick in. BTW, there are 2 fans on the Cav, and they can run in series or in parallel, depending on how hot the radiator has got. Only ever had the low speed going.

The car's done 179,000 miles and the engine is still going strong, although the car's starting to fall to bits. I notice that I get about 5MPG more in the summer than the winter, probably due to the amount of time it takes for it to get up to temp. Lots of smoke if I have to boot it when it's cold, but goes like a good-un when it's warmed up. 52MPG+ is not bad for a totally mechanical 'tractor' engine.
Temp gauge - Astra - Again - jc
I used to have a Fiat with temperatures on the guage and worried;then I then imagined it was a Ford with blue,white and red and ceased worrying-there is no way a guage and sender made that cheap can be that accurate.

Value my car