Vauxhall Astra F - Overheating issue, running out of ideas

Honest John Back Room » Technical matters
View Threaded
Mon 28 Jun 2010 23:14
Vauxhall Astra F - Overheating issue, running out of ideas - Philflies

Hello all,

The wife's Astra (1997, P reg) is overheating and we are stuck for solutions.

Having been a cold running engine for all these years, 3 weeks ago out of the blue, just overheated and spat its coolant all over the engine bay. Topped up coolant and it's not lost a drop since, so no leaks. But it's been running really hot ever since.

Short -wired fan so on constantly, but was barely keeping the temp down.

Replaced Fan temp sensor but now fan kicks in at 100c but going off after 30 secs whether temp has gone down or not. Temperature just carries on climbing.

Had Radiator flushed but to no avail either.

Fairly sure the water pump is ok, both hoses either side of radiator hot and if interior blower, lots of hot air and engine temp reduces quite rapidly, infact this is the only way to get temp down. Return hose to top of expansion tank doesn't seem to get used, not hot. But coolant is expanding into tank and appears to hold pressure.

Any ideas out there? I'm a bit stuck.

Regards

Phil

Reply | Report as offensive | Link
Tue 29 Jun 2010 00:05
Vauxhall Astra F - Overheating issue, running out of ideas - Peter.N.

Have you changed the thermostat? That's the most likely culpret, otherwise if its done a high mileage it may need a new radiator.

Reply | Report as offensive | Link
Tue 29 Jun 2010 13:01
Vauxhall Astra F - Overheating issue, running out of ideas - Philflies

Not looked a thermostat yet. Was going on the assumption that because the reduction in temp when then interior fan is on, the waterflow was ok, and therefore thermostat ok. Do correct me if that assumption is wrong.

86k miles, not too high. Radiator is hot all over, no cold patches.

Reply | Report as offensive | Link
Tue 29 Jun 2010 13:07
Vauxhall Astra F - Overheating issue, running out of ideas - bathtub tom

I'd guess head gasket.

Can you get a garage to do a 'sniff test' of the coolant (it involves analysing gasses in the coolant) and would rule it in or out?

Reply | Report as offensive | Link
Tue 29 Jun 2010 15:52
Vauxhall Astra F - Overheating issue, running out of ideas - Singlish

No, I had exactly these symptoms when I had a defective thermostat in my 1993 8 valve Astra F, the problem with the 8valve engine is that the thermostat housing is tucked away behind the cam belt and cover meaning a difficult job to replace (removing cam belt and back cover!) You may have a 16Valve engine which I believe doesnt have these access problems.

Let us know the result of the problem.

Regards

Andrew

Reply | Report as offensive | Link
Tue 29 Jun 2010 16:44
Vauxhall Astra F - Overheating issue, running out of ideas - Philflies

Indeed it's the 8 valve engine. And yes, the thermostat is behind cambelt.

Mrs Philflies, is reluctant to throw more cash at this so I need to be sure it will fix the problem.

If the thermostat was faulty, wouldn't that restrict coolant flow through the cooling system, including the heater matrix for the interior hot air? I only reiterate this question because putting the blower on 3 or 4 is very effective at bringing the engine temp down. If there was no coolant flow beacause of stuck thermostat, I would have thought the effect be alot less.

Driving around with the heating on full tilt in the current weather isn't very pleasant.

Thanks for the suggestions. Much appreciated.

Phil

Reply | Report as offensive | Link
Tue 29 Jun 2010 16:54
Vauxhall Astra F - Overheating issue, running out of ideas - Collos25

The radiator should not be hot all over,if the water level is not dropping then I would go for the thermostat first but if it keeps overheating then I suggest the headgasget.One thing is for certain if you keep running it overheating then you will definetly end up with a pile of useless metal.

Reply | Report as offensive | Link
Tue 29 Jun 2010 20:58
Vauxhall Astra F - Overheating issue, running out of ideas - Geran1

Only a suggestion you say you think the water pump is OK!! friend of mine had an on going over heat problem as a last resort on removing the water pump he foung the impela had come away and was just sat in the housing doing nothing, hope you sort your problem.

Chris

Reply | Report as offensive | Link
Tue 29 Jun 2010 21:40
Vauxhall Astra F - Overheating issue, running out of ideas - Peter.N.

The thermostat only controls the flow of water to the radiator, so putting the heater on will help cool the engine. A faulty head gasket won't in itself cause the engine to overheat, what happens is that the pressure build up cause the coolant to be blown out.

Reply | Report as offensive | Link
Tue 29 Jun 2010 23:05
Vauxhall Astra F - Overheating issue, running out of ideas - John F

If the thermostat was faulty, wouldn't that restrict coolant flow through the cooling system, including the heater matrix for the interior hot air?

I'm no expert, but I think the water circulates through the heater matrix even when the thermostat is firmly closed. Otherwise, you'd never get warm on a winter's morning!

In the few cars I've had, it only opens when the water approaches boiling point to allow circulation through the radiator.

Reply | Report as offensive | Link
Wed 30 Jun 2010 11:24
Vauxhall Astra F - Overheating issue, running out of ideas - Peter D

If there are no combustion fumes in the header tank sniff test then change the stat, thaey can fail to open fully if they loose some of the thermal wax that is used to force them open against the spring, thus the engine is running hot all the time. Regards Peter

Reply | Report as offensive | Link
Wed 30 Jun 2010 11:28
Vauxhall Astra F - Overheating issue, running out of ideas - Philflies

Thanks for the advice. I will get the thermostat looked at. I'd do it myself but that whole cambelt + housing is too much agro for my amatuer skills.

Any ideas why the fan is kicking in for such a short time? The manual says it clicks in at 100 (which it does) and clicks off at 95 (which it doesn't)

Phil

Reply | Report as offensive | Link
Wed 30 Jun 2010 11:34
Vauxhall Astra F - Overheating issue, running out of ideas - bathtub tom

Those temperatures are probably measured by a radiator sensor, not the temperature gauge in the car.

Reply | Report as offensive | Link
Wed 30 Jun 2010 15:36
Vauxhall Astra F - Overheating issue, running out of ideas - Singlish

I know where you are coming from, but the trouble with this approach is that 90% of the work is taking off the Cam Belt and rear cam belt housing. You will not save much money by getting say a mobile mechanic to do this and then coming back after you replaced the thermostat.

Seeing as they have to turn the water pump to retension the cam belt on reassembly, it would be good practise to replace the pump and cam belt at the same time, sorry but it will save you money in the long term, I believe the 8 valve engine is reliable and is longlived!

Andrew

Reply | Report as offensive | Link
Wed 30 Jun 2010 17:44
Vauxhall Astra F - Overheating issue, running out of ideas - Philflies

No, wasn't suggesting half and half. I'll leave the whole job to someone else.

Will look to replacing cambelt + pump too.

It's been an expensive year so far with whole new set of brakes up front plus exhaust. It's got to the weighing up stage about how much money to throw at it. I think it's worth it this time as the engine is still running really smooth and the body is still sound.

Thanks for the advice. I'll let you know which way things go.

Reply | Report as offensive | Link
Sun 8 Aug 2010 23:46
Vauxhall Astra F - Overheating issue, running out of ideas - Philflies

Just reporting back (sorry for the delay)

It was the thermostat. Replaced the waterpump and timing belt whilst there, but the pump was ok.

Car back on the road with normal temps.

Thanks for the advice.

Phil

Reply | Report as offensive | Link
Mon 9 Aug 2010 08:09
Vauxhall Astra F - Overheating issue, running out of ideas - WellKnownSid

Thanks for keeping us updated.

Reply | Report as offensive | Link

Looking for a garage you can trust? Honest John's Good Garage Guide has thousands of reader recommended garages, plus how-to guides and tips on servicing.

The Good Garage Guide

From which small car to buy at which price point to the best UK-built cars, our Top 10s have the lot. Click now for your shortlist.

Unsure of what to buy? Our Top 10s are here to help you....