My car's lost its cool...
Discussion
Apologies, not the most interesting one but I am seeking some much needed advice. I appreciate this has been covered plentifully across many forums online and I really have done my research but people who have experienced cooling issues will understand the 'needle in a haystack' nature of some of these issues.
I have a mk4 AHF non-pd (110 bhp) tdi golf which has served me well over the last 6 years, however within the last few months it has developed a small coolant loss.
I am not in a financial position to say lets just get the head gasket replaced and be done with it and so have been looking online for the past few months at all the possibilities which I believe have boiled down to the following (no pun intended) -
Hole in heater matrix (expensive dash out bugger of a job, also probably unlikely).
Hole in radiator (nothing shown on pressure test).
Hole in cooling hoses (not visible and not shown up on pressure test)
Small crack in head gasket causing boost to enter the cooling system and the resulting overpressurisation leading to water forced out of the expansion tank lid.
Thermostat dead?!?
Details -
If driven gently (no full throttle but otherwise generally 'normal' driving) no coolant is lost and vehicle is comfortable for any journey which does not require fast (80mph+ dual carriageway/motorway) driving.
Fast driving or full throttle (e.g. max boost) causes overheating which rapidly rises but then drops in response to no throttle. (no overheating damage thus far fingers crossed!)
Coolant evidently escapes from the expansion tank lid (recently replaced with a brand-new unit in order to diagnose this problem).
Slight hissing of pressure from removing expansion lid of coolant system even when cold (indicative of HG crack, overpressurised system etc.)
Extensive pressure test revealed nothing. (i know HG would have not shown anything on a pressure test).
No cream (mayonnaise) on oil dipstick or cap. (From what I read tdi's often do not display this mixing even when HG is gone).
Well done if you've read this far, I know I am in a sense answering my own question here but if anyone has any advice I would greatly appreciate it. Furthermore, I am considering replacing the HG myself and doing cambelt, tensioner and water pump while i'm at it, however mildly concerned about the need for a head skim, although I have heard VW do not advise this for a TDI (may just be pd-engines due to the low clearances)? In terms of garage prices for all the work without the head skim, is £450 reasonable?
Regards,
Freegs
I have a mk4 AHF non-pd (110 bhp) tdi golf which has served me well over the last 6 years, however within the last few months it has developed a small coolant loss.
I am not in a financial position to say lets just get the head gasket replaced and be done with it and so have been looking online for the past few months at all the possibilities which I believe have boiled down to the following (no pun intended) -
Hole in heater matrix (expensive dash out bugger of a job, also probably unlikely).
Hole in radiator (nothing shown on pressure test).
Hole in cooling hoses (not visible and not shown up on pressure test)
Small crack in head gasket causing boost to enter the cooling system and the resulting overpressurisation leading to water forced out of the expansion tank lid.
Thermostat dead?!?
Details -
If driven gently (no full throttle but otherwise generally 'normal' driving) no coolant is lost and vehicle is comfortable for any journey which does not require fast (80mph+ dual carriageway/motorway) driving.
Fast driving or full throttle (e.g. max boost) causes overheating which rapidly rises but then drops in response to no throttle. (no overheating damage thus far fingers crossed!)
Coolant evidently escapes from the expansion tank lid (recently replaced with a brand-new unit in order to diagnose this problem).
Slight hissing of pressure from removing expansion lid of coolant system even when cold (indicative of HG crack, overpressurised system etc.)
Extensive pressure test revealed nothing. (i know HG would have not shown anything on a pressure test).
No cream (mayonnaise) on oil dipstick or cap. (From what I read tdi's often do not display this mixing even when HG is gone).
Well done if you've read this far, I know I am in a sense answering my own question here but if anyone has any advice I would greatly appreciate it. Furthermore, I am considering replacing the HG myself and doing cambelt, tensioner and water pump while i'm at it, however mildly concerned about the need for a head skim, although I have heard VW do not advise this for a TDI (may just be pd-engines due to the low clearances)? In terms of garage prices for all the work without the head skim, is £450 reasonable?
Regards,
Freegs
KIt sounds like quite an old car...not so common as it used to be but have you considered a partially blocked radiator , internally it can sludge up , externally it can be covered in caked crud. Hard use as you describe could then be overloading the radiators causing overheating , same symptoms if thermostat not opening fully. Maybe worth a check... Good luck. Ian
Don't think the leak is from the water pump as it appears to be forced out of the expansion tank cap leaving coolant-coloured drip marks on the outside of the header tank. Furthermore, the water pump was replaced with a metal-impeller unit which I believe are much less prone to failure.
With regards to the radiator, I may have a go at flushing the coolant system with the hose and see if I can clear any crud and/or air locks.
Thanks for the ideas!
With regards to the radiator, I may have a go at flushing the coolant system with the hose and see if I can clear any crud and/or air locks.
Thanks for the ideas!
If the pressure test didn't reveal any coolant loss, I don't believe there's a head gasket problem.
It's overheating, and loosing coolant through the rad cap because it's overheating - which is what is meant to happen in those circumstances.
I'm going with the above - clogged up radiator (when did you last change the coolant?), or failed water pump.
How does it behave in traffic?
It's overheating, and loosing coolant through the rad cap because it's overheating - which is what is meant to happen in those circumstances.
I'm going with the above - clogged up radiator (when did you last change the coolant?), or failed water pump.
How does it behave in traffic?
shtu said:
How does it behave in traffic?
Never overheats in traffic (although I live in Cornwall and we don't get a lot!).I flushed the coolant a couple of days ago in order to try and free any blockages, corrosion crud etc but don't believe I got rid of the full amount of coolant from the system. I suppose it is possible to remove the radiator top and bottom hoses and do a specific high-pressure flush of just the rad?
With the fresh coolant in there I will run it for a few days and then use the ebay sniffer test kit to see if that reveals any exhaust gases.
Edited by Freegs on Monday 28th September 13:19
Cloggie said:
I would still suspect the water pump. They normally produce exactly those symptoms. I have seen quite a few water pumps with friction fit metal impellers fail. The impeller just spins on its shaft when at higher revs.
Removing the top pipe from the expansion tank and revving the engine produces a strong flow of coolant so it would appear that the water pump is preforming well at least at low rpms. Perhaps you are correct though about the high rpm spinning, seems like a crap design as it has a metal impellar pump installed (replacing a broken plastic unit) and has been regularly serviced and maintained.shtu said:
Yes. And before that?
Short answer - coolant is changed every two years not because the antifreeze part stops working, but because the anti-corrosion chemicals are, for want of a better phrase, worn out.
Yes I appreciate this. I believe coolant has been regularly replaced at suggested intervals through standard servicing. However the mileage is now 155,000 and so it may be suffering from some level of corrosion, especially if any coolant replacement has been missed.Short answer - coolant is changed every two years not because the antifreeze part stops working, but because the anti-corrosion chemicals are, for want of a better phrase, worn out.
Here we go with the latest update! Would really appreciate any further guidance.
Today it went in for an MoT and had the radiator replaced as I thought this may be blocked and the source of the overheating problems.
However, much to my disappointment but not necessarily surprise, it is still overheating when pushed hard.
The nature of the overheating was such -
In order to test, the car was brought up to high speeds (80ish) through hard acceleration twice or three times and needle stayed bang on 90 degrees. After about 4 runs, the temperature needle rose quickly as I came OFF the throttle and went from 90 - 110ish at which point I ensured the engine was cooled down rapidly (and the temp did drop very rapidly).
SO. It would seem it is either a faulty thermostat or water pump. My question is, would the above described conditions indicate a faulty thermostat? The temperature rises steadily to 90 and sits at a rock solid 90 until pushed, surely the thermostat is either opening or it's not? Why would hard throttle cause it to suddenly close?
I can see that it may be the water pump, although my mechanic was doubtful that the impeller would have failed this quickly as it has been replaced in the last two years & 25,000 miles.
Lastly, despite being pressure tested and sniffer tested 3 times it could be the head gasket I suppose, or even a cracked block?
Any advice greatly appreciated? These cooling issues couldn't be much more annoying!
Today it went in for an MoT and had the radiator replaced as I thought this may be blocked and the source of the overheating problems.
However, much to my disappointment but not necessarily surprise, it is still overheating when pushed hard.
The nature of the overheating was such -
In order to test, the car was brought up to high speeds (80ish) through hard acceleration twice or three times and needle stayed bang on 90 degrees. After about 4 runs, the temperature needle rose quickly as I came OFF the throttle and went from 90 - 110ish at which point I ensured the engine was cooled down rapidly (and the temp did drop very rapidly).
SO. It would seem it is either a faulty thermostat or water pump. My question is, would the above described conditions indicate a faulty thermostat? The temperature rises steadily to 90 and sits at a rock solid 90 until pushed, surely the thermostat is either opening or it's not? Why would hard throttle cause it to suddenly close?
I can see that it may be the water pump, although my mechanic was doubtful that the impeller would have failed this quickly as it has been replaced in the last two years & 25,000 miles.
Lastly, despite being pressure tested and sniffer tested 3 times it could be the head gasket I suppose, or even a cracked block?
Any advice greatly appreciated? These cooling issues couldn't be much more annoying!
I don't use a "sniff" test on Diesel engines due to it being unreliable. The test is for hydrocarbons in the coolant and as diesel has a low content, it can give a misleading reading. Pull the return off the expansion tank and check the pump flow throughout the rev range, no flow means a goosed pump, reduced flow at high rpm could mean the impeller is slipping. Is the expansion tank pressurised excessively when you remove the cap? A blockage or partial blockage would cause the symptoms you have, a piece of the old pump or possibly some corrosion at the inlet of the heat exchanger is possible as smaller coolant channels are easy to restrict. Pump water into the outlet and see if anything comes back out the inlet.
ETA - I just read the pump is ok. So a restriction is likely.
ETA - I just read the pump is ok. So a restriction is likely.
Edited by bigjobbo on Friday 13th November 22:04
bigjobbo said:
I don't use a "sniff" test on Diesel engines due to it being unreliable. The test is for hydrocarbons in the coolant and as diesel has a low content, it can give a misleading reading. Pull the return off the expansion tank and check the pump flow throughout the rev range, no flow means a goosed pump, reduced flow at high rpm could mean the impeller is slipping. Is the expansion tank pressurised excessively when you remove the cap? A blockage or partial blockage would cause the symptoms you have, a piece of the old pump or possibly some corrosion at the inlet of the heat exchanger is possible as smaller coolant channels are easy to restrict. Pump water into the outlet and see if anything comes back out the inlet.
ETA - I just read the pump is ok. So a restriction is likely.
The expansion tank is often pressurised from cold the day after driving (indicative of blown HG I know) and so hisses when the cap is removed. When you say heat exchanger you are talking about the heater matrix? And pumping water into the outlet of the heater matrix?ETA - I just read the pump is ok. So a restriction is likely.
Edited by bigjobbo on Friday 13th November 22:04
The heater matrix is what I was talking about. Pump water through both connections and see if any dirty water comes out, putting it in the outlet obviously reverses the flow and has a better chance of pushing a restriction out the way it came in.
If the cooling fan is kicking in at 90, and no blockage is found, check that pump. Also, was the pressure test done on a hot engine?
If the cooling fan is kicking in at 90, and no blockage is found, check that pump. Also, was the pressure test done on a hot engine?
It sounds more and more likely to be a HG to me.
You could remove the thermostat to be sure.
I have used this http://www.tunap.co.uk/Products/COOLING-SYSTEM/304... in water loss situations before, and it seems to work well.
I can't imagine it's a massive leak at the mo,so this would be worth a £20 punt.
Cheers
You could remove the thermostat to be sure.
I have used this http://www.tunap.co.uk/Products/COOLING-SYSTEM/304... in water loss situations before, and it seems to work well.
I can't imagine it's a massive leak at the mo,so this would be worth a £20 punt.
Cheers
Freegs said:
SO. It would seem it is either a faulty thermostat or water pump. My question is, would the above described conditions indicate a faulty thermostat? The temperature rises steadily to 90 and sits at a rock solid 90 until pushed, surely the thermostat is either opening or it's not? Why would hard throttle cause it to suddenly close?
The temperature gauge in the dash lies... Anything between say 80 and 100 degrees (I can't remember the exact numbers) gets reported as exactly 90 so the needle looks nice and steady.So if it is failing, either open or closed, the gauge will normally appear fine, but sometimes fairly suddenly drop down to 75 or shoot up to 105 (or whatever) if/when the actual temperature goes outside of its "normal" range.
AJB said:
The temperature gauge in the dash lies... Anything between say 80 and 100 degrees (I can't remember the exact numbers) gets reported as exactly 90 so the needle looks nice and steady.
So if it is failing, either open or closed, the gauge will normally appear fine, but sometimes fairly suddenly drop down to 75 or shoot up to 105 (or whatever) if/when the actual temperature goes outside of its "normal" range.
Are you sure - this is an old style Golf diesel.So if it is failing, either open or closed, the gauge will normally appear fine, but sometimes fairly suddenly drop down to 75 or shoot up to 105 (or whatever) if/when the actual temperature goes outside of its "normal" range.
I'm aware that the BMW electric thermostats have this facility, but I didn't think the VW did. (waits for a torrent of corrections)
bearman68 said:
Are you sure - this is an old style Golf diesel.
I'm aware that the BMW electric thermostats have this facility, but I didn't think the VW did. (waits for a torrent of corrections)
Pretty sure. (This is just the dashboard gauge lying, not an electrically controlled or electrically heated thermostat).I'm aware that the BMW electric thermostats have this facility, but I didn't think the VW did. (waits for a torrent of corrections)
My 2002 diesel Octavia (basically a non-PD Mk 4 Golf) lied and always sat on exactly 90 whenever it was in the "normal" range.
For what it's worth, I know BMWs lied before they got fancy electrically heated thermostats too.
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