no pressure in water tank

martyj200

martyj200

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Hi everyone,
Im having some problems that are leaving me baffled!!Audi A4 1.9 TDI
My temp gauge gets up to 90 but if i turn the heating on it drops down a lot.(heating is piping Hot)
If im driving hard with the heating on it doesnt drop as much but still at least 10 degrees.
when i turn heating off and have been driving for an hour and temp gauge is at 90 i can pull up with
the engine running take the reservoir cap off and there is no pressure and water is cold??
I have replaced my temp sensor 3 times and 4 thermostats and have just had timing belt and water pump done?
Also some times when im driving the temp wont go up at all even after half and hour, i can turn ignition off and straight back on and will go right up to 90. sometimes when i turn ignition off the needle drops to the bottom but then flickers a bit,i have also had a couple of occasions when i have turned ignition off and needle drops to 60 degree and sits there with key out ignition?
Any help very appreciated im going mad!!!
Thanks
 
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I think its possible you may have a faulty temp gauge for a start - its that or a wiring issue which is more unlikely than a faulty gauge. Your cooling system could have an airlock (which could also cause an erratic temp read out if air settles near the temp sensor)

has the cooling system or components on the system been worked on recently ? What engine are we talking about ?
 
I have replaced both the stat and temp sensor in the last week and i ha someone do the water pump an cambelt.
Its a 1.9 tdi. I have been thinking airlock, but have had it running with cap off for a long time and nothing, im also suspect of the gauge as it changes dramatically if i turn ignition off and straight back on, and flickers sometimes when i turn engine off.......but its the fact that it seems to drop from 90 when i turn the hot air up...if i turn heating off or to cold temp goes back up?? thanks
 
audi upgrades
You can expect to lose heat from the engine coolant temp if you turn the heat up in the car - if its only coming down by 10 degrees id say thats normal.

Are you using genuine temp sensors ? Using after market ones are a known big no no for there false read outs
 
i first got my parts from GSF and made no difference, and just recently replaced for genuine audi from my local dealer and no change again. Also even if dropping by 10 degrees is quite normal even if driving for hours, should i not be getting some pressure when i take my water reservoir cap off? and should the water in it be stone cold? thanks
 
No pressure in the header is normal due to the way the system is set up - a cold tank is not normal. I think you need bleed the system first and clear any air in the system - airlocks can cause all of your issues so illuminate that first. By the battery you will see 2 hoses going into the bulkhead to the heater metrics. You can disconnect those to bleed the system but exercise caution. Was the car working normally before the water pump was changed ?
 
The car was the exact same before water pump was done, i got it done as i thought it might be suspect for this issue and needed the cam belt done anyway.
do i just pull back the lower hose untill the bleed hole is revealed to release any air? and do i do this with the engine running?
 
I would do it a few minutes after a start from cold (engine running) and allow it to warm up with bleed open (hose pulled) you will lose water so top up periodically
 
I have read of a lot of people flushing out their heater matrix...but have noticed that all of these people seem to be struggling to get hot air in the car...I have roasting hot air, so would you think i wont need to go as far as flushing the heater matrix and just try bleeding air from the lower hose going into bulk head, thanks warren
 
I don't think your heater matrix is blocked so no i don't think its necessary to go that far - i do think that air is moving around your system and messing with your read out. Does your heating ever go cold ?
 
Ok well thats ok - doesn't mean there is no lock although being in a high point common sense would negate that to be the logical place air may settle. I have the same engine and i needed to bleed the system after a temp sensor and thermostat because the hot air was not coming through. Go for the bleed and let me know how you get on
 
Your welcome - good luck ... If i think of anything else il let you know
 
Just to be safe - ensure you have a genuine temp sensor and thermostat fitted as this could also be an issue. Fit these if not already before you bother bleeding
 
I will do, i did change the audi stat and sensor for other parts as i was told i could have faulty ones from new from dealer, but the other parts made no difference, i will put the audi parts back on,, and i tested the audi stat today in boiled water and opened fine then closed good too
 
Never done a stat on a 1.9. Is it possible to fit it upside down? This may give similar issues to what you have. I know on older Saabs it is possible to fit it upside down.....
 
The stat can be put in upside down on the Saabs. So it never really opened fully as it was operating in reverse if you like. Instead of the water circulating in the engine getting to temp and opening the stat to allow full flow through to the rad, it was just circulating it around the lump. But the stat would open a little as the water was warming it up but the water flowing to the rad was cooling it down. If that makes sense lol

On an old BMW I had it would only fit in one way. Never done or seen a 1.9tdi stat, so not sure if they can only go one way or be fitted either way.
 
Defo sounds airlocked or maybe closed stat/blocked pipes. Does the rad get hot? Try using a header tank on the header tank, i use a 3 litre bottle upside down with the bottom chopped off. Not perfect but puts a little pressure on the system to push air out.
 
That cant be done on the 1.9 - its physically impossible due to the design
 
If his pump was broken he would be boiling over in the expansion tank on longer journeys he's made - not stone cold, even with no pump hot water would expand into the tank. He's also just had it changed so i think the chances are slim
 
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Well given it was the oldest part. ... only other part of the cooling system left if going to be gasket or head related.
 
The radiator never gets hot... and when temp guage gets upto 90 and i pull over with engine running theres no pressure in header tank and water in it is cold. But when i changed the thermostat the other day the water from engine was hot.
 
Just to check - are you feeling the rad from the front surface or the rear ? As the front is the condenser for the air con - Did you have any luck/change with the bleed ?
 
The condenser is in front of the rad which means the one visible at the front of the car is the condenser - which will be cold most of the time as its part of the air con. You need to feel from the rear with hands clear of the fan to check the rad temp
 
i have felt the upper part of the radiator behind the condenser, but i will try feel behind it tomorrow though. wont get a chance to try bleed any air out as we talked about until Monday,my day off
 
Also i noticed today on my way home that the temp got up to 90 in 12 mins.....then 1 min after hitting 90 started dropping again to about 70. also when i set my heater to 27 and 3 bars.....i can look at it a few mins later and will be at 5 bars the a few mins later 3 bars then 4 etc... does it do this automatically when set to a temp..i dont run my heating on auto. thanks
 
I've been doing some thinking and I really think that your car is acting normally, the engine temp vs interior heating demand seems normal as mine also does this. Your header tank like mine does not tend to pressurise. If the water is cold and your temp normal id say your engine is cooling efficiently - remember diesels run at much lower temp than petrol....Your gauge is not behaving normally, your description indicates a faulty gauge or a wiring issue. Address the later first and change the instrument cluster and then you can at least assess the car temp properly
 
The heater will back off automatically when the temp is reached and back on if temp lowers. Auto regulates the temp A bit more intelligently, such as only switching the blower on when heat from the engine is available
 
Do you know if replacing the wire that runs from the temp sensor is a job that a novice could do?
I know what your saying and it seems more likely that the wire will be faulty other than the temp gauge,, but its such an easy job to change the cluster. im not sure how hard the wire fix would be.
 
Its the cluster you should change first mate - its very simple to do. Between the 2 clusters of buttons for setting time and on the other the service button is a black panel - that hides 2 screws ... Undo them and pull and it will come out. Change this first to illuminate the gauge.
 
i will try replacing the cluster then mate,, you think theres any point trying to bleed air given that my heater blows roasting hot air anyway? thanks
 
No don't bother - I'm betting on the gauge if you have a new genuine temp sensor fitted... Wiring is extremely unlikely if its untouched
 
If your gauge sometimes does not settle with ignition off then the gauge is faulty or intermittently faulty .... Just to lead you up the garden path ! Lol
 
thanks for all your advise my friend i will let you know how i get on,just need to locate a good cheap deisel cluster for my model on ebay and i will get it in and let you know how i get on within a week hopefully. all the best.
 
Your welcome - a bit of advice, if you can get the car plugged in id imagine the system can be interrogated... Its always better to get definitive evidence of a failure if you can before shedding out for parts, ... Nothing worse than buying parts only to discover its not the problem. In my opinion a sticky gauge is quite undeniable ....Good luck
 
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