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Does my Audi coupe 2.3e thermostat housing require a gasket


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Hi ive got a 1990 Audi coupe 2.3e b3 and recently put a new thermostat in as my temperature gauge wasnt rising above the top of the cold unless the car wasnt moving then the gauge would reach half way as it should. My heater was also luke warm at best as the gauge was low but warmer once the gauge reached half way. My theory was that the thermostat was jammed open stopping the engine to heat up properly as the radiator was constantly cooling the car. I put a new thermostat in and the issue is exactly the same. I tested the old thermostat and it seemed fine. I noticed that coolant was leaking out of the thermostat housing and the bolts seem tight enough so i wondered if the housing requires a paper gasket. Ive searched for one but cant find one so im not sure if the car even has a housing gasket or should have one. When i changed the new thermostat i took the old one out with the old seal then put the new seal in the engine side, put the new stat in with the narrower end facing the radiator then bolted up the housing filled with coolant and bled the system. Could anyone please tell me if the housing does require a gasket and if they have a part number. Could anyone also tell me if they think ive fitted it correctly. Any help or advice would be really helpful and much appreciated. Thanks Ian! Could anyone also tell me if the leaking housing could allow air into the cooling system? Thanks again!

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Hello Ian,

I too would have diagnosed an open thermostat based on your symptoms. Strange that a new one appears not to have solved the problem.

Perhaps we can take this back to basics, and eliminate a faulty temperature gauge (more likely temperature sender) as leading you astray. Did you check the actual running temp. with the old thermostat? You can do this with a remote ‘point-it’ meter, or as I do, with an older touch probe meter. If you didn’t, then no problem, you can check it with the new thermostat. Point digital meter at the thermostat housing and observe temp. at which it opens ( gets hotter quickly). 

When you say you tested the old thermostat and it seemed fine, how did you test it? I test these by heating it until it opens then passing a length of cotton under the seat of the opening section, and allowing it to shut again when it cools. You can then dangle by the cotton it in a pan of water and gradually heat the water and note the temperature at which it falls into the water ( the valve has opened). Do the same with the new one before fitting, to ensure it works correctly. 

Gasket? Not sure on your engine, but the car is old enough to have had a paper gasket. Nowadays, they tend to have a grommet type rubber ring which sandwiches twixt black and the thermostat housing - could be either. 

Re. new thermostat - what make are you using? Leak at this joint causing issues beyond leak? Not really. 

So there is now a bit of digging and testing to do to find your problem, so it’s one step at a time. 

Way of fitting? Usually self explanatory, but you should find that the spring end points towards the block. 

Hope some of this helps.

Kind regards,

Gareth. 

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Hi thanks for your reply. I tested the thermostat by putting it in a pan of boiling hot water with a cable tie attached and then taking it out and ive had the same results on 3 different thermostats. The opening temperature is 87degrees and they do seem accurate. I could go into more detail and get a temperature probe but i dont think 3 thermostats would be faulty. A friend just told me about an hour ago that the thermostat should go in directly against the engine in the housing then the rubber seal goes over it then the housing cover goes over it. I actually put the seal directly against the engine side then i put the thermostat over the seal. If the seal is on the wrong side of the thermostat then that could be causing my leak. Do you know which side the seal should go? I have also thought about the temp sender being faulty as the coolant was quite sludgy when i bought the car and may be damaged. I do think that the tempersture gauge is accurate and isnt an issue. Thanks Ian!

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Thanks for coming back on this Ian. 

If all 3 (no sure where the extra one comes from) thermostats are opening at (an accurately measured) 87 degrees then they are serviceable, and taking it that one of the 3 was the original, then a stuck-open thermostat was not the cause of your original problem of a low reading gauge. 

Repeating:- you have to get back to basics and measure the running temperature to assess whether it is normal or not. If it is indeed normal, then obviously the gauge is reading incorrectly, and if so, I would suspect the sender - gauges are generally reliable, but don’t assume anything. 

Fitting of thermostat - Sounds like the one you have has a rubber seal rather than a paper gasket. Rubber seal arrangements vary, and as I said, some have an internal groove into which the thermostat lip sits and the thermostat fits into the block with this seal around it and the housing is bolted on - compressing the rubber. Others might just have a rubber seal fitted on the thermostat on the housing side. Whatever, as long as the joint is leak free all should be well. If you have a leak, it is ‘just a leak’ and that leak will not affect the running temperature to any reasonable extent.

it really is back to basics Ian, and to retest my advice would bore, but it has proved sound with me over too many decades! 

Heater running cool. May not be associated with the running temperature, but could be to do with a partially blocked matrix - but that is an assumption. 

Kind regards,

Gareth. 

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Hi Gareth and Thanks for replying again. Ever since ive owned the car the heaters not been great and ive done loads on it recently. Ive totally flushed the whole system with forte biodegreser and replaced all leaking hoses and jubilees. Ive also blown air through the matrix. Radiators fairly new, car has good quality coolant and heater matrix appears clean and doesnt leak coolant into car. What is strange tho is i could drain coolant then refill and bleed system for a good half hour until coolant comes out of the bleeder hose then bleed it again the next day or day after thst and coolant would still come out the bleeder hose again. It does seem as tho air is getting into the system and its only recently ive been getting low temps on the gauge. The car never overheats and ive also replaced expansion tank cap. Everytime i bleed the cooling system nomatter whether its for 20 minutes or even an hour there is always a gurgling noise coming out of the middle of the dash which im told suggests theres still air in there. Since ive put this new thermostat in the heater is warmer but not warm enough. It seems fine coming out of the vents up to the windscreen but cold coming out of the dash vents. Im also suspicious of the water pump as the guy who replaced it has a bad reputation which i didnt know at the time. so many questions. Car runs great tho and never overheats. Ive also read about blend door being an issue with the heater or foam breaking away that acts as insulation to keep heat in. I think il try taking the housing appart and inspecting where the seal goes then replacing the thermostat seal and go from there. Thanks for all your help Ian!

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Hello Ian,

Thanks for the additional information - the story unfolds. 

Poor heating preceded the below- normal coolant reading, so unlikely to be connected to any significant degree. 

Why your gauge reads low - see earlier post.

‘Continually have air in system’. Logic suggests that since you have a closed pressurised system and no significant leaks, then air is unlikely to be drawn into this pressurised system. Despite bleeding, it suggests that you have remaining air in the system, rather than continually introduced air. It suggests you have some constriction somewhere and air is still being trapped. 

Heater issue? Either partially blocked core, or more likely some issue with the operation of the heating selection controls. 

Kind regards,

Gareth. 

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Hi Gareth and thanks for replying again. I think once ive fixed the leak on the thermostat housing hopefully i can concentrste on getting more heat out of the heater. The Heaters never been great since ive owned the car but was excellent on my old coupe.  The thermostat ive just bought for the car and is currently fitted is a circoli and has the part number 209440130. I bought it from euro car parts and was told it is the right one for my registration. It opens at 87 degrees like it should. When i get some time il open the housing up again and take more time to see if the stat has a groove for a seal and make sure ive got the right size seal and its on the right side. Do you think an airlock could stop my temp gauge from rising to half way when driving? Im not too sure why the heat isnt great as all leaking hoses and jubilees have been replaced. Heater  matrix has been totally flushed with forte biodegreaser and water and ive put air through it with a tube as well. It was pretty horrendous the first time i flushed it but its been thoroughly flushed on about 3 different occasions in the last 6 months and my expansion tank was also pretty sludgy when i flushed it first but has been cleaned with hot water and forte biodegreaser twice and is much better. Expansion tank is always cold as well which is strange.  Coolant was brown when i first drained it but is always red now. I know red isnt the correct coolant for the car as it should be green but i find the red is good quality and has not been mixed with any other colour. Do you think it would do any harm to switch the hoses to the heater matrix around to see if that would unblock anything then bleed the system then put them back the correct way and bleed again? Ive also took the glove box out and the panel under the steering wheel and noticed that the foam around the heater passageway looks fine on the drivers side but coming away a bit on the passenger side. I thought about insulating it to see if that helps increase the heat temperature. While i was behind there i noticed the metal mechanisms that move with the heater controls seem to move as they should. Sorry for asking so many questions but the heater has really bugged me since ive owned the car and ive put a lot of time and effort into fixing it as i know its capable of better. Thanks for your time and any advice or tips would be much appreciated. Thanks Ian!

 

 

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You are very welcome Ian,

Circoli thermostats? Um! I must admit that I’m not a great fan of ECP if only for the reason that they seem to trade mainly by attracting customers by offering attractive ‘limited-period’ discounts on so called retail prices. You will often find that competitors sell the same items cheaper - without discount - than they do after you have applied the codes!  Also their subsidiaries can often sell items cheaper than ECP do. Still....

If not fitting a genuine VAG (often at discount) then I would only fit a well know brand such as Bosch or Continental - yes I know they don’t make them, but...  Circoli are very competitively priced, but I don’t buy on price - I go on best quality at best price. 

I’m not claiming this is the cause of your heater problem, but flushing through with flushing agents is fine, and will certainly remove sludge etc. but seldom do they break down scale which actually blocks individual cores. The logic of my argument lies with the fact that the flushing agent will pass through a line of least resistance, by- passing blocked cores. I’ve seen too many old radiator cores still blocked after such treatment, to believe otherwise. 

I still think you have to break this down into the two separate problems you have, and I would be sorting the coolant temperature issue first and getting that needle sitting happily at the normal point. 

Hope some of this helps, 

Kind regards,

Gareth. 

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Hi Gareth and thanks for telling me about circoli thermostats. Do you know of any thermostats that you would recommend or where to get one from? Also do you know of any product that would flush the heater matrix better than the forte biodegreaser ive already used? This may sound totally stupid but do you think it would do any damage if i put washing machine cleaner in the cooling system then flushed it out?                                                                  I was just thinking now when i went for my mot the pulley that my drive belt is attached to makes a kind of a tappety sounding noise  and the mot guy said it looked a bit wobbly when the engines running. He advised me to replace the belt which i havent yet done. Do you think this could be an issue with the car not reaching temperature or even the pulley being worn. I know when i got the water pump replaced the guy who changed it who i later found out by many honest mechanics is dodgy after this should of replaced this belt and changed coolant which he didnt but charged me for. Im thinking maybe if i replace the thermostat and seal then the drive belt and possibly the pulley this might help. I think it might be worth finding something really powerful to flush the matrix with. Thanks for your help again Ian!

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Im also not convinced that the water pump is ok either. I always wonder maybe the pumps not new like ive been told and may be too weak to fully pump coolant around the system and through the heater matrix. So many questions. I wont rest until i fix it. Thanks Ian!

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Hello Ian,

We’ll try to go one step at a time:- 

Flushing agent that would unblock a scaled up and partially blocked heater matrix? If the heater core matches this description, then I can’t see anything will clear the blocked cores for the reasons already stated. 

Thermostats - I obviously cannot claim there is anything wrong with the Circoli stats you have,and it’s just a personal thing that I don’t tend to buy aftermarket parts on price alone - and these are usually sold cheaply. Genuine VAG may be expensive even with discount, but... Alternatives? Bosch, Continental, Gates - of course, you will appreciate that these will not be made in-house, but should be manufactured to a reasonable specification.

Your car has thermostat issues? Would not guarantee that until you have actually measured the the running temperature, rather than depending on a low gauge reading. 

Water pump cause of issues? Yet to find a pump which has failed to circulate coolant without making some protesting noises to let you know it’s not happy. 

Noises associated with drive belts? Always worth investigating. Is the  water pump driven by the cambelt assembly - if your engine has belt driven cams rather than chain driven? 

Hope some of this helps.

Kind regards,

Gareth. 

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Hi Gareth and thanks for getting back to me again. The water pump is belt driven and im not sure whether there is a noise coming from the water pump as the drive belt is making a noise and is right next to the pump. The car doesnt overheat or leak coolant from the water pump so i know it works to a certain extent. It might actually be ok.                                                         With the thermostat i just bought the one that was quickest to get hold of but wasnt sure where i could find a genuine thermostat from. Ive seen some advertised as original quality but dont know if thats true or not. I could get hold of a gates one. Do you think Gates would be ok? Im working every day at the moment so once i get time after christmas il replace the thermostat and seal along with the drive belt and the ultinator belt.                                         With the heater problem i initially thought the matrix might be clogged after seeing the condition of the coolant that came out of it the first time i flushed it so although coolant seems to flow through it fine i wouldnt be surprised if it needed replacing. Apparently its a huge job and i think beyond my capability.       The heater is better than it was tho to be fair but i know it should be hotter.         Thanks for all of your advice and knowledge. Its been a huge help. Thanks and much appreciated Ian!                                                                               

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Hello Ian,

Apologies for the delay. 

Water pump driven by external auxiliary drive belt - and not by a cambelt? If it’s noisy then it should be changed - urgently if it’s cambelt driven ( your description suggests it isn’t). When changing it, if not using VAG ( generally not so expensive than they used to be - particularly with discount - which I can point you to) then go for a reasonable aftermarket such as SKF etc., although I don’t have any direct experience of this brand. 

Thermostats? I would still get back to basics and check the operating temperature first. Apologies for being boring by repeating. Your original might be fine. If you are buying aftermarket again (and again repeating, I’m not claiming your Circoli ones are suspect) then Gates sounds better than most, but Gates make very good belts, but thermostats? 

I would live with the heater until you have fixed the other issues. Yes, you will get a flow through a partially blocked matrix. 

Kind regards,

Gareth. 

 

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3 hours ago, Magnet said:

Hello Ian,

Apologies for the delay. 

Water pump driven by external auxiliary drive belt - and not by a cambelt? If it’s noisy then it should be changed - urgently if it’s cambelt driven ( your description suggests it isn’t). When changing it, if not using VAG ( generally not so expensive than they used to be - particularly with discount - which I can point you to) then go for a reasonable aftermarket such as SKF etc., although I don’t have any direct experience of this brand. 

Thermostats? I would still get back to basics and check the operating temperature first. Apologies for being boring by repeating. Your original might be fine. If you are buying aftermarket again (and again repeating, I’m not claiming your Circoli ones are suspect) then Gates sounds better than most, but Gates make very good belts, but thermostats? 

I would live with the heater until you have fixed the other issues. Yes, you will get a flow through a partially blocked matrix. 

Kind regards,

Gareth. 

 

Hi Gareth im mistaken sorry the water pump is cambelt driven. Which makes me worry as the guy who replaced the water pump also changed the cambelt at the same time which is fine if he has done it. Just heard hes dodgy off many mechanics. The noise seems to be coming from the drive belt tho. When the drive belts rotating if you look at it carefully it looks a bit wobbly. Im not sure if thats just because the belt needs changing or the pulley is worn. I think il just put the original thermostat back that was in the car as it was functioning fine but just thought it might be worth changing due to the lack of heat but that problems not related to the thermostat as far as i know and it seems to function correctly and is as warm as the others. This one has no make or name on it.  Il make sure i get a new seal and it is on the correct side. Il also change the drive belt and see how everything seems. I see your point with checking the temperature the thermostat opens at but i dont have the tools. The fan seems to kick in exactly when it should so im fairly confident all thermostats are opening when they should. As for the heater i agree with you that the other issues need fixing first. What i dont understand tho is if the heater matrix has a partial blockage then how can the heat going up towards the windscreen be fairly warm and the heat coming out of the vents in the dash be much colder? Do you think it would be worth me putting high temp tape around the kind of tunnel that the air travels through behind the dash to the vents where the foam is quite worn? Sorry for asking so many questions and thanks for your patience. Much appreciated Ian!

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Hello Ian, 

Thanks for the additional information.

I really think you have to break all of this down into individual issues, then plan and prioritise your actions. If you don’t, you will be trying to sort 3? problems simultaneously, and you will be at risk of disappearing up a certain orifice! Sorry to perhaps be coming over as critical, but much of your logic is based on assumption e.g. dodgy fitter, so he didn’t change the water pump and that’s what the problem is, etc. I wouldn’t be assuming anything, but I would be testing, rather than simply changing parts and getting no where. 

If this were mine, my priority would be:- 

Belt noise - since we now know this is a belt driven cam/s any noise becomes significant. My belief is ( but I’m not certain from your description) is that you believe the noise is associated with the auxiliary (in caps) belt and not the cambelt. If this is so, then things are potentially less urgently concerning. By auxiliary belt, we are talking about the visible belt which drives the alternator, air con, and power steering if fitted. If this is what you are suspecting the noise is associated with, then the simply elimination/ conformation, is to temporarily remove it to see if the noise disappears. If the noise goes then you will need to ascertain which of the driven components - or tensioner or idler- is the culprit.

If the noise is still there, then sorry, this is worrying so let’s hope it’s not. Just report back on your findings, since we don’t want to confuse things even more. 

Moving on - car not reaching temperature. Repeating, refit the original thermostat and measure the operating temperature at the thermostat housing (when it opens) , using an indirect point-it device. Appreciate you don’t have one, but I doubt if they are that expensive, and you need it to prevent yourself going round in circles. 

Heater - I now gather that certain direction ducts produce warm (hot enough?) air, whereas some don’t. This suggests the matrix is reasonably serviceable, and you have issues with flap/ motors which divert the produced heating. 

I’m old Ian! and I find, and have found, it’s always best to tackle one problem at a time - don’t assume anything until you have test information - and fix the one problem before moving on to the next. If you don’t, you are likely to end up possibly having fixed a problem, but being unsure how, because you have been playing with two things at one time. 

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Hi Gareth your advice sounds very good. I will try and do one thing at a time. Its a good idea what you say about removing the belt to make sure that is where the noise is coming from. Ive actually got a temperature gun which i bought to check my temperature incase i got coronavirus symptons so dont know if that would work but i could try it. Like you said previously about the heater. I should put that on hold as it works but just could be hotter.           My new plan once i get time will be to put the originsl thermostat back in with a new o ring thats on the correct side and then try the tempersture gun on it. Once ive done that or even before i could remove the drive belt to check for noise. One step at a time. Thanks for your advice. Its so easy to try and change or tamper with too many things at once.  Thanks a lot. Very helpful and much appreciated Ian!

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Hi Ian,

Covid gun? Probably far too low a range. Worth looking on EBay to see what you can find, but my priority would definitely still be the belt associated noise - the coolant gets warm, even if not up to normal operating temp., so no great worry. 

If your belt is what I call serpentine, and goes around a number of comment pulleys and tensioner etc., then it’s worth doing a sketch of its routing before taking it off, so you know you’ve put it back correctly! 

Kind regards,

Gareth. 

 

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Hi Gareth sorry for the  late reply. Just been really busy at work and not enough hours in the day. Il have a look on ebay to try and find a temperature gun. It would be a useful tool to have in general. I agree with you about the drive belt. It probably is something that i dont want to leave for too long. I changed the ultinator belt on 176,000 miles which was around 30,000 miles ago so i need to be changing both the drive belt and the ultinator belt asap. Its something i could easily mess up so i might just take it to my local garage who is very good and knows the car fairly well. Its worth doing for piece of mind as well.           Il have a look at putting the new oring on the old thermostat on the correct side this time while ive got some time off over Christmas. Thanks for all of your help and advice. Its been a big help to me. Much appreciated. Thanks Ian!

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  • 3 weeks later...
On 12/16/2020 at 10:50 PM, IHK 11 said:

Hi thanks for your reply. I tested the thermostat by putting it in a pan of boiling hot water with a cable tie attached and then taking it out and ive had the same results on 3 different thermostats. The opening temperature is 87degrees and they do seem accurate. I could go into more detail and get a temperature probe but i dont think 3 thermostats would be faulty. A friend just told me about an hour ago that the thermostat should go in directly against the engine in the housing then the rubber seal goes over it then the housing cover goes over it. I actually put the seal directly against the engine side then i put the thermostat over the seal. If the seal is on the wrong side of the thermostat then that could be causing my leak. Do you know which side the seal should go? I have also thought about the temp sender being faulty as the coolant was quite sludgy when i bought the car and may be damaged. I do think that the tempersture gauge is accurate and isnt an issue. Thanks Ian!

Hi, if you have the rubber O ring it should be fitted with thermostat in block first then O ring then thermo housing, inside the thermo housing you should have two plastic prongs, which are normally broke off but if they are not broke put the Oring onto the housing then put thermostat into housing and then turn thermostat 90 degrees so it locks into housingthen into the block job done.

Kevin

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Hi Thanks for all your replies and help. I recently put the thermostat in the engine then the oring then the housing and all is fine. There are no more leaks at the housing. I bled the system when id finished and took for a drive but the temperature gauge still drops when the car gets up to speed on the road. My heater is nice and warm when the car is idling and the temp gauge sits at half way but as soon as i start driving and get up to about 40 plus mph the temp gauge drops to the top of the cold the heater gets colder. I know my thermostat works as my bottom hose does get hot when my temp gauge nears half way but when driving the temp gauge drops again. Ive now ordered a new coolant temp sender as this could be stopping the temp gauge from rising when up to speed.If that doesnt work then il try ordering a new coolant temp sensor. Im pretty sure the thermo switch on the radiator is fine as the fan comes on as soon as temp gauge passes half way immedietely. Im hoping that a new coolant temp sender may have something to do with the reason my expansion tank is always cold. Thanks for all your help Ian!

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