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Audi straight 5 2.5TDI in 140bhp AEL flavour mounted in an A6 avant. Starship miles, but still running well.
Except, it just will not warm up properly. This has been an issue for a while, but getting worse with the cooler weather.
I’ve had it a very long time and it’s always been fussy about it’s thermostats. Basically if you don’t fit the expensive Wahler rubber sealed ones it doesn’t warm up. Seems to have become more fussy with passing time though and now at the point where I’ve changed the thermostat 3 times and it hasn’t made much difference. It will reach the mark (90C) after a protracted thrashing, but as soon as I back off it’ll cool down to 70C or so, less if the climate control is calling for heat. The oil temperature (it’s got a liquid/liquid oil heat exchanger) follows the same trend so I feel that the temperature gauge is working properly.
It’s as though the thermostats are all passing, but they all look perfect and pass the saucepan test. Nothing obviously amiss with the housing. The radiator barely gets warm.
Only thing obvious that maybe a factor is that the viscous coupled fan doesn’t appear to be uncoupling as it should. Struggling to believe this air cooling is enough to make the difference……. I would just pull the fan off, but it’s well on there and access is very poor.
Need to sort it before real winter arrives, Any thoughts?
Thanks
Nick
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1967 Triumph Vitesse convertible (old friend)
1996 Audi A6 2.5 TDI Avant (still durability testing)
1972 GT6 Mk3 (Restored after loong rest & getting the hang of being a car again)
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Does the car have more than one thermostat? I recall my X-Type Jag diesel did and it confused the hell out of me until I realised and changed the other one.
If the fan isn't uncoupling its not going to help but the thermostat should close more and compensate.
As a temporary quick fix you could just block part of the rad off with some cardboard, i've done that in the past while waiting for parts to repair but keep an eye on the gauge incase it starts to overheat.
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Assuming you can get access I'd remove the fan and carefully try without it.
I've had several engines before where the fan has been completely unnecessary unless you're towing, or in stationary traffic
You can always carry the fan and a spanner, and refit it at the side of the road( again access permitting)
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If it has another thermostat I’ve not found it in 18 years of ownership…… which doesn’t rule it out of course, but I think it’s unlikely. Not sure blanking the rad off will have much effect as it barely seems to get warm anyway. I agree that the fan is likely unnecessary most of the time. Especially in its current, fully engaged state. It has a backup electric one which only ever came on when the AC (currently deceased) was working hard. Removing the fan is the obvious next step but as it appears to be very tight and access is…. Errr…… restricted…… it seems I need some sort of special pin wrench to hold the pulley while I undo the nut. Thanks for your thoughts so far Nick The old beast in need of a wash after Wednesday evening s 12 car rally  |
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1967 Triumph Vitesse convertible (old friend)
1996 Audi A6 2.5 TDI Avant (still durability testing)
1972 GT6 Mk3 (Restored after loong rest & getting the hang of being a car again)
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xfu990
Part of things
Posts: 78
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My opinion for what it's worth is that the fan viscous coupling will not be helping any.
Also, do these engines have two water pumps? Maybe one being electric? Thought being either over circulating or under circulating.
Is the "old" ecu clever enough to recognise a slow warm up and drop the temperature to a "minimum" setting? Therefore keeping it cold?
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No electric water pump. Just the mechanical one driven by the cam belt.
The ECU isn’t very bright (mostly a good thing), but it does adjust fuelling/timing accordingly to engine temperature. The root of the problem is it a very efficient engine that doesn’t put very much heat into the water jacket, but it should be able to do better than it is now.
Going to have another go at getting the fan off……
Also got to change both sidelight bulbs on her TT…. Promises to be a frustrating and bloody afternoon (my blood unfortunately)
Nick
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1967 Triumph Vitesse convertible (old friend)
1996 Audi A6 2.5 TDI Avant (still durability testing)
1972 GT6 Mk3 (Restored after loong rest & getting the hang of being a car again)
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pxr5
Part of things
Posts: 198
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If you get really stuck with this I would just fit a thermostate in the top hose.The old Pug 504 diesels had one that slips into the rubber hose.
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Last Edit: Nov 6, 2021 12:54:46 GMT by pxr5
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ferny
Club Retro Rides Member
Posts: 984
Club RR Member Number: 13
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2.5TDI won’t warm upferny
@ferny
Club Retro Rides Member 13
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My Peugeot Expert with a 1.9 DW8 is exactly the same. It'll sit at 70 all day and only reaches 90 when hitting traffic on a hit day after thrashing it.
I've never solved it either.
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Slightly outside the box, but blocked heater matrix?
Doesn't account for the temperature readings tho 🤔
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xfu990
Part of things
Posts: 78
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No electric water pump. Just the mechanical one driven by the cam belt. The ECU isn’t very bright (mostly a good thing), but it does adjust fuelling/timing accordingly to engine temperature. The root of the problem is it a very efficient engine that doesn’t put very much heat into the water jacket, but it should be able to do better than it is now. Going to have another go at getting the fan off…… Also got to change both sidelight bulbs on her TT…. Promises to be a frustrating and bloody afternoon (my blood unfortunately) Nick Just a thought, maybe the temperature sensor for the ECU? that's if they have two on the Audi i.e. one for the gauge and one for the ECU? Love the 2.5 TDI, you've a posh one, I had the ACV engine in a transporter 102 BHP, the body rotted off it and the engine was still strong at just 380,000 miles. |
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Thanks. It was more or less top of the C4 range when new. SE model too, though very few options added apart from special order “limo paint” as our the company (it was my then bosses company car when new) insisted on solid black, not metallic. It’s lasted well considering it’s done 25 years continuous use, lived outdoors the whole time and covered almost 340k…… Fair to say that polishing it isn’t a very rewarding experience these days though. Interior is still nice, though the drivers seat begins to look a bit used.
Back to the original issue….. I bodged up a pin wrench of sorts and wrestled with the coupling nut for about 90 minutes. Access is limited, a bit like working through a small letter box. And the gent (!) who fitted the coupling saw fit to slather the threads with thread lock, so it fought me to the last half turn, which isn’t ideal when you can only get one flat of movement in between repositioning all tools……
Discovering I still had to partially remove the slam panel to actually get the thing out of its hole was the icing on the cake. Quite grumpy by then. It’s a Topran coupling…. ‘nuff said….
Haven’t tested it yet. Hope it does the trick. Will be quieter at least!
Nick
Edit: Also meant to say that it does have two (at least) coolant temperature senders. The ECU one is giving sensible readings on VCDS and it’s doing it’s usual trick of refusing any glow-plug above 8C, which is irritating as the engine wants it from about 12C. They are known for this…..
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1967 Triumph Vitesse convertible (old friend)
1996 Audi A6 2.5 TDI Avant (still durability testing)
1972 GT6 Mk3 (Restored after loong rest & getting the hang of being a car again)
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My mate uses these engines in a few different vehicles, mostly in old MK1 VW LT models but also in his Opel Kadett c in which it has a whopping 240 bhp.
These are direct injection diesel engines which makes them pretty efficiënt. Not much heat is generated so they don't really heat up fast.
Thermostat is the only controlling factor for the engine temp. With thermostat closed it should warm up.
Might look at Volvo 850 tdi for more thermostat options.
On the Volvo engines they also use 3 glowplugs in the cooling system. These are located in an aluminium housing on the rear of the head, above the gearbox.
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Thanks. I think the three glow-plug water heater was also available as part of the “winter pack” option on the A6. Mine doesn’t have it
Maybe there is a thermostat with a higher opening temperature. I’ve been using ones rated at 87C, which is what is listed for it.
I don’t need 240bhp but 160 - 170 would be nice. Even better would be if the boost came in before 1,900rpm…. Lots before. I see some clever people have fitted VNT turbos to them, but looks like serious work…..
Nick
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1967 Triumph Vitesse convertible (old friend)
1996 Audi A6 2.5 TDI Avant (still durability testing)
1972 GT6 Mk3 (Restored after loong rest & getting the hang of being a car again)
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xfu990
Part of things
Posts: 78
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I don't know about the AEL but on some VAGs using VCDS you can juggle the numbers and have the glow plugs coming on at different temperatures for different durations. My ACV was very sensitive to fuel pump and cam timing (separate belts) once set up right though it always seemed to burst into life on half a turn of the key, it was amazing.
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Absolutely right on the timing thing. First encountered the phenomenon when I did the timing belt the “ghetto” way, just by tooth matching. It had been struggling to start , but started instantly from cold with the new belt. Presumably the old one had stretched a bit.
Don’t think it’s miles off, starts first turn at all times except when ambient is in the 8 - 12 C range.
Do need to work out why my VCDS will no longer accept it’s a full version and let me use the TDI timing function.
Nick
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1967 Triumph Vitesse convertible (old friend)
1996 Audi A6 2.5 TDI Avant (still durability testing)
1972 GT6 Mk3 (Restored after loong rest & getting the hang of being a car again)
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So if you thought taking the fan off would help….. it has. I’m pleasantly surprised. I guess it was air-cooled after all.
Still takes a while to warm up (not unexpected) but it does warm up now, holding just a needles width below 90C. It’s quieter too and maybe even a bit freer-revving (I might be imagining that bit).
Testing will continue through the winter but I’m calling it a win for now.
Nick
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1967 Triumph Vitesse convertible (old friend)
1996 Audi A6 2.5 TDI Avant (still durability testing)
1972 GT6 Mk3 (Restored after loong rest & getting the hang of being a car again)
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Nov 20, 2021 18:22:27 GMT
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Could always try a £5 renault inline thermostat fitted into the hose. Its a good quick fix when the thermostats a pain to get to or you have to buy an expensive housing with inbuilt thermostat.
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Nov 23, 2021 13:25:10 GMT
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So….. the weather has got colder. And the problem has returned. Barely hit 60C after 28 miles today. The heater taking it all probably doesn’t help but it used to do much better.
Pretty much has to be a diff thermostat (another duff thermostat), so tempted to try one of the in-hose solutions suggested.
Nick
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1967 Triumph Vitesse convertible (old friend)
1996 Audi A6 2.5 TDI Avant (still durability testing)
1972 GT6 Mk3 (Restored after loong rest & getting the hang of being a car again)
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xfu990
Part of things
Posts: 78
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Nov 23, 2021 15:05:21 GMT
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Oh dear, I'd go for the genuine part, it may cost but it may also work. I experience was with eurocarpart tat, it was with a circoli thermostat, I wish I'd tested it before fitting as it was a nightmare of a job on a Suzuki at the time and I may have just as well left it out, it would have been as efficient! My son did the Renault thermostat in hose bodge on a Vauxhall 1.6 petrol a few years ago and it worked fine, quick and easy to fit with absolutely no probs. It all came in for less than a tenner from eBay delivered I seem to remember. I'm sad I just can't do this to any of mine, I've got to have it working as per design I'm afraid  |
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Nov 23, 2021 16:23:17 GMT
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The last three have been Wahler ones - identical to OEM and not cheap (though cheaper than going to Audi!). Two have worked initially but apparently “gone soft” early. The current one has never worked properly. To me it seems improbable that three (supposedly) top quality thermostats would be defective, but I’m at a loss to explain the symptoms any other way now that the fan is removed.
Been looking at the inline options. The drawback is that the top hose has an OD of only 40mm. This completely rules out the 504 optionv(56mm OD) and looks a bit unlikely for the R5 one which seems to be 43mm OD (pity, nice simple solution).
I’ve ordered a Mahle equivalent one with a rubber seal and will give that a go …..
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Last Edit: Nov 23, 2021 17:06:50 GMT by vitesseefi
1967 Triumph Vitesse convertible (old friend)
1996 Audi A6 2.5 TDI Avant (still durability testing)
1972 GT6 Mk3 (Restored after loong rest & getting the hang of being a car again)
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