Audi S2 ABY Radiator

[Crasher]

Possible but I have rebuilt the entire car including the engine. New water pump (Febi), electric pump (Bosch), ballast resistor (genuine) fan (Febi), thermostat (Febi), everything. The fan (new rad switch) is coming on all the time whilst idling or slow driving but is fine when the speed picks up and road drought through the (new genuine) supplementary radiator kicks in. I need to put some K type thermocouples in the feed and return hoses to view the temp drop. Suggestions as to what I have missed would be welcome. It has been a while since I drove an S2 so I am used to the modern VAG temperature gauges which lie and say 90 all the time, what would people say is the correct gauge reading around town?

[Tractor Dave]

I don't like the febi thermostat. Wahle are original and best. On a hot day, sitting in traffic, the fan will run on and off continuously. This is normal. Press the ac button to get the slow fan running and this helps considerably. Temp gauge in traffic on a hot day sits just above 90.

[K Simmonds]

As above I don't like the Febi thermostat's either but they should still work okay, I always check new thermostats against the old one in pan of water brought slowly to the boil prior to installation to make sure they actually open and close at the correct temperatures. The Wahle one's are best IMO, they always function well within spec, I have had the odd duff Febi that opens a little late but even then it would only make the engine run slightly hotter.

The temp gauge should generally be on 90 degrees when cruising along but will go just above that line in town or if you're thrashing the car.

[Crasher]

The ac on lifts the idle but it still runs slightly too hot for my liking showing approx 98 on the gauge, I am going to do some thermocouple tests tomorrow because lacking a proper temp readout in measuring blocks, I want some exact figures. If I fit a Pogo ally radiator, I think I will go for a genuine thermostat, £54.78 but when building the engine, I forgot how difficult it is to get at the thermostat when all built up with an ac car. I looked at the thicker Pogo radiator but the “minor adjustments may be required” put me off with everything painted.

[newsh]

There’s a lot of bad MFTS, around, so dash gauge temp readings all over the place, you should be able to get a reading in Vagcom off the sensor at the back of the head.

[K Simmonds]

It's possible to change the thermostat with everything apart from the Aux radiator fitted using a 10mm 1/4" drive socket a, UJ and a long extension, you have to undo the two 10mm bolts through the hole in plastic for the thermostat elbow. It's a fiddle **** job but quicker than having to completely strip all the plastic ducting out of the way.

I always replace the old M6 bolts with A4 SS (marine grade) Allen head bolts with a dab of copper grease on them as I've had an original snap off on me requiring the welder to come out and obviously a full strip down for access. A lot of work to extract one bloody bolt!

I did the cambelts as well as fair bit of other work on couple of 7A's back in May, I found the replacement MFTS senders provided by the owner read way too high on both cars so I cleaned the old ones up and reinstalled them, then I got readings I trusted again. I seem to recall they were Febi or at least one of them was.

[johne]

As mentioned above, the MFTS may well be suspect. The original ones were 4 pin with embedded electronics and accurate. They were "superseded" by a cheaper 3 pin version with no embedded electronics and notoriously inaccurate. Lots of discussion back in old threads. If you've got/get a working 4 pin one, cherish it.

The reason why I was so adamant above that your Nissen's radiator isn't a problem is that I've had one for years. Also, like many others, I've deleted the Aux radiator as well and the engine temps are still fine. Unless you track the car, an Aux radiator isn't needed.

In fact the biggest problem with the S2 is keeping it hot enough as many thermostats open too early and don't close fully. Cruise on the motorway, especially in winter, and you'll see the temperature go down. That's due to coolant leaking past the thermostat and also round the bypass circuit for the turbo cooling.

Wahle thermostats and testing is the way to go, as suggested above.

[hashluck]

I have two 1995 ABY S2 Coupes which both behave exactly the same (both are standard cars and have AC. Aux Rads are still fitted and both have Wahle thermostats fitted).

In traffic the temperature will move up to an indicated 90 and the moment it edges above that, the fan will kick in for a short while. The fan is never continuously on and it never stays on for long, even in hot weather and irrespective of whether AC is on or not. The after-run pumps also work on both but are heard very rarely indeed and not for long.

When cruising on a motorway the indicated reading on both is 80-85, it never gets to 90 until I sit in traffic. It seems previous owners noted this and the thermostats were changed in both cars with no change to the above operation. I have read on here that on the ABY S2, the rush of air over the temperature gauge sender causes it to read slightly low and attempts have been made to insulate it etc.

I am remiss in not having taken an OBD reading of coolant temperature (and in any case the User Manual is nebulous in what forms a correct reading of all the gauges) but the situation has not really concerned me enough to warrant it. Certainly the cars are not in danger of over-heating, They may or may not be running slightly cool on a run but seemingly with no problem.

I also have a 1987 B3 90 quattro. This sits at 90 all the time when warm. In traffic the neelde will move to the centre point on the gauge and then the fan kicks in until it gets back to 90. The after run on this car runs nearly every single time on the 90 whereas it is very rare to hear it on the S2s.

[Crasher]

I have ordered a Pogo radiator and genuine thermostat but I can’t remember where the coolant temp sender came from, I will have to check my spread sheets at work but I have a vague recollection of it being a 3 pin VEMO.

[ert]

I will have to check my spread sheets at work but I have a vague recollection of it being a 3 pin VEMO.

That's the sad part with MFTS's that there are no good suppliers left any more. I tried Vemo sensor and it was lying right out of the box. Showed way higher temps than they actually were. I hope you have more luck than I did. Ended up putting back the old Behr one.

[Crasher]

Yes, it was VEMO and every one of the versions shown on TecDoc are 3 pin.

[JayCab]

That's the sad part with MFTS's that there are no good suppliers left any more. I tried Vemo sensor and it was lying right out of the box. Showed way higher temps than they actually were. I hope you have more luck than I did. Ended up putting back the old Behr one.

Original BEHR MFTS can be obtained from Pete at Quattro Corner. It comes in a blue BEHR box, not an Audi box, and is identical to the original minus the Audi rings. It's over £100 though.
--> Note, I have purchased and installed this, and confirm it behaves identically to the original one. It's probably from the same production line as the original, sans Audi rings.

[JayCab]

I have two 1995 ABY S2 Coupes which both behave exactly the same (both are standard cars and have AC. Aux Rads are still fitted and both have Wahle thermostats fitted).

In traffic the temperature will move up to an indicated 90 and the moment it edges above that, the fan will kick in for a short while. The fan is never continuously on and it never stays on for long, even in hot weather and irrespective of whether AC is on or not. The after-run pumps also work on both but are heard very rarely indeed and not for long.

When cruising on a motorway the indicated reading on both is 80-85, it never gets to 90 until I sit in traffic. It seems previous owners noted this and the thermostats were changed in both cars with no change to the above operation. I have read on here that on the ABY S2, the rush of air over the temperature gauge sender causes it to read slightly low and attempts have been made to insulate it etc.

I am remiss in not having taken an OBD reading of coolant temperature (and in any case the User Manual is nebulous in what forms a correct reading of all the gauges) but the situation has not really concerned me enough to warrant it. Certainly the cars are not in danger of over-heating, They may or may not be running slightly cool on a run but seemingly with no problem.

I also have a 1987 B3 90 quattro. This sits at 90 all the time when warm. In traffic the neelde will move to the centre point on the gauge and then the fan kicks in until it gets back to 90. The after run on this car runs nearly every single time on the 90 whereas it is very rare to hear it on the S2s.

I can confirm that my cooling system behaves similar to hashluck's vehicles,. Mine is a 1999 AAH cabriolet, so shares the key cooling components and control logic, minus the turbo aspects and the aux rad, but with an auto gearbox adding a heat load to the system as well.

However,;
- my vehicle reads 88-90C on the dial at cruise / high airflow, depending on ambient temp and cruise speed.

- my vehicle reads 100-102C at absolute max on the dial in blazing sun at idle after a slowdown from the motorway. At idle, the first stage fan will drop the temp at the needle to about 96-98C before turning off. I think the needle moves slower than the coolant cycle speed simply by being a slow analogue needle. The radiator top is untouchably hot just before fan kick in, and touchably cool at fan shut off.

- if it's one of our 30C + days, and the engine is hot with A/C running as well, it will sometimes run 2nd fan speed (which you really hear)

- my coolant temp at the dash is normally between 90-100. A crack under if cruising in cold air, a crack above if idling in blazing heat.

- behaviour is similar with A/C on, but with the cycle speed slowed down because the fan runs at constant A/C speed (slower than speed 1 triggered by the rad thermoswitch - sounds very quiet). When A/C is running, the cycle is generally between A/C speed and fan speed 1, on a slower cycle, with occasional fan speed 2 on a really hot day.

- I have never heard fan speed 2 with the A/C off on my car, but know the system will do this in hot countries with the same hardware.

I have:
- Brand new genuine thermostat (can still get from Audi - strangely)
- Nissens radiator (the behaviour was identical with the OE rad before it corroded, with all other components being the same)
- ERA 2 stage radiator fan control switch (if someone can get me genuine OE, please reach out :-))
- Genuine original MFTS (have also swapped for BEHR MFTS - with identical behaviour)
- Flushed cooling system refilled with genuine pre-mix G12 Evo coolant

[Crasher]

I have ordered one of the BEHR senders with Pete but he says it is 3 pin, not 4.

[JayCab]

I have ordered one of the BEHR senders with Pete but he says it is 3 pin, not 4.

Yes, that was the last available OE sensor. My original one (1999) was a 3 pin sensor. The OE 4 pins ones pre date my car. It was 3 pin from new. If anyone is interested, I can confirm a 1999 Cab still has the 4 pin harness with the +12v feed.