MFTS rubber boot

[le mans]

My MFTS (Audi RS2) is missing the rubber boot, which I think explains why the water temp gauge under reads all the time.

Can the rubber boot be obtained separately or are there any after market suggestions?

[Monkeymagic]

Why would this cause under reading though?

[le mans]

Fair point, not sure but it does under read consistently by about 20 deg. Temp signal to ECU is accurate I assume as it is right on 90 during a steady drive.

[newsh]

If the rubber boot is missing you will see the temp drop compared to Vagcom when driving on a cold day. I used a piece of silicon hose slid up onto the MFTS which helped this and being open at the bottom, didn't fill with condensation.

The other scenario is that you have an aftermarket MFTS which reads low. there are quite a lot of these about.

[AndyP]

All the aftermarket ones I've seen read high, not low, but only by a few degrees not 20.

[newsh]

Mmm, I think I had one that read low Anyway, best thing to do is check it against Vagcom.

[newsh]

Just re-read and see that you've already compared to the ECU signal (from the other temp sender on the back of the head) .

So a question, does the fuel gauge also read low?

[le mans]

Just re-read and see that you've already compared to the ECU signal (from the other temp sender on the back of the head) .

So a question, does the fuel gauge also read low?

Fuel gauge is OK as far as I can tell. Generally fill up at around 400km intervals and it usually reads a little above empty at that point.

[domas]

interesting topic, so I will hijack it.

Both my temp gauge is slightly low and fuel gauge is quite low.

Temp gauge can be explained by mediocre quality behr MFTS, which is okay compared to other aftermarket crap, it is some 5C low, not a big deal. It got low after i swapped it from another behr sensor that was spot on, but it had false overheat signal.

Fuel is a different story. It show full with the full tank but it is only so because i have adjusted it with adjustment screw to do so. I can see it is not behaveing as supposed, as fuel tank capacity is not linear, and non-linearity is in wrong spot. It just happened at some point that it started to show about 15-20 liters low (80l tank in my car). SO I have just adjusted it according to bentley. I have a spare sender, they both have the same resistance range. Sensor arm in ok shape, not bent or so.

I think there is a problem with my cluster, because:
a) voltage regulator outputs a bit low but within tolerances of repair manual. chaned to spare one, no differnece, same output though. IIRC 9.6V instead of 10v
b) board computer shows that i have 1600-2000 kilometers to go on my tank. should be 800 with full tank. THe value adjusts +-10% with a little potentiometer. but i need like 100%.
c) other 5 BC functions are spot on.
d) Every single solder joint is resoldered in the cluster apart from huge *** chips.
e) tried a different BC, same result.

my car is 200 20v, but the systems are very similar to s23b

any ideas?

[ThatGUY]

So a question, does the fuel gauge also read low?

What is the correlation between the MFTS and low reading fuel gauge?

[domas]

What is the correlation between the MFTS and low reading fuel gauge?

My guess is that both use regulated 10v reference.

[newsh]

Yes they both use the voltage from the regulator bolted to the back of the cluster. What fixed mine was to remove the captive washer from the regulator, it seems there was corrosion or some kind of resistance between the washer and the regulator. My temp and fuel gauges have been fine since.

[domas]

will mess around with mine as well

[ThatGUY]

@Newsh... Great info, cheers

[domas]

i can't stop wondering why could that be the case - as regulator uses 3 pins, vin, gnd and vout. Tab is connected to heat sink which is not connected anywhere. Why would any resistance matter there?