Engine Temperatures & Thermostat troubles.

[davegsm82]

I've just completed a 450 mile stint round Scotland and have some questions for other TDi converts;

1) On an average journey, which at the minute for me is 3-4 miles of town driving then 8-9 miles of fast dual carriageway driving, how quickly will your engine reach normal operating temperature, and;

2) Does it stay there?

3) for E-TDI owners, If you log in to Vag-Com, does your ECU and Dash report the same temperature?

My own experience is, it can take up to 20 minutes of driving before the engine gets up to 'normal', sometimes the needle never even moves off the lower stop. It will get to what I think is normal temperature after a long uphill slog but if you so much as look at the heater (front or rear) it will drop off within a few minutes, also if you then go downhill or even trundle along at 60 on the flat, it will usually just drop below normal.

I took a couple of readings with Vag-com at strategic times which were as follows;

Cold engine (overnight), outside temp approx 4 deg C. ECU reading 19.8 degrees. Dash reading 30 degrees.

Hot engine (on the road, uphill). ECU reading 121.6 degrees*. Dash reading 68 degrees.

*I don't think it was actually at this temperature, I suspect the brand new ECT sensor from euro car parts is 'out of spec'.

I recently changed the thermostat, because I had assumed (possibly incorrectly) that the dash was reading correctly and the engine never reaching temperature, only ever reaching an indicated 80 degrees, which equates to around 68 degrees as in the 'hot' reading as above.

Is anyone aware if the ECU is clever enough to throttle back power when it 'thinks' that the engine is overheating?

Dave.

[lloydy]

as far as i know, coolant temp does not effect power as such. It does sound like your coolant temp sender is faulty.. How are you measuring it at the dash? just from the standard gauge?
i had a few problems with getting a good reading from the dash gauge, the tdi 4 pin sender just did not give an accurate reading. i ended up cutting in T25 sender so the gauge read right.
Anyway, in this sort of weather from a cold start within 2-3 miles of standard town driving the coolant temp is 88deg, the thermostat maintains this very well unless I'm sat in traffic and have the heater fan on full (like never) then it will drop into the 70's. Fan speed one is fine. I would hazard a guess that your stat has failed.

[davegsm82]

Ok, looks like I have a genuine issue then. That's a shame as I replaced the ECT sensor (4 pin one) about 2 month ago because the dash wasn't reading at all.

It's a MK4 golf dash, that's where the reading of 68 degrees came from. I still have the T25 sender screwed into the block but I'm not sure how well this will work with the MK4 golf dash. I can easily re-code the dash to read correctly by modifying the EEPROM values, It's stock currently though.

I replaced the Thermostat on friday before leaving for scotland. Initially it seemed to work ok, heated up in no-time and stayed hot, then about 100 miles into the journey the engine went cold, although this may have just coincided with going down the far side of the pennines.

The 'Stat was a 'Circoli', from Euro Car Parts, 87 degrees stamped on it. I've bought 2 of them, same part numbers, listed as the same stat for my MK4 golf as well. I don't think they are identical to the original so I may just have to take a trip to VW for some genuine ones.

[lloydy]

I've got a genuine one in mine, i think the aftermarket ones are a bit hit and miss. Saying that though, free wheeling for many miles downhill will lower the temps.
i can't really comment on the dash, didn't even know the golf dash gave you an actual temp. You would think though that a golf sender and dash would be calibrated to give the correct reading. i have a passat dash in mine now from syncroandy and the temp gauge works well and gives an accurate reading compared to the scangauge

[davegsm82]

Yea, next stop is genuine for me.

It's a golf dash in mine but the sender is the original AFN one which came with the Sharan engine when I fitted it. Might have to invest in a genuine ECT if they are still available from VW. Even if it doesn't read correctly on the dash, it SHOULD read correctly in the ECU which is a little worrying.

I've discussed the finer points of the MK4 golf dash with syncroandy, he set me a bit of a challenge which helped me get the fuel gauge working correctly. The MK4 dash dial actually shows 90 and 130 as calibrated points, but after analysing it's internal data it actually has a sort of 'kink' which makes it read dead centre (90 degrees) when it's anywhere between about 80 and 100 degrees, bit of a fudge to make it look like it's thermostat is regulating perfectly.

Dave.

[davegsm82]

Did some work on the bus today, measured what resistances relate to displayed temperatures in the ECU and clocks, here is the data in case it can help anyone else.

Unit - Temp Shown in VAG-COM - Resistance

ECU - 100 deg = 185 ohm
ECU - 25 deg = 2.095k ohm
ECU - 4.5 deg = 4.932 ohm

clocks - 130 deg (max) = 140 ohm
clocks - 101 deg = (92 indicated on dial) = 192 ohm
clocks - 31 deg = 747 ohm
clocks - 30 deg (Min) = O/C

While hunting round my junk pile I found an old coolant manifold from an A4 AHF engine, it had the same type of 4-pin plug as the one fitted and was the same physical size so I fitted it and started up. During idle the temperature tracked pretty much exactly between ECU and clocks up to about 60 degrees when I had to switch off so I could change a driveshaft with a modicum of daylight remaining.

I removed the cheap, crappy, EuroCarParts thermostat and replaced it with a 'Gates' unit which was only a tenner (vs £6 for the ECP junk). There was an immediate difference in temperature regulation, after about 5 minutes of driving the needle was sitting smack in the middle of the dial, ECU reporting about 81 degrees and clocks reporting 75.

In closing, AVOID CIRCOLI thermostats from ECP, THEY ARE JUNK!

[lloydy]

cool, glad its sorted