Octavia vRS - Running cold after CTS change

[Keith_VRS]

Evening all,

I done some research and found that an old coolant temperature sensor may be causing a lumpy idle.

I bought and fitted a genuine new sensor the other day, losing minimal coolant in the process.

My engine seems to be running a little smoother, but I believe it's identified a further problem. It's taking much longer to reach 90º and until it reaches it, it tends to fluctuate.

I ran the car after fitting the sensor without the coolant cap on, just to bleed it through and it seemed to do the trick, but I've just put a good 5 miles on the car tonight, about 8º outside, and struggled to get to temperature in mixed driving conditions.

Prior to changing the sensor, it used to warm up within a mile or so and would stay there. Just had to cope with the lumpiness.

What are the odd that it's a faulty sensor? It might be worth going back to the old one to see how the car behaves. Other than this, it's a case of changing the thermostat. Does the ECU take a while to pick up on fresh signals?

The old sensor was a newer green unit but the probe was looking horrible compared to the new golden unit.

Your help would be super.

Cheers,

Keith

[Dean]

Is your check light engine on? if so it will probably be the Thermostat causing the issue. I changed my CTS (Skoda OEM) and my car only reaches 90 if its driven hard or an extremely hot day.

I ran the scan and I still get;

17704 - Error in Mapped Cooling System (check Temp-Sensor and Thermostat) 

Which leaves the TS which will be getting replaced next week along with a full service, MOT and water pump/cambelt. The joys!

[YellowCar]

Sounds like thermostat to me. For what it's worth mine played (sticking open so overcooling) and never threw a code or EML. It's definitely what I'd try next if I were you.

[Keith_VRS]

Thanks for the reply.

No CEL as of yet, it's been in since Saturday and driven for a few hours, so I'd like to think that if the light was coming on, it'd appear by now.

It's a bit concerning, but I do 50 miles each way for work, all motorway. I'll see what happens during the commute. Be ironic to find the thermostat failed right as I changed the sensor.

Anyone local to Gateshead willing to see what Vagcom has to offer?

Thanks,

Keith.

[Dean]

Thanks for the reply.

No CEL as of yet, it's been in since Saturday and driven for a few hours, so I'd like to think that if the light was coming on, it'd appear by now.

 

I find if someone dc the battery it's around 100 miles till the CEL comes back on, also tested this myself. So keep a look out to see if it comes on. But keep the new CTS as it is and just change the TS and go from there....

 

If after all of that you find it's still lumpy the next call is the 'Coil Packs'.

[Keith_VRS]

I changed a couple of the coil packs about a week after buying the car. Didn't look great and I had a stutter going through the gears.

Is it worth disconnecting the battery overnight and starting a fresh?

Like I said, strange for the stat to fail around about the same time. I initially thought it might just be normal, with the ECU picking up on a more accurate temperature reading.

[Dean]

It's possible, but ideally you'd need to get it scanned.

[Liverpool-Lad]

If you need to swap it use a genuine thermostat, not a cruddy GSF or ebay one.

[hardcorehobbit]

I changed my thermostat and cts together, or rather, they were done for me.

Afterwards I had a car that would never get to 90 unless stuck in traffic or working hard on track. Would cool right off again if the traffic cleared.

Changed the stat again and all is well now. Both were genuine from tps. Seems some of them are just a bit rubbish.

[YellowCar]

I changed my thermostat and cts together, or rather, they were done for me.

Afterwards I had a car that would never get to 90 unless stuck in traffic or working hard on track. Would cool right off again if the traffic cleared.

Changed the stat again and all is well now. Both were genuine from tps. Seems some of them are just a bit rubbish.

True that, even gen ones are a bit of a lottery but probably more likely to be ok than non gen.

[trundlenut]

The CTS in the octavia is a twin circuit one. One feeds the engine ecu, the other goes to the instruments. So if one is giving a duff reading the other can be fine.

So the question is whether it is running cold or not?

Using Vcds, or the torque app will tell what the ecu thinks the coolant temperature is.

Sent from my D5803 using Tapatalk

[shivadow]

17704 (p1296) change temp sensor and thermostat. Most likely MAF sensor faulty, bad wiring, corroded contacts at the plug, MAF reporting wrong values (reset maf using vcds and run the car).

I just had the same sounding issue.. It was my MAF sensor reporting the wrong values.

[shivadow]

Oh, and make sure the thermostat inner o ring is seated properly against the block. They slip out at install if not done correctly!. Fyi- all thermostats are the same genuine or not and very likely to NOT be at fault unless you use tap water in your cooling system (very stupid idea to do so!!).

Even though maf isn't mentioned by obd i bet my left testicle its the problem.

Edited 4 October, 2015 by shivadow

[Keith_VRS]

Thanks for the replies, all.

 

Quick update.

 

Drove 50 miles to work this morning, it's about 50/50 motorway to country roads, sitting at around 60 on both. It took around 18 miles for the temperature to finally hit 90°, and even then, it would fluctuate ever so slightly from there, probably as low as 85°. I suppose critically, it's not overheating in any way, so I'm confident the coolant is circulating properly and without any air locks.

 

I filled up with fuel and reset the mpg readings, it's offering the same readings as it always does, anywhere between 40 and 43. It's definitely running smoother than before, without the lumpy idle once warmed up. The CEL is yet to flag up on the dash, but we'll see if that appears on the way home.

 

I'm assuming it's a 10 year old thermostat. Is it possible that when de-pressurising the system and removing the original sensor, the surge has unseated the thermostat from it's closed position and it's stuck in place due to wear and tear?

 

The comment above about the twin circuit, I suppose this could be eliminated by reverting to the older unit, which would get up to 90° and stay there after ~1 mile.

 

Frustrating either way. Sort one problem and create another.

 

Guess it's time to acquire some diagnostic equipment.

 

Cheers,

Keith.

 

[Edit]

 

I just had a quick look on clickmechanic.com who quote £51.45 for a thermostat change, including parts, labour and presumably, coolant. Doesn't look like a bad price if it's going to be around £25 for the stat and coolant. Spares me the scuffed knuckles. Your thoughts?

Edited 5 October, 2015 by Keith_VRS

[shivadow]

The car shouldn't take that long to heat up. 18 miles.. Too long. Mine has just had all that done and gets warm in about 2 miles, driving with minimal load. A mile if i stamp my hoof on the pedal..

[Keith_VRS]

I know, not happy with that.

 

It was a genuine VAG sensor that I fitted (059 919 501 A) from here.

 

Mine has just had all that done and gets warm in about 2 miles, driving with minimal load.

 

Are you referring to CTS and thermostat? As mentioned, mine would get up to temp on the dash in similar time.

 

It's definitely getting hot. When I worked on it the other day, I had the engine running and the hoses were hot at the top and much cooler down the bottom. This was also the case with the radiator. I had this problem on an old motorbike, just keeps on circulating through the radiator and draws away too much heat from the engine.

[shivadow]

Both an more. Cts, thermostat and maf recalibration. Misfires solved. Intake gasket got swallowed too but that was way before the misfires. Check the thermostat o ring is seated correctly too.

[Keith_VRS]

Commute home seemed like a marginal improvement. Seemed to get to 70 degrees quite quickly then about 5 or so miles to reach 80 before finally creeping up to 90. It maintained that until I made it to the motorway where it fluctuated ever so slightly.

Can only assume there's no change, barring ambient temperature tonight compared to how baltic it was this morning.

My trusty mechanic has said it'll take him about an hour to swap the stat and get it bled with fresh coolant. Might hold him to it and just get it done.

Damm nuisance, it feels like it's running so much better than previously.

[Keith_VRS]

Just an update on this one.

 

I've had the thermostat changed and while it's cured one problem, it still takes an age to get up to temperature on the gauge.

 

At least now it seems to get to 90°C and stay there, so I'm confident that the thermostat was causing a problem.

 

I'm going to leave it until the weekend and swap the coolant temperature sensor out for the old one. It used to work fine and I only changed it as a fault finding exercise. There's every possibility that the unit I've fitted is a bit faulty.

 

Watch this space!

[Dean]

Mine got changed on Tues and it's cured my problem. I also have a oem cts from skoda.

[Keith_VRS]

Wish mine was fixed, turns out the needle isn't as stable as I'd hoped. I just hope the old CTS solves the problem that never originally existed!

[Keith_VRS]

Update, changed the CTS back to the one I originally removed and it's running perfect. Back upto temperature within a mile or two and stays put.

 

I'm convinced the replacement switch was faulty, but as the thermostat is mechanical, why would this influence the cold running of the car?

 

It's not like it was sending a dodgy signal to keep the thermostat open, just a bad signal to the clocks, and possibly the ECU but surely that would only harm the performance / economy?

[Dean]

Well least it's fixed! Should see improved mpg if you don't have a heavy right foot :P

[02VRS]

I've recently bought a mk1 vrs and had this fault code, mate cleared it and I got a new CTS but haven't fitted yet. Have done around 200 miles and the light not come back on yet. Had it on a good run the other day, around 110mile round trip with mix of driving. Temp sat at approx 80 most of the time, went up to 90 when around town etc, is that normal enough? Got 40mpg overall which I was happy enough with.

[Liverpool-Lad]

No, the thermostat should not deviate from 90