Cooling system a little too efficient?

[markrtw 0]

I need a little guidance please. Recently my 94 VR6 temp gauge has been showing a very low temp (70 - 75 degrees) and I think it's been running a little rich as the end of the exhaust is rather black with carbon (especially after a motorway run), mpg is down a touch and it feels not quite so zesty (if you know what I mean).

If I am stopped in traffic the temp gauge starts to rise, but then returns to the low 70s again when moving.

 

I have tested the Thermostat - the bottom rad pipe stays cold until the engines quite warm and the thermostat opens (it has been replaced twice in recent years with VAG part) (In fact, apart from a couple of pipes, the whole cooling system is under 2 years old). When I switch on the ignition (before cranking over the engine) I can hear a gurgle from the cooling system so there must be a bit of air in it, but after a lot of trying I cannot get rid of it (answers on a postcard please - N.B. the aux water pump is about 2 years old (bosch) couldn't be on the way out already could it?).

 

I have run VAGCOM on it to see what the water temp is according to the ECU temp sensor and it appears to be a happy 82 degrees on my 15 mile open road trip home in 1 degree outside temp. (Log file attached - .CSV changed to a .TXT file extension so it can be uploaded). Is this healthy? An O2 Active figure is between 0.8 and 1 - is this the lambda reading and is this as it should be?

 

Could someone cast a knowledgeable eye over the log file and advise if anything looks amiss?

 

The temp sensor from the thermostat housing is about a year old and black. I take it this has no bearing on the fuelling as that must be dictated by the ECU temp sensor?

 

I have been scouring the forum, but out of answers, so if anyone can give me some good suggestions it will be much appreciated. (at least it's not running hot!)

 

Thanks in advance,

Mark

[millerman 0]

blimey to read that you need to be a binery scanner :lol:

 

i take it the 3 senders on the thermostat housing are in good working order ??

[markrtw 0]

To open the log file change the file extension from txt to csv and open it up in excel and then it makes sense.

 

I think the 3 senders are OK. is there anyway of testing the temp sender? Check its resistence?

[millerman 0]

To open the log file change the file extension from txt to csv and open it up in excel and then it makes sense.

 

I think the 3 senders are OK. is there anyway of testing the temp sender? Check its resistence?

 

which the one in the rad ? if so im sure ive seen that posted on here a while ago

i know if the blue one goes in the stat housing you only get a max of 77 degs on the dash !

[fla 9]

ambient temp will affect cooling as its a touch nippy atm. Have you flushed out the coolaing system? Have a look at the colour of teh water in the reservoir? It should ideally be clear, not cloudy. You can get a flushing solution from VW, its orange and costs about £30. Drain the coolant, add the system flush run the engine up to temp and drain it. The rinse the system thoroughly. Try it and see how you get on.

[ww-promo 0]

Just reading your thread as I have the same problem with my VR. Have you managed to sort it? I have my MOT next week so will ask my garage what they think. Ta.

[Critical_Mass 10]

Had a similar issue with mine where the guage was always at about 70 but when stuck in traffic it would rise a bit, but then drop when on the move again. The bottom rad hose was warm and vagcom was reading higher then the temp guage on the dash. I changed the yellow temp sender and its now fine. Though it the guage was under reading, but as mentioned above the ambient temp can affect this. Since its warmed up a bit, the guage site bang on 90!

 

As for the soot on the the tailpipe i dont think thats anything to worry about. If it was still running in cold start mode then it would really drink fuel.

 

Take the car for a good run and then plug vag com into it. If the ECU reading on vagcom matches the guage you know there is a problem with either the blue temp sender or the thermostat - either will cause the ECU to run in cold start mode. If vagcom reading appears correct and is a fair bit higher then the guage, then the guage is at fault.

[fla 9]

Just to add my recent experience to this - replaced my stuck thermostat with a new VAG one, plus replaced my rad (which was actually quite clean) with an almost new one (courtesy Chris), flushed and refilled with deionised water and G12++ and my fuel consumption has improved considerably - had a good blast and the car still showed 28mpg for the trip (MFA 1)! So dont underestimate the efficiency gains from a well set up cooling system.

[markrtw 0]

My problem in the end was a little air lock which seemed to be by the sensor. Topped up the system from the top rad hose and it was fine.