overheating yellow temp, blue temp, thermostat which one... HELP needed ASAP

[edd 0]

Hi All

 

The VR has been off the road for the winter as i have been borrowing another car, now have to give it back so decided to test alls well........ and all is not.

 

Temperature guage on the dash is exceeding 110oC with coolant light flashing (only once warm) and fans seems to be slightly tempremental. I.e. not always coming on but have seen them on when very hot

 

Have checked all visible fuses from within the car - all fine

 

removed the fan stage 1 and 2 temp sensor and bridged across them, stage 2 is working but nothing from stage 1 - does that mean a wiring issue here i.e. not sensor related??

 

Have bridged black temp sensor stage 3 fans come on

 

Bridged across yellow temp and fans came on, can hear aux pump working when ingnition on too

 

With engine warm i.e. guage showing 110 and coolant/temp light flashing bottom rad hose was still cold.

 

Im therefore thinking yellow temp not working properly and/or thermostat stuck closed (what about blue temp sensor??)

 

any other thoughts, is there any other reason other than wiring why the stage 1 fan did not come on when i bridged the connections.

 

Need this sorted by Thursday aaargghh

 

I also broke the plastic collar on the expansion tank return hose trying to get hose off to check return was working (it was) so got one of them coming off ebay. Boll*&ks

 

Cheers for any help

 

Edd

Edited February 20, 2011 by edd

[fla 9]

stage 1 fan speed is direct and independent of the sensors - it hink its triggered by the rad sensor, but someone can confirm this later. Is the coolant flowing through the rad? Check the bottom hose is also getting warm. If not the thermostat is probably stuck closed.

What is the colour of the coolant? Is it murky and cloudy or relatively clear? If the former, then the rate of heat transfer will be less. When did you last drain & flush the system? Blue temp is more related to fueliing afaik, ie when the temp is low it will be on the 'cold' cycle hence more fuel will be chucked into the engine. Yellow i beleive is for the dash gauge and fans. Haywire has put a very comprehensive thread on overheating - have a look through and check off the points he's got there. Let us know how you get on.

[edd 0]

pretty sure it must be a stuck closed thermostat due to botom rad hose not warming up, if it has been in the closed postion for a 3 months without being warmed up is this a likely scenario??

 

Back on the stafge 1 fan not working though assuming wiring is okay from stage 1 and 2 thermoswitch and it is a direct link is this likely ot be a fault in the fan motor circuitry??

[fla 9]

looks like you've found the problem if teh bottom hose is cold. Chnage the stat, but do this - take the old stat out, fill the system with water and a cooling system descaler (get teh orange one from vw). Let is culculate for 20-25 minutes. Drain refill, cuculate drain again. Then, fill the system with water, start the car, get a hosepipe and pop it into the header tank. Open the drain hole at the crack pipe. Keep the engine running and let the water drain until clear. Keep the level topped up by a constant flow at teh header. When teh water runs clear you're done. Refit the thermostat, refill will the correct amount of G12+ and you're done.

 

For speed 1 fan, just bridge the connector going to the rad stat and the fan should come on, doesnt matter if the engine is on or not.

[edd 0]

right so changed the stat but im no better for it just angry and less well off, im in exactly the same boat, water temp getting hot quickly so temp light flashes and bottom rad hose staying cold. I tested the old and the new thermostats in a saucpan of boiling water and both appeared to be working fine i.e. spring becoming loaded when it reaches boiling point. i have return flow back into the header does this mean i can assume the water pump is okay, i can also hear the auxilary pump with the ignition on. If i fill up the rad from the top water will come out the bottom so no blockages in there.

 

Im stumped any ideas - the rado is off after this - after 8 years of rado ownership i think i have finally had enough :(

[Jon_vr6 1]

Similar thing happened to me where the water temp would keep going up and up past the 100 degrees mark and then the coolant light would flash no fans would come on or anything. Was diagnosed as the yellow temp sensor on the thermostat housing. That was changed and was all back to normal cant remember if my bottom rad hose was cold or not so may or may not be your problem

[fla 9]

If the bottom rad hose is still cold despite the stat opening it points to a blocked rad. did you flush the system out?

Try this then - remove the top and bottom hoses to the rad and put the hosepipe in at the top, keeping the pipe vertical, not too high a flowrate and see if any water comes out the bottom. Bear in mind its got to go through a load of tubes it will take a little while to get to the end! Dont give up, i cant see it being anything too complex, you've done the hardest bit of changing the stat anyway. If you have the time, then chuck some soda crystals into the coolant to remove any crud if you dont want to do teh long winded way i suggested. They're caustic so will remove a lot of the crud.

[edd 0]

Yeah i checked this before as i poured water into the top of the rad via the top rad hose with a watering can and it came out the bottom rad hose that was disconnected at the thermostat end, so im assuming rad is not blocked

 

Any more ideas?? Think ill but a new yellow temp sensor as a matter of course i.e. temp reading wrong but surely this would have no effect on situation of stat not appearing to open.

 

AArrrgggg...

[fla 9]

yes then its a faulty sensor - did the car actually overheat or was it just going off the scale immediately? Could you test it on a local drive for 20 mins or so to get up to temp and then check the lower rad hose?