VR6 Overheating.......advice please!

[anubis 0]

Hey,

My VR6 is overheaing all the time. Once the car's been running for more than about 20 minutes, either in traffic or on the motorway it reaches 110°C [the 2nd level fan starts], then continues to slowy rise until about 115°C, when the coolant light comes on. Before this I have to turn the heater on to help cool the whole thing down, but this is obviously not a permenant solution.

 

I've checked the fuses for the fans, and in the last few months the following has been replaced;

 

Water pump

Radiator fan switch

Thermostat [+ housing]

 

Does anyone know what else could be causing this?

 

Cheers in advance.....

[Crasher 3]

Read the post, doh.

[Toad 0]

Expansion tank cap?

[bigbluec 0]

Think toad has hit the nail on the head, either that or thermostat has packed up in closed/semi closed position.

[RS VR6 0]

Are you having powerloss? May be the headgasket.

 

If its the expansion tank...you should see residue from the coolant all over it.

[Goldie 2]

Expansion tank cap?

 

How would you know if this was knackered??

[Toad 0]

I don't know if there is an easy test.. I suppose borrow one that you know is fine and see what happens.

 

The middle section of mine came away from the rest of it, so I had a pretty good idea about mine :wink:

 

But the rubber O ring will fail as well as the cap not holding the correct pressure.

[Toad 0]

how does the VR6 thermostat fit, is it at an angle or is it vertically? if so, is the little hole at the top?

[Andy T 0]

Is it definately the 2nd stage fan coming on? Does the first stage come on before it?

 

My temps were up to 110-115° and it turned out to be a naff yellow temp sensor from GSF (far left position in the thermostat housing) that was reading 15° too high.

 

What oil temps are you getting, are they way lower than the water temp?

[dr_mat 0]

A failed expansion tank cap will either cause over-pressure or it won't allow the pressure to build up at all and you will lose coolant as steam.

[bigbluec 0]

A failed expansion cap noramlly has both of these symptoms:

1, As you look at the underside the core with the O ring doesn't move (it should wobble)

2, When the car is running the pipes are almost impossible to squeeze due to over pressurization.

 

The VR6 Thermostat fits vertically but be warned you're 99.9% going to need a new thermostat casing, to be fair it's not ridiculous money but that's not the point!

 

There are plenty of other threads on all these subjects if you need more info.

[Republic Of Mancunia 0]

I've also got the same problem although my coolant temp doesn’t exceed 110°c and the coolant light doesn't come on. But my oil temperature can hit 140°c. I noticed the other day when checking my levels that there was coolant on the outside of the expansion bottle, it was on the middle rim. I was a little confused as to where this had come from as the cap was on so tight I had to tap it with a hammer to loosen it.

[anubis 0]

Thanks for the replies so far guys. To answer a few of the questions, the car's had both a new expansion tank [& cap] and a head over the last year & a bit, so it's probably not them.

 

Andy T , have you got a part number for this temperature sensor you mentioned? Don't know what the oil temps are, as I'm not sure how to check them [ashamedly].

[Andy T 0]

Part no. for 4-pin yellow sender (now black with blue line) on my VAG receipt is 701 919 369 D.

 

Price was £22.37 including VAT.

 

Your oil temp is displayed on the digital MFA readout in the clocks, press the button on the end of the wiper stalk and it shows different info, Oil temp is the one showing an oil can icon.

 

If your oil temp reading is significantly lower than water temp when the engine is cold/warming up, i.e water temp 80, oil temp 60-65, i'd suspect a faulty yellow sender.

[anubis 0]

Andy T, changed the sensor but nothing's changed :( Was speaking to a guy at VW, and he seesm to think it's that the Aux water pump isn't coming on when this sensor fires. Anyone else had problems with this?

 

Cheers

[Andy T 0]

Aux. pump should be running with ignition on, even if engine stopped, put your hand on the pump you should feel it whirring.

 

There is a test you can do on the yellow sensor connector (bridging terminals I think) I'll have a look in the bentley manual.

[anubis 0]

Thanks Andy. The pump doesn't feel as if it's whirring, I guess I'd be able to tell if it was seperate from the engine vibrations!

 

Anyway, while looking at that, I felt a few of the hoses, all boiling hot, obviously.........except one. Wierd, since the car had been running for an hour & reached 110°C+. It's one of the hoses coming out of the block into the radiator [i think]....I took a pic in case my fantastic description isn't helping! Question is, shouldn't this be hot too?

[dr_mat 0]

Check the aux pump when the engine is OFF, as stated above. It runs 100% of the time when the ignition is on, whether the engine is running or not.

They are VERY quiet though, it's easy to assume it's not working when it is working fine. Another good check is to open up the expansion tank cap and look for water circulation - again when the engine is off.

 

Kinda sounds like you've either got a blocked radiator or a stuck thermostat though.

[tonedef 9]

Thanks Andy. The pump doesn't feel as if it's whirring, I guess I'd be able to tell if it was seperate from the engine vibrations!

 

Anyway, while looking at that, I felt a few of the hoses, all boiling hot, obviously.........except one. Wierd, since the car had been running for an hour & reached 110°C+. It's one of the hoses coming out of the block into the radiator [i think]....I took a pic in case my fantastic description isn't helping! Question is, shouldn't this be hot too?

 

I just started mine up to check it and the bottom hose starts to heat up at about 86°C. Sounds like you thermostat is not opening to me?

[Andy T 0]

Does look like a stuck thermostat but I thought you'd checked it/fitted a new one?

 

If thermostat is ok, might be worth droppping the coolant and checking if water flows through the rad freely with a hosepipe.

[anubis 0]

Thanks for the continued input guys....

 

OK, I've checked it with the ignition on, but not the engine, and all the noise was coming from the side of the block, which I'm assuming is the main water pump? What I think is the Aux water pump [top of the block under the housing, on the right of the pic] isn't making any noise that I can detect [ see pic below ].

 

The thermostat was replaced only two weeks ago, so I doubt it's that.

[tonedef 9]

On your photo, the part you have circled "Noise" on the "back" of the block is the Aux water pump, the part cirled "No Noise" appears to be the ISV, don't expect that to make noise.

 

The main water pump is mechanically driven by the serpentine belt, it's on the "front" of the block hidden by the alternator and only turns when the engine is running.

 

As Andy T suggests, try a hosepipe in the top of the rad and see if water flows out of the bottom, it would explain why there's no cooling if the rad's blocked.

[dr_mat 0]

Did this problem exist BEFORE you had the thermostat replaced? Did they test it before they put it in? (Can you tell I troubleshoot for a living?!?!)

[anubis 0]

lol......Yep, this problem existed before I got the thermostat replaced. I'd read that this sort of thing could be caused by the thermostat not opening properly, but it's still the same.

 

I'll do the hose / radiator test at the next opportunity. If there is a blockage in the radiator, is it stopping coolant getting into some parts of the engine completely, and causing damage?

[dr_mat 0]

I'll do the hose / radiator test at the next opportunity. If there is a blockage in the radiator, is it stopping coolant getting into some parts of the engine completely, and causing damage?

 

Well since a closed thermostat prevents water going round the radiator too, I would imagine the answer is "no". Apart from the obvious problem of your car overheating all the time, which can cause significant damage on it's own.